Electrically conductive "alkylated" graphene paper via chemical reduction of amine-functionalized graphene oxide paper

Surface Mapping of Functionalized Two-Dimensional Nanosheets: Graphene Oxide and MXene Materials

In this study, we characterized the morphology, composition, and surface properties of individual flakes of graphene oxide and Ti3C2Tx MXene chemically modified with ethylenediamine, dopamine, and (3-aminopropyl) triethoxysilane (APTES). Individual monolayers of modified Ti3C2Tx MXene and graphene oxide nanosheets were deposited using the Langmuir-Blodgett technique. We compared the chemical surface modification of these two-dimensional (2D) flakes by employing advanced atomic force microscopy (AFM) modes, including quantitative nanomechanical (QNM) mode, Kelvin-Probe force microscopy (KPFM), and Nano-IR imaging. This approach reveals the distribution of mechanical, electrical, and chemical properties on individual flakes at the nanoscale. QNM analysis confirms that the flakes exhibited full surface coverage after the chemical modification process. In modified MXene flakes, we observed a decrease in apparent elastic modulus and an increase in adhesion of up to four times after their functionalization. Nano-IR imaging demonstrates that chemical modification uniformity is highest for graphene oxide species, while the complex surface distribution was observed for dopamine-modified MXene flakes, with a difference between the inner flat surface and their edges. KPFM indicates greater uniformity of surface electrical potential in differently modified graphene oxide, while a significant increase in surface potential of MXene flakes is seen when modified with dopamine. We suggest that a combination of the added dielectric layer and different grafting densities across the flakes is responsible for the increased or changes in apparent surface potential. Overall, a combination of AFM probing modes is needed for understanding how these functionalized nanosheets can be integrated into diverse polymer matrices.

MXene-based solvent-responsive actuators with a polymer-intercalated gradient structure

Actuators based on electrically conductive and hydrophilic two-dimensional (2D) Ti3C2T X MXene are of interest for fast and specific responses in demanding environments, such as chemical production. Herein, Ti3C2T X -based solvent-responsive bilayer actuators were developed, featuring a gradient polymer-intercalation structure in the active layer. These actuators were assembled using negatively charged pristine Ti3C2T X nanosheets as the passive layer and positively charged polymer-tethered Ti3C2T X as the active layer. 2D wide-angle X-ray scattering and simulations related the gradient polymer intercalated microstructure in the polymer/MXene composite active layer to the counterintuitive actuation behavior. The bending of the bilayer films in solvent vapor is triggered by the gradient polymer-intercalation and the differing diffusion rate of solvent molecules through the MX and MX-polymer layers of the bilayer actuator. With their ease of fabrication, remote light-control capabilities, and excellent actuation performance, the Ti3C2T X -based bilayer actuators reported here may find applications in areas such as sensors for monitoring chemical production, infrared camouflage, smart switches, and excavators in toxic solvent environments.

In Situ Growth of Highly Compatible Cu2O-GO Hybrids Via Amino-Modification for Melt-Spun Efficient Antibacterial Polyamide 6 Fibers

Polyamide 6 (PA6) fiber has the advantages of high strength and good wear resistance. However, it is still challenging to effectively load inorganic antibacterial agents into polymer substrates without antimicrobial activity. In this work, graphene oxide is used as a carrier, which is modified with an aminosilane coupling agent (AEAPTMS) to enhance the compatibility and antimicrobial properties of the inorganic material, as well as to improve its thermal stability in a high-temperature melting environment. Cuprous oxide-loaded aminated grapheme (Cu2O-GO-NH2) is constructed by in situ growth method, and further PA6/Cu2O-GO-NH2 fibers are prepared by in situ polymerization. The composite fiber has excellent washing resistance. After 50 times of washing, its bactericidal rates against Bacillus subtilis and Escherichia coli are 98.85% and 99.99%, respectively. In addition, the enhanced compatibility of Cu2O-GO-NH2 with the PA6 matrix improves the orientation and crystallinity of the composite fibers. Compared with PA6/Cu2O-GO fibers, the fracture strength of PA6/Cu2O-GO-NH2 fibers increases from 3.0 to 4.2 cN/dtex when the addition of Cu2O-GO-NH2 is 0.2 wt%. Chemical modification and in situ concepts help to improve the compatibility of inorganic antimicrobial agents with organic polymers, which can be applied to the development of medical textiles.

