Acetamiprid removal was investigated by synthesized Graphene oxide, multiwall nanotube and graphite from an aqueous solution. For this propose, FT-IR, XRD, UV–Vis, SEM and EDS were used to characterize the synthesized nano adsorbents and to determine the removal process. A novel PVC membrane electrode as selective electrode made for determining the concentration of acetamiprid. Batch adsorption studies were conducted to investigate the effect of temperature, initial acetamiprid concentration, adsorbent type and contact time as important adsorption parameters. The maximum equilibrium time was found to be 15 min for graphene oxide. The kinetics studies showed that the adsorption of acetamiprid followed the pseudo-second-order kinetics mechnism. All the adsorption equilibrium data were well fitted to the Langmuir isotherm model and maximum monolayer adsorption capacity 99 percent. Docking data of adsorption have resulted in the same as experimental data in good manner and confirmed the adsorption process. Therefore, there is serious need for unsophisticated, cheap, and valid procedures aimed at monitoring and detecting the pesticide residuals in different food productions5.Insecticides or pesticides have currently led to significant challenges concerning the safety issues and contamination of foods. Careless consumption of such compounds regardless of controlling or optimizing their concentrations may threaten humans’ lives and health due to their toxic nature. Unfortunately, pesticides are used both in agriculture and non-agriculture fields11, clothianidin, and dinotefuran employed for a wide range of pests14. Organophosphates are becoming more and more common as pesticides across the world and have recently replaced organochlorine insecticide15. As chemical pesticides control the pests and different diseases, they play a significant role in increasing agricultural yield while helping in the prevention of diseases brought by insects, such as malaria, dengue, encephalitis, filariasis, and so on in the field of human health16.The design of new members of these compounds has led to promising results in recent years. In fact, the nitro group fixation in a cis configuration for different neonicotinoid types has yielded compounds with certain biologic functions and behaviors, supporting their potential efficiency to elucidate the pharmacology and characteristics of the neonicotinoid binding sites. Neonicotinoids consist of 5-membered ring derivatives, including imidacloprid and thiacloprid, 6-membered ring compounds, including thiamethoxam, and also noncyclic structures such as nitenpyram, acetamiprid18, combined photo-Fenton and biological oxidation19, developed oxidation procedures21, aerobic degradation24, nanofiltration membranes25, ozonation26, coagulation28, fluid extraction30, solid phase extraction31, well as adsorption36. Kyriakopoulos and Doulia37 examined pesticide adsorption on carbonaceous38 and polymeric39 substances from aqueous solutions. In another study, Ahmad et al. and Hameed40 examined pesticide residuals detoxification using activated carbon. Adsorption can be utilized to decontaminate water as it is a popular equilibrium separation procedure and performs effectively in this regard16.Pesticides are mainly regarded as chemical mutagens. Pesticide elimination from the water system has currently become an important environmental issue. This is because, the residuals of these compounds have entered into underground water, resulting in serious concerns due to their significant growth in recent years. Conducting research to find out a unique approach aimed at removing these harmful chemicals worldwide is very challenging due to the extensive scope of pesticides used globally. There are a variety of techniques to remove pesticides, including photocatalytic degradation2 hybridized carbons41. Scientists and researchers have been interested in this material since it was discovered in 2004, because it showed specific characteristics, including considerable quantum Hall impacts, high mobility, great electronic42 and mechanical properties43, specific magnetism and high thermal conductivity44, There have been investigations on the use of graphene-based materials to manage the environmental issues related to pollution45.The current developments in carbon materials have led to graphene as a fundamental component of graphitic materials of all other ranges, representing a single atomic layer of graphite with hexagonally bonded and spIn this study, acetamiprid removal was investigated by three different nano carbon materials. Acetamiprid adsorption with the use of GO, multi-wall nanotubes, and graphite has not been previously examined through comparative studies. However, investigations revealed that time, temperature and acetamiprid concentration variations affected the adsorbents. The study also conducted the theoretical calculations.3, MWNTC, graphite, potassium permanganate, Peroxide hydrogen, sulfuric acid, (provided by Merck), which means that they did not need any additional purifications. Technical materials of acetamiprid, with a purity level higher than 95%, were obtained from Giah Company, Iran.The materials used in this study included reagent grade dioctyl phthalate (DOP), dibutyl phthalate (DBP), dimethyl sebacate (DMS), 2-nitrophenyloctyl ether (NPOE), tetrahydrofuran (THF) and high molecular weight PVC (provided by Merck). The study used highly pure sodium tetraphenyl borate (NaTPB), NaNO47. was utilized to synthesize graphene oxide. The addition of graphite powder (3.2 g) and NaNO3 (3.2 g) into 98% H2SO4 (140 mL) took place in an Erlenmeyer flask (800 mL), in an ice-bath (˂ 10 °C) while constantly stirred. Gradual addition of KMnO4 (18.5 g) to the suspension was done after the compound was stirred for a four-hour period in this temperature, after which the suspension was stirred for another one hour at a temperature of < 15 °C. Then, the gradual addition of 300 mL distilled water to the crude mixture was followed by stirring the mixture for another two hours, raising the temperature to 35 °C with constantly stirring for 2 h. In the next step, addition of 60 mL of a H2O2(30%) aqueous solution led to changes in the color of the mixture from dark brown into yellow. The obtained compound underwent centrifugation at 4400 rpm over a 20-min period, followed by its frequent washing by 5% HCl solution and deionized water to reach a gel-like substance with neutral value. The obtained substance was centrifuged and then vacuum dried at a temperature of 70 °C to produce the powder of graphene oxide.Modified Hummers’ technique with slight changes49 of qe:The present research carried out acetamiprid equilibrium adsorption on graphene oxide, multi-walled nanotubes, and graphite in polyethylene tubes. The study also considered constant concentrations of acetamiprid in different time and temperature conditions with the use of an orbital shaker which operated at 150 rpm agitation speed. It also utilized 10 ppm stock solutions of acetamiprid. Analysis of the solution for concentrations of acetamiprid and its adsorption on the adsorbent at equilibrium time with the use of UV–Visible spectroscopy were conducted following magnetic separation and filtration. The relation below was used to calculate the acetamiprid adsorption on the adsorbent at equilibrium timeIn which, Co, Ce, V, and m represent the primary acetamiprid concentrations (mg/L), acetamiprid concentrations (mg/L) in solution following the adsorption, the solution volume (L), and the mass (g) of graphene oxide, multi-walled nanotubes, and graphite, respectively. the following relation was used to calculate the percentage of acetamiprid removal:In which, Co and Ct indicate the primary acetamiprid solution concentrations (mg/L) and the ultimate concentrations (mg/L) following the process of adsorption, respectively. Relation In which m and V represent the adsorbent dose (mg) and acetamiprid solution volume (L).51. Dissolution of the sensor material, with acetophenone (0.002 g) acting as a plasticizer, and PVC (0.004 g) was done in 2 ml THF. NaTPB (0.001 g) played the role of an additive in several cases and graphite, graphene oxide and multi-wall nanotube (0.002 g) as ionphore. To obtain an oily concentrated compound, slow evaporation of the THF solution was conducted at ambient temperature. Formation of a transparent membrane with a thickness of around 0.3 mm resulted from dipping a Pyrex tube (3–5 mm i.d.) into the obtained compound for an approximately 10-s period. After pulling the tube out of the compound and keeping it at ambient temperature for a 1-h interval, internal filling solution (1.0 × 10−2 M acetamiprid) was used to fill it. Ultimately, electrode conditioning was obtained as it was soaked in a 0.1 M acetamiprid solution for a 36-h period.Preparation of the membrane electrode took place according to previous reports−2 M acetamiprid | sensor membrane | sample solution | reference electrode. A saturated calomel electrode with an Orion digital research pH-mV meter were considered to make the emf observations. The emf of acetamiprid solutions whose concentrations ranged from 10−1 to 10−9 M by serial dilution was measured to investigate the electrode performance. Stirring of the solutions and recording of the reading potentials after reaching stability were performed in the next steps, followed by plotting as a logarithmic function of acetamiprid activities, based on γ as the activity coefficient. Debye–Hückel relation52, which can be also applied to acetamiprid was used for data calculation:The study applied a cell assembly of the type described below: Ag/AgCl | 10In which, µ represents the ionic strength and Z is the valency. The temperature of 25 ± 0.1 °C was considered to carry out all measurements. Fresh preparation of the acetamid solutions took place using precise dilution from their stock standard solution of 0.1 M, with distilled, de-ionized water.The initial step was allocated to full geometric optimization of acetamiprid molecules, carbon nanotubes, graphene oxide, as well as graphite using density functional theory (B3LYP and basis set 6-311G(d)), by drawing 3D structures by guass view 5 software, determining the energy groups and composed molecules of each. The ArgusLab molecular modeling software was used for a quest of conformations, after which the molecular adsorption energies, density of states, ESP, and chemical parameters could be calculated., the functionality of which was supported by Fourier transform infrared spectroscopy. According to Fig. −1 in the area with high frequency due to O–H bond stretching mode, revealing that hydroxyl groups are present in GO. The carboxyl group had a band at 1720 cm−1. The stretching and bending vibrations of OH groups found in water molecules adsorbed on GO resulted in a dramatic or resonance peak at 1615 cm−1. The peaks at 1356, 1225, and 1056 cm−1 denote the C–OH group, C–O–C stretching, and the C–O group vibration mode, respectively.Hummer method was used for synthesis of graphene oxided-spacing. The increasing interlayer distance among the successive carbon basal planes shows associations with the intercalation of oxygen functional groups and water molecules into the structure of carbon layers53.The crystalline characteristics and phase purity of the synthesized graphene oxide are characterized through XRD analyses as shown in Fig. Figure max 620 nm as shown by acetamiprid and acetamiprid-adsorbent UV–Vis spectra in Fig. max of acetamiprid is eliminated following adsorption at the presence of the adsorbent because of perfect omission in the solution6.The highest absorption peaks were found to be at λ−1 because of stretching vibrations of –OH, C=O (carboxyl), C–OH, and C–O. Acetamiprid54 had peaks at 3000 because of –CH stretching, 2240, 1640 and 1500 cm−1 because of CN (nitrile), C=N (Imine) and C=C aromatic, correspondingly as shown in Fig. −1 because of graphene backbone chain skeletal vibrations. The peaks of acetamiprid were at 2976 