The paper reviews the network of cellular signaling pathways activated by Functional Graphene Nanomaterials (FGN) designed as a platform for multi-targeted therapy or scaffold in tissue engineering. Cells communicate with each other through a molecular device called signalosome. It is a transient co-cluster of signal transducers and transmembrane receptors activated following the binding of transmembrane receptors to extracellular signals. Signalosomes are thus efficient and sensitive signal-responding devices that amplify incoming signals and convert them into robust responses that can be relayed from the plasma membrane to the nucleus or other target sites within the cell. The review describes the state-of-the-art biomedical applications of FGN focusing the attention on the cell/FGN interactions and signalosome activation. Since iThe reduction of GO to G-Red restores the structure and properties of G. In comparison with GO, G-Red is known to have an increased conductivity, and mechanical strength, the fact that makes it a more attractive tool for applications in theranostic nanomedicine. However, the π–π stacking of aromatic rings and van der Waals interactions limit its dispersion in a biological medium and induce aggregation, so only functionalized pristine G or functionalized G-Red can be used in nanomedicine. The chemical functionalization of graphene-based materials  tunes the structural, physical, chemical and electronic properties together with the biological responses . In the literature, the term “Graphene” refers to a broad family of graphene products that include, among others, reduced graphene oxide, graphene oxide, graphene nanoplatelets, etc. They possess a different structure and very diverse physicochemical and mechanical properties that affect the biological responses. In addition, these graphene products, in turn, are not homogeneous materials, rather a mixture with various oxidation states, different lateral sizes, varied number of layers, and different colloidal stability. The lack of standardized ways of reporting the characterization of graphene materials and the presence of traces of impurities  make difficult, sometimes, the reproduction of published biological experiments . In addiTaking in account the impossibility to give a univocal classification to the broad family of graphene products and the presence in literature of comprehensive recent reviews that describe the different aspects of biomedical applications of graphene ,12,13, tIn the last years, the applications of FGN in biomedical fields have prompted great interest and a wide number of compounds have been exploited to convey specific biological properties to graphene materials. Among the different chemical modifications of graphene-based materials, some of them have been designed to generate FGN targeted to mammalian cells , bacteria, yeast, and viruses.The combination of graphene-based materials with polymers has been tailored to synergistically combine the characteristics of both components to obtain multifunctional nanocomposites with a superior performance for biomedical applications . The funEscherichia coli (E. coli); after the recognition and capturing of E. coli by mannose ligands anchored on the platform, the near-infrared (NIR) laser irradiation induced a complete microbial elimination (>99%) ), activated the epidermal growth factor receptor (EGFR) by inducing a transient membrane depolarization and consequent influx of Ca2+ from the extracellular space, leading to an enhanced cellular uptake of the drug-loaded nanoparticles via pinocytosis into tumor cells that over-express EGFR  .,39.38,39The integrity of lysosome compartment is dependent by FGN concentration; no significant effects on the integrity of the lysosomal membrane have been reported at low FGN concentrations (20 μg/mL), while the membrane permeabilization can be affected at high FGN concentrations (100 μg/mL), which can result in cell death via different pathways, including lysosome/mitochondria-dependent apoptosis, lysosome-dependent necrosis, and lysosome-dependent autophagy) . AutophaCombined approaches can be used to monitor the activation of autophagic flux and the autophagosome accumulation induced by graphene exposition. That accumulation can be related to an increased autophagosome synthesis or to decreased autophagosome turnover .The microtubule-associated protein 1A/1B-light chain 3 (LC3) is used as a biological marker to identify autophagy induced by graphene exposition. During autophagy, cytosolic LC3-I is converted to LC3-II and associates to the autophagosomal membrane. Thus, the levels of the LC3II protein, the GFP (green fluorescent protein)-LC3 dot number and the treatment with chemical autophagy inhibitors are employed to determine cellular autophagosome accumulation. In addition, to monitor the autophagic flux activation, the p62 expression levels, normally reduced during the autophagy process, can be evaluated. After the graphene internalization by endocytosis, an increase of LC3II on the autophagosomal membrane corresponds to the accumulation of the p62 protein, indicating the autophagy induction mediated by graphene which does not evolve in the degradation of engulfed contents in the autolysosome vesicles. Further studies should be carried out to clarify why graphene or another type of nanomaterials are sequestrated into lysosomal organelles but not degraded. The consequences of graphene on autophagy are not completely clarified and different effects have been reported. Ji et al. demonstrated that the increased accumulation of autophagosome after GO quantum dots treatment resulted by the block of autophagy flux due to the low degradative activity of lysosomes . In anotThe anticancer drug delivery system induces the initiation of autophagy, which precedes cellular death. In particular, the nuclear translocation of either the LC3 autophagic marker and the chemotherapy drug is stimulated and results in the shut off of the late autophagy events and activation of cell death signals .Deeper studies on the molecular dynamics related to the graphene nanomaterials exposition are still necessary in order to understand whether the graphene endosomal trafficking concludes with lysosomal compartmentalization or involves the recycling of unengulfed materials.Glycyrrhiza glabra) loaded with Dox has been developed (FGN-GA/Dox). From these studies emerged that after internalization, FGN-GA/Dox is transported from the early endosome, gradually maturing into a late endosome and eventually into a lysosome that subsequently transferred mainly to mitochondria due to the targeting properties of FGN-GA. About 82.5% of Dox was delivered into mitochondria and 11.7% of Dox was delivered into the cell nucleus. The FGN-GA/Dox-induced mitochondria-mediated apoptosis (MMA) of cancer cells and exhibited greater antitumor activity compared with Dox·HCl in vitro and in vivo [Recently, particular attention has been devoted to the development of drug delivery strategies targeting subcellular organelles such as mitochondria . Antican in vivo . The nuc in vivo .1O2, at the targeted site of cancerous tissue [The targeted drug delivery strategies have also been investigated to maximize the anticancer effects of photothermal therapy (PTT) or photodynamic therapy (PDT). The basis of these therapeutic strategies is that light is utilized to activate a non-toxic photosensitizer (PS), provoking the formation of heat and highly toxic ROS, mainly singlet oxygen, s tissue . A PS lis tissue .A subcellular targeting for PDT was achieved by the conjugation of GO with integrin αvβ3 monoclonal antibody; after endocytosis, the escape of the nanosystem from lysosomes and the transfer to the mitochondria was observed. The PS  loaded on the nanosystem became in the “on” state into mitochondria performing its effective phototoxicity to kill cells by increasing the MMA .2+ homeostasis [1O2 in aqueous media) and a small diffusion radius (about 0.2 μm for 1O2) in biological system [It was demonstrated that the mitochondrial structure is affected by treatment with GO at low concentrations (<4 μg/mL), resulting in a decline in the membrane potential and the dysregulation of mitochondrial Caeostasis . Considel system , the spal system . From ex1O2. Hence, mitochondrial-specific PDT with in-situ 1O2 burst leads to the decrease of the mitochondrial membrane potential inducing irreversibly tumor cell apoptosis [Recently, in order to optimize the PDT effectiveness and therapeutic efficacy by increasing ROS production directly in mitochondria, a rare-earth doped upconversion nanoparticle (UCNP) was coupled with GQD and a rhodamine derivative  for mitochondrial targeting. The system exploited the properties of UCNP, which can emit UV/VIS light under NIR excitation, and GQD, which can efficiently generate poptosis .Although the mechanism is not clear, the nuclear sub-localization of graphene-based materials has been ascertained in some cases ,53. The The analyses of the literature data suggest that it is hard to predict the exact internalization mechanisms and the subcellular localization of graphene derivatives. Due to having a great diversity of structure, dimension, charge and colloidal stability, the cellular uptake is probably the result of the combination of different endocytotic pathways that might be associated with passive internalization.The studies on the different internalization pathways and the intracellular fate of graphene nanocarriers should be in deep, since they may enlighten the research on organelle-targeting drug delivery systems.The intracellular internalization of graphene-based materials triggers a wide variety of cellular responses mediated by the activation of the intracellular signaling network, which affects the cell environmental ,55,56. TThe modulation of immune response related to graphene exposition was studied in primary murine and immortalized macrophages. Zhou and collaborators  have demA potential branch of cancer gene therapy is represented by immunotherapy approach that stimulates directly the immune response against cancer. Therefore, the evaluation of the impact of the graphene sheets on the cellular environment and the potential modulation of the key components of the immune system could be interesting for a new immunotherapy approach. It has been found that the lateral dimensions of GO can modulate the expression of immune genes encoding for chemokines, cytokines and cytokine receptors. A deep and interesting study by using a genomic approach was conducted by Orecchioni M. et al.  on humanSingle-cell mass cytometry analysis in combination with whole-transcriptomic analysis was performed on purified PBMCs treated with GO and amino GO. The amino functionalization on GO reduced the necrotic events, incremented the CD25 and CD69 expression levels in active T cells, as well as the gene expression for pro-inflammatory cytokines, regulators for an innate and adaptive response. These data suggested the enhanced biocompatibility of GO due to functionalization .Caenorhabditis elegans. In addition, Kang et al. [Current knowledge has demonstrated that the graphene nanostructure triggers an in vitro programmed cell death mechanism in a dose-dependent manner. During earlier events of apoptosis, the translocation of phosphatidylserine occurs from inner to the outer leaflet of the plasmatic membrane. The fluorochrome-labeled Annexin V analysis allows detecting the interaction between Annexin V and the phosphatidylserine exposed on the outer surface, through a flow cytometry assay. Tabish et al. showed that lung cancer cells exposed to a lower concentration of G-Red exhibited late stage of apoptosis, rather than early stages, with a consequent formation of the apoptotic bodies and damage of cell membrane . Insteadg et al.  have demGraphene-based materials have emerged as a subject of enormous scientific interest because of its exceptional properties and they have been proposed for various biomedical applications, such as biosensors, tissue engineering, and drug delivery. However, until now, to the best of our knowledge, no graphene-based materials have progressed to the clinical stage. The main obstacles to this advancement are the non-homogeneous nature of graphene materials and the lack of standardized ways of reporting their characterization. Moreover, along with detailed in vitro characterization of graphene derivatives, more attention should be focused on their evaluation in vivo with respect to inflammatory responses, biocompatibility, and signaling pathways. Thus, the road of graphene in biomedical/pharmaceutical applications seems still very long and winding. However, the enthusiasm of the scientific community is providing a host of very interesting breakthroughs, which place graphene in a pole position in the fields of theranostics and tissue engineering. The present review deals with modified graphene materials in which the structural, physical, chemical, and electronic properties and the biological response  are tuned by organic functionalization and highlights the advances in the investigations of FGN in nanomedicine. The interactions of FGN with cells, the different pathways of cellular uptake and the sub-cellular localization have been dealt. The current knowledge about the intracellular pathway activated by FGN appears still fragmentary and the correlations between the graphene surface functionalization and intracellular signaling network are not yet sufficiently clarified. These aspects should be deeply investigated considering the importance of graphene-based nanomaterials to modulate a cellular microenvironment.


