Graphene Surface Research Articles

Robust ceramic-based graphene membrane for challenging water treatment with enhanced fouling and scaling resistance.

Membrane fouling and scaling are two challenges for efficient treatment of hypersaline wastewater, greatly hindering separation performance and operation stability of desalination membranes. In this work, we report a smooth ceramic-based graphene desalination membrane, exhibiting enhanced anti-fouling and anti-scaling ability and operational performance for efficient treatment of both synthetic and real industrial wastewaters, outperforming polypropylene (PP) membrane. For treatment of hypersaline waters containing organic or inorganic substance, we demonstrate that the graphene membrane exhibits more stable water flux and almost complete salt rejection (>99.9%) during constant operation. Enhanced anti-fouling and desalination performance of graphene membrane could be attributed to the lower attractive interaction force with foulant (-4.65 mJ m-2), lower surface roughness (Ra=2.2±0.1nm) and higher affinity with water than PP membrane. Furthermore, an anti-scaling mechanism enabled by graphene membrane is evidenced, with a highlight on the roles of smooth graphene surface with lower roughness, less nucleation sites and lower binding force with scaling crystals. Importantly, even for industrial petrochemical wastewater, such a graphene membrane also exhibits relatively more stable water flux and promising oil and ions rejection during long-term operation, outperforming PP membrane. This study further confirms a promising practical application potential of robust ceramic-based graphene membrane for efficient treatment of more challenging hypersaline wastewater with complicated compositions, which is not feasible by conventional desalination membranes.

Role of graphene in scavenging methyl cations: a DFT study.

It is known that methylating agents methylate DNA by transferring a methyl cation (CH3+) to the nucleophilic sites in DNA bases and DNA methylation is implicated in cancer and other pathological conditions. Therefore, it is important to scavenge CH3+ ion in order to protect DNA from methylation. Graphene is considered to be a versatile material for use in a wide variety of fields including sensors, antioxidants, drug delivery and DNA sequencing. In this work, we have theoretically investigated the interaction of CH3+ ions with graphene surface with an aim to understand if pristine graphene can be used as a substrate to adsorb CH3+ cations generated from harmful methylating agents. The computed adsorption energies show that adsorption of one, two and three CH3+ ions on graphene is favourable as the adducts thus formed are found to be substantially stable in both gas phase and aqueous media. The Bader charge transfer analysis and density of states (DOS) calculation also indicate a strong interaction between graphene and CH3+ ions. Thus, our results show that pristine graphene can be used as a substrate to scavenge CH3+ ions. The spin polarised density functional theory (DFT) calculations employing PBE functional, ultrasoft pseudopotentials and plane wave basis set having kinetic energy cut-offs of 40 Ry and 400 Ry, respectively, for wave functions and charge densities were carried out to study the adsorption of CH3+ ion(s) on the pristine graphene surface. The Grimme's DFT-D2 method was used for the estimation of van der Waals interactions. The 'dipole correction' along z-direction was also applied for adsorption study. The Marzari-Vanderbilt smearing and Monkhorst-Pack k-point grid were employed for the Brillouin zone sampling. A 6 × 6 graphene supercell with a vertical cell dimension of 18Å was considered for the adsorption study. The charge transfer between the CH3+ ion(s) and graphene was estimated using Bader charge analysis. The implicit solvation model (SCCS) was used to estimate the solvent effect of aqueous media. All the calculations were performed using QUANTUM ESPRESSO package.

One-Step Synthesis of Fragment-Reduced Graphene Oxide as an Electrode Material for Supercapacitors.

We herein report for the first time a simple environmentally friendly hydrothermal method for one-step synthesis of fragment-reduced graphene oxide (FrGO) under mild conditions without the addition of reducing agents, and we applied it as an electrode material for a supercapacitor. The characterization results show that the introduction of Al2O3 as a spacer and HCl as an etchant results in a macroporous/mesoporous structure, increases the fragmentation of the FrGO microtopography, shortens the electron/ion transport path, and increases the contact between the electrode material and the electrolyte. Compared to the traditional hydrothermal reduced graphene materials, FrGO shows a larger specific capacitance. The results indicate that suitable hydrothermal temperature and time can effectively promote the retention of more oxygen-containing functional groups on the graphene surface. The first-principles density functional theory (DFT) calculation results show that the electrostatic potential in carbonyl group graphene is more negative, favored by the H+ adsorption, and provides the system with a pseudocapacitive effect. Under optimized conditions, FrGO (1:4, 180 °C, 3 h) exhibits 417 F/g at 1 A/g with an outstanding capacitance retention of 78.51% at 50 A/g and exhibits remarkable stability over 20 000 charge/discharge cycles. The proposed FrGO-based synthesis method can be used to guide the development of electrode materials for various supercapacitor devices.