because of –CH stretching, 2267, 1514 and 533 cm − 1 because of CN (nitrile), C=C aromatic and C–Cl53.IR spectroscopy illustrates acetamiprid adsorption on graphene oxide, multi-walled nanotubes, and graphite. As shown in Figs. −1 because of CN (nitrile), C=C aromatic and C–Cl of Acetamiprid.As shown in Fig. 53.The surface morphologies of the adsorption materials were examined by field emission scanning electron microscopy  as shown in Fig. Figure The study examined the contact time effects related to adsorption characteristics of graphene oxide, multi-walled nanotubes, and graphite, as shown in Fig. Application of Langmuir and Freundlich adsorption isotherms, as shown in Fig. −2 M of the respective solutions). Accordingly, evidence shows that graphene oxide-based PVC membranes could appropriately determine the highest sensitivity of responses in various adsorbent experiments. Besides, EMF responses found for acetamiprid selective were considerably lower compared to Nernst equation predictions, which may be related to the selective behaviors shown in the figure for possible responses of different PVC membrane electrodes with graphite, graphene oxide, and multi-walled nanotubes. The function of graphene oxide in opposition to acetamiprid was compared with different adsorbents while examining the fast exchange kinetics resulted from graphene oxide-acetamiprid complexes. The potential responses with the required stability were produced by the ionophore PVC-based membranes  functioning as selective electrodes for acetamiprid. The solution used in this experiment contained 0.1 M acetamiprid following 36-h conditioning. These treatments led to Nernstian responses in various concentrations of acetamiprid solutions, while the slope was nearly fixed.Graphite, graphene oxide and multi-walled nanotubes are all insufficiently insoluble in aqua while having carbon atoms and heavy electron density, leading to their desirable performance as carriers in the PVC membranes concerning specific pesticides as acetamiprid of appropriate size and charge. Therefore, preliminary studies have employed it as a neutral carrier for the preparation of membrane electrodes based on PVC for acetamiprid. Figure 55, increased in the case of long range interaction, including hydrogen bonding through a Coulomb Attenuating Methodology while restricting electron spin. The Gaussian 0956 software package was used to perform the required calculations, which were carried out in the gas phase as shown in Figs. 24 show their high likelihood to act as the sites for initiating interactions. Nevertheless, constructive reactions can only occur through coordination at the less electron rich C=N moiety. Thus, it can be hypothesized that adsorption initiation in neutral circumstances is carried out through coordination of adsorbent molecules with the nitrogen atoms of the C=N moiety, leading to a bonded complex and allowing close associations of the two reacting species.A moderate, inexpensive, but valid doubly split valence basis set with polarization functions on heavy atoms: 6–311 g (d) was used to optimize and calculate the energies, enabling to accurately map n-electrons and prevent overestimation of excessive energy. Correction of fermion exchanges took place through the 3-parameter hybrid function of Becke (B3), while electron correlations were considered using the model of Lee, Yang and Parr (LYP)The density of states (DOS) necessarily represents the number of various states at a certain level of energy occupied by the electrons, which means how many electron states can be found in each unit volume and unit energy. This function affects different bulk characteristics, including specific heat, paramagnetic susceptibility, and various transport processes associated with solids having conductivity. The overall distribution of states can be determined as an energy function using calculations of density of states, while the energy bands spacing is also determined in semi-conductors. Its mathematical representation shows distribution by a probability density function, typically representing an average across the domains of space and time in different states that the system occupies. DOS has direct associations with the dispersion relations of the system properties. Higher density of states at a certain level of energy reflects availability of a great number of states to be occupied. Continuity is generally a feature of the matter DOS. Yet, the isolated systems, like atoms or molecules in the gas phase, have discrete density distributions similar to a spectral density. Local DOS or LDOS represents local changes which are mostly because of distorted original system.k. It is necessary to know the system-specific energy dispersion relationship between E and k to enable converting between the density of states as an energy or the wave vector function. Overall, the system’s typological features, including the structure of the band, affect the characteristic of DOS significantly. The 3D Euclidean topologies can be observed in the highly popular systems such as neutronium in neutron stars and free electron gases in metals (instances of degenerate matter and a Fermi gas). On the other hand, 2D Euclidean topologies are found in systems with lower popularity, including 2D electron gases of 2DEG in in graphite layers as well as the quantum Hall effect systems in devices of MOSFET type. The 1D typology can be also observed in those systems with the least popularity, including carbon nanotubes, the quantum wire, and Luttinger liquid. Given the achievements in the field of nanotechnologies and nanomaterials, the last two typologies which are less familiar have the potential of becoming more common. As shown in Fig. It is possible to calculate DOS for electrons, photons, or phonons considering the quantum mechanical system, whose results may be provided through a function of energy or the wave vector Table The study examined Acetamiprid/graphene oxide, Acetamiprid/graphene and Acetamiprid/multi-walled nanotubes nanocomposites ability to comparatively remove and adsorb acetamiprid from aqueous solutions. Thorough analysis showed that graphene oxide layers contain a large variety of oxygen functionalities and Based on evidence obtained from experiments, the acetamiprid aqueous solution were independent from pH for the efficiency of their adsorption. Evidence also showed increased absorbent performance in adsorbing acetamiprid, according to which Acetamiprid/graphene, Acetamiprid/graphene oxide and Acetamiprid/multi-walled nanotubes had respective efficiencies of 97.5%, 92.5% and 95.3%. Based on the results obtained from experiments, the adsorption nature was in favor of Langmuir and Freundlich isotherm in the three adsorbents under study. According to data from equilibrium adsorption, the pseudo-second order had the greatest fitness, while the involvement of the chemisorption mechanism could be also observed. The studied adsorbents were increasingly stable and reproducible. Similar results were shown in theoretical and docking as well as empirical analyses.


The DFT results revealed that two-boron- and three-nitrogen (pyridinic)-doped graphene exhibited plausible reaction pathways at the lowest overpotentials, especially during the charging process (approximately 200 mV), thus, significantly improving the oxygen reduction and oxidation reactions of pristine graphene. In addition, pyridinic nitrogen-doped graphene meaningfully increased the equilibrium potential by approximately 0.30 eV compared to the other graphene-based materials considered in this study. This detailed DFT study provides valuable data that can be used for the successful development of low-cost and efficient graphene-based catalysts for sodium–air battery systems operating with non-aqueous electrolyte.In this work, we performed density functional theory (DFT) analysis of nitrogen (N)- and boron (B)-doped graphene, and N,B-co-doped graphene as potential catalysts for rechargeable non-aqueous sodium–air batteries. Four steps of an NaO We performed density functional theory analysis of heteroatom doped graphene as potential catalysts for rechargeable non-aqueous sodium–air batteries. Pyridinic nitrogen and boron doped graphene exhibited too low overpotential reaction pathways. Recently, there has been considerable interest in Na–O2 due to its relatively high energy density and capacities, operation at low dis/charge overpotentials, high electrical energy efficiency (approximately 90%), and operation over multiple cycles with chemical reversibility comparable to that of lithium ion batteries.8–12 Most importantly, due to the abundance of sodium in the Earth's crust , the cost of a rechargeable sodium–air battery is the lowest compared with other battery technologies  and hybrid electric vehicles (HEVs) to compete with conventional automobiles built with internal combustion engines.13,14In an attempt to make batteries viable for use in future transportation, there has been significant research and development of rechargeable metal–air batteries  can accumulate onto the air cathode material and easily clog the diffusion pathways, resulting in the deterioration of Na–O2 battery performance due to the steric barrier for Na+/O2 diffusion.13 In addition, during the charging process of the Na–O2 battery, the polarization is increased due to the over-accumulation of insoluble discharge products, which have a very low electrical conductivity, and thus tend to exhibit sluggish reaction kinetics during the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).15A non-aqueous sodium–air battery system can be constructed by combining a porous carbon material as an air/oxygen cathode and pristine sodium metal as an anode material. In the discharge process, NaO2 batteries.15–19 Different air cathode materials have been used to improve the sluggish reaction kinetics. These include carbon-based,16,18–23 noble metals,24–26 metal oxides,27–31 and metallic alloys,32,33 and they are among the numerous proposed potential catalysts for ORR and OER. In particular, carbon-based materials are advantageous for such uses due to their large specific surface area, high conductivity, and low cost.Therefore, development of inexpensive, stable, and highly efficient air cathode materials with high catalytic efficiency for the OER and ORR is of high importance for the development of efficient non-aqueous rechargeable Na–O2-bonded carbon atoms, is widely used as a cathode material in metal–air batteries due to its extraordinary properties such as lightest weight (approximately 2 g cm−3), ultrahigh theoretical surface area (2630 m2 g−1),34,35 extremely high chemical stability,34,36 and superior electronic conductivity and mechanical strength (100–300 times higher than steel).37,38 However, its application in various energy-related devices is limited due to the unusual semi-metallic nature of graphene with its zero band gap at the Dirac point.39 Although some methods exist for opening the zero band gap in graphene,40–42 heteroatom doping has proved to be effective in improving the semiconducting properties of graphene. The dopant atom modifies its electronic band structure and opens up an energy band gap between the valence and conduction bands.16–19,43–46Graphene, a two-dimensional nanomaterial with sp47–52 Experimentally, it has been proved that graphene nanosheets (GNSs) can act as potential cathode materials in Na–air batteries, with a high discharge capacity at a high current rate and stable cycling behavior that was maintained up to 10 cycles.53 In another study by Li et al.45 nitrogen-doped graphene nanosheets (N-GNSs) were studied as a cathode material in Na–O2 batteries. They reported that the N-GNSs exhibited more optimal electrocatalytic activity for the ORR and lower overpotentials than pristine GNS. Additionally, the results also revealed that the discharge capacities of N-GNSs were twice as much as those of pristine GNSs at all considered current densities.45 The experimental