Graphene is a very promising material for electronics applications. In recent years, its sensitivity to ultraviolet (UV) irradiation has been studied extensively. However, there is no clear answer to the question, which factor has a key influence on the sensitivity of graphene to UV. In order to check the influence of the final substrate on the electrical response, graphene transferred on polymeric and non-polymeric substrate was investigated. To achieve this goal three polymeric and three non-polymeric substrates were tested. The results of the preliminary tests indicated the different character of the reaction on UV irradiation in each of group. To explain the reason of the difference, the complementary studies were done. The samples that were resistant to high temperature were annealed in a vacuum at 500 °C to get rid of water trapped between graphene and the substratum. The samples after annealing reacted less dynamically to UV irradiation. Moreover, the progress of changes in electrical response of the annealed samples had a similar character to the polymeric substrates, with the hydrophobic nature of the surface. These studies clearly prove that the sensitivity of graphene to UV irradiation is influenced by water trapped under the graphene. Due to the fact that 2D materials are only the surface, they are extremely sensitive. Graphene can interact with both the substrate on which it is placed and the surrounding atmosphere. Due to the promising electrical properties of graphene, there have been attempts to use it for the construction of various types of sensors, for example: gas, X-ray [3, NO2, O2,) from graphene [2 substrate [The dynamic technological development observed in recent decades has contributed to increase the efficiency of electronic devices reducing their size. As a result, conducted research on 2D materials has increased. One of the most popular in this group of materials is graphene—single layer of sps, X-ray ,2,3. Anos, X-ray ,5. But tgraphene ,7,8, theubstrate . There aThe authors of this study investigated the reactions of graphene transferred on six different substrates to UV irradiation. The Raman spectroscopy revealed that only the region with monolayer of graphene strongly reacts to UV irradiation. The reaction of multilayer to UV was almost nonvisible. The contact angle measurement pointed that the polymeric substrates are more hydrophobic. The results of the preliminary tests indicated that polymeric materials are less sensitive to UV irradiation, and the character of reaction to UV is different. The complementary studies unambiguously confirm that the water trapped between graphene and substrate has the superior influence on the sensitivity of graphene to UV irradiation.3. Before a graphene transfer, the target substrates were cleaned in acetone, and the gold electrodes were sputtered. The tests were performed on six different substrates belonging to two groups: polymer  (PEN) and poly (tetrafluoroethylene) PTFE and non-polymer (Si/SiO2 (280 nm), Al2O3 and quartz glass). The active surface area of graphene was 3 × 3 mm.High Strength Metallurgical Graphene (HSMG) produced on a bimetallic substrate  was used2 substrate. The power of the laser on the surface of the examined samples was 10 mW and the applied magnification was 100×. All measurements were carried out in ambient conditions and at room temperature.Before UV irradiation a set of tests was done to characterize the substrates as well as the graphene quality after transfer. Water contact angle measurements for all used substrates were performed using the FM40 Easy Drop system with Drop Shape Analysis software (Krüss GmbH). Each measurement was performed on cleaned surfaces such as prepared before transfer. The sample was mounted on the system table, then a 30 μL droplet of deionized water was placed on its surface and contact angle measurement was taken instantly. Graphene quality on different substrates was examined using scanning electron microscope . Raman spectroscopy  with an excited wavelength of 532 nm was used to characterize the graphene before and after irradiation on Si/SiOUV irradiation was carried out at ambient temperature, at atmospheric pressure in air. Samples were irradiated with a UV diode with a wavelength of 270 nm, impulse irradiation at 50% completion time was used. The distance between the UV source and the sample was 3 cm. During the experiment, the resistance changes progress over time was recorded. Comparative measurements of carrier concentration and mobility were determined by measuring the Hall effect in the electrode system according to the Van der Pauw method. The measurements were carried out in a magnetic field with an induction of 400 mT at a sample current of 1 mA.2 contains silane groups and adsorbs water on the surface. On the one hand, this allows for better positioning of graphene on the surface; on the other hand, it traps water between graphene and the substrate [In the wet method of transfer, water is used as a medium positioning graphene on the target substrate. Because of that, substrates’ wettability has a key impact on the quality of the transfer. The polymeric substrates used for the research were characterized by a contact angle exceeding 76°, and the ceramics had the wetting at a similar level. Low contact angle values were noticed for silicon substrates: 46° and 57° .. Previoubstrate ,12. Poly2, quartz glass, kapton and PEN are characterized by a smooth surface. The other two substrates have porosities, but in the case of ceramics, the number of pores is much higher. 2, kapton, PEN and even on Al2O3, are the places where the discontinuities of the graphene layer are present. SEM images do not allow to indicate the cause of graphene’s heterogeneity. Graphene can be mechanically damaged during the transfer process. [To show the state of the substrates surface and the quality of graphene after the transfer, SEM photos were taken. The research reveals that Si/SiOprocess. . Defectsprocess. . The SEM−1) and 2D (~2700 cm−1) peaks are characteristic for graphene Raman spectrum. The G band is the only band coming from a normal first order Raman scattering in graphene [−1 and widens when the amount of graphene layer increases or when defects occur. The ratio of 2D to G peak intensity (I2D/IG) amounts to 4 for pristine graphene and decreases when defects occur [−1) and D’ (~1620 cm−1) bands are activated by single-phonon intervalley and intravalley scattering process. Presence D and D’ peaks on Raman spectrum confirm the defect occurring [The Raman spectroscopy is a very useful method to analyze the quality of graphene. The G ~1585 cm85 cm−1 agraphene ,17. The ts occur ,19. D (~nd D’ ~16 cm−1 ban2D/IG was made (−1—to three (the fitting of this peak is presented in D/IG) (D) was calculated (D/ID’) after UV irradiation, it can be concluded that UV radiation changes the nature of defects. Referring to the values obtained for the graphene monolayer given by A. Eckmann et al.  it can be concluded that UV radiation can cause the formation of sp3 bonds [3-like bonds on the bounder of SiO2 and graphene [To test the graphene quality, Raman map Iwas made . The ratin D/IG)  can be olculated . The calp3 bonds . As it winitial and Rtime are the sensor resistance change within time in response to UV irradiation.The sensitivity of graphene to UV was measured by the change in resistance value. The results obtained for various types of substrates are shown in 2 and PEN are characterized by a completely different UV response: Si/SiO2, 92%; PEN, 23%, while ceramics with high initial resistance exhibit sensitivity at 55%.The tested samples were characterized by different values of initial resistance from approx. 1.6 kΩ to approx. 5.7 kΩ . The reaOn the graph of resistance changes, the relationship between the final substrate and the character of changes in graphene response to UV is clearly visible. Graphene transferred on polymeric substrates is characterized by greater dynamics of reaction and reaches the maximum value of the resistance faster . In the The influence of UV irradiation on the carriers’ concentration and their mobility for all substrates was also examined. For each of the substrates, a decrease of carriers’ concentration was observed with simultaneous increase in their mobility due to irradiation . The gra2, quartz glass and Al2O3) was annealed at 500 °C under 2∙× 10−3 Pa. That allowed to clean the graphene surface and get rid of water trapped between graphene and the substratum. After annealing, the samples were kept under ambient conditions for 24 h. This time was enough to adsorb the water vapor on the graphene. Then the samples were irradiated according to the previously adopted scheme.To check which interactions with graphene are predominant, an additional test was performed. Graphene on substrates that are resistant to high temperatures (Si/SiO2, 2 kΩ; quartz glass, 5.14 kΩ and Al2O3, 50 kΩ. The reason for the increase in resistance may be graphene damage during heating through the release of water. The release of a large amount of water trapped in the pores of the Al2O3 was a very dynamic process and led to a significant damage of graphene. The samples reacted less dynamically to UV irradiation after annealing. There was only a few percent increase in UV resistance. The progress of resistance changes for all tested samples had a similar character to the unheated polymer substrates (2O3 substrate and was the lowest for Si/SiO2.For all tested samples, an increase in resistance after annealing was observed: Si/SiObstrates  (respons2. For the remaining substrates a few percent carrier concentration increase was observed (A decrease of carrier mobility was observed. It may be associated with the increase of amount of defect created in graphene during annealing. Differences were also observed in change of carrier concentration. A slight decrease in concentration after irradiation was observed for Si/SiOobserved .2 exhibit hydrophilic properties, while polymeric substrates and ceramics are hydrophobic. Depending on wettability of the surface, the amount of water enclosed under the graphene surface varies. It is greater for hydrophilic materials and smaller for hydrophobic materials, which results in a difference in the nature of changes in the electrical response. An exception is ceramics, which despite the hydrophobic properties have the ability to accumulate more water in the pores. Because of that, their electrical response is similar to hydrophilic materials. Annealing of the samples allows to get rid of water trapped under graphene, making graphene much less sensitive to UV radiation.The results indicate the relationship between the sensitivity of graphene to UV irradiation and the amount of water trapped under graphene during the transfer. Quartz glass and Si/SiO2O3 is water adsorbed in the pores. The water is not completely removed during the heating. The lowest sensitivity of graphene transferred on Si/SiO2 indicates the almost complete removal of water below the graphene. Trying to explain the nature of phenomena affecting the electrical response of the sensor under the UV irradiation, it can be concluded that the dynamic increase in resistance in the initial phase of irradiation is related to the purification of graphene from water. The drop of resistance observed in the last phase is caused by the interaction of graphene with the substrate. The stabilization stage is a temporary balance between the two above-mentioned processes.The reason for the highest electrical response obtained for AlThe subject of the research was the influence of the final substrate on sensitivity of graphene to UV irradiation. To determine this correlation, the electrical response of graphene was measured. The most important feature that has an influence on sensitivity of graphene to UV is the ability of the substrate to accumulate the water on the surface. The high amount of water adsorbed on the final substrate surface affects both the dynamics of the electrical response of the sensor and the progress of the character of resistance changes. Getting rid of water trapped on the graphene-substrate boundary results in a decrease in the sensitivity of graphene to UV irradiation. Summarizing, the final substrate used in UV sensors should be characterized by hydrophilic properties to provide the appropriate amount of water on the boundary.


