The possibility of printing electronic circuits will further promote the spread of the Internet of Things applications. Inks based on graphene have a chance to dominate this technology, as they potentially can be low cost and applied directly on materials like textile and paper. Here we report the environmentally sustainable route of production of graphene ink suitable for screen-printing technology. The use of non-toxic solvent Dihydrolevoglucosenone (Cyrene) significantly speeds up and reduces the cost of the liquid phase exfoliation of graphite. Printing with our ink results in very high conductivity (7.13 × 10 Printed conductive inks show promise for future electronic device applications. Here, the authors report synthesis of graphene inks with conductivity of 7.13 × 10^4 S/m by Cyrene assisted liquid phase exfoliation, and their applications in data communication and RF energy harvesting. As conductor is the core component in printed electronics, efforts have been mainly focused on providing highly conductive metal nanoparticle inks, especially using silver nanoparticles9. Silver nanoparticle inks are widely used because of their high conductivity and good levelling property. However, silver is too expensive to be employed for low-cost applications10. Other metal nanoparticles such as copper or aluminium are much cheaper but can be easily oxidized. To avoid oxidation, a sintering process is necessary after printing12. However, in the case of heat-sensitive substrates , sintering cannot be applied. Conductive polymers can also be fabricated as conductive film. This technique is however both chemically and thermally unstable13. Carbon nanotubes (CNTs) were once seen as an alternative for metal nanoparticles. The extremely high junction resistance between CNTs results in lower surface conductivity and hinders their applications14. The printed electronics industry has long been crying out for low-cost highly conductive inks.Development of printed conductive inks for electronic applications has grown rapidly due to widening applications in transistors15, screen printing16, inkjet-printing18 and doctor-blading19 techniques. For antenna printing applications, spraying is a less reported method, suffering from lacking of flatness in films. Inkjet-printing and doctor-blading methods are complementary, the former having high accuracy and cost, in contrast to the latter. In addition, inkjet-printing has to print many cycles20 to achieve low sheet resistance, which costs time and is not economically viable for mass production. Considering costs, printing accuracy and surface conductivity, the screen printing technique is the best candidate for industrial scale production. However, few screen-printed graphene devices have been reported including electrodes22, electronic circuits23 and antennas24. Most graphene ink processes use organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF). They are toxic, with low concentrations, and unsustainable, preventing them from using for industrial scale production.Graphene ink, a dispersion of graphene flakes in solvents, can be easily patterned via spraying−1) has been developed and was further concentrated to 70 mg mL−1 for screen printing. More importantly, we have demonstrated that printed graphene antennas, ranging from high-frequency band (a few tens of MHz) to microwave band (a few tens of GHz), can be applied across the entire RF spectrum. As critical demonstrations, a printed graphene-enabled battery-free wireless body temperature sensor, RFID tags and RF energy harvesting system for powering battery-free devices that are capable of sensing resistive and capacitive sensors are presented, illustrating the potential of low cost, screen-printed graphene enabled wearables for IoT applications such as healthcare and wellbeing monitoring, also embodying sustainability and disposability, all of these are critical factors to enter the mass-produced market.Here we report the use of a cellulose derived solvent, dihydrolevoglucosenone (Cyrene), which is not only non-toxic, environmentally friendly and sustainable but also can provide higher concentration of graphene ink, resulting in significant cost reduction for large-scale production. In this work, low cost, environmentally friendly and sustainable, highly conductive graphene ink  graphene slurry in water, but oxidization on the edge of graphene flakes still degrades its conductivity.Conductive graphene ink has been researched for a number of years. It is now possible to obtain defect free, less oxidized and stable graphene flakes by liquid phase exfoliation29. The solvent not only has appropriate polarity34 and surface tension35 which are especially suitable for graphene ink preparation, but also the concentration of dispersion where graphene can exist stably is at least an order higher than other organic solvents29. Moreover, Cyrene is non-toxic and easily extracted from cellulose which is abundant on Earth, has a great potential for low cost, environmentally friendly and sustainable industrial scale graphene ink production. However, for printed electronic applications, the most crucial property, electrical conductivity of Cyrene-based graphene ink, has not been reported, nor have its electronic applications.Bio-based Cyrene (CAS: 53716-82-8) was first identified as a high-performance solvent for graphene dispersion in 201736. For wireless connectivity applications, the conductivity of the printed graphene pattern is crucially significant. Thin graphene flakes allow for the best stacking, however, they end up with the maximum number of interfaces, which potentially can increase the resistance. Thick graphene flakes allow one to reduce the number of interfaces between the flakes, but they do not guarantee good stacking and result in a number of voids when printed. The conductivity can be maximized by selecting flake thickness, otherwise low conductivity increases connection loss and jeopardizes the ink applications. To evaluate conductivity, the sheet resistance variations of the graphene laminate under different sonication time in both NMP and Cyrene solvents were plotted in Fig. −1 h−1 between 4 and 8 h. The minimum sheet resistance of Cyrene ink is 0.78 Ω sq−1, which happens at 8 h sonication. After that, the sheet resistance rises as sonication time further increases because the longer sonication time leads to smaller flake sizes as well as damages sp2 network of graphene flakes36, affecting the graphene flake’s electrical conductivity, which is not recoverable. For NMP solvent, the decreasing rate of sheet resistance is slower. The minimum sheet resistance is 0.77 Ω sq−1, happens at 48 h sonication. That said, although the physical properties of both solvents are quite similar29, the best sonication time for NMP is six times longer than that for Cyrene, which indicates that Cyrene has better exfoliation efficiency compared to NMP, providing an advantage in time saving and cost reduction for large-scale graphene ink production.In this work, expanded graphite was added into Cyrene and NMP (as comparison). Graphene flakes were produced during sonication treatment. Firstly, the sonication time for exfoliation was investigated as it is of significance for large-scale ink production. Samples were extracted at different sonication time. It is easy to remove unexfoliated graphite particles in extracted samples via centrifugation and filtration (see Methods). It has been noticed that long sonication period also affects the quality of graphene flakes and degrades the conductivity of graphene4 S m−1, higher than any work reported so far39, confirming that Cyrene is an excellent solvent with higher exfoliation efficiency and less defects on graphene flakes for replacing traditional toxic organic solvents.The electrical conductivity of dried and compressed graphene laminate  is 7.13 × 1040. However, the adhesion was less impressive. For practical applications, adhesive materials are normally added in the ink. The drawback for adding adhesive materials is that it will significantly degrade the ink electrical conductivity. In this work, cellulose acetate butyrate (CAB) was added into the Cyrene graphene ink, acting as a polymer-assisted agent. CAB can stabilize the ink because the electrostatic repulsion between CAB molecules prevent graphene flakes from restacking and aggregation41, also enhance adhesion and anti-scratching performance of the printed pattern. However, addition of CAB to the ink decreases its conductivity dramatically. In order to understand the relationship between CAB concentration and sheet resistance, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 5 and 10 mg CAB was dissolved into 1 mL of pristine graphene ink  with a short period of sonication treatment. As can be observed in Fig. −1 but slowly increases while the CAB concentration is between 100 μg mL−1 and 1 mg mL−1. The sheet resistance is about two times higher than that of pristine graphene laminate when the concentration of CAB is 1 mg mL−1. The sheet resistance increases logarithmically for CAB concentration over 1 mg mL−1. To achieve good conductivity as well as printing quality, 1 mg mL−1 CAB concentration was applied in this work. The inset in Fig. Binder-free graphene ink and its applications have been reported−1 with 8 h sonication). Clear graphene flakes are shown in Fig. 3 nm2  was used to characterize graphene flakes  and −COOH (∼1710−1720 cm−1) groups are detected for the exfoliated graphene43 . A characteristic peak is seen at 1756 cm−1 attributed to CAB (C=O stretch) which can also be observed on graphene/CAB (red line). Raman spectroscopy of exfoliated graphene is shown in Fig. 2 carbon atoms at D-band (1355 cm−1), G-band (1583 cm−1), associated with in-phase vibrations of the graphite lattice, the relatively wide 2D-band at 2731 cm−1 and an overtone of the D-band44. A low D/G ratio indicates fewer defects on graphene flakes45, which is significant for electron flow and no structure change of graphene flakes can be detected by Raman in the graphene/CAB sample.Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to investigate the quality of exfoliated graphene flakes. Fig. −1). Hence, the following compression process is significant for improving sheet resistance. A paper rolling machine  was used to compress the printed patterns. As it can be seen in Fig. −1 on average, 30 times smaller than uncompressed patterns.Morphological features of graphene/CAB laminate were investigated by using a scanning electron microscope. Graphene flakes can be clearly seen at Fig. −1) screen-printing ink was achieved via rotary evaporation from 10 mg mL−1 graphene/CAB ink, as seen in Fig. 46. The average thickness of screen-printed graphene laminate is 7.8 μm and conductivity can therefore be calculated as 3.7 × 104 S m−1, which is approximately about half of that of the pristine graphene ink (without CAB) but still has about the same conductivity as recently reported work47 which however requires high temperature (350 °C) annealing. Additional bending and adhesion performance of the printed graphene/CAB pattern were tested. Low residual blue tape (BT-150E-KL) was used to test adhesion performance by sticking and peeling off from printed pattern repeatedly47. The sheet resistance of pristine graphene pattern doubled after first cycle. In the meantime, the sheet resistance of graphene/CAB pattern increased 5%. After 10 cycles, the sheet resistance of graphene/CAB pattern increased 40% whereas pristine graphene pattern was peeled off from paper completely and its sheet resistance became too large to be measured (>20 MΩ sq−1) at cycle 7. In a bending test, a 3 cm × 1 cm rectangular pattern was printed and compressed. The pattern was bent from 0° to 90° for 2000 cycles while its resistance only increased 5%, which is comparable to other published works48.A commercial manual screen printer was used in this work. Fig. u ultra-wideband slot antennas  and functional NFC chip , as shown in Fig. r, which can be calculated by50In order to further demonstrate the potential of printed graphene antennas, a UHF RFID antenna has been designed, optimized and printed for long read range communication, as shown in Fig. λ is the wavelength, Pt is the transmitted power from the reader antenna, Gr is the gain of the reader antenna, Gt is the gain of tag antenna, Pth is the minimum threshold of the power needed to activate the RFID chip and τ is the matching factor, which varies from 0 to 1 and is given by51where Zc and Za represent chip impedance and antenna input impedance, respectively. Rc and Ra are the real parts of the chip and antenna impedance. Conjugate impedance matching is required between the RFID antenna and the chip in order to maximize the matching factor, resulting in maximal read range. The maximum read range of the printed graphene UHF RFID antenna vs. frequency is illustrated in Fig. 19, rival to aluminium etched commercial RFID antennas and silver ink printed RFID ones52. For a more intuitive demonstration, the radiation pattern in the E-plane at 915 MHz was plotted against maximum read range instead of antenna gain and the data was recorded for every 10° rotation, as shown in Fig. where S11) of the printed graphene ultra-wideband slot antenna. The 10 dB bandwidth is from 3.8  to 15.5 GHz, achieving more than 120% fractional bandwidth. This wideband characteristic is very useful for upcoming 5G mobile communication and ultra-wideband radar applications53. The fundamental resonance of the slot antenna is around 5 GHz and low reflection extends close to 9 GHz. Above 9 GHz, the higher resonance modes start to play the major role. The fundamental and higher mode resonances overlapped around 9 GHz, resulting in a wide bandwidth , which can be further improved by using diodes with lower barrier height in the voltage multiplier. From the view of IoT applications, high quality printed 2D material sensors57 can be embedded into the system with the same printing process. A prototype of RF powered, battery-free low-power square wave oscillator which converts the sensors’ analogue outputs to frequency modulated signals is developed and demonstrated here. The oscillator consists of two CMOS NOR gates (SN74AUP1G02), variable resistor (resistive sensor) and variable capacitor (capacitive sensor), as shown in Fig. There are various wireless signals in free space at any moment of time. Such wireless energy can be harvested and stored to power up low-power, battery-free electronic devices intermittently. This strategy is becoming highly desirable due to the fast development of wireless sensor networks (WSNs) and IoT technologies−1. Using Cyrene has eliminated the use of toxic solvents, significantly simplifying post production treatments, especially propitious for industrial scale manufacturing. Exfoliation times and conductivity of Cyrene graphene ink were measured and compared to those of NMP one. Conductivity of 7.13 × 104 S m−1 has been achieved after compressing, which is the highest reported so far. After adding CAB as a stabilizing agent and rotary evaporation, the further concentrated graphene ink (70 mg mL−1) becomes screen printable. The printed graphene/CAB laminate still achieved a high conductivity of 3.7 × 104 S m−1. The prototype NFC antenna in the high-frequency region, high-performance RFID antenna working in ultrahigh-frequency band and ultra-wideband antenna operating in microwave bands all provide evidence that printed graphene antennas can replace traditional metal antennas for wireless identification, sensing and data communications for low cost and ubiquitous wireless connectivity. Furthermore, graphene-based NFC temperature sensors for healthcare and wellbeing monitoring and graphene enabled energy harvesting system that can power battery-free CMOS oscillator have been successfully demonstrated, opening an avenue for low cost, environmentally friendly and sustainable printable devices at upcoming IoT applications.Environmentally friendly, sustainable, low cost, highly conductive and concentrated screen printing graphene/CAB ink has been developed. High-quality pristine graphene sheets were exfoliated and dispersed in Cyrene with the concentration of 10 mg mLN-methyl-2-pyrrolidinone  was from Alfa Asia. CAB (butyryl content 35–39%) was from Arcos Organics. Graphene nanoflakes were obtained via the liquid phase exfoliation method. Expandable graphite were placed in a ceramic crucible and then heated in an 800 W commercial microwave oven for 30 s to obtain expanded graphite with fewer layers. The expanded graphite flakes were stirred and washed in deionized water to remove residual acid until the pH is close to 7. Then, the mixture was dried in an oven for 5 h at 100 °C. Dried expanded graphite was deposited into NMP solvent (10 mg mL−1) and Cyrene (10 mg mL−1), respectively where these organic solvents provide appropriate surface energy for sonication processes. After that, the mixture was sonicated in an ultrasonic bath . Samples were extracted at 0, 2, 4, 6, 8, 10, 12, 14, 16, 20, 24, 32, 40, 48, and 56 sonication hours for sheet resistance measurement.Expandable graphite with +50 mesh flake size was purchased from Sigma-Aldrich. Cyrene  was provided by Circa Group Pty Ltd. −1 with vacuum rotary evaporation (Buchi R-114 Rotavap evaporator). CAB was added into Cyrene as a polymer-stabilizing agent to increase the stable existence of graphene flakes in Cyrene and improve the printing performance. In order to achieve appropriate viscosity for screen-printing, the graphene concentration of 70 mg mL−1 was achieved  by vacuum rotary evaporation. Before printing, the mixture was mechanically agitated for 5 min and bubbles inside the ink were removed after a short period of vacuum treatment. The printing screen with 62 mesh was specially fabricated with capillary film  to achieve uniform laminate of graphene paste. Then, the sample was dried and annealed in an oven (vacuum) at 100 °C for 5 h (comparison of antenna gains printed with Cyrene-based graphene ink (8 h sonication time) and NMP-based graphene ink (20 h sonication time) can be found in Supplementary Figure The exfoliated graphene nanoflakes were obtained in the dispersion after sonication. A 300-mesh stainless steel screen filtered the mixture first. After that, unexpanded graphite particles were removed after 5 min low-speed centrifugation (500 rpm). After that, the graphene dispersion was concentrated to 10 mg mLBoth of Graphene, CAB and Graphene-CAB samples were annealed in an oven (vacuum) at 100 °C for 48 h to ensure dryness and avoid errors of measurement. They were mixed with potassium bromide (KBr) with 1:20 mass ratio and ground in an agate mortar, respectively. FTIR data were recorded by a Fourier transform infrared spectrometer (Nicolet 5700).2/Si substrate. Raman spectra were acquired with a Renishaw System 1000 Raman Spectrometer. Micro-Raman spectrometer at a ×50 objective, with an incident powder of 2.3 mW. The system has within 1.5 cm−1 spectral resolution at 514 nm.Films of exfoliated graphene (without CAB), graphene/CAB ink and CAB were coated on SiO−1 and 100 μL ink sample was spin-coated  on a clean SiO2/Si substrate and washed by acetone, distilled water and isopropyl