results showed that the synergistic effect of N and B co-doped graphene materials also increased the cathodic current in acidic and basic medium,54–58 proving enhanced performance of N,B co-doped graphene towards the ORR process.There has been great interest in nitrogen- and boron-doped graphene sheets due to the comparable atomic sizes between N and B and the C atom and their strong probability of entering a graphene lattice and forming p-type and n-type semiconducting graphene, which allows the fabrication of modern graphene-based electrochemical energy storage materials.2 batteries. A recent computational analysis of non-aqueous Li–O2 batteries indicated that heteroatom-doped graphene can significantly reduce the activation barrier of O2 evolution in the OER pathway.16–19 Among the five N-doped graphene configurations studied by Jing and Zhou,17 in-plane pyridinic N-doped graphene exhibited a more optimal performance in the catalytic activity of the ORR process. A density functional theory (DFT) analysis also predicted that B-doped graphene can be a good catalyst in Li–air batteries by reducing the oxygen evolution barrier due to its p-type behavior.19Apart from experimental studies, the computational insights into ORR/OER are also a useful tool to carefully investigate the catalytic mechanism in non-aqueous metal–O2 batteries. It was found that B-doped graphene presents the lowest discharge and charge overpotentials compared with N,B co-doped graphene, indicating the best catalyst for both the ORR and the OER processes in Li–air batteries.16 Despite the experimental investigation of the performance of doped graphene in non-aqueous-based Na–O2 batteries, there is limited information regarding the theoretical prediction of ORR/OER mechanisms. Moreover, to the best of our knowledge, there is no theoretical information regarding the effect of doped graphene on the growth/depletion of NaO2, which is the main discharge product in Na–O2 batteries, on B- and N-doped surfaces and their co-doped graphene in Na–air batteries.Recently, the ORR/OER performance of pristine graphene, N-, B-doped graphene, and N,B co-doped graphene was predicted using DFT for potential catalysts for the ORR/OER in non-aqueous Li–O2 battery system operating with an aprotic electrolyte. The effect of doping heteroatoms (B and N) on graphene sheets at various doping concentrations on NaO2 growth and depletion pathways, overpotentials, and equilibrium potentials was studied. Moreover, the charge transfer properties of pristine, doped, and co-doped (B and N) graphene materials were investigated using Bader charge analysis. A 6 × 6 × 1 graphene supercell containing 72 carbon atoms was arranged to examine the catalytic effect of heteroatom doping in ORR/OER mechanism studies. The number of B and N dopant atoms were increased from one to two and one to three, respectively, in the graphene structure, and doping occurred by substituting some of the carbon atoms of the graphene. Furthermore, N,B-co-doped graphene structures with separated and bonded sites were also considered in this study. This detailed computational investigation on heteroatom (B and N)-doped and co-doped graphene will increase our understanding of the NaO2 growth and depletion (ORR/OER) processes in rechargeable non-aqueous Na–O2 batteries and will provide clues regarding the design of novel doped graphene-based catalysts for rechargeable non-aqueous sodium–air batteries.Herein, DFT calculations were employed to investigate the catalytic activity of pristine graphene, B- and N-doped graphene, and B,N co-doped graphene materials towards ORR/OER for an Na–O2.59,60 calculations were performed with the grid-based projector-augmented wave method (GPAW) code61,62 through the atomic simulation environment (ASE).63 A real space grid basis set on the projector augmented wave (PAW) function method with frozen core approximation64,65 was used with 0.18 Å grid point spacing. Electron exchange and correlation was managed by the generalized gradient approximation (GGA) of the Perdew–Burke–Ernzerhof (PBE) functional.66 A 6 × 6 × 1 graphene supercell with 72 carbon atoms was employed for all structures considered in this study. Heteroatom (B and N) doping on graphene sheets was possible by substituting some of the carbon atom/s of the graphene sheet with the heteroatom/s of interest. The vacuum layer along the z-axis was set to be 20 Å to avoid any interlayer interactions in all calculations. The k-points were sampled with 4 × 4 × 1 Monkhorst–Pack grids, and 0.18 Å grid point spacing is used. Atomic energy optimization calculations were performed until all forces were less than 0.03 eV Å−1. The charge population was calculated by using Bader charge analysis. The stability of the chosen structures was estimated from the formation energies using the following equation:Ef denotes the formation energy, Eslab denotes the DFT total energy calculated for the slab model, and Ni and μi represent the total number and chemical potential of each atom, respectively. The chemical potential of carbon (μC) is defined as the total energy of graphene per carbon atom, and the chemical potential (μN) of N is taken as one-half of the total energy of the N2 molecule in the gas phase. The chemical potentials of the other atoms were obtained from their bulk phases. According to Ef of pristine graphene is naturally set to be zero and taken as the reference.DFTU). Thermodynamic potentials for the charging and discharging processes were deduced by calculating free energies of all intermediates shown in the elementary reaction steps. It is assumed that Na+ + e− are in electrochemical equilibrium at U = 0 V with a bulk Na metal. It is also assumed that the electrochemical potential of an electron shifts by −eU when electrode potential U initiates according to Nernst equation (U0 = ΔG/ne), where ΔG denotes the change in Gibbs free energy, n denotes the number of electrons involved with the electrochemical reaction, and e indicates the elementary charge. We defined overpotential for the discharging (charging) process as the maximum (minimum) potential to shift the free energies of all intermediates of ORR/OER downhill.To identify a potential-limiting step, thermodynamic free energy diagrams were calculated for the ORR/OER in the graphene, B- and N-doped and their co-doped graphene surfaces as a function of electrode potential . Hence, the corrected energy per formula unit of O2 was calculated according to E2ODFT denotes the calculated ground-state DFT energy, ZPE denotes the zero-point energy, and the integral is over the constant-pressure heat capacity of the O2 molecule.Large systematic errors in the description of superoxides, peroxides, and monoxides have previously been documented by various groups and have been accounted for in various ways.) and chemical (involving O2) species. In this study, only the thermodynamically favorable path  was determined by comparing the free energies of (electro) chemical reaction steps. The free energy of the intermediates in each step was calculated using energy-corrected O2 and sodium chloride (NaCl) as references, and is thus given as:G denotes the calculated free energy difference, ΔE, ΔZPE, T, and ΔS indicate the DFT total energy difference, changes in zero-point energy, temperature, and entropy of the slab of intermediates adsorbed on the catalyst surface at 300 K, respectively. In the case of solid–solid reactions, the change in ΔZPE and ΔS is often small, and ΔE becomes the predominant contributor in the free energy. However, due to the adsorption of gaseous molecules on the surfaces of solids, the change in entropy can be significant, and contribution should be considered (TΔS (O2) = 0.63 eV and ΔZPE (O2) = 0.131 eV).The ORR/OER process was described by the adsorption/desorption of both electrochemical (involving either Na* or Eads) of intermediates on the catalyst surfaces were calculated by the following equation:E(intermediate + substrate), E(intermediate), and E(substrate) refer to total energy of intermediate with a substrate, intermediate molecule, and a substrate alone, respectively.The adsorption energies  for the NG structure is increased from that of the pristine graphene. When the number of doped nitrogen atoms increased from one to two (the content of N is approximately 2.78 wt%) by replacing two C atoms from the graphene structure (Ef (1.696 eV) of 2NG was increased from that of NG  were doped into the structure of graphene (pyr-3NG) , it reveEf was higher in the 2BG structure (1.537 eV) as compared to that of the BG structure (0.300 eV), indicating that the formation of the 2BG structure is less favorable than that of the BG structure  and separated by a C atom (s-NBG) see . The N–C2 structure, which is in agreement with previous studies.16,18 As listed in 16 The stability sequence for NG, BG, s-NBG, graphene, and b-NBG obtained in this work is in agreement with other research performed to obtain potential catalysts in non-aqueous Li–O2 batteries.16Our calculation shows that the most stable B- and N-doped graphene and their co-doped graphene materials have a planar sp73,74 and the ability to activate sluggish carbon electrons for O2 utilization.75,76 Here, Bader charge density calculations were performed to determine how doped atoms influence electron distribution  showed negative electron transfer. The number of transferred negative electrons increased with increasing number of doped N atoms in the structure of graphene . Due to In B-doped graphene, approximately 0.47 electrons are transferred from B to C atoms of the graphene sheet . In this75,76 However, events can differ in the presence of sodium atoms. In general, it can be concluded that heteroatom dopants and increasing the number of dopants can improve the electronic structure of the graphene sheet via charge transfer and chemical reactivity.However, due to the neutralization of the vacant orbitals of B atoms by the lone-pair electrons from the N atom, high-electron density accumulation occurs between the N–B bonds in b-NBG. Therefore, b-NBG transfers the lowest number of electrons, indicating the creation of lower active sites in the doped structure and will result in unsatisfactory performance towards the ORR. However, when N and B atoms were co-doped and separated by the carbon, more electrons were transferred, indicating that more active sites are created around the doped atoms and more optimal ORR performance can be compared with b-NBG structure ; see FigFor increased understanding of the change in the electronic structure caused by dopants, the total density of states (DOS) was calculated for pristine and all doped graphene configurations, as shown in z orbital of nitrogen does not change in pyridinic nitrogen-doped graphene, but it causes a C vacancy, and the system loses one electron compared to pristine graphene. Thus, the system is like a p-doping semiconductor that shifts the Dirac point down. The DOS near the Fermi level is increased  shows semi-metallic behavior similar to that of pristine graphene (N-doping graphene (NG and 2NG) can be regarded as an electron donor, which contributes one more electron to the delocalized π bond than the C atom. Thus, the Dirac points move towards the valance band below the Fermi level, and the DOS intensity near the Fermi level increases ; thus, tncreased , and conncreased , indicatgraphene . The con3.2 species) and chemical (involving O2 species) reaction steps were considered. The thermodynamically favorable path  was determined. The overpotential is used as an evaluation parameter to compare the catalytic effect of the substrates. As illustrated in 2 on the most stable doped graphene structures, via a series of four elementary steps:where * denotes adsorbate intermediate in a catalyst surface.First, a graphene cluster that contains one nitrogen dopant atom was built and explored to determine the ORR process. Then, the number of nitrogen dopant atoms was increased from one to three. Reversible potentials