The oxidation mechanism of CO on W-embedded graphene was investigated by M06-2X density functional theory. Two models of tungsten atom embedded in single and double vacancy (W-SV and W-DV) graphene sheets were considered. It was found that over W-SV-graphene and W-DV-graphene, the oxidation of CO prefers to Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanism, respectively. The two surfaces exhibit different catalytic activity during different reaction stages. The present results imply that W-embedded graphene is a promising catalyst for CO oxidation, which provides a useful reference for the design of a high-efficiency catalyst in detecting and removing of toxic gases. As a common 5d transition metal in the sixth period, the supported tungsten and its oxides by graphene are widely used in many fields of photocatalyst, antibacterial, anticancer agent, and gas sensors [3(001) surface systematically, their calculation results show that this tungsten oxide is one of the most promising gas sensor candidates due to its high activity toward CO oxidation. To the best of our knowledge, the mechanism of CO oxidation on tungsten-embedded graphene is still lacking in experimental and theoretical investigations. Does this composite also exhibit excellent activity for CO oxidation? What kind of mechanisms are adopted in the reaction process? In order to understand the related mechanism more deeply, in the present work, the tungsten-embedded graphene was taken as the computational model, the related oxidation mechanism was investigated through theoretical calculation. The purpose of this study is not only to evaluate the activity of this catalyst, but also to reveal the microscopic mechanism of this kind of reaction, and to understand the activity of different oxygen species and different types of vacancies  during the reaction process. Environmental pollution caused by automobile and industrial emissions has become a serious threat to human health and ecological safety; carbon monoxide is one of the main pollutants in these exhaust gases. It is well known that catalytic oxidation of carbon monoxide with noble metals such as Au, Pt, and Pd as catalysts is an effective method to eliminate this hazardous gas, but the high cost will undoubtedly limit their widespread use ,2. There sensors ,27,28. R sensors . Moreove sensors . Theoret sensors ,32. The  sensors  have invads) was calculated as Equation (1):In the present work, the density functional theory (DFT) method is employed to study the detailed reaction mechanism at the molecular level. The geometry optimization and the subsequent frequency analysis of the complexes involved in the reaction were performed using the M06-2X density functional, all the calculations were performed using the Gaussian 09 package ,35. In t−1, respectively. So the tungsten atom could be stabilized both at the single and double carbon defects on the graphene substrate. According to the SIM0 structure in −1, which is in good accordance with the results of −156.8 and −200.6 kcal mol−1 obtained by Zhang [First, the geometric structures of tungsten atom adsorbed on single and double vacancy (SV and DV) of defective graphene were investigated, as summarized in by Zhang  and Tangby Zhang , respectSIM0, which can help us understand the adsorption properties of tungsten on graphene vacancies. As can be seen from d orbital property of the tungsten atom, which will not only provide d electrons for the adsorbed molecule, but also allow one electron to occupy this LUMO. The above observations indicate tungsten may be the activated site for the adsorption of electrophilic probe molecules. In addition, the calculated molecular electrostatic potential (MEP) map of this graphene composite molecule shows the electrophilic region near the metal site (see DIM0). The calculated adsorption energy of tungsten atom on the double vacancy is −238.1 kcal mol−1, indicating much stronger interaction between the inpurity atom and surface in W-DV-graphene. Molecular orbital analysis and NBO results show that this configuration has electronic properties similar to that of the W-SV-graphene.site see . The mor2 and CO on W-graphene were obtained, as summarized in SIM1 with the adsorption energy of −79.26 kcal mol−1. The NBO analysis indicates, the charge transfer from W-embedded graphene to O2 is about −0.578 e  forms superoxide on both surfaces, and it can become an active center for subsequent reactions. The adsorption behavior of gas molecules on the surface of catalyst could play a significant role in subsequent catalytic reactions. The most stable adsorption configurations for O78 e see , occupyi−1 on the W-SV-graphene and W-DV-graphene surface, respectively, which are much weaker than that of O2. sd hybrid orbital of W, and the d electrons of W feed back into the π* orbital of CO. The net result is that the charges of −0.088 and −0.246 e of CO molecule transfer to the surface of W-SV-graphene and W-DV-graphene respectively, which is different from the adsorption of O2, the surface play a role of electron withdrawing here. Compared with free CO (1.132 Å), the bond lengths of the two adsorption configurations have no significant change .With respect to CO, the calculated adsorption energies are −25.39 and −18.14 kcal mol2 molecule is activated first, then the CO in gas phase gets closer to the reactive oxygen species to generate CO2 directly. While in the latter, O2 and CO co-adsorb on the surface and form CO2 directly. As mentioned above, the adsorption of O2 on W-embedded graphene surface is much stronger than CO, suggesting that O2 molecule will preferentially adsorb on the two surfaces. Therefore, the tungsten site will be mainly covered by the oxygen molecule if a mixture of O2 and CO is injected as the reactants, and the formation of O2-W-graphene complex (IM1) can be considered as the initial step of CO oxidation.It is well known that there are two feasible mechanisms for CO oxidation, named Eley-Rideal (ER) mechanism and Langmuir-Hinshelwood (LH) mechanism. In the ER mechanism, the adsorbed O2 and followed by the oxidation of CO as presented in Equations (2) and (3).The ER mechanism over the W-SV-graphene is discussed first, that is, the activation of OG of all species is provided in 2 activation. This reaction starts with the formation of O2-W-graphene (SIM1) complex, which is −79.26 kcal mol−1 below SIM0 + O2. SIM1 can rearrange to form SIM2 with an energy barrier of 44.49 kcal mol−1 (STS12). As shown in STS12 is almost broken as the bond length is elongated to 2.036 Å. In SIM2, the activated O2 molecule forms two adsorbed oxygen atoms on the surface: one is located above the tungsten site while the other co-binds with the tungsten and a neighboring carbon atom, named Otop and Ostep respectively. NBO analysis shows that the negative charges on these two O are −0.330 and −0.248 e, respectively. The O− species is formed, which is beneficial to the adsorption of CO and other probe molecules. The calculation shows that the activation reaction of oxygen over W-DV-graphene follows a similar mechanism with that on the W-SV-graphene, both reactions are greatly exothermic processes and spontaneous in energy. According to NBO analysis, a large number of electrons on the catalyst surface are transferred to oxygen species, the catalyst plays the role of electrons donor in both cases. Starting from SIM2, when CO attacks oxygen atoms at different adsorption sites, there are two possible ways to generate CO2 through ER mechanism. When CO attacks Otop in complex SIM2, SIM4 and CO2 can be generated after overcoming the activation energy of 52.71 kcal mol−1 (STS24). Alternatively, if the carbon atom in CO attacks Ostep, it can also produce CO2 by overcoming STS23, leaving the Otop adsorbed on the tungsten site. However, the activation energy of this step is quite high . Apparently, on the surface of W-SV-graphene, Otop has stronger activity than Ostep toward CO oxidation. The relative Gibbs free energy ΔSTS24) and 0.245 e (STS23) respectively, whereas the charge on the graphene is decreased from −0.119 e in SIM2 to −0.150 (STS24) and −0.330 e (STS23) respectively. Therefore, the graphene surface acts as an electron acceptor during the oxidation of CO, which is different from that of O2 activation over W-embedded graphene. The desorption of CO2 will leave atomic O species on the surface. (see SIM3 and SIM4). The oxygen in SIM3 and SIM4 can extract charge from tungsten easily due to its strong electronegativity. According to the NBO analysis, in SIM3 and SIM4, there are 1.022 and 1.002 e on the W sites, while −0.531 and −0.603 e on the oxygen atoms, indicating the W–O site might be the active centre for adsorbing and oxidating CO, which will be discussed in the later section.According to NBO results, the charge on carbon monoxide is increased to 0.100 , which is the most stable species on the PES with the relative energy of −158.23 kcal mol−1. Along the reaction coordinate, after passing the transition state STS53, one of the W–O bonds and a C–O bond break simultaneously to produce SIM3 and CO2, this reaction requires 23.12 kcal mol−1 activation energy. From SIM1 + CO→SIM5→SIM3 + CO2 is less feasible in energy than the two ER oxidation mechanisms discussed above. The NBO analysis shows that during the whole process of CO oxidation, the positive charge change on tungsten atom from SIM1 to SIM3 is not distinct, so the metal centre only acts as a bridge for transmitting electrons. The third feasible ER oxidation pathway was identified by calculation, as described in 2 is the most feasible as it requiring lowest activation energy  on this surface. After comparing the potential energy curves on two different surfaces in Three possible reaction pathways of CO oxidation over W-DV-graphene using ER mechanism were identified also, as shown in 2 + CO system. Though in the structure the oxygen chemisorbs on the Sn-graphene while the CO physically adsorbs on the Sn site, their calculated results indicate the LH reaction as the first step is more feasible rather than the ER reaction. Obviously, the adsorption properties of CO do not determine the mechanism of oxidation. In this study, the co-adsorption of O2 and CO over two different W-embedded graphene were obtained, with the adsorption energy of −76.62 and −64.71 kcal mol−1, respectively, which are close to the adsorption of oxygen alone, indicating the oxygen and carbon monoxide molecules may co-adsorb on the tungsten site, so the possibility of CO oxidation using LH mechanism should be considered also.In a previous research about CO oxidation over Sn-embedded graphene, Esrafili et al.  located 2 and CO are co-adsorbed on the surface, CO extracts one oxygen atom from the O2 molecule which has not been activated completely to produce SIM3 and CO2 directly. The energy barrier (STS13) of this step is 38.6 kcal mol−1. From SIM0 + O2 + CO→SIM1 + CO→STS13→SIM3 + CO2 via LH mechanism is spontaneous in energy and exothermic by −141.40 kcal mol−1, so this mechanism is the most feasible CO oxidation channel on the surface of W-SV graphene. Similarly, CO has a possible oxidation path on the W-DV-graphene surface using the LH mechanism. After the transition state DTS13, CO extracts one oxygen atom from the pre-adsorbed oxygen to generate carbon dioxide and DIM3 directly, but the activation energy of this step is higher than that of DTS15 . So it is more