alcohol sequentially. The AFM sample was dried in an oven for 5 h at 100 °C.Atomic force microscopy imaging of few layer graphene was measured with a Bruker Dimension Icon in tapping mode. The concentration of graphene/CAB ink is 10 mg mLScanning electron microscopy was performed using a ZEISS Sigma HV. Aperture size is 7 μm. The field emission gun is 5 KV and signal was acquired from InLens. For the cross-section measurement, the paper with printed graphene on top was soaked in liquid nitrogen and cut by a scalpel.Sheet resistance is used to describe the thin film resistance regardless of film thickness, it can be written asRs is sheet resistance, ρ is the resistivity of the film and t represents the thickness of film. For the measurement of sheet resistance variation with different ultrasonic treatment times, the ink was first filtered via a 300-mesh stainless steel screen. Small unexpanded graphite particles were removed after 5 min low-speed centrifugation . To avoid coffee-ring effect, a filter paper  was held on a glass funnel (140 mL Aldrich Buchner funnel) by vacuum. After that, 60 μL of the filtered sample was dropped on filter paper. The ink was annealed in an oven for 5 h (100 °C) and compressed with the rolling machine. The sheet resistance was measured using 4-point probe station  and semiconductor characterization system .where S11), the ultra-wideband slot antenna was directly connected to a calibrated Vector Network Analyzer .For reflection coefficient measurement  connector was connected with the antenna using conductive epoxy (Circuit works CW2400). The measurement distance between any two adjacent antennas is 0.6 m, satisfied with far field requirement. The three antennas measurement method does not need a calibrated reference antenna; the gain of the antennas can be solved after measuring Ga is the measured graphene antenna gain, S21 [in dB] between different antennas . The last term describes free space loss and depends on wavelength λ and distance d between measured antennas.where u band .Radiation patterns of the antenna were recorded using an antenna measurement system  and N9918A VNA. The data were recorded every 2° rotation. Standard horn antenna was used as transmitting antenna. Different bands of horn antennas were used: C, X bands  and KRead range and radiation pattern measurement was performed using a professional RFID measurement setup (Voyantic Tagformance Measurement System) with EIRP=4 W. Before measurement, the system was calibrated and the effects of receiver antenna gain, cable and free-space loss were eliminated. For read range measurement, the system sweeps linearly from 800 MHz to 1 GHz with 3 MHz steps. For radiation pattern measurement, the frequency is 915 MHz and data were recorded every 10° rotation.The antenna total efficiency was measured by using rotary table, Antenna Measurement Studio 5.5 and N9918A VNA. The circuit conversion efficiency was measured using RF CW source  and precision multimeter .Supplementary InformationPeer Review File


Water permeation experiments show that changes are localized to grain boundaries. Electron microscopy is further used to correlate the global vapor phase conditions and the boundary defect types. Such thermodynamic control is essential to enable consistent growth and control of two-dimensional layer properties over large areas.Research efforts in large area graphene synthesis have been focused on increasing grain size. Here, it is shown that, beyond 1 μm grain size, grain boundary engineering determines the electronic properties of the monolayer. It is established by chemical vapor deposition experiments and first-principle calculations that there is a thermodynamic correlation between the vapor phase chemistry and carbon potential at grain boundaries and triple junctions. As a result, boundary formation can be controlled, and well-formed boundaries can be intentionally made defective, reversibly. In 100 µm long channels this aspect is demonstrated by reversibly changing room temperature electronic mobilities from 1000 to 20,000 cm 2 V−1 s−1.Engineering the grain boundary size of chemical vapor deposited monolayer graphene can reversibly tune its electronic properties. Here, the authors report a thermodynamic correlation for 100 μm long channels in graphene by reversibly changing its electronic mobilities from 1,000 to 20,000 cm Continuous monolayers are formed on the metal surface by the nucleation and coalescence of graphene domains. Hence, grain boundaries (GB) and triple junctions that are a part of any polycrystalline material are also present in large area monolayer graphene9. These GB have been extensively studied and their defect density has been theoretically shown to be mainly dependent on the extent of misorientation between the grains12. However, in CVD graphene, the defect density at a boundary is not determined by the misorientation angle alone. Tsen et al.14 studied the effect of source gas flow conditions on the quality and type of GB structures formed in CVD grown graphene. Using transmission electron microscopic (TEM) analysis of the boundary along with electrical transport measurements, they reported that the samples grown at higher methane flows had smaller grains, uniform coverage and most importantly, lower GB resistance. Samples grown using lower methane flows were found to have boundaries with overlaps and voids, resulting in higher resistance14. The results are markedly important in two aspects. First, the GB defect density was shown to depend not only on the geometric aspects of the grains such as tilt misorientation and edge type, but also on gas flow conditions. Second, electrical transport characterization was found to be an effective tool to inspect the defect density of GB. Their study, however, did not address the correlation between the physico-chemical state of the growth system and defects at GB. More recently, calculations by Dong et al.15 showed that one can toggle between covalently bonded boundaries and hydrogen terminated edges by changing hydrogen pressure.The chemical vapor deposition (CVD) of graphene for large area applications is typically carried out by transition metal  catalyzed hydrocarbon  and sheet resistance (Rs) can be reversibly changed by more than an order of magnitude. This control has allowed us to synthesize graphene with µcm of 20,000 cm2 V−1 s−1 in device with dimensions of 100 µm × 100 μm. Our results are compared against reported literature in Supplementary Note 17 are insensitive to the changes occurring in it. Hence, to supplement the electrical transport measurements, water permeation measurement technique is used to identify and spatially locate the incorporated changes in the monolayer. The results highlight the importance of GB closure in obtaining graphene with the best of electronic properties over large areas, in the regime in which the yields of increasing grain size start diminishing  on the Cu surface. Equation (21. The free-energy change driving the growth or supersaturation (ΔG) is then given byKeq is the value K at equilibrium, PCH4, PH2, T, and R represent CH4 partial pressure, H2 partial pressure, temperature, and the gas constant, respectively. Details of the experimental conditions used and the resulting supersaturation, calculated using standard formation energies22, are given in the Supplementary Note 1–G4, were studied as summarized in Table 1–S4, one from each of these groups, to be discussed in this paper are presented in Fig. Graphene synthesis using Cu catalyzed dehydrogenation of methane can be described by the following equation.G = Greactants−Gproducts, is established in the reactor in the growth stage during which sequential methane dehydrogenation produces a population of adatom species on the Cu surface. Graphene growth then proceeds through the four stages of incubation, nucleation, growth, and coalescence. Following the 6-minute point, certain samples, see Table In the schematic representation shown in Fig. G ≤ 32 kJ mol−1, graphene grains either did not nucleate or the rate was so slow that no growing domains were observed until a reasonable growth period of 20 min. Upon increasing the ΔG to 36 kJ mol−1, group G1, the surface remained unmodified up to 1 min as shown in Fig. 1. Surface images of Cu growth surface at 10 mins and 13 mins are shown in figure D/IG ratio decreases sharply upto a growth time of 6 min and then saturates in the period from 6 to 14 min. Thus, it appears from these characterization methods that monolayer deposition is complete by 6 min. Graphene growth by CVD on Cu is typically modeled as a self-limiting catalytic process4, which can explain the SEM snapshots and ID/IG saturation behavior. However, as can be noted from Fig. µcm increases rapidly only after 6 min of growth—the point at which the monolayer seems complete—and saturates at 13 min. The µcm here is obtained from the constant mobility fit described by Venugopal et al.23 as explained in 24. A Gompertzian fit, shows that µcm increases by a factor of 4 from 1000 cm2 V−1 s−1 at 6 min to saturate at 3600 cm2 V−1 s−1 at 14 min. Sheet resistance decreases by a factor of 2 and attains a saturation value of 790 Ω☐−1 at 14 min. These observations belong to the sample set G1 in which a constant ΔG of 36 kJ mol−1 was maintained through all stages of growth. This sharp change in electronic properties, beyond the point at which the other structural characterization methods and Raman defect density measurements do not suggest any significant change in the quality of graphene is the first interesting observation. All the electrical measurements, except for