Wet etching of gold on graphene for high-quality resist-free graphene surfaces

Wet etching of gold on graphene is challenging due to the weak adhesion of the resist mask to graphene. We report an operating procedure for alkali ion-free wet etching of gold on graphene using a mixture of hydrochloric and nitric acids (aqua regia) with a high lateral resolution down to 100 nm. We investigate the role of positive and negative resists, electron beam lithography (EBL) dose, hard-bake, oxygen etching, aging, and sensitivity to the etch parameters, such as the freshness of dilute aqua regia, etch time, and the order of etched samples. The negative-tone resist provides the best results. The over-dosed EBL exposure can enhance the resist adhesion, as hard-bake below the glass-transition temperature and well-defined wet etch of the resist-residua-free gold surface. We also present a cleaning procedure to avoid bubble formation after the hard bake. Our results demonstrate that wet etching of gold on graphene using aqua regia is a viable method for achieving high-quality resist-free graphene surfaces. This method has potential applications in graphene nanoelectronics and nanophotonics, where high-quality graphene surfaces are essential for device performance.

(Invited) Reaction of Elemental Sulfur at the Surfaces of Carbon Nanotubes and Graphene

The chemical functionalization of nanocarbons is key for ensuring their processability in solution and to derive new surface functionalities for applications. For this respect, the oxidation reactions of graphene and carbon nanotubes by strong oxidants is nowadays among the most significant to both clean the raw materials and add functional groups, such as what is present at the surfaces of the graphene oxides (e.g. GO and RGO) and oxidized carbon nanotubes. Because of the harsh conditions (e.g. strong acids), the oxidation process gives rise to a great variability of surface groups (e.g. epoxide, hydroxyl, carbonyl) from which the chemical behavior is rather complex. The reaction also leaves acidic residues in quantities that can be environmentally hazardous. Here, we explored an alternative approach to functionalize carbon nanotubes and graphene using a direct reaction with elemental sulfur. Depending on the conditions, we find that the sulfur atoms can modify irreversibly the surfaces with a covalent episulfide functions. The sulfur reaction is extensive, and it is therefore presented here as a green alternative for the chemical processing of nanocarbon materials.

Reversible Iron Oxyfluoride (FeOF)-Graphene Composites as Sustainable Cathodes for High Energy Density Lithium Batteries

Two large barriers are impeding the wide implementation of battery electric vehicles, namely driving-range and cost, primarily due to the low specific capacity/energy and high cost of mono-valence cathodes (e.g. LiNi0.8Co0.1Mn0.1O2) used in lithium-ion batteries. Iron is the ideal element of choice for cathode materials considering its abundance, low cost and toxicity. Two fundamental challenges, in particular, the poor reversibility of (de)lithiation and low electronic conductivity, prevent those iron based high specific capacity/energy multi-valence conversion cathodes from practical applications. In this work, we have developed a sustainable FeOF nanocomposite with extraordinary performance. In particular, we were able to reach the theoretical specific capacity of 621 mAh·g-1 and 1,124 Wh·kg-1 specific energy (2.1-valence change/2.1 Li+ stored per unit) and more than 100 cycles with 80% capacity retention at 0.1C (realizing the reversible (de)lithiation), which is 3 times of the specific capacity, and 2 times of the specific energy of current mono-valence intercalation LiCoO2 respectively (i.e., 145 mAh·g-1 and 551 Wh·kg-1). This is the result of an effective approach, combing the nanostructured FeOF with graphene sheets to solve these challenges, realized by (1) making the (de)lithiation reversible by immobilizing FeOF nanoparticles and the discharge products of Fe nanoparticle and LiF over the graphene surface, and sandwiching them between graphene sheets to prevent them from migration and dissolution into electrolytes and (2) providing the inter-particle electric conductivity. In situ high energy synchrotron X-ray absorption spectroscopy (XAS) reveals that this new FeOF composite has a different but reversible (de)lithiation mechanism. Importantly, it demonstrated that introducing small amount of graphene can create new materials with desired properties, opening a new avenue for altering the (de)lithiation process. Such extraordinary performance represents a significant breakthrough in developing the sustainable conversion materials for replacing the intercalation compounds, eventually overcoming the driving range and cost barriers.