Experimental and computational studies of crystal violet removal from aqueous solution using sulfonated graphene oxide

Positively charged contaminants can be strongly attracted by sulfanilic acid-functionalized graphene oxide. Here, sulfonated graphene oxide (GO-SO3H) was synthesized and characterized for cationic crystal violet (CV) adsorption. We further studied the effect of pH, initial concentration, and temperature on CV uptake. The highest CV uptake occurred at pH 8. A kinetic study was also carried out by applying the pseudo-first-order and pseudo-second-order models. The pseudo-second-order's adsorption capacity (qe) value was much closer to the experimental qe (qeexp:0.13, qecal:0.12) than the pseudo-first-order model (qeexp:0.13, qecal:0.05). The adsorption performance was accomplished rapidly since the adsorption equilibrium was closely obtained within 30 min. Furthermore, the adsorption capacity was significantly increased from 42.85 to 79.23%. The maximum adsorption capacities of GO-SO3H where 97.65, 202.5, and 196.2 mg·g-1 for CV removal at 298, 308, and 328 K, respectively. The Langmuir and Freundlich adsorption isotherms were applied to the experimental data. The data fit well into Langmuir and Freundlich except at 298 K, where only Langmuir isotherm was most suitable. Thermodynamic studies established that the adsorption was spontaneous and endothermic. The adsorption mechanism was revealed by combining experimental and computational methods. These findings suggest that GO-SO3H is a highly adsorbent for removing harmful cationic dye from aqueous media.

Aramid Nanofibers/Reduced Graphene Oxide Composite Electrodes with High Mechanical Properties

In this work, aramid nanofibers (ANFs)/reduced graphene oxide (ANFs/RGO) film electrodes were prepared by vacuum-assisted filtration, followed by hydroiodic acid reduction. Compared with thermal reduced ANFs/RGO, these as-prepared film electrodes exhibit a combination of mechanical and electrochemical properties with a tensile strength of 184.5 MPa and a volumetric specific capacitance of 134.4 F/cm³ at a current density of 0.125 mA/cm², respectively. In addition, the film electrodes also show a superior cycle life with 94.6% capacitance retention after 5000 cycles. This kind of free-standing film electrode may have huge potential for flexible energy-storage devices.

Effects of Moisture and Synthesis-Derived Contaminants on the Mechanical Properties of Graphene Oxide: A Molecular Dynamics Investigation

This paper reports on the effects of the chemical composition of graphene oxide (GO) sheets on the mechanical properties of bulk GO. Three key factors were analyzed: (i) the oxygenated functional groups' concentration, (ii) the content of intersheet water (moisture), and (iii) the presence of residual contaminants observed from the synthesis of GO. Molecular dynamics simulations using the reactive force field ReaxFF were conducted to model tensile strength, indentation, and shear stress tests. The structural integrity of the carbon basal plane was the primary variable that determined mechanical behavior of GO slabs. Hydrogen-bond networks played an essential role in the tensile fracture mechanism, delaying the onset of fracture whenever strong hydrogen bonds existed in the intersheet space. The presence of interlayer sulfate ion contaminants negatively impacted the tensile strength, stiffness, and toughness of GO. Moreover, it was observed that intersheet sulfate ions improved the resistance to fracture of GO at low sulfur concentrations, while lower fracture strains were observed beyond a critical concentration. Alike the tensile stress findings, the indentation properties were determined by the integrity of the carbon basal plane. Our findings agree with experimental mechanical property measurements and reveal the importance of considering synthesis-derived contaminants in molecular models of GO.

ZnO and reduced graphene oxide electrodes for all-in-one supercapacitor devices

Reduced graphene oxide/zinc oxide (rGO/ZnO) hybrid nanocomposites were prepared from synthesized GO and high energy ball milled (HEBM) ZnO for supercapacitor electrodes. Evolution of intrinsic point defects and defect-induced morphological, structural and size-dependent properties of rGO/ZnO hybrid nanocomposites were investigated using electron paramagnetic resonance (EPR) spectroscopy. CV, PEIS and GCPL techniques were employed to investigate the electrochemical behavior of the electrode materials and the effects of defects on the electrochemical performance of the electrodes by using the standard two-electrode cell in a 6 M KOH electrolyte. Analyses of the obtained CV and impedance profiles have shown the pseudocapacitive and EDLC-type contributions in the supercapacitors. Cycling stabilities were evaluated using galvanostatic charge-discharge curves at current densities between 0.10 and 2.40 A g^-1. The capacitance retention of all electrodes was found to be 100% after 30 cycles at 0.30 A g^-1. The electrochemical analyses revealed that the incorporation of ZnO that is rich in core defects improved the charge transfer performance and ion diffusion of the rGO electrode.