feasible to adopt ER mechanism to oxidize CO on the surface of W-DV-graphene.The LH mechanism of CO oxidation on the surface of W-SV-graphene was studied firstly, and a feasible reaction channel was determined. As shown in STS12 or STS15. As the activation barrier of these steps are high, reaching 44.49 kcal mol−1 or 56.92 kcal mol−1, so the activation of O2 is rather difficult. If the LH mechanism is adopted, the pre-adsorbed oxygen will react with CO to produce carbon dioxide directly, the energy barrier of rate-determining step during SIM1 + CO→SIM3 + CO2 is 38.68 kcal mol−1, so for the CO oxidation over W-SV-graphene surface, the LH mechanism is more feasible. On the contrary, over the surface of W-DV-graphene, CO inserts and activates pre-adsorbed oxygen molecule to form peroxide species OOCO and then dissociates into carbon dioxide and DIM3, which is the most feasible of all CO oxidation channels, so the ER mechanism is dominant on this surface. The above calculations also show that W-DV-graphene has higher catalytic activity than W-SV-graphene for CO oxidation, regardless of ER or LH mechanism.From 2 is released through either ER or LH mechanism, an O atom is left on the surface of W-embedded graphene. On either surface, the product IM3, that is, the oxygen species on the top of the metal (named Otop), can be obtained through the most feasible oxidation pathway. Now turn to the second CO oxidation pathway involved by Otop, which may lead to catalyst recovery. From STS60, the carbon, tungsten and Otop form a three-membered ring transition state, the product (CO2 + SIM0) is yielded at last after overcoming activation barrier of 22.95 kcal mol−1. For an excellent catalyst, its recovery and reuse is of utmost importance. The present calculation shows that the catalyst has good recovery as the surface can be recovered after second CO oxidation. Of course, in the actual production, some advanced catalyst recovery methods such as membranes, will help to recover the catalyst effectively [2 + DIM0). This reaction requires a high activation energy , suggesting the remaining Otop species on W-DV-graphene has weaker activity toward CO oxidation.From the above calculations, it can be seen that when COectively . In addiThe above results show that the surface of pure W-DV-graphene has stronger activity for CO oxidation than W-SV-graphene. After a period of reaction, the surface metal sites will be covered by a certain amount of Otop. Although this Otop species remaining on the surface also has a certain oxidation capacity toward CO, the oxidation activity of Otop over W-SV-graphene surface is significantly higher than that on W-DV-graphene surface, so the recovery of the latter surface is more difficult. Therefore, it is important to control the ratio of SV to DV on W-graphene surface in the design of catalyst to achieve the best catalytic activity.Up to date, compared with the surface of SV-graphene, there are few studies on the CO oxidation over DV-graphene surface. In the present research, the CO oxidation reactions over the two different tungsten-embedded graphene have been explored comprehensively and compared. The results show the catalytic oxidation of carbon monoxide over the two embedded graphene surfaces follows different mechanisms, these two surfaces show different catalytic activities in different reaction stages. Previous experiment has confirmed that both single vacancy (SV) and double vacancy (DV) can exist simultaneously on the surface of graphene . In expeIn general, the oxidation of carbon monoxide on embedded graphene has attracted considerable interests over the last few years. After comparing these related studies, it is found that both noble metals and non-noble metals, and even some non-metallic-embedded graphenes have superior catalytic activity for the oxidation of CO. The present research show that, although not as good as these noble metals, tungsten-embedded graphene also has a high catalytic activity for CO oxidation. Considering the low cost and high activity, we believe tungsten-embedded graphene is also a good catalyst toward CO oxidation, which can be used as a gas sensor candidate for monitoring and removing toxic gases.2 over W-SV-graphene and W-DV-graphene have been investigated using the DFT approach. The LH mechanism is preferred for CO oxidation on a W-SV-graphene surface with an energy barrier of 38.68 kcal mol−1, while over W-DV-graphene, the catalytic process is likely to proceed with the ER mechanism, the calculated energy barrier is only 25.72 kcal mol−1. During different reaction processes, the catalyst substrate plays different roles of electron donor or acceptor. For the second CO oxidation, the Otop over W-SV-graphene surface shows significantly higher activity than that on W-DV-graphene surface with the energy barrier of 22.95 kcal mol−1 and 58.20 kcal mol−1, respectively. As the two surfaces exhibit different catalytic activities during different reaction stages, the ratio of SV to DV should be adjusted reasonably in the process of catalyst design to obtain the best catalytic performance.The CO oxidation reactions by O


The crystallinity of the grown single layer graphene is relatively good due to high distribution percentage of FWHM values of 2D band that is below 30 cm−1. However, the defect concentration is relatively high, and it suggests that a flash-cooling technique needs to be introduced.We present a synthesis of large-area single-layer graphene on copper substrate using a refined cooking palm oil, a natural single carbon source, by a home-made spray injector-assisted chemical vapor deposition system. The effects of the distance between spray nozzle and substrate, and growth temperature are studied. From Raman mapping analysis, shorter distance of 1 cm and temperature of around 950 °C lead to the growth of large-area single-layer graphene with a coverage up to 97% of the measured area size of 6400 μm Its extom thick , super com thick , solar com thick , and senom thick . In factom thick . Thus, iom thick , 9, chemom thick , 11. In om thick . Generalom thick . In CVD om thick , acetyleom thick , and proom thick  via low-om thick  or atmosom thick , which l2) carrier gas. The growth was performed at temperature of 900 °C for 15 s, before it was rapidly cooled down by the flash-cooling technique. However, the coverage of the grown graphene is relatively low of around 60%. In this paper, we demonstrate an alternative route to synthesize large-area single-layer graphene with the coverage up to 97% utilizing a homemade spray injector-assisted CVD system without introducing H2 during the growth for the first time. This spray injector enables the atomization of precursor into micron-sized droplets. The atomized droplets enable better decomposition kinetics due to the increase of surface compared to conventional CVD methods. One more privilege is that the precursor injection flow rate allows the control of the droplet flux which controls the mass transfer rate during the vapor deposition [Many benign alternative attempts have been made to replace these typical precursors with moderate hazardous hydrocarbon supplied from liquid or solid carbon sources. For an example, Weiss et al. investigated the growth of graphene on copper (Cu) substrate by utilizing ethanol . Choi etposition .2O (1:10) at 60 °C for 30 min. Then, this Cu sample is rinsed with isopropyl alcohol and acetone for 10 min in an ultrasonic bath  to remove any contamination and native oxide from the surface. Then, the Cu sample is dried using a nitrogen blow. Figure A commercial Cu foil  is used as a metal catalyst. Firstly, a Cu foil cut into 1 cm × 1 cm is rinsed with distilled (DI) water, followed by a treatment using 1 M acetic acid/Hd, are studied. Here, d is set at 1, 3, and 6 cm. The substrate is heated to the set growth temperatures, T, i.e., 900, 950, and 1000 °C while keeping the reaction chamber in Ar environment. After reaching the set temperature, hydrogen (H2) of 40 sccm is introduced for 20 min. This annealing treatment in H2 is performed with the purpose to further remove the remaining contamination and to reduce the roughness of the Cu surface. After that, the flow of H2 is stopped and a refined cooking palm oil is injected for 1 s (~ 0.05 ml) into the reaction chamber using a computerized fuel injector (car fuel injector). Then, the growth (or heating) is kept at the set temperature for 10 min. After the growth, the heater is turned off and the sample is cooled down to a room temperature in vacuum ambient with continuous evacuation. Since an automated spray injector is used in this work to control the carbon (C) amount or concentration, it is expected that the C element should be able to reach and spread uniformly on the heated substrate after the effective thermal decomposition of refined cooking palm oil. The decomposition can be expressed by the following reaction:The effects of the distance between the nozzle and the substrate, The growth mechanism is assumed to follow the well-accepted mechanism described in , 23. HerThe optical microscopy is used to observe the morphology and homogeneity of the as-grown graphene films on Cu substrate. The structural characteristic, such as the number of graphene layers, homogeneity, and defects, are examined using micro-Raman spectroscopy (WiTec Alpha 300) at an excitation laser wavelength of 514 nm. Here, a × 100 magnification lens is used, giving a laser spot size of about 400 nm. The time integration is 0.5 s, and the laser power is kept below 1 mW to avoid any damage or heating on the sample, which may induce the desorption of the adatoms from graphene. The spectrometer is equipped with a piezoelectric stage that allows Raman mapping of an area up to 200 μm × 200 μm. To investigate the inhomogeneity of the graphene film, Raman mapping is used to collect a large quantity of spectra with different amount of disorder. Here, the analyzed number of spectra is 1024 for the size of 80 × 80 μm. Raman measurements are done without transferring the graphene film onto a new flat substrate. Hence, it can be said that the data presentation of graphene is in its original state. It is worth to note that the strong background signal from the Cu substrate has been removed from each spectrum by manual subtraction.qxy is the heat flux in the x and y directions (W/m2), k is the thermal conductivity constant (W/m K), and T is the temperature (K).Figure A finite difference method was used to solve the equation. Thus, for the sake of differential control elements, only the factoring of steady-state conduction of energy conservation takes place as in Eq. d = 1, 3, and 6 cm, respectively, grown at temperature of 1000 °C. It is well reported that higher temperature is better for the complete decomposition of source as well as for uniform absorption of C element into the Cu substrate. As can be seen in Fig. d = 3 cm. However, many black spots are observed for the samples grown at d = 6 cm, indicating the formation of amorphous carbon in the cavities (holes), and scratches of Cu substrate [2 annealing can reduce the roughness of the surface [d = 1 cm is the best distance to produce uniform few graphene layers with excellent suppression of amorphous carbon structures.Respectively, when the substrate temperature is set in the range of 800–1000 °C. Such locations have been selected in this study so that the palm oil is injected from