Characterizing the Non-Covalent Binding of a Pyrene-Derived Linker for DNA Immobilization on Graphene Field-Effect Transistors

Graphene field-effect transistors (G-FETs) constitute an emerging platform for biosensing applications. Most genomic applications with G-FETs use single-stranded DNA (ssDNA) as probes in order to capture a specific target DNA sequence and to detect the corresponding change in the electrical response of the sensor1. Controlling the distribution of DNA probes on the graphene surface is crucial to the sensitivity, selectivity and reproducibility of the sensors1. The most popular immobilization approach uses a non-covalent linker molecule named 1-pyrenebutanoic acid succinimidyl ester (PBASE)1. This bifunctional molecule binds to the graphene surface through non-covalent π-π interactions via its aromatic pyrene group, and on the other end, its succinimidyl ester group can form a covalent bond with amine groups added to the terminal end of ssDNA probes. However, the adsorption process of PBASE molecules is not well controlled, which represents a limitation in the optimization of G-FET biosensors.Here, we present an investigation of the kinetics of the non-covalent adsorption of PBASE on graphene, in order to control the density of ssDNA probes for biosensing applications with G-FETs. We fabricated G-FET sensor arrays using CVD-grown graphene and photolithography techniques, as described previously2. First, we investigated the effect of incubation time on PBASE coverage on graphene, using electrical curves as well as Raman hyperspectral imaging (RIMA). We report a significative and reproducible electrical signature for the PBASE compared to the control without PBASE. We find that this electrical signature appears and saturates quickly compared to the timescales usually reported in the literature. Corroborating results were obtained with RIMA spectroscopy, showing a rapid response of the graphene modes following PBASE incubation. Next, we studied the effect of PBASE accumulation on the assembly of ssDNA probes. We will discuss the combined effect of PBASE accumulation and screening effects in saline buffer on the electrical signature of ssDNA probes. Our results will enable a better control on the non-covalent functionalization of graphene with PBASE for the assembly of various biomolecular probes for biosensing applications.1. Béraud A, Sauvage M, Bazan CM, Tie M, Bencherif A, Bouilly D. Graphene field-effect transistors as bioanalytical sensors: design, operation and performance. Analyst. 2021;(146):403-428.2.Bazan CM, Béraud A, Nguyen M, Bencherif A, Martel R and Bouilly D. Dynamic Gate controlled of Aryldiazonium chemistry on Graphene field-effect transistors. Nano Lett. 2022;22(7):2635-2642.

Van der Waals Interaction Mediated Redox on Graphene Electrode

Graphene, unlike (defective) graphene oxide, is generally not considered to be a highly efficient electrochemical electrode except for activity at the edges. This is because, graphene forms a highly stable hydration bilayer that screens the electric field emanating from the electrode to drive the electrochemical process. A remarkable electrochemical electrode property of graphene is discovered and explored. The property emerges from graphene’s single crystal, aromatic structure. The redox behavior of an aromatic compound, methylene blue (MB) and non-aromatic compounds, such as , potassium ferric cyanide are compared. The electrochemical behavior on monolayer of graphene is quantitatively measured by a novel opto-electrochemical instrument for both electrochemical and structural information. The instrument called, the Scanning Electrometer for electrical Double-layer (SEED) allows local measurement of redox on a 10 micron laser spot to exclusively measure redox signal away from the edges of graphene. Two distinct peaks for both reduction and oxidation during conventional cyclic voltametric (CV) waveform are observed by SEED (Figure 1). The two peaks were attributed to two distinct orientation of MB chemisorption on graphene and subsequent electron transfer. One of the peak depended on precise orientation of the MB on single crystal graphene surface indicating pi-pi interaction mediated chemisorption (Figure 2). The other peak is independent of graphene orientation. MB redox on Au showed a single peak (Figure 1) and was independent of orientation (Figure 2). The effect of the two modes of chemisorption on ionic strength was studied and compared with MB redox on pure gold performed on the same chip. The two peaks were not distinguishable by CV or differential pulse voltammetry (DPV) measured on the same sample under similar conditions. This indicated the sensitivity of SEED to obtain structural information and its ability to measure electrochemical activity on micro-spot. All the three measurements, SEED, DPV and CV were performed without taking the sample out of the solution. The redox of non-aromatic compounds showed no orientation effect. The distinct van der Waals interaction mediated chemisorption by pi-pi stacking on graphene electrode may have distinct advantage to design highly sensitive and specific sensors and biosensors in future, for example, in DNA and RNA sensing. Figure 1