samples grown below 4 min , were performed on 100 μm by 100 μm graphene devices  in large area CVD graphene and over such large device sizes (100 µm × 100 µm). The Raman ID/IG ratio again remains flat. Thus, from the VCG stage at which the structural characterization methods seem to have become insensitive to changes in the graphene layer, further processing has thus resulted in a 20-fold increase in µcm. This value is also five-fold higher than the saturation mobility observed under a constant ΔG = 36 kJ mol−1 in G1 , sample S2. Without breaking vacuum these samples were now exposed to decreasing values of ΔG down to 36 kJ mol−1 for 4 min and 12 min. A different growth run was used for each value of lower ΔG used during the reversal. It was observed that the difference in µcm values between the 4-min exposure and the 12-min exposure was within experimental error. Hence, all subsequent exposures to lower ΔG were limited to 4 min. The results of these measurements are presented in Fig. µcm values decrease as ΔG is lowered in the reactor and trace back the preceding rise almost exactly but for a small hysteresis.Additional experiments were performed to determine whether the rise in mobility in Fig. An atomistic picture of the nucleation, growth, and coalescence process of graphene is now discussed to help analyze these mobility results and the ones to be discussed in the next section. It is shown that the reversible phenomena is due to grain boundary thermodynamics and not owing to growth kinetics. From a growth perspective, it is important to establish this fact, as thermodynamic control is more robust than a kinetic one.Cv) in the form of the methane partial pressure. Methane decomposes on the catalyst and yields a surface carbon potential (Cs). Crystalline graphene domains with a potential Cg  nucleate and grow by consuming the surface carbon. Cs at any point on the growth surface will vary with time and will be determined by the balance between carbon addition by adsorption and decomposition and carbon removal by desorption, nucleation, and attachment to growing edges. With an increase in coverage, as the domains get closer to form boundaries, the Cs values will get lowered due to reduced catalyst site availability and increased consumption. The reduced Cs will lower lateral growth rates and in the extreme case prevent complete coalescence in reasonable time periods. In addition to these three potentials, carbon atoms in the defect structures such as GB, triple junction and line defects in the graphene monolayer will be at higher carbon potentials (Cd) than Cg and are shown in Fig. The atomistic picture is shown schematically in Fig. Cs became equal to Cg during growth, a coverage saturation will happen despite a global supersaturation (Cv being higher than Cg). If Cs were raised by increasing Cv (increasing ΔG), the degree of coverage will increase in a given time of growth. Such growth is termed kinetically controlled and the coverage saturation owing to kinetic limitations has been described before by Celibi et al. using a Gompertzian model24. Thus, the increase in mobility with ΔG or methane partial pressures in Fig. Cv still higher than Cg) should not reverse the mobility gains as observed in Fig. If Cv to be greater than Cd as shown in Fig. Cs determined by the relative rates of adsorption–attachment and desorption were to become lesser than Cd. On the other hand, if the situation shown in Fig. Cd>Cv will never form as it will not be energetically favorable for carbon from the vapor phase to become part of these defect structures. Increasing/decreasing Cv will then add/remove carbon from these structures, thus healing/forming defects, vacant carbon sites, reversibly at these locations. The spatial and temporal variation of Cs is difficult to estimate quantitatively. Hence, in the next section we compare the energetics of Cv, with that of boundary energies to determine if such an effect is possible.Thermodynamically, the ability to form a particular boundary structure that will complete the coalescence process, will require the global carbon potential, 15 have shown that by changing the hydrogen potential in the reactor, one can replace covalently bonded boundaries by hydrogen terminated ones and vice-versa. The experimental work presented here involves changing the carbon potential in the reactor resulting in reversible exchange of carbon atoms between the boundary and the vapor phase. To model this process . The ΔG variation with methane partial pressure is plotted in Fig. “C′” represents grain boundary carbon and the equation shows a defect removal and its replacement by an edge. In order to determine whether an edge state with lower energy can exist, two graphene grain boundary configurations and their corresponding edges, Fig. equation   not only have a larger sheet resistance but also the highest increase on hydrogen annealing. This indicates that the defects are predominantly created at the GB.In the previous discussion, we had hypothesized that vacant carbon sites can be annihilated and created reversibly at GB causing the mobility reversal with change in vapor phase carbon potential. First principles calculations supported this idea. In this section we provide experimental proof. A simple experiment was first performed in which graphene samples with decreasing grain sizes, obtained by increasing supersaturation in the nucleation stage itself , the changes should be happening at length scales that the mapped average does not reflect. To understand the physical picture behind the reversible defect density-mobility trend, a method involving preferential water permeation through defects in graphene followed by etching of an underlying Ge film26 was employed on the four samples listed in Table 1) is examined by this method, the etch pattern formed within just 1 min of permeation, involving 50–100 µm sized grains, corresponds to the microstructure of the Cu substrate on which the monolayer was synthesized  that are not detected by the permeability measurements. To determine if this is so, sample S4 was annealed in pure hydrogen at a pressure of 4 Torr. Even in this case as can be seen from Fig. µcm, Fig. G. The type of defects (structure) and their density along the GB of different samples were inspected using a high resolution TEM. Imaging in a 200 kV TEM was first performed over large areas to establish that the graphene being studied was indeed predominantly a monolayer using tilt diffraction measurements  hydrogen, and nitrogen flowing through a purifier, 99.98% pure methane and 99.98% pure Cu from Sigma Aldrich were used for synthesis. Although growth was done at 1000 °C, reactor chemistry was changed to vary carbon potential by varying methane and hydrogen flows. Gas flows for the supersaturation used in this article are shown in Supplementary Fig. 27 was used to transfer graphene onto a 285 nm thermally grown silica/heavily doped p-type Si substrate.Graphene was grown in a custom-made CVD reactorEach data point in Figs. Raman spectroscopic measurements on these transferred layers were carried out with a LabRAM HR spectrometer fitted with a 532 nm laser source. The instrument was fitted with precision micrometer stage for mapped measurements. Further details on Raman spectroscopic measurements are provided in Supplementary Note 8 A/cm2 for 3 min under a pressure of 4 × 10−5 mbar of air. Given that the average grain size is ~ 7.08 μm (standard deviation of 0.88 μm), (See Supplementary Fig. Van der Pauw devices for sheet resistance measurements and MOS FET structures for mobility measurements were fabricated using standard optical lithographic techniques and the graphene channel was defined using a mild oxygen plasma etch using an Oxford reactive ion etcher. Except for electrical measurements below 4 min in Fig. 25, were conducted using an Olympus made immersion lens setup fitted with an Olympus optical acquisition system at room temperature and in open air. The etch profile measurements25 were performed using a Bruker made atomic force microscope.Ge etch experiments to characterize defects, developed in our groupDiffraction measurements were performed using a FEI T20 transmission electron microscope at 200 kV and the STEM measurements were made using an aberration corrected Nion Ultra STEM 100 microscope operated at 60 KV.Supplementary Information