three different region of temperatures, i.e., 800–1000 °C (1 cm), 600–800 °C 3 cm), and 400–600 °C (6 cm). Figure  cm, and ubstrate . It is w surface . Howeverd = 1, 3, and 6 cm, respectively. Three intense peaks at ~ 1350 cm−1, ~ 1560 cm−1, and ~ 2691 cm−1 corresponding to G, D, and 2D bands, respectively, can be clearly observed in all samples. A peak corresponded to D + D’ band (~ 3250 cm−1) is only observed in the sample grown at d = 6 cm indicating the existence of amorphous carbon in the structure, as shown in Fig. I2D/IG), Fig. ID/IG), and Fig. I2D/IG, ID/IG, and FWHM are presented in Fig. d = 1 cm tends to be dominated by single-layer graphene, whereas the samples grown at d = 3 and 6 cm are dominated by bilayer and multilayer graphene. It is worth to note that the determination of layer thicknesses is made based on the following values: single layer, I2D/IG ≥ 2; bilayer, 1 ≤ I2D/IG < 2; and multilayer, I2D/IG < 1 [d = 1 cm seems to generate less defect concentration as compared to the sample grown at d = 6 cm as can be understood from Fig. −1 indicating relatively high crystallinity of the grown graphene as shown in Fig. Figure D/IG < 1 , 29. Thed = 1 cm since this distance is found to be a suitable distance to obtain the best quality of graphene. As shown in Fig. I2D/IG, ID/IG, and FWHM of the 2D band for the sample grown at 950 °C, respectively. It clearly shows that the grown film possesses excellent layer uniformity by referring to the uniform color distribution. Histograms driven from these Raman mapping are used to indicate the distribution percentages of the I2D/IG, ID/IG, and FWHM as presented in Fig. −1 indicating relatively high crystallinity of the grown graphene as shown in Fig. Figure 2 was obtained at optimum process conditions . The crystallinity of the grown single-layer graphene is relatively good with high distribution percentage of FWHM values of 2D band that is below 30 cm−1. However, the defect concentration is relatively high, and it suggests the requirement of a rapid cooling treatment. Further studies on the properties such as atomic structure, transmission, and resistance will further justify the performance of the present graphene as compared to the other grown graphene.A growth of large-area single-layer graphene on Cu substrate using a refined cooking palm oil, a natural single carbon source, by a home-made spray injector-assisted chemical vapor deposition system was performed. The effects of the distance between spray nozzle and substrate, and growth temperature are studied. The growth of large-area single-layer graphene with a coverage up to 97% of the measured area size of 6400 μm


Worldwide consumption of coffee exceeds 11 billion tons/year. Used coffee grounds end up as landfill. However, the unique structural properties of its porous surface make coffee grounds popular for the adsorption of gaseous molecules. In the present work, we demonstrate the use of coffee grounds as a potential and cheap source for biochar carbon. The produced coffee ground biochar (CGB) was investigated as a sensing material for developing humidity sensors. CGB was fully characterized by using laser granulometry, X-ray diffraction (XRD), Raman spectroscopy, field emission-scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and the Brunnauer Emmett Teller (BET) technique in order to acquire a complete understanding of its structural and surface properties and composition. Subsequently humidity sensors were screen printed using an ink-containing CGB with polyvinyl butyral (PVB) acting as a temporary binder and ethylene glycol monobutyral ether, Emflow, as an organic vehicle so that the proper rheological characteristics were achieved. Screen-printed films were the heated at 300 °C in air. Humidity tests were performed under a flow of 1.7 L/min in the relative humidity range 0–100% at room temperature. The initial impedance of the film was 25.2 ± 0.15 MΩ which changes to 12.3 MΩ under 98% humidity exposure. A sensor response was observed above 20% relative humidity (RH). Both the response and recovery times were reasonably fast (less than 2 min). Carbon might be the most widely-used material in sensor applications. It has the combined properties of a porous surface, electrical conductivity, biocompatibility, and chemical and electrochemical stability ,2. Many Coffee is one of the most important commodities and widely consumed beverages all around the world and grown in about 80 countries . The gloOn the other hand, an estimated 380,000 tons of brewed coffee waste is discarded each year . The polThere has been a significant amount of research activity going on in the area of waste coffee and its by-products utilisation during the last years. Numerous studies on the use of coffee waste lead to the conclusion that coffee by-products and wastes can be used in a variety of ways . Most ofConsidering the literature and waste brewed coffee powder (WBCP) availability in massive amounts, WBCP is a qualified raw material as a carbon material source for environmentally friendly treatments like pyrolysis ,10. The A WBCP  was utilized as starting material for carbonization . The lefField Emission-Scanning Electron Microscope  observations were carried out on the CGB powders with an IN-LENS detector equipped with a dispersive X-ray detector (Oxford Energy) while for low resolution and EDS we use an ETD detector (EVERHART-THORNLEY) and HV 12 to 25 Kv.Particle size distribution was evaluated through a laser granulometer . The measurements were carried out after dispersion in ethanol (500 ppm in volume) and sonication for 5 min.Thermogravimetric-Differential Thermal Analysis TG-DTA  was performed on CGB powder in the temperature range 25–700 °C with a heating ramp of 10 °C/min under static air. TGA was also performed on the WBCP under a 25 standard cubic centimeters per minute (SCCM) flow of argon in the same temperature range. A Renishaw micro-Raman  equipped with a green laser (514 nm) was utilized to study the disorder and graphitization grade of the CGB under test. Raman characterization were performed at room temperature. The samples, in powder form, were exposed, to the micro laser beam (2 µm in diameter) for 10 s without any pre-treatment.X-Ray Diffraction (XRD) investigation was also performed on CGB powders and spectra were recorded on a Pan’Analytical X’Pert Pro instrument  working with Cu K_ radiation (0.154056 nm) in the range 5–70° of 2θ, with a step size of 0.05° in 2θ. XRD analysis was carried out with the aim of evidencing any possible crystallization peak on CGB powder. Diffraction patterns were indexed by means of the Powder Data File database .The chemical and electronical states of the CGB surface were studied by X-ray photoelectron spectroscopy (XPS) analysis, realized with a PHI 5000 Versaprobe  scanning X-ray photoelectron spectrometer .Resistive-type humidity sensors generally contain noble precious metal electrodes either deposited on a glass or ceramic substrate by thick or thin film deposition technique ,39,40. Iv is the actual partial pressure of moisture content in air and Ps is the saturated pressure of moist air at the given temperature [Relative humidity is defined as the ratio of the amount of moisture content of air to the maximum (saturated) moisture level that the air can hold at a same given temperature and pressure of the gas . RH is aperature ,41. CGB sensors were placed in a laboratory apparatus  built wiSubsequently, the as-fabricated sensors’ selectivity was evaluated by exposing an already tested for relative humidity CGB sensor to ozone 200 ppb, nitrogen dioxide 200 ppb, ammonia 50 ppm and carbon dioxide 500 ppm . All measurements were carried out at 27 ± 0.5 °C and under a constant flow of 1000 SCCM, and sensors were put in a three-neck glass flask chamber of 0.1 L volume. Dilutions of the target gas were performed with air by means of flow meters . Ozone was generated by a UV lamp of Hg  from a constant air flow of compressed air. Ozone concentration was determined by the length of lamp exposed, in accordance with the manufacturer’s calibration curves. The response times  and the recovery times  were also calculated in the present work. 0 is the initial film impedance under dry air and Zg is the impedance under humidity/gas exposure. The CGB sensor response (SR%) is calculated as follows (Equation (2)):According to the FE-SEM investigation in 2, the CGB chemical composition  reveals a 95–96.8 wt.% of carbon, with oxygen concentration between 2.4 and 3.1 wt.% and traces of other elements like Mg, P and K still present after the pyrolysis. Laser granulometry of CGB powders evidenced that this biochar exhibits a bimodal distribution with two maxima at 23 and 192 µm  under an argon flow (100 SCCM) was performed. The heating ramp of the furnace was maintained at 5 °C/min until 700 °C. The pyrolysis conditions were maintained for 1 h at 700 °C. The TG-DTG plots are shown in The total weight loss observed was 82%, in accordance with the yield of WBCP pyrolysis that was 18 wt%. The first derivative confirms three exothermic peaks at 66 °C, 305 °C and 388 °C. Maximum weight loss rate was observed at 305 °C.The pyrolysis process took place in three decomposition stages. The first one occurred from 25 to 200 °C, corresponding to a small mass loss of 9% due to dehydration and a slight release of volatile organic compounds. The second one, ranging between 200 to 500 °C, was associated to the major mass loss of 71%, that is attributed to devolatilization, including release from biomass degradation due to the decomposition of its main constituents . The laFrom the TG-DTA investigation under static air , at 700 In the Raman investigation, different regions of the CGB sample were studied and the results are exhibited in 2 carbon-based disordered structure. The two main regions of interest are 1000–1800 cm−1 (where the D and G peaks are found) and 2400–3200 cm−1 where the overtones of the first one is present . The first region cannot be properly fitted by using only two peaks, but rather four are needed, one for each Raman mode . The ratio between sp2 and sp3 carbon is equal to 4.1. Peaks related to C-O at 288.3 eV, C=O at 290.5 eV and COOR at 293.1 eV are minor, accounting respectively to 9.3%, 2.8% and 3.9% of the total carbon. Considering the deconvolution of the oxygen peak in due signals, the peak at 532.8 eV due to C-O is higher  compared to the signal at 531.2 eV generated by C=O , in accordance with the high-resolution C peaks. XPS spectra are drawn in This analysis shows also the presence of the elements such as nitrogen (2.9 wt.%), phosphorous (0.5 wt.%) and calcium (0.9 wt.