of ORR sub-reactions on these doped graphene sheets were calculated and compared each other. For comparison, pristine graphene sheet with the same configuration was also constructed. To generate entire reaction pathways and to determine the minimum theoretical overpotential, both electrochemical , the first intermediate step was found to be the addition of a NaOgraphene  and S3†.U = 0 V  reach 1.15 V, 1.06 V, 1.13 V, and 1.82 V in pristine graphene, NG, 2NG, and pyr-3NG, respectively. The catalytic effects of N-doped graphene are evaluated by overpotential, which is defined by ηdis = U0 − Udis and ηch = Uch − U0 for the discharge and charge process, respectively. Hence, we identified each overpotential of the catalysts toward ORR in the discharging process as 0.76 V (pristine graphene), 0.84 V (NG), 0.92 V (2NG), and 0.40 V (pyr-3N), respectively, as shown in The calculated free energy diagrams of the discharge process in pristine graphene, B,N-doped, and their co-doped graphene are all downhill at ηdis/ηch, the adsorption energy of intermediates in each dis/charge limiting potential were calculated, and the ηdis/ηch was plotted as a function of adsorption energy , where the adsorption energy of NaO2 on the catalysts is the determining factor for the ηdis. The larger the adsorption energy, the more difficult it is for NaO2 to be involved in the subsequent reaction step, corresponding to a higher discharge overpotential. As can be seen in Fig. S6a,†ηdis increases as the adsorption energy increases, following the order of pristine graphene < NG < 2NG < pyr-3NG. Even if the limiting discharge potential of pyr-3NG is the formation of Na3O6 or addition of the third NaO2 species, its adsorption energy is less than that of pristine graphene, NG, and 2NG.To further clarify the relationship between dis/charge limiting potential and y Fig. S6. As ment4O8 is the limiting charge potential, and the ηdis also shows a positive correlation with the adsorption energy of Na4O8, as shown in Fig. S6b.ηdis/ηch through affecting its next step reaction. Moreover, the lower adsorption energy in dis/charge limiting potential has a positive effect on decreasing the ηdis/ηch. The relationship between ηdis/ηch and charge transferred was also evaluated by calculating the charge transfer of the intermediates after the growth mechanisms were completed, using Bader charge analysis. As shown in Fig. S7,ηdis/ηch as a function of charge transfer plot revealed that the larger the amount of charge transferred from the adsorbent (Na4O8) to the N-doped graphene surfaces, the less dis/charge overpotential they possess.Similarly, for pristine graphene and pyr-3N, depletion of Na3.32 battery system was computationally investigated. As illustrated in  species were successively adsorbed to the B-doped graphene surface to complete the growth mechanism during the discharge process. Addition of the first NaO2 species on all B-doped graphene surfaces was found to be the limiting discharge potential. Adding the second and third NaO2 was the potential limiting step for the charging process for BG and 2BG, respectively. The discharge overpotentials of BG and 2BG were identified as 0.37 V and 0.28 V, respectively  have a direct relationship. NaO2 is the limiting discharge potential for BG, while the limiting discharge potential for 2BG is Na3O6. The larger the adsorption energy, the greater the difficulty for NaO2/Na3O6 to be involved in the subsequent reaction step, corresponding to a higher discharge overpotential. To understand the underlying physical nature of the catalytic effect of B-doped graphene on the ORR/OER in a Na–O2 battery, Bader charge analysis was also performed. Table S3 and Fig. S94O8 to catalysts plays an important role in reducing dis/charge overpotentials. The charge transferred from Na4O8 to catalysts increases in the sequence of pristine graphene (0.1) < BG (0.45) < 2BG (0.50), indicating that 2BG is most active toward the ORR/OER as compared to pristine graphene and BG. However, relative to N-doped graphene clusters, both B-doped graphene exhibit lower dis/charge overpotentials. In our model, one and two of 72 C were replaced by one and two B atoms, and it is likely that a high-percentage doping will be more effective.As shown in Fig. S8,3.42 batteries. Similarly, four-step reaction mechanisms were considered, and all reaction steps were found to be electrochemical, which is the successive addition of four NaO2 species to the doped graphene surfaces to complete the growth mechanism  and separated by a C atom (s-NBG) was evaluated for its catalytic performance towards ORR/OER for non-aqueous Na–Oechanism  and S5†.2 batteries. As one can see from The discharge overpotential of the catalysts toward the ORR in the discharging process was identified , which i4.2 batteries. It was confirmed that both single- and double-boron-atom-doped graphene exhibited too low dis/charge overpotentials, indicating high catalytic activities towards both the ORR and OER processes compared to other doped graphene samples. Nevertheless, one- and two-nitrogen-doped graphene essentially did not exhibit improvement. Introducing pyridinic nitrogen (pyr-3NG) into the structure of graphene revealed a higher equilibrium potential and significantly boosted the catalytic activity for both the ORR and OER processes as compared to the other doped graphene sheets considered in this study. The findings of this research partly confirm previous reports, which state that a combination of two different heteroatoms  resulted in more optimal catalytic activity for the ORR and OER, and subsequently enhanced the battery performance compared to pristine graphene.Density functional theory analysis was employed to investigate the catalytic activities of B-doped, N-doped and B,N-co-doped graphene with varying dopant concentrations for the ORR and OER in rechargeable non-aqueous Na–O2 batteries. The NaO2 growth and depletion study with two-boron and three-nitrogen (pyridinic)-atom-doped graphene revealed too low limiting discharge/charge overpotential reaction pathways for both the oxygen reduction and oxygen evolution reactions, which elucidates the future design of non-precious carbon-based efficient catalysts in rechargeable non-aqueous Na–O2 batteries.Our DFT results suggest the viability of boron and nitrogen  doping in graphene sheets as potential catalysts for the ORR and OER in rechargeable non-aqueous Na–OThere are no conflicts to declare.RA-010-D0RA03126G-s001


The photovoltaic performance of a graphene/n-MoS2/a-Si:H/p-cSi/Au single facial HIT solar cell has been studied using AFORS-HET v2.5 simulation software. A maximum output efficiency of 25.61% has been achieved. The obtained results were compared with the results from a commercially available a-Si:H layer and p-cSi wafer after simulation. Moreover, the dependence of the cell performance on changes in the TCE and the back contact materials has also been studied. Finally, it has been demonstrated that the graphene layer and n-MoS2 layer could act as a TCE and an efficient emitter layer, respectively, in a n-MoS2/p-cSi based HIT solar cell.The efficiency of a Si-HIT (heterojunction with intrinsic thin layer) solar cell based on a graphene/MoS 2 and silicon-based HIT solar cell with 25.61% output efficiency.Graphene, MoS This deficiency of heterojunction solar cells can be overcome by the introduction of a thin intrinsic layer between the two doped layers of the heterojunction. Such a structure is known as a heterojunction with intrinsic thin layer (HIT) structure.1 In a HIT structured solar cell, the intrinsic layer-like a-Si:H reduces the interfacial recombination state density to the minimum level between two doped layers2 and reduces the leakage current.3 Recently, SANYO Ltd reported attaining a 20% output efficiency in HIT solar cells based on n-type Si.4 Furthermore, Panasonic has achieved the world's highest efficiency of 25.6% in a HIT cell based on an n-type c-Si.5The output efficiency (−1) and high optical transparency (85%) mean that indium tin oxide (ITO) is a commonly used TCE in photovoltaic (PV) applications. However, the high cost, rarity and mechanical rigidity of ITO have limited its use for future flexible devices and these drawbacks initiated the search for new TCE materials.6 Recently, pristine graphene has been reported to have an optical transparency as high as 97.7% (single layer graphene) with a work function of 4.31–4.5 eV  and –NH2 can increase the work function of graphene (ΦGr) to 1.20 eV and 0.46 eV from 4.31 eV (pristine graphene). Kim et al.8 demonstrated that, after being irradiated by an α beam the work function of graphene increases to 4.9 eV. Conversely, the low photoresponsivity, poor external quantum efficiency, and low absorption of light reduces the application of graphene as an emitter layer instead of the TCE layer in HIT solar cell.10 Unlike graphene, another 2D material, molybdenum disulfide (MoS2) has emerged as a complement 2D material for graphene as an emitter layer in HIT solar cells. MoS2 has a mobility of 200 cm2 V−1 s−1 in the monolayer and approximately 517 cm2 V−1 s−1 in few layers, as well as a high on/off ratio in the order of 108  dopant17 and polyethyleneimine (PEI)18. PEI reduces the sheet resistance of MoS2 2.6 times.18 These properties mean that MoS2 can be utilized as an emitter layer in MoS2/silicon HIT solar cells.In a solar cell, a transparent conductive electrode (TCE) is required to ensure the easy transportation of carriers from the emitter layer to the external circuit. The low sheet resistance  flow owing to the gradient of the corresponding quasi-Fermi energy (En/pF). Within the semiconducting layer, this is equivalent to the sum of the diffusion and drift current with the corresponding mobility μn/p.The electron/hole currents (ϕ(λ) of the incoming photon flux), the super-bandgap optical generation rate  from the valence band into the conduction band of the semiconductor layers can be evaluated by considering the Lambert–Beer absorption model by specifying the spectral absorption coefficient α, as well as specifying the dielectric properties  of each layer. An optical sub-bandgap generation  from a defect to the conduction/valence band can be defined by specifying the optical emission coefficients eon(E),eop(E) ≠ 0 for the defect state.If the heterostructure is illuminated ).Recombination from the conduction band into the valence band may occur directly  and χ), the bandgap (Eg) and the effective conduction/valence band density of states  will depend on the position x within the interface layer.The transportation across the heterojunction interface is modeled by drift-diffusion. In order to do so, an interface layer is considered. The specified interface defects are distributed homogeneously within this layer. The cell currents have to be evaluated directly from the gradient of the corresponding quasi-Fermi energies. The electron affinity , large quantities of lattice defects are produced and this increases the recombination at the interface. Thus, the introduction of an intrinsic (i) buffer layer a-Si:H could be beneficial to balance the carrier injection and reduce the leakage current in the cell.3 Therefore, the as-synthesized MoS2 is an n-type semiconductor24 and p-type silicon is more popular in the PV industries.4 Thus, in this simulation, we have used p-cSi as a base material. Moreover, the minority carrier diffusion length in p-cSi is also reported to be higher than n-cSi.25 Furthermore, Fan et al.26 have reported that ultrathin gold (Au) contacts provide a better electrical conductivity and optical reflectance-scattering to maintain the performance of the cell compared with ITO. Also, it has been demonstrated that an Au/Si interface formed by using novel transfer printing technology makes excellent electrical contact and exhibits a low contact resistance in comparison to that formed by vacuum deposition of Au on Si.27 Therefore, the proposed structure of the single facial HIT solar