Structure and Dynamics of the Electrical Double Layer during the Rapid Alternating Polarity Electro-Synthesis

Conventional electrochemical organic synthesis uses direct current (DC) condition, where the electrode polarity is not changed during the operation. Unlike DC, alternating current (AC) introduces two more tunable parameters into the potential or current profile: frequency and waveform, allowing new possibilities for modulating reaction efficiency and selectivity. Several very recent AC electrosynthesis examples have shown that the AC can lead to enhanced chemoselectivity that cannot be reproduced by their DC counterparts1–3. For instance, Hayashi et al. presented a highly selective and easily scalable Birch-type reduction of heteroarenes by rapid alternating polarity (rAP) waveform3. AC voltage transforms the reaction kinetics presumably by affecting the mass transfer of reactive species both in the bulk solution and the electrical double layers (EDL). However, the mechanistic origin of the unique reactivity in AC electrosynthesis is underexplored. Molecular-level details are still in lack to possibly guide the rational design of AC reaction parameters.In this study, we have chosen the rAP heteroarene reduction as the example system and employed classical molecular dynamics (MD) simulations to reveal the liquid structure and dynamics in bulk and interfacial electrolyte. To capture the electrode-electrolyte interfaces, a slab-geometry simulation cell was used, where a 10 nm thick liquid electrolyte is sandwiched between two oppositely charged graphene surfaces. The multicomponent electrolyte was composed of ethanol and tetrahydrofuran (THF) as the co-solvent, [(CH3)4N]+[(BF4)]- as the salt, and a heteroarene substrate. Based on the charge distribution function statistics, the EDL layer was about 1 nm thick, so if any of the oxygen atom in the ethanol or THF is within 6 Å to the electrode surface, they are considered to be within the EDL. Under both AC and DC, the ethanol to THF ratio was higher than that in the bulk electrolyte due to stronger ion-ethanol attraction. The EDL structure responded to electric field polarity change at different time scales. First, the molecule orientation would flip also within the picosecond time scale after the polarity switch. By tracking the number of molecules in the EDL, we have found that the compositional fluctuation in the EDL converges in about 40 ps. Although it is the ion migration that gets directly affected by the alternating electric field, diffusion of charge-neutral molecules was also found to be accelerated under AC, according to the higher mean squared displacement calculated from the movement of all molecules of each species in the simulation box. This accelerated diffusion spans a larger length and longer time scales. A multi-scale model is proposed to describe both reaction kinetics and liquid structure dynamics simultaneously.

Functionalized boron doped graphene (BGP) as smart nanocarrier for delivery of hydroxyurea (HU) drug

The concerning toxicity associated with hydroxyurea (HU), an anticancer drug used in cancer treatment, has spurred significant attention within the research community over the years. To address this adverse effect, there is a critical need for a smart and targeted drug delivery system (Nano carrier) that can effectively deliver the drug to the tumor site while minimizing side effects for the patient. In this study, we employed density functional theory computations at (DFT)/ωB97XD/6–311++G (d, p) level of theory to evaluate the adsorption properties of functionalized boron-doped graphene (BGP) surfaces, namely COOH@BGP, NH2@BGP, and OH@BGP, for the delivery of the HU anticancer drug. The electronic properties analysis revealed that COOH@BGP/HXU (M2) exhibited the most favorable reactivity with an energy gap value of 5.3756 eV, making it the most reactive surface compared to other complexes investigated. Moreover, a comprehensive natural bond orbital analysis was conducted to investigate hyper-conjugative effects, hybridization, charge transfer, and H-bonding interactions within the systems studied. The results confirmed the following trend: HXU-COOH@BGP (M2) > HXU-OH@BGP (K2) > HXU-NH2@BGP (Q2). Additionally, topological analysis (QTAIM) and Non-covalent interaction (NCI) analysis were performed to ascertain the interaction forces at play. The results strongly support the significant electrostatic force of interaction in the M2 complex, suggesting the presence of hydrogen bond interactions that facilitate the doped surface's ability to bind with HXU and enhance the smooth delivery of the investigated drug. Furthermore, the adsorption studies revealed negative adsorption energy values, indicating favorable adsorption. Among all the analyzed complexes, M2 nanocarrier demonstrated the most suitable characteristics for the delivery of the HXU anticancer drug. These findings hold promise for the development of an efficient and targeted drug delivery system that could potentially mitigate the toxicity associated with HU and enhance cancer treatment outcomes."