Dysmobility syndrome (DMS) was considered as a comprehensive approach to evaluate the condition of musculoskeletal system and adverse health problems in older population. The objective of our study was to examine the association between metabolic syndrome (MetS) and DMS in a U.S. adult population. 1760 eligible participants from the National Health and Nutrition Examination Survey (NHANES) 1999–2002 were enrolled in the study. The criteria of DMS consisted of six domains including increased body fat, declined muscle mass, reduced muscle strength, osteoporosis, slow gait speed, and balance problem. A multivariate regression analysis was investigated to clarify the relationship among MetS and its components and DMS. A positive association between increased number of MetS components and the presence of DMS achieved significance . Among the components of MetS, hyperglycemia had a central place in the DMS after adjustment of clinical variables . Notably, insulin resistance assessed by homeostatic model assessment (HOMA-IR) was correlated to increased body fat , osteoporosis  and balance  among these participants with MetS. Our study demonstrated a strong relationship between DMS and the presence of MetS and its components in elderly population, highlighting a possible mechanism through insulin resistance. In the recent decades, several medical terms were used to address the association between musculoskeletal system, physical function, and body composition for evaluating the decline in health and aging. However, not only the term “sarcopenia” but alsThere had been a substantial body of studies in the literature concerning the relationship among MetS, frailty, and sarcopenia. MetS was a cluster factors contributing to multiple chronic diseases and increased risk of all-cause and cardiovascular mortality and was The study sample was derived from the National Health and Nutrition Examination Survey (NHANES) 1999–2002, which was a multistage and population-based survey consisted of detailed home interview and a health examination for collecting information on the health and nutrition status to obtain a representative sample of the United States noninstitutionalized civilian. All measurements in NHANES were approved by the National Center for Health Statistics (NCHS) Institutional Review Board , and written informed consent was obtained from all subjects.According to the flow chart of the study , 1760 elAccording to the criteria defined by National Heart, Lung, and Blood Institute, a partiBinkley et al. presented the original definition of DMS included six domains: increased body fat, declined muscle mass, reduced muscle strength, osteoporosis, slow gait speed, and balance problem, which subject had at least 3 of the following 6 conditions was classified as having DMS × fasting plasma glucose [mmol/l])/22.5. The labp-value of ≤ 0.05 was regarded as the threshold for statistical significance. A linear regression model was performed for the association between number of MetS components and DMS, and the relationship between individual MetS component and DMS. We adjusted for pertinent variables in this linear regression model as follows: Model 1 = unadjusted; Model 2 = Model 1+ . Model 3 = Model 2+ . Model 4 = Model 3+ . Pearson correlation was used to examine the correlation between HOMA-IR with components of DMS.All statistical data were analyzing by the Statistical Package for the Social Sciences, version18.0  for Windows. One-way analyses of variance and Pearson's chi-square tests were utilized to examine the differences between the groups in terms of demographic information, anthropometric parameters, and laboratory data. A two-sided The association between number of MetS components and DMS was conducted by the multivariate linear regression model . ParticiIn In addition to low muscle mass , there were no correlation between HOMA-IR and other components of DMS in subjects without MetS . In the In the present study, we observed the positive association between the increased number of MetS components and the presence of DMS among older adult population. Notably, patients with high serum glucose had significantly associated with the existence of DMS after multi-model adjustment. No significant difference was noted between other components of MetS and DMS. HOMA-IR, a method used to quantify insulin resistance and beta-cell function, was of paramount importance with individual components of DMS. To the best of our knowledge, this study was the first to examine the association between MetS and DMS which data was derived from the large-scale population survey.Before the concept of DMS, several terms were applied to accurately identify older people most at risk of serious declines in health, independence, and function. Frailty, an age-related decline in multiple physiological domains, manifested an increased vulnerability to adverse health outcomes and resulted in high risk for falls, disability, hospitalization, and mortality. MetS waSkeletal muscle was a major target of insulin and insulin receptors in the muscle played an important role in glucose regulation, and muscle is a major site of glucose disposal. The devIn the present study, HOMA-IR was correlated to body fat, osteoporosis and balance problems in subjects with MetS and low muscle mass in participants without MetS. Insulin was a catabolic hormone, which induced the process of protein degeneration and synthesis in skeletal muscle. Lee et Although all efforts went into this study, there were several potential limitations should be noted. First, the present study was a cross sectional approach that no casual association between MetS and DMS. Future studies are warranted to assess the prospect by using longitudinal design with large sample size. Second, there was no muscle pathology from muscle biopsy reporting in our study, and we could not confirm the hypothesis. Third, sex difference was not analyzed during this study. Further studies should address the association of sex, MetS and DMS. Next, selection bias is existed in the present study. NHANES data are not obtained using a simple random sample. Rather, a complex, multistage, probability sampling design is used to select participants representative of the civilian, non-institutionalized US population. Oversampling of certain population subgroups is done to increase the reliability and precision of health status indicator estimates for these groups. In the present study, we included participants who had finished examinations of DMS: body composition measurement, bone mineral density measurement, gait speed test, and muscle strength measurement. There were 581 subjects with DMS and 1179 without DMS. A randomized controlled trial is needed for further research to examine the association between MetS and DMS. Finally, the generalization of the findings to other populations with different race/ethnicity may be limited.The present study highlighted a strong relationship between DMS and the presence of MetS and its components in elderly population. Notably, this dynamic interplay between DMS and MetS underlined the pathophysiology of insulin resistance. MetS aggravated inflammation and insulin resistance, which harbored a predisposing milieu for developing DMS. Our findings brought new insights for the development of this new field. Further researches should explore the underlying mechanisms for the clinical observations and therapeutic strategies to encounter the adverse health problems.S1 Data(RAR)Click here for additional data file.


Raman and SEM images revealed that the as-prepared date syrup-based graphene sand hybrid (D-GSH) had imperfections with macroporous 2-D graphene sheet-like structures stacked on the inorganic sand support. The applicability of the D-GSH for decontaminating the water from cationic  and anionic  dye and heavy metals (Pb2+ and Cd2+) was tested. Batch experiments demonstrated that D-GSH showcased exceptional capability for both dye and heavy metals removal with fast adsorption following pseudo-second-order kinetics. The adsorption capacities for MV, Pb2+, and Cd2+ were respectively 2564, 781 and 793 mg/g at 25 °C, the highest capacity graphene-based adsorbent reported in the literature to date. In addition, D-GSH also exhibited high adsorption capacity for anionic dye, CR (333 mg g−1) and good recyclability (3 cycles) for all the contaminants. The thermodynamic studies further confirmed that the adsorption of all contaminants was thermodynamically feasible, spontaneous and endothermic with ∆H° of 48.38, 89.10, 16.89 and 14.73 kJ/mol for MV, CR, Pb2+ and Cd2+, respectively. Thus, utilization of a simple one-step strategy to produce graphenic sand hybrid using date syrup helped in developing a cost-effective and environmentally friendly dye and heavy metal scavenger that can be used as a one-step solution for water decontamination.Here we demonstrate, a facile  Consequently, numerous efforts are emerged to develop cost-effective and appropriate remediation materials and technologies that can regulate the amount of these toxic and persistent water pollutants to permissible levels before being discharged to the water bodies. To date, different treatment technologies such as photodegradation6, precipitation8, coagulation & flocculation9, membrane separation10, and ion exchange12 have been tested for removing different harmful pollutants from wastewater. These conventional methods suffer from severe drawbacks in terms of cost-effectiveness, performance efficiency, applicability for a wide range of pollutants, or reusability. Comparatively, adsorption is a relatively mature, globally acclaimed, versatile, economically feasible, and highly efficient technology for pollutant remediation16. Traditional carbon-rich adsorbents such as charcoal, soot, and biochar are widely used because of their low cost and high surface area18. However, its condensed structures consume large sorption potential via limiting internal sites and thus cannot treat and produce adequate clean water. Moreover, owing to the increase in water demand coupled with stringent environmental guidelines to create public health sustainability, there is still an increasing demand for the development of effective carbon-based sorbents with higher surface areas, partition coefficients, and sorption capacities21.Water is one of the world’s valuable resources, and only 1% of the global water supply is available for consumption and domestic use. With the augmented urbanization and substantial industrialization activity, enormous amounts of hazardous chemicals are discharged into the receiving waters every day. Among the emerging inorganic and organic contaminants, heavy metals and dyes are frequently found in the industrial effluents, which if untreated become a principal concern to the environment and public health as they are non-biodegradable and tend to accumulate in