cell is configured as graphene/n-MoS2/a-Si:H(i)/p-cSi/Au, as shown in t〉 ≤ λF, in which 〈t〉 is the average system of the 2D electron system, λF is the Fermi wavelength which is equal to nm, and n2D is the carrier density in cm−2.28 Following this condition as reported by Sarma et al.29 and Suh et al.30 even n ∼ 105 cm−3 in graphene and n ∼ 1.8 × 1014 cm−3 in MoS2 cannot satisfy the above described conditions respectively. It has also been reported that doping in 2D materials increases the interlayer spacing.31 Thus, we consider graphene and MoS2 quasi 3D in nature instead of 2D. The quantum confinement in the structure was achieved by controlling the layer number of n-MoS2. In the proposed HIT structure, as shown in c-axis. Details of the front contact and the back contact parameters of the proposed structure are given in Table 16,7,26,32–37 and the parameters, as well as the ranges of the n-MoS2, a-Si:H and p-cSi are given in 2 as 0.65 nm.19,38,39 However, we started our simulation from five-layer (5L) graphene (1.67 nm) and six-layer (6L) MoS2 (3.9 nm) by considering the high overlapping probability of the graphene and p-cSi. It was also reported that the Raman spectrum of 6L MoS2 is very close to the bulk37 and the optical transparency of 5L graphene (88.5%) is more than that of ITO (85%).6 The parameters considered for optimization of the MoS2 layer were the donor concentration (ND), NC/NV, Eg, layer thickness, χ, dielectric constant (εr) and electron mobility (μn). The values of these parameters were kept within range and these and the results of the above mentioned previous literature are tabulated in 3,40–47 To simulate and optimize the other parameters the bulk and interfacial defect distribution and recombination rates were kept constant in the software. Furthermore, the MS-Schottky contact model was selected for the graphene/n-MoS2 and p-cSi/Au interfaces and the drift-diffusion model was selected for the n-MoS2/a-Si:H and a-Si:H/p-cSi interfaces. The values and parameters of these interfaces48 are listed in −2 and a temperature of 300 K. In order to study the effect of the layer parameters on the cell performance, the open-circuit voltage (VOC), short circuit current density (JSC), fill factor (FF) and efficiency (η) were analyzed. After optimizing the parameters of n-MoS2 further simulation was extended to the a-Si:H layer and the thickness and bandgap were optimized. The values and ranges of these parameters were obtained from previously published studies.4,49–51 Further simulations were performed to optimize the parameters, such as the NA, NC/NV, χ, and thickness for p-cSi. The values and the ranges of the parameters for the p-cSi layer were taken from the previously published research.4,47 The defect properties were kept as the default. Finally, we optimized the parameters of the contact materials, that is graphene, Au, ITO, Ag, and so forth. The work function (Φ) and the number of layers were optimized and other parameters were fixed, as found in the literature.7,8,34–37,52Layered structure MoS2.32 and p-cSi are brought into contact, a heterojunction forms and bending of the energy bands occur close to the Fermi level. This built-in potential (Vbi) is developed at the MoS2/p-cSi interface. This voltage facilitates the separation of photo-generated carriers in the solar cell. Generally, in the p–n junction solar cell, the interfacial defect density reduces the overall efficiency of the cell. Therefore, better surface passivation between the two layers is required to reduce the defect density at the interface. Here, an intrinsic layer a-Si:H is inserted between n-MoS2 and p-cSi. This layer can be deposited on Si using the plasma-enhanced chemical vapor deposition method at a low temperature (<200 °C) without degrading the bulk properties of the Si substrate.4 Also, it introduces band offsets between the active and emitter band which are also beneficial to obstructing the reverse flow of the charge carriers. The schematic energy band diagram of the proposed HIT solar cell is shown in eVbi) in the HIT solar cell is defined as:e, Eg, ΔEC and ΔEV, k and T are the electric charge, bandgap, the conduction band offset and valence band offset, Boltzmann constant, and the temperature in Kelvin, respectively. NA and ND represent the acceptor and donor concentrations and NC and NV are the conduction band and valence band density.53 In this HIT cell, a barrier for hole transportation is built at the interface between n-MoS2 and the pristine graphene corresponding to the potential energy of eVbi which can be expressed using the following equation:54Φ2MoS and ΦGr are the work functions of n-MoS2 and pristine graphene respectively. As reported in previously published literature,16 the Φ of a six layer MoS2 (∼5.4 eV) is greater than that of pristine graphene (∼4.1 eV).If n-MoS3.3.1ND of the n-MoS2 layer in the range from 1012 to 1018 cm−3, and other parameters such as the thickness, NC/NV, Eg,χ and εr are kept at feasible values as shown in ND was increased from 1012 cm−3 to 1016 cm−3, the VOC remained constant at the value of 636.7 mV. At ND > 1016 cm−3, the VOC increased to 646.1 mV as ND was increased to 1018 cm−3. At a low value of ND, the consistency of VOC indicates that it does not depend on ND unless the condition Δno ≫ ND is followed, as reported previously,56 in which Δno represents the excess electron–hole pairs. At ND > 1016 cm−3, the VOC increases owing to enhancement in the eVbi according to ND, this might keep JSC constant at 32.33 mA cm−2. Similarly, the FF was found to be constant at 76.71% until the ND reached 1016 cm−3 and then the FF slightly reduced to 75.73%. This is due to an increase in the recombination rate at a higher ND (1018 cm−3). As we have observed, the ND controls the VOC, thus the η of the cell remained constant at 15.79% as the ND increases, and a maximum of η = 15.82% was obtained at ND = 1018 cm−3.In this section, we have optimized the donor NC/NV is related to the effective mass of the electrons  and holes  as follows: . Furthermore,  is related to the mobility (μe/h) as follows: . From these two relationships, it can be concluded that with the change in mobility (μe/h) the conduction and valence band density (NC/NV) also changes. It has been reported that the mobility of the charge carriers in MoS2 changes with the change in the number of layer. MoS2 has a mobility of 200 cm2 V−1 s−1 in the monolayer and approximately 517 cm2 V−1 s−1 in few layers.11 Therefore, after optimization of ND to 1018 cm−3, the NC/NV was optimized in the range 3 × 1018 to 9 × 1020 cm−3 as shown in VOC increased from 646.1 to 668 mV with an increase of the NC/NV from 3 × 1018 cm−3 to 1020 cm−3. The increment in VOC can be understood by considering the equation:  in which ni is the carrier concentration, n is the intrinsic electron concentration and p represents the intrinsic hole concentration. Here, n = no + Δn and p = po + Δp, in which no and po are the concentrations of the electrons and holes in the equilibrium condition and Δn, Δp are the excess photo-generated electron and hole concentrations, respectively. As, nopo = ni2, n = ND and Δn = Δp, VOC can therefore be rewritten as .57 We can assume that VOC increased with NC/NV owing to an increase of Δp and Δn. As shown in VOC decreased a little bit to 666.4 mV as the NC/NV increased to 9 × 1020 cm−3, which is due to the decrement of eVbi according to JSC was found to remain constant at 32.33 mA cm−2 with an increase of NC/NV from 3 × 1018 to 9 × 1020 cm−3. Although the generation rate (G) of the photo-generated carriers is reported to increase with higher values of NC/NV.58 The constant JSC indicates that the photo-generated carriers either recombine or are trapped close to the metal/semiconductor interface. As with the VOC, the FF is also found to increase and a maximum value of 82.33% was obtained at NC/NV = 3 × 1020 cm−3. Therefore, η was found to be enhanced from 15.82% to a maximum value of 17.73%.The ND and NC/NV to values of 1018 cm−3 and 3 × 1020 cm−3, respectively we varied the bandgap (Eg) in the range 1.41–1.47 eV  was increased from 3.7 to 4 eV. Upon a further increase in the χ to 4.1 eV, a small increase in the VOC to approximately 691.4 eV was obtained owing to an increase in the eVbi. A constant JSC of 33.63 mA cm−2 was found in the range 3.74–3.90 eV of χ and this was enhanced to 34.16 mA cm−2 for χ = 4.1 eV. A small increase in the ΔEC  to 83.41% (@ χ = 4.1 eV) as a result of the reduction in the sheet resistance. Therefore, η was found to increase from 18.54% to 19.19%. ΔEC see  was obse2 layers is sensitive to the substrate that is used and the dielectric effect relies on the thickness of the sample.43 The effect of the dielectric constant (εr) on the cell parameters is depicted in VOC does not depend on the variation of εr and it was found to be a constant at 691.4 eV. However, the JSC shows a light decrement from 34.83 to 34.39 mA cm−2 with an increase of εr up to 14. In a p–n junction, , which affect the relative permittivity of the MoS2 layer.54,57 The generation of the e–h pair increases in the MoS2 layer with an increase in the εr following Coulombs law as , in which F is the electrostatic force between the electron and holes, but at the same time the increase in εr reduces eVbi. As a consequence of both of these effects, we obtained a constant VOC. In contrast, under short circuit conditions, the photo-generated carriers experienced reduced eVbi, which boosts the recombination of the carriers. Thus, the JSC was found to decrease. The FF showed a minor increase from 82.43% to 83.41% when εr was increased from 4 to 6. After this the increase in FF slowed down and only reached 83.49% for εr = 14. In η was found to largely depend on the VOC and remained constant at 19.91% with εr. The cell parameters of the proposed cell were found to be independent of the electron mobility (μn) of the n-MoS2 layer, which has been varied in the range of 517–50 cm2 V−1 s−1.It has been found from electric transportation measurements that the dielectric response of the MoS3.251 Moreover, the insertion of the thin intrinsic layer also contributes to the depletion region, as well as to the drift current and electric field strength.59VOC was slightly enhanced from 691.4 to 693 mV owing to a minor increase in the barrier height at the a-Si:H(i) layer and p-cSi interface.43 The VOC then became constant at 693 mV upon further increasing the thickness of a-Si:H(i). The JSC was found to decrease linearly from 34.56 to 34.08 mA cm−2. It is reported that a thicker intrinsic layer increases the series resistance in the cell.50 Therefore, we observed a tiny change in the JSC. Thus, the FF was found to reduce from 83.32% to 82.43%. Consequently, the η obtained reduced from 19.91% to 19.51%. To observe the cell performance for the optimized bandgap energy of a-Si:H(i), a further simulation was carried out by varying the Eg a-Si:H(i) in the range 1.6 to 2 eV. However, the maximum η = 19.19% was only obtained at Eg = 1.6 eV. This might be because the absorption of the photons by the MoS2 layer only corresponds to this Eg of the a-Si:H(i) layer.In the HIT solar cell, an intrinsic layer of a-Si:H is inserted, mainly for passivation of the c-Si surface in the cell.3.32 and a-Si:H(i) parameters to their optimal values, the simulation was further performed to optimize the parameters of the p-cSi layer, while keeping the parameters of n-MoS2 and a-Si:H(i) at their optimal values, as discussed in the previous section. The results of the cell performance against variation in the NA variation of p-cSi are shown in NA is increased from 1015 to 1017 cm−3, the VOC also increased from 691.2 to 699.2 mV owing to the higher eVbi with NA according to JSC was also found to increase from 34.23 to 39.15 mA cm−2 as the increased eVb pushes the photo-generated carriers effectively from the depletion region into the contact region without experiencing a recombination effect or the charge carrier trapped effect in the neutral