%) still present after the pyrolysis of WBCP. Moreover, from the high-resolution spectra of C1s peaks, it is possible to notice that disordered spThe results of CGB sensor exposure towards different humidity levels are shown in When CGB sensors are exposed to humidity at 27 °C, they behave like an n-type semiconductor. In fact, the SR% slope is positive, which means that the conductivity of the screen-printed films increases at higher humidity levels. More in detail, the sensor 1 response starts around 20% of relative humidity, while sensor 2 responds around 30% of RH, with SR% respectively equal to 51% and 61% under humid atmospheres (98–97% of RH). In the first case the impedance decreases from 25.2 MΩ in dry conditions until 12.3 MΩ, while in the second case the Z values drop from 23 MΩ in dry conditions until 8 MΩ in humid conditions. The high initial impedance value is probably due to the limited thickness of the sensing film .The desorption process was also monitored and the maximum hysteresis of 15% in the sensor 1 response was measured under 74% of RH, confirming that the kinetics of desorption is comparable with respect to the adsorption one. Sensor response and recovery times were determined by exposing the CGB sensor after 1 year at different pulses of relative humidty, as illustrated in From Furthermore, cross-sensitivity tests were carried out on the CGB sensor in order to evaluate the selectivity of the film for humidity and the results are displayed in Generally, negligible interferences were detected for carbon dioxide 500 ppm, ozone 200 ppb, nitrogen dioxide 200 ppb and ammonia 50 ppm, as depicted in 2/sp3, as confirmed by our Raman and XPS analyses. In fact, a value equal to 4.2 for this parameter was calculated from XPS investigation. These defects act also as adsorption sites for water molecules. Moreover, the presence after the pyrolysis of oxygen derivatives improve the hydrophilic properties of the carbon surface [It is well known that the presence of defects in the carbon surface improves the sensor response towards humidity ,44 and t surface . When th2/g and pore volume = 8.7 × 10−3 cc/g.The CGB sensor morphology is probably characterized by connected channels, forming a wide number of paths through the tubes, called percolation paths. CGB has mesoporous structure with multi point calculated BET surface area = 5 m2O to CGB causes a shift of the valence bond of CGB away from the Fermi level, resulting in an electron accumulation layer that decreases the impedance values when increasing the H2O concentration [The water molecules act as reducing species and a charge transfer from Hntration .3O+ is a thermodynamically favoured process in liquid water. Protons are the dominant charge carriers of water into the mesopores of the CGB sensor, leading to a fast increase in the layer conductivity at high humidity amounts.The exponential trend of the sensor response with RH amounts could be a consequence of the fact that up to 60% of RH more water molecules are adsorbed on the surface at room temperature, forming clusters of multi-layer of water molecules that are hydrogen-bonded . In addi2/sp3 ratio [In addition, the hydrophilic character is characterized by high values of spp3 ratio ,46 equalp3 ratio ,45. In Ziegler et al.’s  researchThis work could open an interesting way of producing humidity sensors that are low cost, fast, environmentally friendly and selective for humidity measurements at room temperature. As a future perspective, possible ageing phenomena will be investigated by controlling if the sensor response towards humidity will be affected by storage after a long period of time.In this work, coffee ground biochar (CGB) was evaluated as a novel humidity sensing material. The sensors were realized by a screen-printing technique, and the humidity sensing features were studied at room temperature in a relative humidity range from 0 to almost 100%. The as-realized CGB biochar was obtained from pyrolysis at 700 °C of waste brewed coffee powder (WBCP). The sensor impedance variation under humidity starts from 20% of relative humidity. The CGB exhibits a n-type semiconductor behaviour between 20–100 RH% with an exponential trend with increasing humidity amount. The response and recovery times were very fast under 50% of humidity (15–20 s), and the cross-sensitivity to carbon dioxide, ammonia, nitrogen dioxide and ozone was negligible.


Electrical conductivity (σ) and Seebeck coefficients (S) were measured in a vacuum for supported graphene on SiO2/Si FET (Field Effect Transistor) substrates so that the charge carrier density could be changed by applying a gate voltage (µ) values of 529, 459, and 314 cm2/V·s for holes and 1042, 745, and 490 cm2/V·s for electrons for the three grain sizes of 4.1 µm, 2.2 µm, and 0.5 µm, respectively, were obtained from the slopes of the measured σ vs. k) decreased by one quarter for the same grain decrease. Finally, the resulting ZT increased more than two times when the grain size was reduced from 4.1 µm to 0.5 µm.The grain size of CVD  graphene was controlled by changing the precursor gas flow rates, operation temperature, and chamber pressure. Graphene of average grain sizes of 4.1 µm, 2.2 µm, and 0.5 µm was synthesized in high quality and full coverage. The possibility to tailor the thermoelectric conversion characteristics of graphene has been exhibited by examining the grain size effect on the three elementary thermal and electrical properties of  The thermoelectric effect enables direct energy conversions between temperature and electric voltage differences. When a temperature gradient is applied, the momentum difference between charge carriers causes them to shift to one side, yielding voltage potential inside the materials. Since it allows for the conversion of wasted heat into electrical energy, having control over the thermoelectric effect would give rise to one of the most promising sources of renewable energy, because the eco-friendly generation of electrical energy only requires a temperature difference to reuse the wasted heat energy.Graphene has high potential for becoming a thermoelectric material due to its high electrical conductivity and Seebeck coefficient. Its high thermal conductivity, however, has prevented graphene from being used as a thermoelectric material in reality. In order to enhance graphene’s thermoelectric properties, many ideas have been proposed aimed at lowering its thermal conductivity, including defect controlling  and manain sizes ; howeverσ) and the Seebeck coefficients (S). Graphene was synthesized on Cu foil using the LPCVD  method, which allows for the control of the grain sizes, and then subsequently transferred onto a SiO2/Si (450 nm/525 µm) FET substrate. The electrical properties (σ and S) of graphene were measured using the four-point technique for three different grain sizes of 0.5 µm, 2.2 µm, and 4.1 µm, while the charge carrier density was controlled by varying the gate voltage levels.In this paper, as there is still a need for examining the ZT values, we focus on measuring both the electrical conductivity , and pressure (P) of the chamber. Details of the synthesis conditions are shown in While the details on the CVD graphene sample synthesis have been discussed in our group’s previous publication , we hereT and under high P to make the nucleation density higher, whereas graphene with larger grain sizes was synthesized at high T and low P to make the nucleation density lower, as depicted in 4 and H2 were set relatively low so that graphene could grow slowly with enlarged grain sizes; second, the gas flow rates were set high in order to supply enough of a carbon source to ensure the full coverage of graphene. For the 0.5 µm graphene, it was synthesized in a single step with high gas flow rates so that the graphene would grow rapidly while the grain size stayed small. This also enabled full coverage of graphene.CVD graphene with smaller grain sizes was synthesized at low 2 layer on the top surface. Graphene was patterned between the electrodes via photolithography, and the electrodes were connected above the graphene through e-beam lithography.The FET substrate was fabricated through lithography, as schematically shown in The 4-point measurement d is an ep-doped upon exposure to the oxygen and hydrogen atoms in air. Since we wanted to observe the Dirac point, we needed to minimize the p-doping effect by means of vacuum annealing. Annealing under excessively high temperature and/or overly long duration is known to attach graphene to the substrate too strongly, so much so that it degrades the quality of graphene [p-doping effect would be sufficiently reduced without degrading the graphene sample.After fabricating the FET substrates, graphene was transferred onto it using the well-established PMMA method. CVD graphene is naturally graphene ,6,7. Acc−1, respectively, and the 2D/G peak ratio is greater than two for all three samples, indicating that high quality single layer graphene was properly transferred onto the SiO2/Si substrate [The SEM image was taken once during the intermediate growth of grains and again after the full growth on the Cu foil a. The leubstrate ,10,11,12ubstrate . In FiguS) are shown in µ) of graphene =CSih groups ,22,23,24Previously published Seebeck coefficient data are summarized in S, and T, together with the thermal conductivity k data measured for a similar configuration by our group’s previous report, as 2660, 1890, and 680 W/m·K for grain sizes 4.1 µm, 2.2 µm, and 0.5 µm, respectively [k decrease: the PF decreases to 1/2, while k decreases to 1/4. Consequently, when the grain size is reduced from 4.1 µm to 0.5 µm, the ZT value . The detrimental effect of the grain size on k becomes more significant when the grain size is comparable to the phonon mean-free-path (MFP) of about 800 nm [The thermoelectric figure-of-merit ZT=σSTk is detZT value b increash is Planck’s constant, e is the elementary charge, µ is the electrical mobility, and n is the charge carrier density. Mobility values obtained as functions of gate voltage in 12–1013 cm−2, which corresponds to the gate voltage range larger than 13 V [It is well known that the electron scattering increment at the grain boundaries reduces the electrical transport and properties ,17,20. Than 13 V .ballG is the ballistic thermal conductance (~4.2 × 109 W/m2K at room temperature), Gl is the grain size, and λ is the phonon MFP. The estimated phonon MFP’s are 476.9 nm, 360.1 nm, and 152.4 nm for the grain sizes of 4.1 µm, 2.2 µm, and 0.5 µm, respectively  and Seebeck coefficients (S) were measured for three different grain sizes: 4.1, 2.2, and 0.5 μm, using a FET 4-point measurement technique. Since the decrement of the corresponding thermal conductivity (k) was larger than the decrement of the PF, more than two times the original ZT value was observed as the grain size was decreased from 4.1 μm to 0.5 μm. We have shown the possibility that ZT can be tailored by altering the grain size of graphene, which is a crucial factor in CVD graphene synthesis. Furthermore, this enhancement of the thermoelectric properties opens the possibility of graphene to be considered as a more realistic thermoelectric material.We investigated the dependence of the thermoelectric figure of merit, ZT, on the grain size of CVD graphene. Electrical conductivity (