Simulation of BioGFET sensors using TCAD

We used a commercial TCAD simulator for the study of liquid-gate Graphene FETs as antibody-based sensors. To model the graphene layer, a zero-bandgap semiconductor with a linear density of states relationship in both the conduction and valence bands near the edge of the bands was adopted. The electrolyte which forms the liquid gate was also modeled as a semiconductor with tuned parameters to reproduce the behavior of a dilute PhosphateBuffer Saline (PBS) solution with pH = 7.4. Antibodies are anchored to the graphene surface and their effect is simulated with a charged cube box with a size similar to the one of the IgG antibody and a charge concentration similar to the charge usually carried by an anibody. The binding of the antibody with the antigen protein (Ab-Pr) complex is also represented in the simulator with a charged box carrying a different charge. We have calculated the ID-VFG curves for different numbers of antibodies anchored to the surface of the graphene and analyzed the behavior of the sensor as a function of the number of antibody-protein complexes.

Effect of surface curvature on the hydrogen storage capacity of the Sc-, Ti-, and V-doped graphene surfaces: Theoretical study

Hydrogen (H2) is an excellent energy carrier and can be produced in an environmentally friendly way. The H2 binding performance of different Sc-, Ti-, and V-doped carbon surfaces (i.e., graphenes, circumcoronenes, and circumtrindenes) is investigated using density functional theory. The calculated H2 binding energies are ranging from −12 kJ mol−1 to −22 kJ mol−1 for one H2 molecule per transition metal (TM) atom. Such binding energies are suitable for reversible H2 adsorption and desorption cycle. Obtained results suggest that the curvature of the TM-doped carbon surfaces enhances their H2 binding ability. TM atom in the curved carbon surfaces, representing an active site, is sterically more easily accessible for H2 binding than in the case of the planar metal-doped graphene surfaces. For comparison, the N2 binding ability of the same set of TM-doped carbon surfaces is studied as well.

Adsorption of Tunable aryl alkyl ionic liquids (TILs) on the graphene and Defective graphene nanosheets: A DFT Study

Optical and electronic characteristics of the graphene nanosheets (GNS) could be altered by some structural defects such as double-vacancy and Stone-Wales ones. The physisorption manner of [MPI][BF4], [MPT1][BF4], [MPT2][BF4], and [MPTT][BF4] ionic liquids on intact and defective GNS surfaces were investigated using M06-2X/cc-pVDZ computational method. Capability for adsorption on the DV and SW graphene surfaces by TILs is increased by about 1.0–4.3 and 0.4–2.0 kcal/mol respectively. The electrostatic potential of the GNS-DV surface is more negative than the GNS-SW one which enables it to interact with cation parts of the adsorbed TILs so extensively. The highest adsorption energy belongs to the [MPI][BF4]/GNS-DV system. Adsorption of the TILs on the GNS surfaces leads to a decrease in the energy of the LUMO molecular orbital as well as their energy gap of them. Results revealed that the electrical conductivity, as well as absorption spectra of the GNS surfaces, are affected by TILs adsorption and defect nature.

A DFT investigation of the catalytic oxidation of benzyl alcohol using graphene oxide.

Metal-free heterogeneous materials have attracted great interest due to their potential to facilitate various organic transformations in line with circular economy and green chemistry principles. Among various 2D materials, graphene oxide (GO) is considered an attractive material for numerous applications in physics, chemistry, biology, material sciences, and catalysis. Furthermore, graphene-based catalysts exhibit good catalytic activity toward the selective oxidation of benzyl alcohol to benzaldehyde or benzoic acid under eco-friendly conditions. In this regard, a theoretical investigation was carried out to study both catalytic oxidation reaction pathways (i.e., benzyl alcohols to aldehyde and to benzoic acid) using GO as an eco-friendly and metal-free catalyst. In this study, we report a theoretical investigation at the B3LYP/6-31G level to better understand the oxidation of benzyl alcohol using GO as a metal-free catalyst. The possible bond formation was investigated using the global and local reactivity indexes derived from Fukui functions. Furthermore, we performed a non-covalent interaction (NCI) analysis to unveil the stability and the interaction nature between both reagents and GO surface. The effect of the solvent on the oxidation efficiency was also performed and the results indicate that the solvent significantly affects the decrease of reactivity by increasing the activation barriers through oxidation reactions of benzyl alcohol. Additionally, the electron localization function (ELF) analysis was performed for all intermediates showing the ionic nature of the studied epoxide structure of GO and rules out any type of covalent interaction during the oxidation reaction of benzyl alcohol. All these obtained results are in good agreement with experimental observations and reveal that the epoxide functions on the graphene surface promote an excellent catalyst turnover.