region. This resulted in an increment in the JSC.57 The increment in the FF from 81.48% to 82.76% can be attributed to the reduction of the sheet resistance as JSC is also increased. These changes lead to an improvement in η from 19.46% to 21.88%. Hence, NA = 1017 cm−3 with a maximum η of 21.88% is considered to be the optimal value for the c-Si layer.After optimizing the n-MoSNC and NV on the performance of the HIT solar cell, we varied these parameters within the range of 3 × 1019 to 1 × 1021 cm−3 for the p-cSi layer. It can be observed from NC/NV, the VOC decreased linearly from 699.2 to 560.2 mV. According to NV of p-cSi layer the eVbi decreases and therefore VOC also decreases. In contrast, the value of JSC shows a small increase from 37.81 to 37.91 mA cm−2 with NC/NV. It has also been reported that NC/NV influences the bandgap as well as the absorption of photons.58 It can be estimated that for NC/NV > 3 × 1019 cm−3, the high absorption of photons in the active silicon layer increased the G of electron–hole pairs. In η dropping to 17.2% from 21.88%. The maximum value of η = 21.88% was obtained at NC/NV = 3 × 1019 cm−3.To understand the effect of VOC remains constant at 699.2 mV. Upon a further increase in the thickness, the VOC reduced sharply to 697.7 mV and again remained constant up to a thickness of 350 μm. Above this thickness, the VOC was found to deteriorate to the value 696.1 mV and becomes independent of the change of thickness. This variation may be due to the variation in the recombination of the photo-generated carriers under open circuit conditions. The observed enhancement in the JSC from 36.22 to 40.09 mA cm−2 can be ascribed to the boost in the generation of the charge carriers with the increase in the p-cSi thickness under short circuit conditions. The FF was observed to increase slowly from 82.72% to 82.96% owing to the reduction in the series resistance. These processes help to increase the η from 20.95% to 23.15% at a thickness of 500 μm.In solar cell technology, the thickness of the p-cSi wafer plays an important role in the fabrication of HIT solar cells. 2 and the a-Si:H(i) layer thickness with the best optimized p-cSi parameters, the proposed cell was again simulated by varying the number of layers of MoS2 and the thickness of a-Si:H and the results are depicted in VOC increased from 696.1 to 699.2 mV when the number of layers of n-MoS2 was increased from 3 to 5. Furthermore, the increase in the number of layers to 6VOC remains constant at 699.2 mV. On the other hand, the JSC, FF, and η were observed to decrease with the increase in the number of layers. The JSC decreased from 40.09% to 39.42%, the FF from 82.96% to 82.25 and the η from 23.15% to 22.67%. In VOC gave a constant value of 696.1 mV and increased slightly to 697.7 mV when the thickness was increased to 6 nm. The VOC then became independent of the thickness even when it was increased to 10 nm. The JSC was found to decline from 40.09 to 39.05 mA cm−2 with the thickness of a-Si:H(i). The FF was found to decrease from 82.96% to 82.38% and a minimum η of 22.14% was achieved at 10 nm.To study the role of the number of layers of n-MoS3.4VOC remained constant at 697.7 mV. The reason behind this consistency might be the decrease in the recombination rate which limits the reduction of the charge carrier generation under open-circuit voltage conditions. However, upon further increasing of the graphene layer number to 4, the absorbed light might not be sufficient to produce an efficient electron–hole pair, which causes the VOC to slightly decrease to 696.5 mV and then become constant with an increase in the layer number. On the other hand, the JSC was observed to decline linearly from 44.25 to 40.09 mA cm−2. When the number of layers of graphene was increased the optical transmittance reduced and thus the G of the charge carriers decreased and therefore the JSC reduced too. Under short circuit conditions, the photo-generated carriers could be trapped close to the graphene/n-MoS2 junction. Therefore, we have observed a linear decrease in the JSC, which also, in turn, reduced the η from 25.61% to 23.15%. An insignificant change in the FF was found from 82.95% to 82.96%.In a solar cell, contact plays a transparent conducting electrode role in the solar cell by allowing the light to transmit through and maintain a high electrical conductivity. 60,61 Usually, the contact resistance is a vital factor that affects the solar cell performance.62 However, many experimental reports suggest that by controlling the Fermi level (i.e. the work function) of graphene, the contact resistance can be minimized in the graphene/MoS2 interfaces.63,64 Therefore, in this work, we have focused primarily on the work function of graphene. The depicted results shown in ΦGr) from 4.31 to 4.9 eV. A large reduction in the VOC was observed in ΦGr. From ΦGr, the potential barrier energy eVbi of graphene/n-MoS2 decreases. It has also been reported that when the ΦTCO (contact) of Si HIT solar is low, the eVbi of the TCO (transparent conducting oxide)/n-type emitter has the same direction as that of the eVbi of the n-emitter/p-Si. On the other hand, when the ΦTCO (contact) is high, the eVbi of the TCO/n-type emitter contact will have an inverted direction to that of the eVbi of the n-emitter/p-Si junction. Moreover, with the increase in the Φ of the TCO contact in the silicon HIT solar cell, the depletion region in the emitter region increases and widens and results in the overlap of the contact/n-type emitter region and the n-type emitter/p-type silicon junction region if the emitter is not sufficiently thin enough.4 Thus, the higher ΦGr might increase the possibility of overlapping between the graphene/n-MoS2 depletion region and the n-MoS2/p-cSi depletion region, which has resulted in a reduction in the VOC. In contrast, owing to the overlap of the graphene/n-MoS2 depletion region and the n-MoS2/p-cSi depletion region, the eVbi of n-MoS2/p-cSi reduces. This results in a reduction of the built-in electric field which is unable to push the photo-generated carriers effectively to their respective sides under short circuit conditions and thus the JSC is observed to decline linearly from 44.25 to 40.09 mA cm−2 with an increase in the ΦGr. The overall reduction in the VOC and JSC reduced η from 25.61% to 23.15%. The maximum η = 25.61% was achieved at ΦGr = 4.31 eV of pristine graphene.The presence of a strong covalent bond between the C and Mo atoms or the presence of a dangling bond of sulfur present in the interfaces affects the interfacial barrier height and a variation in the barrier height results in a variation in the contact resistance.2 and a-Si:H(i) with the practically available p-cSi parameters by varying the ΦGr and p-cSi thickness within the range of 4.31–4.9 eV and the 50–500 μm range respectively, as depicted in 52,65 It can be seen from η = 25% was obtained at ΦGr = 4.31 eV, which is close to our best-optimized results as shown in η = 25% was achieved for a 500 μm thick p-cSi wafer.To validate our simulated results, a comparison has been performed by considering the best-optimized values of n-MoS3.519 and the back contact to Ag. As seen in ΦITO has been varied from 4.40–4.50 eV.34 The maximum values for VOC, JSC, FF and η were obtained and found to be 625.8 mV, 31.47 mA cm−2, 80.41% and 15.33% respectively. Similarly, in ΦAl was varied, the maximum values for VOC, JSC, FF, and η were found to be 650.8 mV, 4.36 mA cm−2, 82.79% and 2.353%, respectively. In both cases, η was significantly lower than that of η obtained using the graphene layer as a contact.In this section, a comparison of the cell parameters has been performed by changing the front contact material graphene to ITO and AlΦ of Ag was maintained from 4.64 to 4.74 eV. It was observed that in this range of Φ for Ag, the VOC increased from 664.8 to 677.3 mV, whereas the JSC remained constant at 42.76 mA cm−2. The FF and η were observed to decrease from 82.72% to 83.5% and 23.51% to 24.19%, respectively. This η was close to our simulated ηmax value, that is, 25.61% when we used Au as a contact. Here, the back contacts have been considered as the uniform thin film deposited on the backside of p-cSi.3.6IV characteristics of the best optimized solar cell generated by the software are shown in Rs), was calculated from the IV characteristics and found to be 25.4 mW cm−2 and 2.5 Ω cm2 was achieved respectively /p-cSi/Au structure has been proposed and simulated using AFORS-HET v 2.5 software. The individual effects of the six parameters of the n-MoS2 layer were analyzed individually. After optimizing the parameters of the n-MoS2, a-Si:H(i), and p-cSi layers, an optimum efficiency of 23.15% was achieved. As the contact material in a solar cell has an adverse effect on the cell performance, a further simulation was performed to observe the effect of graphene on the proposed HIT solar cell by varying the number of layers and the work function. From this simulation, a maximum efficiency of 25.61% was achieved for single-layer graphene at a work function of 4.1 eV. On the other hand, by changing the front contact graphene to ITO and Al we achieved efficiencies of 15.33% and 2.35%. This confirms that graphene could be an efficient contact material for use in an n-MoS2/a-Si:H(i)/p-cSi/Au HIT solar cell. Our simulated results establish that the graphene layer could be an effective contact TCE material and n-MoS2 could be an efficient emitter layer in a single facial n-MoS2 and p-cSi based HIT solar cell.In order to develop an efficient HIT solar cell, a graphene/n-MoSThere are no conflicts to declare.NA-002-D0NA00309C-s001


This paper is concerned with an analysis of the electrical conductivity of graphene/cement composites by means of DC (direct current) and AC  techniques. Moreover, the micrograph and element composition of composites have been characterized through SEM (scanning electron microscopy) and EDS (energy-dispersive spectrometers) techniques, respectively. Results revealed that a percolation transition region Φ2–Φ1  can be observed in the S-shaped curve. In addition, the logistic model has been recommended to characterize the relationship between the conductivity and the graphene concentration, which ranged from 0.001% to 2.5%. The micrographs obtained by SEM technique clearly indicate a complete conductive network as well as agglomeration of graphene slices when the graphene content reaches the threshold value. Furthermore, graphene slices can be distinguished from the cement hydration products by means of the analysis of element composition obtained through the EDS technique. It is promising to apply the graphene/cement composites as intelligent materials. The electrical conductivity of plain cement paste under dry condition usually ranges from 8.7 × 10Ω−1·cm−1 ,3,4. Hen−1·cm−1. Much attention has been paid to improvement of the conductivity of cement paste by means of graphite [−1·cm−1. In addition, Xu et al. [2 v−1 s−1) and large theoretical specific surface area (2630 m2 g−1) [Chung  comparedgraphite , carbon graphite ,8, and cgraphite ,10. Chengraphite  found ou m2 g−1) . Moreove m2 g−1) ,14,15. T m2 g−1) ,17,18,19Concerning the relationship between the conductivity and the content of conductive materials, the percolation transition zone has been widely found in the curve, which could be explained by the application of percolation theory. Based on this, a percolation equation has been used to characterize the relationship between conductivity and conductive material content . HoweverIn this study, the conductivity of graphene/cement composites was investigated by direct current (DC) and alternating current (AC) techniques. In addition, both logistic model and percolation theory were used to describe the relationship between the conductivity of cement/graphene composites and graphene concentration. The micro-morphology and element compositions of composites could be obtained by means of SEM and EDS methods.The cement used was PI 52.5 