We proposed an all-pass filter based perfect absorber scheme which also can function as a highly efficient transmissive modulator. We theoretically analyzed the proposed scheme using the temporal coupled mode theory and showed that near-perfect absorption could be achieved with practically modest deviation from the critical coupling condition. We also demonstrated the feasibility of the proposed scheme in a grating-based all-pass filter device with a variable loss implemented by two separate graphene layers, achieving an absorption of ~99.8% and a transmission modulation depth of ~70 dB in a terahertz frequency range. We also numerically investigated the tunability of the designed device. In order to further develop the applications of the THz technology, the means to control and modulate the THz wave propagation should be developed, which, however, is still challenging since it is difficult to find materials responding to THz wave. To solve this problem, metamaterials, which are artificial structures enabling a variety of exotic electomagnetic properties, and their active control have been studied widely12. Recently, graphene has attracted a lot of interest as the means to enable the active control of the metamaterials due to its easily controllable permittivity via carrier density variation20. Moreover, an ultra-wide absorption bandwidth of graphene makes it considered as a promising candidate for a THz absorber. A myriad of studies to enhance the low absorption efficiency of atomically thin monolayer graphene have been conducted and many kinds of graphene-based THz perfect absorbers have been suggested32. In most of the previously suggested THz perfect absorbers, absorption enhancement is achieved by adopting a reflector as well as a resonant structure such as the metamaterial or a grating. Two representative types of the reflectors used in the previously THz perfect absorbers are a metallic mirror29 and a distributed Bragg reflector (DBR)33. Due to the aforementioned controllable permittivity of graphene, those perfect absorbers based on graphene can also work as modulators by introducing a proper capacitive structure to apply gate voltage to graphene, in which, however, only the reflected wave can be modulated because of the reflectors. So, if a perfect absorber can be realized without a reflector, a transmissive modulator of a high modulation depth is accompanied. In this work, we propose the reflectorless near-perfect graphene absorber scheme based on an all-pass filter composed of two identical gratings and numerically demonstrate ~99.8% absorption and its transmissive modulator operation with a ~70 dB modulation depth in a THz frequency range. We have theoretically investigated the operation principle of the proposed scheme using temporal coupled mode theory (TCMT)34. The numerical simulation was conducted using the rigorous coupled wave analysis (RCWA) method35 -based commercially available tool (DiffractMOD), and the particle swarm optimization (PSO) method36 was used for the device design.Recently, terahertz (THz) technology has been developed rapidly relying on the advances in source and detector developmentτL1 and 1/τL2, but otherwise identical, having the same decay rates to the wave propagation channel 1/τ. The schematic diagram of the coupled resonators is presented in Fig. Q of the two resonators is related to the resonance frequency (ωo) and the decay rate 1/τ of the resonators through the relationship θ and directly through evanescent coupling with a coupling coefficient of µ. The temporal change of the normalized mode amplitudes of the two resonators (a1 and a2) can be described as follow:μ is real and 34.We performed the TCMT analysis for two lossy resonators with different loss rates of 1/37. Assuming In this work, we assumed that the all-pass filter conditions for the lossless case was satisfied, which are r = t = 0) is obtained only when 38. So, the perfect absorber based on the lossy all-pass filter can be understood as the variation of the lossy one-port resonator-based perfect absorber: the reflector is eliminated by placing another identical resonator with a mirror inversion symmetry. In another words, two resonators excited with the phase retardation of θ = π/2 is equivalent to placing a 100% mirror at the distance of λ/4 from one resonator .From (2), it is found that perfect absorption  near the perfect absorption condition, a very low transmission value can be obtained even for modest deviation from the perfect absorption condition, enabling a high transmission modulation depth with variation of the loss rate or the resonance frequency. The resulting absorption  around the critical coupling condition still resulted in quite low transmission of ~−50 dB at the resonance frequency. So, if we can somehow change the losses of resonators from δ = 0.02τ), the minimum transmission of ~−80 dB and a modulation depth of ~70 dB can be achieved. If the loss variation is increased by choosing the smaller loss close to zero  of the low state relies on the balance between the total loss and the leakage, not the absolute value of 2/τ, which is associated to the quality factor of the resonator (Q = ωοτ/4). The only constraint for the high modulation depth with near perfect absorption is that the background loss should be smaller than 2/τ. Our TCMT modeling reveals that a background loss rate of 1/τ can achieve a considerably high modulation depth of ~70 dB for a 4% loss difference between two resonators in the proposed scheme.The loss in the TCMT modeling is the summation of all kinds of losses such as material absorptions and scattering/radiation losses of the resonators:entclass1pt{minimatg, a period P, and a fill factor FF (=wg/P), formed on a Si layer of thickness tSi and separated by an air gap with a distance d. The gratings made of Si or PDMS were considered in this work. One device with Si gratings was designed, having a quality factor of ~103 and the other with PDMS gratings was designed to have a much higher quality factor of ~105. The direct coupling coefficient and the phase retardation in this device are controlled by d and a lateral shift distance s39. Two graphene layers separated by a thin SiO2 layer with a thickness tgate are embedded in SiO2. The graphene absorbing layers and the all-pass filter are separated by a distance tbuffer. To tune the loss via variation of the complex permittivity of graphene, a gate voltage Vgate is applied between the two graphene layers. The complex permittivity of graphene was calculated using the Kubo formula40 with following assumptions: the thickness of graphene was 0.34 nm, the Fermi velocity VF was 106 m·s−1, and the mobility μ was 1000 cm2·V−1·s−1. The permittivity of Si and SiO2 were assumed to be 3.41672 and 2.12692, respectively.Based on the theory described in the previous section, we designed a terahertz near-perfect absorber based on a graphene-assisted all-pass filter. The schematic diagram of the device is presented in Fig. 35 -based commercially available tool (DiffractMOD), and the PSO method36 was used for the device design. In our design process, the grating fill factor and the gap between the graphene layers were fixed at FF = 0.5 and tgate = 7 nm. When the chemical potential (Fermi level) of graphene is 0.1521 eV, the optimal design parameters for the device with Si grating were found as follows: tg = 0.593 µm, P = 18.775 µm, tSi = 2.67 µm, d = 1.486 µm, s = 7.703 µm, and tbuffer = 8 µm. In the rest of this paper, these parameters are used unless otherwise indicated. Because tbuffer is much larger than d, the loss rates of the two resonators due to the presence of the graphene layers would be very close, causing the structure to operate in the near-perfect absorber mode. One can easily decrease both τL1 and τL2 simultaneously simply by increasing tbuffer, and there should be a proper tbuffer where the near-perfect absorption condition is satisfied. Therefore, simply by changing tbuffer, one should be able to find a point where nearly perfect absorption occurs without modifying parameters of the all-pass filter structure. Likewise, one could also change both τL1 and τL2 simultaneously by changing the gate voltage applied between the graphene layers, which causes the change of the chemical potential of graphene.In our design, the structural parameters denoted in Fig. Ef = 0.1521 eV, the near-perfect absorption is achieved: the transmission dip is ~−70 dB is at the resonance and the reflection is ~−30 dB, resulting in an absorption of ~99.84%. When Ef = 0 eV, which corresponds to the case of almost the same and relatively low losses for two resonators, the reflection is as low as ~−50 dB, but the transmission is quite high, so that we obtain low absorption. This implies that we can achieve a transmission modulation depth of ~70 dB by changing the chemical potential from Ef = 0 eV (the high transmission state) to Ef = 0.1521 eV (the low transmission state). When the chemical potential is varied slightly around the optimal value, the resonance frequency variation is negligible, but the minimum transmission increases considerably due to the broken critical coupling condition resulting from the loss rate change. One can see that the minimum transmission increases up to ~30 dB for Ef = 0.16 eV. When the chemical potential is increased to 0.3 eV, the loss of the graphene layers decreases way below the perfect absorption condition and the transmission becomes rather high with low absorption. At the same time, the reflection also increases due to the enhanced conducting property of highly doped graphene layers while the relative difference in the loss rates of two resonators is kept about the same. Since the variation of the chemical potential changes both the real and the imaginary parts of the graphene permittivity, the shift of the resonance (minimum transmission) frequency is observed when Ef varies. Figure Ef = 0.1521 eV), indicating very strong resonance of the all-pass filter despite the presence of resonator losses. Figure o) and the loss rate (1/τL) change as expected. Whereas, it appears that the leakage rate of the resonator (1/τ) is mainly determined by the grating structure, not by the graphene chemical potential for tbuffer = 8 µm. The relative loss rate difference (δ/τ) is not affected by the chemical potential change either, which seems to be closed related to the location of the graphene layers (tbuffer).Figure d) with all the other parameters kept the same. Quite reasonable performance of ~−30 dB minimum transmission can be achieved while the operating frequency is fine tuned. Figure We also investigated the resonance frequency tunability of our device. Figure buffer, where the trade-off between the insertion loss and the chemical potential change required for the full transmission modulation. When the graphene layers are closer to the all-pass filter, the loss is higher and thus, the insertion loss for the high transmission state is higher (Ef = 0). At the same time, the optimal graphene loss coefficient to satisfy the critical coupling condition decreases because the field confinement in the graphene layers increases while the quality factor of the all-pass filer remains the same. Note that the location of the graphene layers does not affect the quality factor of the all-pass as mentioned earlier. Then, the chemical potential change for the full transmission modulation becomes smaller. Note that the loss of graphene increases as the chemical potential increases for a wavelength longer than ~10 μm40. So, in terms of the insertion loss, the larger tbuffer is desirable, which, in return, increase the chemical potential variation required for the full transmission modulation. If the insertion loss below 1.0 dB  is required, according to our investigation, the optimal condition appears to be tbuffer = ~8 μm and the low transmission state of Ef = ~0.1521 eV.Figure In this work, we have provided the theoretical framework of a lossy all-pass filter based near-perfect absorber. Based on this, we have designed a graphene-assisted all-pass filter, which is composed of two identical gratings, for a tunable THz transmissive modulator with near-perfect absorption, and numerically demonstrated an absorption