living organisms2 hybridized carbon atoms arranged in a honeycomb structure and has attracted tremendous research interests owing to its unique physicochemical and mechanical properties22. The high theoretical surface area (~2600 m2 g−1) combined with its versatile chemistry like electron-rich π-system and the highly hydrophobic surface has led to the use of graphene as a potential revolutionary adsorbent for environmental pollutant management25. Compared to CVD graphene, reduced graphenes are widely exploited for chemical and environmental application27. The highly hydrophobic carbon conjunction surface of graphene acts as potential adsorption sites for organic pollutants through π-π interactions. Furthermore, the presence of defects, step-edges and groove/wrinkle areas on the graphene are considered as high-surface-energy adsorption sites which are preferentially occupied by external molecules28. Nevertheless, a key barrier in the practicability of pristine graphene nanosheets for water purification is its high cost and post-treatment-handling, including recovery after the decontamination process as they aggregate heavily in water due to their large-area π-π interactions and strong van der Waals forces between the graphene layers29. To overcome these engineering issues, it is indispensable to anchor these graphene nanosheets onto an economical and reliable inorganic substrate such as sand. The preparation of these graphene sand hybrids would not only allow the full expression of the graphene adsorption sites but will also ensure dispersibility and easy separation from water. Recently, several synthetic routes have been reported for the preparation of graphene sand hybrids from diverse sources of carbon such as sugar31, gelatin32, palm sugar, asphalt33, etc. This is crucial as chemically different carbon sources are available in different parts of the world where their molecular and compositional chemistry are expected to play a key role in controlling the properties of the as-prepared graphene sand hybrids. Nevertheless, it is of paramount importance to apply an environmentally friendly and renewable raw material source for the sustainable production of graphene-based nanomaterials to cope up with the alarming challenges facing its mass production.With the advent of nanotechnology, researchers have intensely explored the use of carbon nanomaterials for water purification with the hope that it may open new fruitful pathways to curb the existing water shortage. Graphene, the newest addition to carbon family is a novel 2 D one atom thick nanomaterial sheet made of spin-situ synthesis strategy, a large scale of graphenic material could be synthesized economically and immobilized on abundant desert sand without the use of any external chemical agents. It is believed that during pyrolysis the naturally abundant sucrose and fructose molecules in the date syrup undergoes complete exfoliation to form graphene nanosheets on the desert sand surface, thereby exposing the powerful adsorption sites concealed in the stacked graphene. Furthermore, an extensive investigation was carried out to understand the applicability of the as-synthesized carbonaceous material for purifying water from anionic and cationic contaminants such as dyes and heavy metals. The main novelty of the work is the development of graphene nanosheets on a desert sand surface using date syrup as a sustainable carbon source to be used as an eco-friendly graphenic adsorbent for the complete removal of heavy metals and toxic dyes from water treatment. In short, the work was designed to develop a simple, low cost, green chemistry-based graphenic adsorbent which exhibits superior separation capacity and regeneration capability for a variety of organic and heavy metals based contaminants that are ubiquitous in water. The adsorption capacity of the as-prepared adsorbent far surpassed the adsorption capacity of similar reported graphene-based adsorbents. This will undoubtedly open new avenues for the practicability of graphenic material to curb the existing water shortage.In this work, we proposed a single-step strategy to develop efficient and eco-friendly graphene sand hybrids using date syrup, a widely available and sustainable carbon source in the Mediterranean region via pyrolysis. Through this 2-flow (100 mL/min.) Prior to starting the heating program, the air inside the furnace was replaced with high purity N2 gas. The mixture was heated to 750 °C by following the heating protocol as described in Scheme 1 to ensure complete graphitization of the date syrup. After the completion of the experiment, the furnace was allowed to naturally cool down to room temperature and the obtained carbonaceous and fluffy graphene-like material referred as “D-GSH” was further characterized and used for batch adsorption experiments.The schematic preparation procedure of D-GSH from date syrup and desert sand is shown in Fig. qe), was calculated using the Eqs. , respectively, m is the dry mass of D-GSH (g), V is the volume of the contaminant solution (L).A 1000 mg/L stock solution of dyes and heavy metals was prepared by dissolving an appropriate quantity of respective dyes or heavy metal salts in deionized water, and solutions of desired concentrations were prepared by successive dilution of the stock solution. Batch mode of adsorption experiments was performed in 25 mL conical flasks containing 10 mL of contaminant solution with a known initial concentration. A fixed quantity of D-GSH adsorbent was added and the stoppered conical flasks containing the mixtures were shaken mechanically in a temperature-regulated water bath  at a constant speed of 140 rpm and predetermined temperature and time. Detailed methods regarding the effect of various experimental conditions such as sand particle size, adsorbent dosage, solution volume, pH, time, initial concentration, and temperature and data analysis of sorption kinetics and isotherms of dyes and heavy metals were given in the Supporting Information. On completion of adsorption experiments, supernatant samples were withdrawn, and the residual dye concentration was analyzed using UV-vis spectrophotometer  at the maximum wavelengths of 590 nm for MV, 497 nm for CR, 668 nm for MB and 507 nm for MO. The residual heavy metals concentration was analyzed using an inductively coupled plasma optical emission spectrophotometer . All the experiments were performed in duplicates, and the reported results are average values ± standard deviation. The percentage removal and amount of dye/heavy metal contaminant adsorbed at equilibrium  with a strongly adhered char deposit on the surface. The Raman spectrum shown in Fig. −1, 1580 cm−1, and 2760 cm−1, corresponding to D (defects and disorder), G (graphitic) and 2D bands (number of graphene layers), respectively. These results reveal that D-GSH has largely sp2 frame graphene-like carbon material obtained by the conversion of sucrose and fructose molecules present in the date syrup. The intensity ratio, ID/IG of 0.94 indicates that D-GSH has a structural disorder same as that of graphene oxide34. On the other hand, the I2D/IG ratio was found to be 0.43, attributed to the presence of multilayer graphene on D-GSH35. The powdered X-ray diffraction (XRD) spectra of D-GSH showed (002) a sharp peak at ~23.2° (2θ) with an interlayer spacing of 3.72 Å and could be attributed to the (002) diffraction pattern of multilayered graphenic structures present on the surface of the D-GSH. The spectra also depicted several other small and medium peaks at various 2θ values and these could be assigned to the highly crystalline desert sand support used in this study and corresponds to the characteristic diffraction pattern of quartz and silica as indicated by the symbols ‘o’ and ‘ + ’, respectively in Fig. 36. Furthermore, the XRD spectrum of D-GSH showed the presence of few additional peaks at 2θ of 18° and 34.2° corresponding to the (111) and (311) plane of Fe3O4 particles, respectively37. These peaks confirm the presence of iron particles present in the date syrup. Both Raman and XRD indicate that the as-prepared D-GSH is in close relation to the graphenic material reported in literature38.Figure 2/g. Even though pristine graphene sheets have a high theoretical surface area (2630 m2/g), D-GSH exhibited a relatively low surface area. The surface area of D-GSH largely depends on the sand particles present in the hybrid material when graphene was coated on the sand. This is in agreement with the results reported by Yang et al.29, wherein the specific surface area of pristine graphene sheets reduced drastically when it was coated onto SiO2 particles.The porosity of D-GSH was characterized using the nitrogen adsorption/desorption isotherms at 77 K and pore-size distribution plot of D-GSH calculated using the Barrett–Joyner–Halenda (BJH) method Fig. . The iso−1 attributed to C=O stretching of –COOH groups and C-H stretching vibrations, respectively; were present. These observations serve as a piece of evidence for the complete graphitization of sucrose and fructose fragments on sand surface36 resulting in a carbonaceous adsorbent with many oxygen functional groups  which can act as binding sites for contaminants. Furthermore, strong absorption bands at 792 and 707 cm−1 consistent with the symmetric Si-O stretching and bending vibrations of the SiO2 functional group were conspicuously present in the spectra, which confirms the presence of quartz in the sand39. Whereas, the sharp band observed at 874 cm−1 can be assigned to the Ca-O stretching of the calcium carbonate species present in the sand40. On the other hand, after