Biosensor Based on Graphene Directly Grown by MW-PECVD for Detection of COVID-19 Spike (S) Protein and Its Entry Receptor ACE2.

Biosensors based on graphene field-effect transistors (G-FET) for detecting COVID-19 spike S protein and its receptor ACE2 were reported. The graphene, directly synthesized on SiO2/Si substrate by microwave plasma-enhanced chemical vapor deposition (MW-PECVD), was used for FET biosensor fabrication. The commercial graphene, CVD-grown on a copper substrate and subsequently transferred onto a glass substrate, was applied for comparison purposes. The graphene structure and surface morphology were studied by Raman scattering spectroscopy and atomic force microscope. Graphene surfaces were functionalized by an aromatic molecule PBASE (1-pyrenebutanoic acid succinimidyl ester), and subsequent immobilization of the receptor angiotensin-converting enzyme 2 (ACE2) was performed. A microfluidic system was developed, and transfer curves of liquid-gated FET were measured after each graphene surface modification procedure to investigate ACE2 immobilization by varying its concentration and subsequent spike S protein detection. The directly synthesized graphene FET sensitivity to the receptor ACE2, evaluated in terms of the Dirac voltage shift, exceeded the sensitivity of the transferred commercial graphene-based FET. The concentration of the spike S protein was detected in the range of 10 ag/mL up to 10 μg/mL by using a developed microfluidic system and measuring the transfer characteristics of the liquid-gated G-FETs. It was found that the shift of the Dirac voltage depends on the spike S concentration and was 27 mV with saturation at 10 pg/mL for directly synthesized G-FET biosensor, while for transferred G-FET, the maximal shift of 70 mV was obtained at 10 μg/mL with a tendency of saturation at 10 ng/mL. The detection limit as low as 10 ag/mL was achieved for both G-FETs. The sensitivity of the biosensors at spike S concentration of 10 pg/mL measured as relative current change at a constant gate voltage corresponding to the highest transconductance of the G-FETs was found at 5.6% and 8.8% for directly synthesized and transferred graphene biosensors, respectively. Thus, MW-PECVD-synthesized graphene-based biosensor demonstrating high sensitivity and low detection limit has excellent potential for applications in COVID-19 diagnostics.

Structural Study of Diketopyrrolopyrrole Derivative Thin Films: Influence of Deposition Method, Substrate Surface, and Aging.

We report the morphology and microstructure of n-dialkyl side-chain-substituted thiophene DPP end-capped with phenyl groups (Ph-TDPP-Ph) thin films and compare the influence of deposition method and substrate surface using thermally oxidized Si and graphene substrates as well as monolayer graphene surfaces with an underlying self-assembled octadecyltrichlorosilane monolayer, complemented by an aging study of spin-coated films over a 2 weeks aging period. A distinct difference in morphology was observed between spin-coated and vacuum-deposited thin films, which formed a fiber-like morphology and a continuous layer of terraced grains, respectively. After an initial film evolution, all combinations of deposition method and substrate type result in well-ordered thin films with almost identical crystalline phases with slight variations in crystallinity and mosaicity. These findings point toward strong intermolecular forces dominating during growth, and the templating effect observed for other oligomer films formed on graphene is consequently ineffective for this material type. Upon aging of spin-coated films, a noticeable evolution involving two different morphologies and crystalline phases were observed. After several days, the thin film evolved into a more stable crystal phase and a fiber-like morphology. Moreover, slight variation in optical spectra were elucidated on the basis on density functional theory calculations. These results demonstrate that thin-film properties of DPP derivatives can be tailored by manipulating the film formation process.

Quality Assessment of Processed Graphene Chips for Biosensor Application.