of ~99.8% and a transmissive modulation depth of ~70 dB via graphene chemical potential variation of ~0.15 eV.3. A grating structure with a quality factor of ~103 was fabricated and a ~80% guided-mode resonance (GMR) reflection peak at λ = 742.5 nm was experimentally demonstrated41, corresponding to a background loss of ~0.25/τ. This implies that the constraint for the high modulation depth with near perfect absorption  can be met in a practical grating with a quality factor of ~103. Moreover, ~95% GMR reflection peak of ~700 quality factor at λ = ~1550 nm (corresponding to a background loss of ~0.06/τ) was fabricated42, where authors claimed that the high reflection peak was achieved via fabrication process improvement. This implies that the dominant source of the background loss in gratings is not the material loss, but the scattering loss due to the imperfect fabrication. Assuming an extremely advanced fabrication technology development, a device with a much higher quality factor can be designed with a modified grating structure, as well. As an example, we designed the device with the gratings made of PDMS (n = 1.5290). When the chemical potential of graphene is 0.148 eV, the optimal design parameters were found as follows: tg = 0.63001 µm, P = 19.92114 µm, tSi = 2.49017 µm, d = 1.50903 µm, s = 8.327 µm, and tbuffer = 22.2 µm. Due to the decreased leakage rate, the graphene layers are located farther away from the all-pass filter to satisfy the critical coupling condition. As seen in Fig. 5.In our design of the transmissive modulators in the previous section, the gratings were assumed to be made of Si for the convenience of simple design, which has a modest quality factor of ~102 (glass) substrate after the Si substrate is thinned down to the designed thickness. One of the SiO2 (glass) substrate should be prepared to have two graphene layers, which can be conducted with a standard graphene transfer process and SiO2 depositions using an atomic layer deposition (ALD) and a low-pressure chemical vapor deposition (LPCVD) processes.In the fabrication of the proposed device, the realization of two identical gratings is quite important. One possible way to realize two identical gratings is to halve a single large grating and put them together facing each other. The Si grating structure can be fabricated on a Si substrate and put on the SiOThe proposed transmissive modulator with a high modulation depth can be used in terahertz communications. Since a signal-to-noise ratio after passing through a modulator is directly related to the modulation depth of the modulator, our high modulation depth device will be quite useful in terahertz communication applications. Besides, the resonance frequency of our device can be sensitively tuned by the air gap distance change, which implies the refractive index change in the gap will also change the resonance frequency. This feature can be exploited for bio-chemical sensor applications. As shown in Fig. 43, ring resonator44, or planar types45, potentially opening a new class of devices capable of operating in a wide variety of environments. Since the critical coupling condition is relaxed, as long as the all-pass filter condition can be achieved, by tuning the loss rate, we can potentially achieve near-perfect absorption at any wavelength desired.Our proposed scheme can be applied to other types of all-pass filter realized by photonic crystal34. The numerical simulation was conducted using two-dimensional RCWA 35, where more than 300 harmonics were applied to guarantee accuracy near the resonant frequency. For the optimal device design, the particle swarm optimization (PSO)36 method was applied. In all RCWA calculations, the complex permittivity of graphene (εg) was calculated using Kubo formulation based on the local random phase approximation for various Ef40, assuming graphene thickness of 0.34 nm, Fermi velocity of 106 m/s, and mobility of 0.1 m2/Vs.To theoretically investigate the operation principle of the proposed scheme, we used the temporal coupled mode theory (TCMT)


Unsworth et al. estimate relative exposure and use with a parental questionnaire and obtain performance measures through spontaneous speech production as well as standardized vocabulary measures. Their results indicate that language use is a stronger predictor of proficiency than exposure, pointing to its importance for dominance.It has long been established that bilingual speakers are rarely balanced in their languages so that one language is dominant. The contributions to Bilingual Language Development: The Role of Dominance focus on the potential effects of language dominance on the competence and processing of bilinguals, covering a large variety of language combinations and domains. Important aspects of such work are the interplay of L1-maintenance/attrition and possible L2-dominance, the direction of cross-linguistic influence (CLI) or code-mixing, as well as the effects of bilingualism on cognitive development, each addressed in several contributions. However, such research presupposes a definition of dominance, which is far from being settled. This gives rise to considerable differences in the operationalization of the concept across studies. Among other factors, many researchers use proficiency to determine dominance  it is recommended to test children in both languages or at least in their dominant language and adjust norms according to dominance  not licit in Spanish, and one of Spanish more restricted in Catalan, Differential Object Marking (DOM), the authors observe CLI for DOM but not for NCIs. L1-Spanish/L2-Catalan speakers over-accept DOM in Catalan, suggesting that their dominance in Spanish influences the directionality of CLI, which the performance of the L1-Catalan/L2-Spanish group confirms.CLI and language mixing provide more evidence for the importance of a dominance definition. Investigating the acquisition of residual V2-structures in English by three Norwegian-English simultaneous bilingual children, Gagarina and Klassert investigate the L1-competence of bilingual children in such a dominance-shift context: the systematic exposure to L2 in kindergarten/preschool. They examine experiential factors, such as input provided by the nuclear family, as predictors for lexical and  morphological development in L1 after change of input dominance. Interestingly, age, gender, and L2-AoO all differently impact these domains. Importantly, verbal inflection proves to be more robust than case inflection. The latter finding ties in with the longitudinal study of Schulz and Grimm investigating experiential measures and, crucially, timing in acquisition as factors influencing development of the majority language. The study compares simultaneous to early-L2 bilingual children and shows that while age of onset affects early-acquired phenomena such as subject-verb-agreement, this is not the case for late-acquired phenomena such as case marking. Clearly, timing modulates age effects. Dominance, determined by experiential measures, does not play a role for early or late acquired phenomena in simultaneous bilinguals.It has been observed that language dominance may shift during development, and Köpke and Genevska-Hanke. Among several studies on L1-attrition, Schmid and Yilmaz offer an integrated perspective investigating the role of various experiential and proficiency predictors of language dominance in four migrant populations. Focusing on dominance shifts and factors facilitating L1-attrition/maintenance, they suggest that different aspects of bilingualism affect language development in different ways. For L1, measures of informal language use play a role in determining whether a bilingual is a good maintainer, while success in L2-acquisition depends heavily on personal factors such as the educational level. Similarly, Montrul et al. find effects of exposure and use on the knowledge of Hindi-case marking in Hindi-English bilinguals with different dominance patterns: balanced bilinguals in India outperform unbalanced L2 and heritage speakers in the US, who show instability in their production/knowledge of the Hindi case system. In contrast, the study of Mitrofanova et al. finds that a combination of experiential and proficiency measures is the best predictor for different attrition/maintenance patterns. Studying the acquisition of gender in Russian by Russian-Norwegian bilingual children in Norway they show that bilingual and monolingual children were sensitive to phonological gender cues, albeit to different degrees.Language dominance and attrition are interrelated, established with similar measures and influenced by the same factors so that they might represent two stages of the same phenomenon as suggested by Caloi et al. provide a broader view. They compare adult heritage speakers of Italian, late L2-learners with L1-Italian, and Italian monolinguals as to the strategy employed when answering new information questions. Monolinguals prefer a Verb-Subject-structure, whereas heritage and L2-speakers behave alike, but different from monolinguals, in opting for Subject-Verb-answers. These group comparisons lead the authors to remind the reader that a “bilingual speaker is not two monolinguals in one”  in a speaker of (pro-drop) L1-Bulgarian and (non-pro-drop) L2-German, who had late L2-onset and fairly long residency in Germany. The authors argue that attrition of a highly-entrenched L1 affects language processing not underlying representations, and that it does so temporarily only, disappearing fast after a limited re-exposure to L1-input. This opens the question if re-exposure to Italian would have changed the performance of the bilinguals in the study by Caloi et al..Turning to psycholinguistic aspects of bilingualism and language dominance, Nicoladis et al. contribute to the discussion whether the need to access each language depending on context accounts for flexibility by investigating whether balanced bilinguals have an advantage over other bilinguals. Study of French-English bilingual children shows that none of the experiential or proficiency measures predicts cognitive flexibility. Also focusing on cognitive aspects, Altman et al. investigate the influence of dominance on metalinguistic awareness, MA, and whether MA mediated by dominance influences vocabulary size. Crucially, only the Hebrew vocabulary size of the Russian-dominant children is affected by MA. They rely on their fast mapping abilities to expand vocabulary, which, the authors argue, reflects their level of vocabulary development in the societal language.Regarding notions of language accessibility, an advantage in cognitive flexibility has been attributed to bilinguals (Bialystok, The studies in this volume present a multifaceted picture of the role of language dominance for L1-maintenance/attrition, L2-development and CLI. Though a unified story cannot emerge for such a complex subject, interesting new venues are explored including the impact of dominance shift during L1-re-exposure, comparisons of different types of bilingual groups, or operationalization of dominance through experiential measures. The variety of approaches and results is in part owed to the many language combinations studied and the fact that bilingual children, adults and atypical speakers are investigated. This diversity constitutes the interest of this volume.All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.