dye adsorption, the band intensity at 1451 cm−1 was reduced significantly and shifted to a lower wavelength of 1420 cm−1 and the peak at 1154 cm−1 completely disappeared owing to the utilization of functional groups during adsorption. A new band was formed at 1172 cm−1 indicating the presence C-N stretching after dye adsorption. After heavy metal adsorption, a new absorption band at 1154 cm−1 with remarkable intensity and vibrational bands attributed to metal oxide (Cd-O and Pb-O) appeared at low wavenumbers (518 and 457 cm−1) of the spectrum, further verifying the successful interaction of metal ions onto the binding sites of D-GSH adsorbents through complexation41.The presence of graphene on sand particles as well as the interaction of the functional groups of D-GSH in the adsorption of organic dyes and heavy metals were demonstrated using Fourier transform infrared (FTIR) spectroscopy analysis Fig. . In the 42. Along with the layered structure, the extremely rough and wrinkled surface with predominantly macropores helped in maintaining a high active surface. Theoretically, these characteristics are believed to play a crucial role in providing active sites for dye and heavy metal adsorption. Furthermore, it was noteworthy to mention the presence and uniform distribution of C element on the corresponding EDX spectrum of D-GSH . The so-obtained HR-TEM images  and CR & MO (anionic) with varying initial concentrations in the range of 5 to 200 mg/L were exposed to the D-GSH and desert sand (DS) (25.0 mg) for 4 hours to reach an equilibrium. From the results Fig. , it is e44. The highest removal efficiency of 93% was obtained at a dose of 25.0 mg owing to the increase in the availability of the active adsorption sites. Further increase in dosage did not show any improvement in removal efficiency due to the agglomeration of the adsorbent particles leading to longer diffusive path lengths for dye molecules46. Moreover, on increasing the D-GSH dosage beyond 25.0 mg, the CR adsorption capacity was reduced. Thus, an optimal adsorbent dosage of 25.0 mg/10.0 mL was chosen for all subsequent CR dye adsorption experiments. On the other hand, increasing the D-GSH dosage showed a negligible effect on MV adsorption. For a fixed volume of dye solution (10 mL), with the decrease in W/V ratio, the MV uptake capacity of D-GSH increased from 399.8 mg/g to 1983.9 mg/g, while 99.9% MV removal was attained even when the initial MV concentration was 1000 mg/L. This is because 5.0 mg of D-GSH was enough to adsorb the dye contaminants present in 10 mL of solution providing more uptake per gram of the adsorbent. The decrease in uptake capacity with an increase in adsorbent amount was attributed to the presence of some unsaturated sites available on D-GSH during adsorption47. For the same initial MV concentration, varying the MV dye solution volume from 10 to 20 mL for a fixed weight of D-GSH, say 5.0 mg  with an increase in sand particle size, whereas CR dye removal efficiency slightly decreased from 96% to 86%. This conclusion was drawn after performing batch MV and CR adsorption experiments using the as-synthesized D-GSH adsorbent on desert sand supports of various particle sizes such as 0 to 200, 200 to 500, 500 to 1000 and 1000 to 1500 µm  to 1000 mg/L (1987.98 mg/g). This increase is attributed to the increase in the number of available MV molecules which provides a higher driving force for overcoming the diffusion resistance between the adsorbate and adsorbent phases. A similar trend was observed during CR adsorption as well. The experimental MV and CR adsorption kinetic data were quantitatively modeled using pseudo-first order48 and pseudo-second order49 models. The mathematical representations of these models, as well as the calculated kinetic parameters obtained for both MV and CR adsorption, are given in the Supplementary Information  at all temperatures; suggesting that adsorption of MV and CR on D-GSH was a monolayer process wherein the active sites are distributed homogenously on the adsorbent surface50. As presented in Table Qe of D-GSH for MV was extraordinarily high (2564 mg/g) at 25 °C. This remarkable removal capacity of D-GSH compared to pristine desert sand further indicated the potential adsorption capacity of the well-dispersed graphene on the sand surface. To author’s best knowledge, D-GSH is the highest-capacity ranked adsorbent known to date for MV adsorption; five times greater than that of previously reported graphene-based adsorbents . Considering the slightly higher removal efficiency, Pb2+ and Cd2+ were chosen as model heavy metal pollutants for subsequent experiments. Similar to MV dye adsorption, Pb2+ and Cd2+ removal efficiency remained almost constant (>99%) for sand particle size ranging from 0 to 200 and 200 to 500 µm  are depicted in Figure 46.The excellent dye adsorption ability encouraged us to further investigate the metal ion binding ability of D-GSH in aqueous solution. Furthermore, the removal of heavy metals is of great concern owing to its high toxicity to both human beings and ecosystems. Interestingly, the preliminary adsorption experiment Fig.  carried ion Fig.  increase2+ and Cd2+ onto D-GSH also followed pseudo-second-order . These results essentially support that D-GSH has a homogeneous surface that can adsorb a monolayer of heavy metal ions and the removal efficiency of D-GSH would drop sharply once these available surface sites are filled-up. The monolayer Pb2+ and Cd2+ adsorption capacity, qmax of D-GSH was estimated to be about 781 mg/g and 793 mg/g, respectively at 25 °C. The determined adsorption capacity for Cd2+ and Pb2+ ions outperformed all other previously reported graphene-based adsorbents  was slightly lower than Cd2+ (98.31%). On the other hand, in a solution containing a mixture of MV dye and Pb2+ heavy metals with each having an initial concentration of 100 mg/L, D-GSH successfully removed 99.99% of dye as well as 99.75% of Pb2+ ions  and qm,j (mg/g) are the amount of contaminant j adsorbed in a single and multi-component system with equal concentration, respectively. From the values of RQ the interaction between each contaminant can be verified as follows: (i) when RQ <1, antagonism, i.e., the presence of the concomitant pollutant inhibits the adsorption of contaminant j; (ii) when RQ = 1, non-interaction, i.e., both contaminants do not affect each other; (iii) when RQ >1, synergism, i.e., the presence of the concomitant pollutant enhances the adsorption of contaminant j. From the Rqvalues obtained at the different initial concentration in the multi-component heavy metal system  steric hindrance effect between the heavy metals and the oxygen-containing groups such as –OH and –COOH/–COO− at high metal concentrations56.Real wastewater contains a mixture of heavy metals as well as organic dyes. Hence, it is of utmost importance to test the selectivity of D-GSH in a multi-component system consisting of both heavy metals as well as dyes. Single solute experiments indicate that D-GSH can potentially remove more Cdons Fig. . While atem Fig. , we can 2+ multi-component system . Basically, this indicates that the presence of MV does not pose a negative impact on the Pb2+ adsorption as there is no interaction between the Pb2+ ions and MV molecules when the initial concentration of MV was low (100 mg/L). However, at higher MV concentrations, even though MV removal is less affected , a slight decrease in Pb2+ adsorption . However, besides electrostatic interaction, the possibility of π-π bonding also played a crucial role in dye adsorption57. This was evident as the adsorption of anionic dyes was facilitated, even though the adsorbent and adsorbate had the same charge. This is attributed to the sp2 hybridized structure of graphene on D-GSH, which could present the possibility of π-π bonding with the aromatic rings of dyes contaminants. Additionally, van der Waals interactions such as hydrogen bonding between the carboxyl and hydroxyl groups on dyes and graphene as well as hydrophobic interactions are also believed to enhance the anionic dye adsorption capacity of D-GSH greatly58. Thus, the versatile chemistry of graphenes, such as the presence of negatively charged surface functional, abundant sp2 carbon sites and hydrophobic nature along with porous structure contributes to the extraordinary dye removal capacity showcased by D-GSH. Similar to dyes, heavy metal ion binding ability of D-GSH is primarily ascribed to its interconnected porous structure, which provides ample adsorption sites for heavy metal adsorption. The ion-chelating negatively charged surface functional groups present on D-GSH is believed to render the adsorption of heavy metals such as Pb2+ and Cd2+53,54. Moreover, the oxygen functional group present on the surface of D-GSH further enhances the metal adsorption via hydrogen bonding or complexation59. Thus, the wrapping of graphene on sand using date syrup as a precursor not only produced a versatile adsorbent with very high dye (anionic and cationic) and heavy metal adsorption capacity but also provided a facile green methodology to utilize graphene for water treatment. The whole plausible mechanism involved in the adsorption of cationic and anionic contaminants on to D-GSH composites is as shown in Fig. To get a better perspective of the high extraction efficiency of D-GSH for both heavy metals and organic dyes, it is essential to unravel the interaction mechanisms involved in the adsorption process. Desert sand is a well-known inorganic substrate with a hydrophilic surface rich in -OH groups. After the immobilization of graphene on desert sand, the