Portland cement. The relevant performance is shown in The water/cement ratio was set as 0.5, and 2.0 cm × 2.0 cm × 6.0 cm specimens were cast with 15 levels of graphene content, ranging from 0% to 2.5% by mass of cement. Before casting, graphene and cement were mixed in a commercial mixer with a rotating speed of 120 r/min for ten minutes. A specimen was filled with four pieces of conductive mesh electrodes (20 mm × 25 mm × 0.5 mm) with a spacing of 2 cm. Specimens were demolded after 24 h and then cured in a room under the condition of 95% RH and 25 °C for a month.The specimens were dried in a drying oven at 45 °C for 2 days in order to ensure completely dried specimens. Then, the specimen was conducted with direct current (DC) as well as alternating current (AC) measurements. It should be pointed out that the DC measurement was performed by means of the four-probe method. Moreover, the AC measurement was carried out using a Princeton Applied Research (PAR) START 2273 Potentiostat with a sinusoidal potential perturbation of 10 mV at the open circuit potentials and a frequency in the range from 10 mHz to 100 KHz. A detailed introduction concerning these two measurements is shown in R) depends on the geometry of specimens, as expressed by Equation (1):The electrical resistivity .A technique using scanning electron microscopy  equipped with energy-dispersive spectrometers (EDS) was used to investigate the micro-morphology and element composition of the graphene/cement composites. Small-cored samples (approximately 2 mm × 2 mm × 0.5 mm) were collected from specimens and then used for SEM observation. These small-cored samples were immersed into a 95 vol% ethanol solution to stop hydration and then dried in an oven at 45 °C for 3 days. The surface of small-cored samples was covered with a thin gold layer before SEM observation.−6, and this value grows slowly with the increase of graphene content. However, an abrupt increase of conductivity value has been observed once the graphene content exceeds 0.5% vs. cement. The conductivity changes by several orders of magnitude when the graphene content is more than 1.8% vs. cement. It is apparent that the composite’s conductivity is dependent on the graphene content.The electrical resistivity and conductivity values of the graphene/cement composites determined by direct current (DC) measurements versus the graphene content are plotted in Even though the DC measurement technique has some advantages, such as quick response and easy operation in measurement of the conductivity of composites, polarization has a heavy influence on the accuracy of results . Therefocusp, referred to as the electrical resistivity at high frequency, is also highlighted in There exists a narrow region in which the electrical conductivity increases quickly. This feature has been defined as the percolation phenomenon; based on this, this narrow region was usually defined as percolation transition zone research , Equatiording to . On the lue of 2 . In addiRE) is introduced to evaluate the difference between the measured (M) and predicted (P) values, which is expressed by Equation (6):This equation shows good agreement because the correlation coefficient for this model is as high as 0.9929. It accurately describes the relationship between the conductivity of composites and graphene concentration ranging from 0.001% to 2.5 % with respect to the mass of cement. In addition, it can precisely predict the evolution of the conductivity of composites with the graphene concentration. Some extra graphene contents in the graphene/cement composites and relevant conductivities are presented in RE values for these chosen graphene concentrations are lower than 10%, which indicates that the predicted values calculated by Equation (5) have a small deviation compared to those measured values. This logistic model is recommended by the authors to characterize the relationship between the conductivity and the content of conductive materials such as steel powder, graphite powder, carbon fiber, carbon nanotube, and graphene in the composites.As shown in 3 Ω−1·m−1) and plain cement paste (about 10−6 Ω−1·m−1) conductivities is near to infinity σcIn addition, the ratio of the conductivity of composites (when the graphene particles are conducting at high frequency) to the conductivity of matrix is associated with the resistances in the EIS measurements given by:Therefore, combining Equations (7) and (8) and rearranging yields:Equation (9) indicates the whole contribution of graphene particles to the conductivity of graphene/cement composites. However, it must be pointed out that graphene dispersion issues, including orientation, coarse-scale isolation, and local aggregation, may be much too difficult to quantify for graphene/cement composites.EDS analysis results of the chosen points in This work measured the electrical conductivity of graphene/cement composites with different graphene additions by means of DC and AC methods. Through comparison, the conductivity of graphene/cement composites measured by AC technique is more accurate than that of DC due to the little influence of polarization.There exists a percolation transition region The micromorphology clearly indicates a complete conductive network as well as agglomeration of graphene slices when the graphene content reaches the threshold value. In addition, graphene slices can be distinguished from cement hydration products by their special morphology and elemental quantification through EDS technique. As far as we are concerned, it is promising to use graphene/cement composites as smart materials.


In the system, oil and other impurities in wastewater are isolated by an oleophobic/hydrophilic membrane before detection. The concentration of Cd2+ is then detected by a graphene field-effect transistor with a Cd2+ aptamer modifying the graphene channel. Finally, the detected signal is collected and processed by signal processing circuits to judge whether the Cd2+ concentration exceeds the standard. Experimental results demonstrated that the separation efficiency of the oleophobic/hydrophilic membrane to an oil/water mixture was up to 99.9%, exhibiting a high oil/water separation ability. The A-GFET detecting platform could respond to changes in the Cd2+ concentration within 10 min with a limit of detection (LOD) of 0.125 pM. The sensitivity of this detection platform to Cd2+ near 1 nM was 7.643 × 10−2 nM−1. Compared with control ions , this detection platform exhibited a high specificity to Cd2+. Moreover, the system could send out a photoacoustic alarm signal when the Cd2+ concentration in the monitoring solution exceeds the preset value. Therefore, the system is practical for monitoring the concentration of heavy metal ions in oily wastewater.The discharge of oily industrial wastewater containing heavy metal ions with the development of industry severely threatens the environment and human health. Therefore, it is of great significance to monitor the concentration of heavy metal ions in oily wastewater quickly and effectively. Here, an integrated Cd 2+ in oily wastewater without sample collection and pretreatment.An integrated system realizes the direct detection of Cd Heavy metals, such as lead, cadmium, and mercury, can cause serious harm to biological systems, such as the nervous, respiratory, and cardiovascular systems, when the concentration exceeds normal values.3–7 Therefore, it would be of great significance to monitor the concentration of heavy metal ions quickly and effectively. In the integrated wastewater discharge standard issued by the State Environmental Protection Administration of China, the maximum allowable emission concentrations of heavy metals in wastewater are specified,8 and the emission standards of some heavy metals are shown in Table S1.9–12 These traditional methods generally require overnight pretreatment of the samples. Additionally, the relatively long detection cycle and large bulk of the detection equipment mean that the conventional methods cannot meet the needs for rapid, effective, and on-site detection. Portable devices that could achieve the rapid and effective detection of metal ions could play an important role in preventing heavy metal pollution in oily industrial wastewater.With the development of industry, the pollution of heavy metals in the water environment is becoming increasingly severe due to the discharge of oily industrial wastewater containing heavy metal ions.13 Owing to its high sensitivity to its surface charge distributions, a graphene-based field-effect transistor can convert changes in the charge distribution on the graphene surface into detectable electrical signals.14,15 As a new identification element obtained by systematic evolution of ligands by exponential enrichment (SELEX) technology, aptamers have the advantage of being easy to synthesize and having good stability compared with antibodies, enzymes, and other biological probes.16–18 Aptamer-graphene field-effect transistors (A-GFETs), in which the aptamer is modified on the surface of the graphene channel for use as a biological probe, have been successfully applied in the detection of DNA,19 proteins,20,21 and other organic compounds.22 Moreover, several studies using A-GFETs for ion detection have also been reported, with the transistors exhibiting high specificity, fast response, and low limit of detection compared with traditional detection methods.23–25 The A-GFET sensor can be fabricated on a tiny silicon chip (2 × 2 cm); thereby promoting the development of miniaturization and portability of the ion-detection equipment. Nevertheless, some problems remain to be solved when the A-GFET is applied for the detection of metal ions in oily wastewater.Graphene, a two-dimensional material with excellent electrical properties, has attracted considerable attention since it was first prepared in 2004.21,26 In particular, the difficulty of achieving oil/water separation further limits the application of A-GFETs for detecting heavy metal ions in oily industrial wastewater. Hence, the antifouling treatment of graphene surface is a critical challenge in applying A-GFET biosensors to actual samples. In recent years, despite selectively wetted surfaces having attracted considerable attention due to their high separation efficiency for oil/water separation,27–30 the problem of oil deposition on the graphene surface has still not been effectively solved.Currently, most studies of A-GFETs have been conducted using artificial samples with a relatively simple composition since the surface integrity and electrical properties of graphene are highly susceptible to other substances in the detecting environment.2+ in oily wastewater. In this system, the prepared oleophobic/hydrophilic membrane could effectively achieve the filtration of oil pollution in wastewater, thus allowing solving the problem of oil deposition on graphene surfaces in practical applications. At the same time, the integrated circuit board could realize the timely collection and processing of signals, meeting the needs for on-site detection. Also, the application of such A-GFET detection technology in Cd2+ detection could effectively shorten the required time for performing the detection process. In addition, the integrated monitoring system prepared in this study is more portable compared with the conventional ion-detection equipment owing to the small size of the system components.In this study, an integrated monitoring system consisting of an aptamer-graphene field-effect transistor, oleophobic/hydrophilic surfaces, and monitoring-alarm circuits is presented. Benefiting from the effective filtration of the oleophobic/hydrophilic membrane for oil, the integrated system could realize the direct detection of Cd2+-detection process in oily wastewater is shown in 2 nanoparticles, and stainless-steel mesh to stop the oil and other solid pollutants from contacting the graphene channel. Second, the A-GFET detecting platform was prepared to achieve the detection of Cd2+. In this setup, the solution, after filtration, is in contact with the graphene channel, and the Cd2+ in the solution is captured by aptamers modified on the surface of the graphene simultaneously. The aptamers transform from an extended long-chain structure into a compact and stable structure after combining with Cd2+, which can pull more negative charges produced by the hydrolysis of phosphate groups in aptamers close to the surface of the graphene, changing the surface charge distribution of graphene. As a result, the electrical signal of the graphene-based field-effect transistor changes accordingly. Finally, the detected signal is collected and processed by the monitoring-alarm circuits, which allows then judging whether the Cd2+ concentration exceeds the standard. The integrated monitoring system is a practical solution for monitoring the concentration of heavy metal ions in oily wastewater.The Cd2+ concentration within 10 min with high specificity and a low LOD of 0.125 pM. Also, the oleophobic/hydrophilic membrane could effectively eliminate the influence of oil pollution on the detection performance of the A-GFET detection platform for Cd2+, achieving a high separation efficiency of over 99.9% for oil/water mixtures.The experimental results demonstrated that the A-GFET detecting platform could respond to changes in Cd22.12/Si was ordered from UniversityWafer Inc. . 