The quality of graphene intended for use in biosensors was assessed on manufactured chips using a set of methods including atomic force microscopy (AFM), Raman spectroscopy, and low-frequency noise investigation. It is shown that local areas of residues on the graphene surface, formed as a result of the interaction of graphene with a photoresist at the initial stage of chip development, led to a spread of chip resistance (R) in the range of 1-10 kOhm and to an increase in the root mean square (RMS) roughness up to 10 times, which can significantly worsen the reproducibility of the parameters of graphene chips for biosensor applications. It was observed that the control of the photoresist residues after photolithography (PLG) using AFM and subsequent additional cleaning reduced the spread of R values in chips to 1-1.6 kOhm and obtained an RMS roughness similar to the roughness in the graphene film before PLG. Monitoring of the spectral density of low-frequency voltage fluctuation (SU), which provides integral information about the system of defects and quality of the material, makes it possible to identify chips with low graphene quality and with inhomogeneously distributed areas of compressive stresses by the type of frequency dependence SU(f).

Phytic acid assist for self-healing nanocomposite hydrogels and their application in flexible strain sensors

Nanocomposite hydrogels have been applied in the field of flexible sensors to monitor human body signals. In this manuscript, phytic acid (PA) was successfully adsorbed on the surface of graphene oxide@polydopamine (GO@PDA). The obtained graphene oxide@polydopamine-phytic acid (GO@PDA-PA) was further implanted to the poly acrylic acid (PAA) hydrogels as flexible strain sensors. Dopamine (DA) was self-polymerized on both two sides of GO by mussel-inspired chemistry to synthetize GO@PDA. PA was decorated on the surface of GO@PDA to obtain GO@PDA-PA nanocomposites with Pickering emulsion in oil-in-water (O/W) emulsion. The GO@PDA-PA hydrogels’ self-healing efficiency (98.6%) and mechanical strength (1.77 MPa) were both improved due to the presence of reversible interaction such as hydrogen bond and metal-ligand coordination. The wearable flexible sensors based on the prepared GO@PDA-PA hydrogels have high sensitivity (gauge factor (GF) = 3.3), stability, durability and high response ability. It can detect the sharp movement signals of human body and tiny movement signals such as breathing. The excellent performance of nanocomposite hydrogels is expected to promote the evolution of flexible sensors.

Ice adhesion mechanism on the patterned surface of aluminum matrix and array graphene based on molecular dynamics simulations

Solving fundamental problems in engineering application can drive rapid industrial development. The solid–ice interface adhesion mechanism on anti-icing materials has attracted strong interest from researchers. In this work, the ice adhesion mechanism at the solid–ice interface was investigated based on water molecule behavior on an aluminum matrix/array graphene (M/G) surface. We counted the number of water molecules in the gaps of the array graphene structure and measured ice and array graphene of stress changes during ice removal. The multilayer array graphene structure relies on “adhesion-type” ice removal mechanism. It was attributed to the increased horizontal displacement of ice due to the stress matching of ice/array graphene. The solid-ice interface adhesion mechanism of patterned surface is understood at the molecular-scale.

Molecular modeling study on the water-electrode surface interaction in hydrovoltaic energy

The global energy problem caused by the decrease in fossil fuel sources, which have negative effects on human health and the environment, has made it necessary to research alternative energy sources. Renewable energy sources are more advantageous than fossil fuels because they are unlimited in quantity, do not cause great harm to the environment, are safe, and create economic value by reducing foreign dependency because they are obtained from natural resources. With nanotechnology, which enables the development of different technologies to meet energy needs, low-cost and environmentally friendly systems with high energy conversion efficiency are developed. Renewable energy production studies have focused on the development of hydrovoltaic technologies, in which electrical energy is produced by making use of the evaporation of natural water, which is the most abundant in the world. By using nanomaterials such as graphene, carbon nanoparticles, carbon nanotubes, and conductive polymers, hydrovoltaic technology provides systems with high energy conversion performance and low cost, which can directly convert the thermal energy resulting from the evaporation of water into electrical energy. The effect of the presence of water on the generation of energy via the interactions between the ion(s) and the liquid–solid surface can be enlightened by the mechanism of the hydovoltaic effect. Here, we simply try to get some tricky information underlying the hydrovoltaic effect by using DFT/B3LYP/6-311G(d, p) computations. Namely, the physicochemical and electronic properties of the graphene surface with a water molecule were investigated, and how/how much these quantities (or parameters) changed in case of the water molecule contained an equal number of charges were analyzed. In these computations, an excess of both positive charge and negative charge, and also a neutral environment was considered by using the Na+, Cl−, and NaCl salt, respectively.