adsorption capacity of D-GSH has improved remarkably. The wrapping of graphene on sand is believed to open up the stacked interlamination of graphene and thereby exposing the powerful adsorption sites available in the interlayers. Furthermore, with the presence of a hydrophobic graphene sheet with spin-situ strategy has been reported for the production of graphene sand hybrid using date syrup (D-GSH) via a one-step pyrolysis. The applicability of D-GSH as an eco-adsorbent for decontaminating wastewater was evaluated through batch adsorption using MV, CR and Pb2 +  and Cd2 +  as model pollutants. The so produced composite showcased highest adsorption capacity for MV (2564 mg/g), Pb2+ (781 mg/g) and Cd2+ (793 mg/g) at 25 °C along with a high adsorption capacity for CR (333 mg/g) and good recyclability (3 cycles). The appropriate adsorbent dosages for MV, CR, and heavy metals adsorption onto D-GSH were 5.0, 25.0 and 10.0 mg/10 mL, respectively at a shaking time of 45 min and temperature of 25 to 45 °C. Kinetically, the pseudo-second-order model well fitted the experimental data. Thermodynamically, the Langmuir model best described the equilibrium data for all the contaminants. The adsorption isotherm fitting and thermodynamic calculations suggest a strong electrostatic interaction between the cationic adsorbate  and the adsorbent. The highly hydrophobic effect and van der Waals interactions contributed to the adsorption of anionic contaminants such as CR. Furthermore, the D-GSH adsorbent showed remarkable efficiency in simultaneously removing both dye and heavy metals from the multi-component systems. Thus, the exceptional water-treatment capabilities of D-GSH confirm its great potential as an adsorbent material resource for water purification.A simple and facile D-GSH Supplementary Information


In this paper, we look at the work of a classical plasmon-induced transparency (PIT) based on metasurface, including a periodic lattice with a cut wire (CW) and a pair of symmetry split ring resonators (SSR). Destructive interference of the ‘bright-dark’ mode originated from the CW and a pair of SSRs and resulted in a pronounced transparency peak at 1.148 THz, with 85% spectral contrast ratio. In the simulation, the effects of the relative distance between the CW and the SSR pair resonator, as well as the vertical distance of the split gap, on the coupling strength of the PIT effect, have been investigated. Furthermore, we introduce a continuous graphene strip monolayer into the metamaterial and by manipulating the Fermi level of the graphene we see a complete modulation of the amplitude and line shape of the PIT transparency peak. The near-field couplings in the relative mode resonators are quantitatively understood by coupled harmonic oscillator model, which indicates that the modulation of the PIT effect result from the variation of the damping rate in the dark mode. The transmitted electric field distributions with polarization vector clearly confirmed this conclusion. Finally, a group delay  Plasmon-induced transparency (PIT) is achieved with the same properties of the traditional EIT that allow a distinct transparency window in broad absorption or transmission spectrum , also knIn general, PIT behavior mainly from two different destructive interference mechanisms, including the result of engaging “trapped mode” resonances ,17 or byIn practice, an active modulation of the PIT response, to achieve the well-controlled group delay, as well as many other practical function units, such as plasmonic switching, are highly attractive. Gu et al. achieved the complete modulation of EIT effect in classical metamaterials by photoactive Si-integrated functional unit cells and the optical pump-terahertz probe (OPTP) measurement methods . Xu et aIn this paper, we propose a design of a classical Al-based terahertz metasurface, consisting of a CW element and an SSR element on a semi-infinite Si-on-sapphire substrate, to achieve PIT effects. The CW serves as an electric dipole antenna to support the ‘bright’ mode resonance, whereas the SSR serves to support the ‘dark’ mode by being indirectly excited with a far-field coupling. We further discussed the resonance mechanism of the destructive interference in ‘bright-dark’ modes with respect to the electric field and surface current distributions. With simulations, we explore the effects of the coupling distance between the relative modes resonators, and the vertical distance of the split gap on the PIT effect. Furthermore, we integrate a continuous graphene strip monolayer into the metamaterial, and realize an active control of the amplitude and line shape of the PIT transparency peak, by manipulating the Fermi level of graphene. The coupled harmonic oscillator model and nonlinear fitting are applied to quantitatively understand the near-field coupling in the relative modes. It is shown that the modulation of the PIT effect results mainly from changes in the damping rate of the dark mode, and the transmitted electric field distributions with the polarization vector clearly confirms this conclusion. Finally, a group delay The metamaterial, with classical structure  but Here the parameters gσ is derived from the intra-band and inter-band transitions, which can be expressed as gσ, mainly comes from the intraband process in the lower THz band [The conductivity of the graphene monolayer inter(ω) . Accordiinter(ω) , the conTHz band :(2)σg(ω)ℏ and e are Planck constant and the electron charge, respectively. Here ke model ,46:(3)σgIn calculations, we set eference . The reax and y directions, and perfectly matching layers are applied in the z direction. In calculations, good convergence of the calculated result can be obtained with the non-uniform mesh setting.The 3D finite-difference time-domain (3D-FDTD) method was employed in our work. Periodic boundary conditions are applied in the To investigate the resonant features of the Al-based metamaterials without graphene integration, the corresponding transmitted profile of the individual CW arrays, SSR-pair arrays, and the combination PIT metasurface, are shown in z-component of the electric field (zE) distributions , the dip widens and becomes deeper, which confirms that the spatial separation determines the strength of near-field coupling [h varies from 0 μm to 8 μm (d is kept at 3 μm). The transmission dip on the resonance frequency is clearly lowered as the split gap deviates from its own center. As △h increases, the overall coupling coefficient decreases with the breaking of the symmetry of the dark atom structure.As illustrated above in fE of the graphene wires (blue line). It is clearly seen that a complete on-to-off modulation of the PIT transparent window can be achieved at the original resonant frequency. Compared to the configuration without graphene, in fE = 0.1 eV. With the Fermi level increasing to 0.8 eV, the PIT transparency peak gradually disappears, leaving an LSP-like resonance dip in the transmission spectrum. It is worth noting that the modulation of the graphene Fermi level does not cause a notable frequency shift.Apart from amplitude modulation of EIT, based on adjusting the coupling coefficient by structural reset method, a continuous graphene monolayer is integrated in the original structure to achieve dynamic modulation of the EIT effect. Here, a 7 μm wide graphene strip is deposited between the originally subradiant resonator (SSR) and the Si-on-sapphire substrate, as shown in fE of graphene, the coupled harmonic oscillator model and nonlinear fitting are applied to quantitatively understand the near-field coupling in the relative modes. The destructive interference in the proposed PIT metasurface can be described by the following equations [g means the coupling strength of the ‘bright’ modes resonator with the incident light and To further explain the underlying physical mechanism of graphene modulation on the effect of PIT, the corresponding transmitted electric field |E| distributions at 1.148 THz resonant frequency are shown in quations ,4,(4)x1T can be calculated byAccording to Equations (4) and (5), the susceptibility lated as ,51(6)χ=fE. Thus, the theoretical model indicates that the dynamical tunability of the PIT effect results from the change in the damping rate of the ‘dark’ mode. With increasing Fermi level, the surface conductivity of graphene The transmission spectra analytical fitted according to Equation (7) are shown in Slow light is one of promising findings in the generation of EIT phenomenon, resulting from strong dispersion at the transparent window ,7. Slow given by (8)tg=dφd between the two resonators (CW and SSR) and the vertical distance h of split gap, play an important role in the coupling strength on the EIT effect. Furthermore, a complete modulation of the PIT system was shown by introducing a continuous graphene monolayer strip into the metamaterial. The coupled harmonic oscillator model and nonlinear fitting are applied to fully understand the near-field coupling in the relative modes. The theoretical analysis indicated that the dynamical tunable of the PIT effect arises from the change in the damping rate of the ‘dark’ mode. The vector diagram of the electric field clearly confirmed this conclusion. Finally, the largest group delay We presented a design of a classical Al-based metasurface consisting of a cut wire (CW) and a symmetric split ring resonator (SSR). The destructive interference of the ‘bright-dark’ mode originated from direct-excited plasmon resonance in the CW and the coupling excited resonance in the SSRs pair. In the simulation, we demonstrated that the relative distance