1-Pyrenebutanoic acid succinimidyl ester (PASE), dimethylformamide (DMF), and ethanolamine were purchased from Sigma-Aldrich . Cadmium chloride hemi(pentahydrate) was purchased from Aladdin . The Cd2+ aptamer (sequence 5′-NH2- CTC AGG ACG GGT TCA CAG TCC GTT GTC -3′) was synthesized and purified by Sangong Biotech . Fluorosurfactant FS-50 was purchased from Dupont . Spray-Mount Super 75 adhesive was purchased from 3M . Titanium oxide (TiO2) anatase (100 nm) was purchased from Macklin . The main agent and curing agent of 184 silicone rubber (PDMS) and AB adhesive were purchased from Yihui Adhesive .Chemical vapor deposition (CVD) graphene was purchased from Graphenea , while 285 nm SiO2.22 (285 nm) are illustrated in Fig. S1.The fabrication processes for the gold electrodes on the surface of a silicon wafer covered with a layer of SiOPASE was used as a linker to modify the aptamer onto the graphene surface. The silicon wafer was first immersed in 5 mM PASE solution at room temperature for 3 h and then rinsed with DMF to remove free PASE not fixed to graphene. Subsequently, a droplet of aptamer solution (50 μl) with a concentration of 100 nM was dropped onto the graphene overnight at room temperature. Finally, the A-GFET detecting platform was immersed in 100 mM ethanolamine for 1 h to inactivate the reactive groups in the PASE molecules that were not bound to the aptamer, and then rinsed off with ethanol and deionized water successively.2+ detection are shown in Fig. S2 and S3.†The pyrenyl group at one end of the PASE molecule was combined with graphene by π–π stacking, while the ester group at the other end was combined with the amino group on the aptamer by Schiff base condensation to achieve modification of the aptamer on the graphene surface. The principles for the graphene surface modification and Cd2.32 nanoparticles was added to the FS-50/ethanol solution. The mixture was stirred magnetically at room temperature for another 1 h to form a suspension. Subsequently, the suspension was evenly sprayed on the surface of the stainless-steel mesh after cleaning with alcohol. A layer of 3M adhesive was sprayed on the surface of the stainless-steel mesh before spraying the suspension, which could allow the nanoparticles to adhere to the surface of the stainless-steel mesh tightly. Finally, the stainless-steel mesh was put into a drying box at 80 °C for 30 min to evaporate the ethanol.28 The physical model of the oleophobic/hydrophilic membrane is shown in Fig. S4†To fabricate the oleophobic/hydrophilic membrane, 3 g of fluorosurfactant (FS-50) was added to 50 mL of ethanol. The mixture was then stirred at room temperature for 20 min. Then 1.2 g of TiO2.4Vds) output and gate voltage output (Vg). A Vds of 10 mV was supplied by a voltage regulator circuit, and the Vg was supplied by DAC8831IBD, ranging from 0 to 0.5 V in steps of 1 mV. During the detection process, the drain-source current (Ids) of the A-GFET detecting platform was converted into a voltage signal by an amplifier circuit and then collected by the A/D converters ADS1274 and THS4524. The collected signal was processed by the microcontroller STM32F429IGT6, and the system would send out a photoacoustic alarm signal if certain preset conditions were met.The system included a power supply, voltage output, signal acquisition, signal processing, and photoacoustic alarm circuits. In the power-supply circuit, the voltage of 5 V was supplied directly by the transformer, while a voltage of 2.5 V was outputted by the REF5025 while voltages of 1.8 and 3.3 V were outputted by the AMS1117 power-supply modules. The voltage output circuit included a drain-source voltage  and 2D-peak (2700 cm−1). After PASE modification, a D-peak appeared at 1300 cm−1, and G-peak splitting at 1620 cm−1, where the peak ratio of the 2D-peak to G-peak in the Raman spectrum of graphene decreased from 1.91 to 1.04, which could be due to the binding of graphene and the pyrene groups on PASE. In addition, the full width at half maximum (FWHM) of the 2D-peak was always 28 cm−1, both before and after PASE modification, which could be evidence of the monolayer graphene. That is, the modification of PASE was successful. Compared with the PASE molecule in the chemical element composition, the aptamer (single-stranded DNA) had phosphorus. Energy dispersive spectroscopy (EDS) showed that the phosphorus on the graphene surface was significantly increased after aptamer modification  of graphene before and after aptamer modification to solutions with Cd2+ concentration of 1 nM and 100 nM were measured respectively  of the detection platform for Cd2+ was 0.125 pM  with a concentration of 100 nM was measured , Vds output, alarm module (buzzer and LED light), power-supply module (REF5025 and AMS1117), voltage/current conversion module , and detection platform interface.Alarm experiments were carried out to verify the function of the circuits. As shown in 2+ in industrial wastewater is 0.1 mg L−1 (0.9 μM).8 In the actual detection, as a real-time monitoring system, we hoped that the system would send an alarm signal before the concentration of Cd2+ in oily wastewater increases to the limit concentration rather than when it has reached the limit concentration. Therefore, we introduced a security coefficient (k) to reduce the concentration of Cd2+ and to trigger the alarm signal. After introducing the security coefficient k, the alarm concentration (climit) can be obtained by cstandard is 0.9 μM, and the value of k can be taken as 1.2. By calculation, the value of climit is 0.75 μM. The moving dimension of the gate voltage at the Dirac point (ΔVdirac) corresponding to the climit can be determined by M is the compensation factor, c is the concentration of Cd2+ in the solution, P is the synergistic factor, and Kd is the constant of dissociation equilibrium. The values of M, Kd, and P could be obtained by the fitting process of Vdirac-max was 50 mV. After calculation, the ΔVdirac that triggers the alarm signal was 46.8 mV. As shown in 2+ concentrations of 10 pM, 100 pM, 1 nM, 10 nM, and 100 nM, respectively. When the graphene channel was exposed to Cd2+ solution with a concentration of 1 μM, in which the moving dimension of the gate voltage at the Dirac point exceeded 46.8 mV, the circuit board sent out a photoacoustic alarm signal.The maximum discharge standard of Cd3.42 nanoparticles induced multilevel roughness on the surface of the stainless-steel mesh, which enhanced the surface wettability by increasing the surface area.28 The contact angles of vegetable oil, kerosene, and water on the membrane surface are shown in n-hexadecane/water) were prepared. Oils and water were dyed by Sudan III and methylene blue, respectively, before separation so that the oil–water boundary could be investigated clearly. In the process of the experiment, the water passed through the membrane while the oils were trapped on top of the membrane surface  . The SEM surface . After sectively . These r3.52+ in oily wastewater, an oil-containing solution was prepared by adding 25 mL oil to 100 mL Cd2+ solution with a concentration of 100 nM and then stirred magnetically at room temperature for 30 min. Subsequently, the solution was divided equally into two parts labeled solution A and solution B. Solution A was directly added to the graphene channel in the A-GFET detecting platform, and solution B was added to the graphene channel after filtration by the membrane. The transfer characteristic curves of graphene's response to solution A and solution B are shown in x-axis, the correct transfer characteristic curve of graphene could not be obtained under the influence of oil when the A-GFET detecting platform was exposed to solution A, indicating the membrane can avoid the influence of oil on the detection performance.To verify that the membrane could effectively eliminate the influence of oil pollution on the detection performance of the A-GFET detection platform for Cd2+-monitoring system was programmed to detect the transfer characteristic curve of graphene every 10 min. The voltage at the Dirac point in each detection was screened out to subtract it from the first detection, except for the first one. The Cd2+-monitoring system will send out a photoacoustic alarm signal until the deviations exceed the preset value. To investigate the monitoring ability of the system to Cd2+, the sensing part of the Cd2+ monitoring system was immersed in artificial oily wastewater without Cd2+. Then Cd2+ was added to the artificial oily wastewater every 10 min. The oil was blocked from the Cd2+-monitoring system by the barrier of the membrane, while the Cd2+ could pass through the membrane and contact with the graphene channel of the A-GFET detecting platform, thereby achieving the concentration monitoring of Cd2+. During detection, the concentration of Cd2+ in the oily wastewater was increased to 100 pM, 10 nM, and 1 μM by adding Cd2+ every 10 min. The monitoring system sent out a photoacoustic alarm signal until the Cd2+concentration went up to 1 μM with a preset value of 46.8 mV. Furthermore, the system did not send out an alarm signal when the sensing part was immersed in oily wastewater with a concentration of Cd2+ less than 1 μM (100 pM and 10 nM) and kept in solution for 30 min  of 0.125 pM. Also, compared with control ions, such as Cr3+, Pb2+, Mg2+, and Fe3+, the detecting platform exhibited a high specificity to Cd2+. Second, the oleophobic/hydrophilic membrane was prepared using the fluorosurfactant FS-50, TiO2 nanoparticles, and stainless-steel mesh to stop the oil from contacting the graphene channel. The membrane exhibited a good oleophobic property with a contact angle of 140° to vegetable oil and 130° to kerosene. Also, the membrane also exhibited a high separation efficiency for oil/water mixtures. Finally, monitoring-alarm circuits, including power supply, voltage output, signal acquisition, signal processing, and photoacoustic alarm circuits, were designed to collect and process the signal produced by the A-GFET detecting platform. The collected signal was processed by the microcontroller STM32F429IGT6 after being converted into the voltage signal by an amplifier circuit. Following this, the instructions were sent to the alarm module if the alarm condition was triggered. The Cd2+-monitoring system could achieve Cd2+-concentration monitoring in oily wastewater with different limits of Cd2+ concentration by changing the alarm condition, thus demonstrating great potential for monitoring the concentration of heavy metal ions.In this work, a CdThere are no conflicts to declare.NA-005-D2NA00416J-s001