Gas permeation and microstructure of reduced graphene oxide/polyethyleneimine multilayer films created via recast and layer-by-layer deposition processes

Nowadays, graphene/polymer composite films with multilayer structure have attracted significant attention for gas barrier application. In this study, a series of reduced graphene oxide/polyethyleneimine (RGO/PEI) composite films were created via recast and layer-by-layer deposition processes. By using the recast process, the myriad PEI molecules in the precursor solution (the PEI : GO feeding ratio is 0.02 : 0.1, 0.05 : 0.1, 0.1 : 0.1, 0.3 : 0.1 and 0.5 : 0.1) ensure more effective reduction and surface modification of the graphene oxide (GO) sheets, while the undesirable free PEI molecules are eventually removed via a filtration process. Then, the RGO/PEI composite films were synthesized on PET substrate using a layer-by-layer assembly. The resulting films show a homogeneous and compact brick-wall structure with excellent gas barrier properties. Barriers against water vapor, nitrogen/oxygen, and carbon dioxide require different content of PEI in the composite film for optimal performance; the ideal values are 19.7, 23.8, and 24.1 wt%, respectively. These values are much lower compared with previously reported studies. Further, the permeability, free volumes, component ratio, morphology, and density of the RGO/PEI composite films have been carefully investigated and discussed. The results revealed that the mechanism behind the excellent gas barrier property of the RGO/PEI composite films is a synergistic effect created by the combination of the brick-wall structure, the small free volume holes, the suitable PEI content (ranging from 19.7 wt% to 24.1 wt%), the high density, and the hydrophobicity.

Fluorometric and colorimetric detection of cerium(IV) ion using carbon dots and bathophenanthroline-disulfonate-ferrum(II) complex

Cerium, an abundant lanthanide element, is widely used in human industry. The accumulation of Ce⁴⁺ ion, however, will damage the environment and biological organism. Therefore, its facile detection is highly needed. Herein, we design a hybrid sensing platform consisting of carbon dots (C-dots) and bathophenanthroline-disulfonate-Fe²⁺ complex (Bphen-Fe²⁺) for trace-level determination of Ce⁴⁺. Based on inner filter effect (IFE), the red-colored Bphen-Fe²⁺ complex severely quenches the fluorescence of C-dots. After addition of Ce⁴⁺, Fe²⁺ is oxidized to Fe³⁺, and the colorless Bphen-Fe³⁺ complex generates, which weakens the IFE efficiency and leads to the fluorescence recovery of C-dots. Meanwhile, due to the decreasing amount of Bphen-Fe²⁺ upon Ce⁴⁺ addition, the red color of the solution gradually fades, which enables visual detection of Ce⁴⁺ by the naked eyes. Under the optimized conditions, the C-dots/Bphen-Fe²⁺ system realizes the fluorometric and colorimetric sensing of Ce⁴⁺ in the range of 0.5-100 and 1.9-80 μM, with the limits of detection as low as 0.5 and 1.9 μM, respectively. This method also shows high selectivity over other common ions, and has an excellent applicability for monitoring of Ce⁴⁺ in real water samples.

Synthesis of “(aminomethyl)phosphonic acid-functionalized graphene oxide”, and comparison of its adsorption properties for thorium(IV) ion, with plain graphene oxide

The current study presents a simple and scalable method for the synthesis of (aminomethyl)phosphonic acid-functionalized graphene oxide (AMPA-GO) adsorbent. The chemical structure of the new material was disclosed by different instrumental analyses (e.g. FTIR, Raman, XPS, AFM, TEM, XRD, CHN, and UV), and two pertinent mechanisms namely nucleophilic substitution and condensation were suggested for its formation. Adsorption experiments revealed that both AMPA-GO and plain GO have a high affinity toward Th(IV) ions, but the AMPA-GO is superior in terms of adsorption capacity, rate of adsorption, selectivity, pH effect, etc. Indeed, the AMPA-GO can uptake Th(IV) nearly instantaneously, and coexisting Na+ ions have no effect on its adsorption. Thanks to Langmuir isotherm, the maximum adsorption capacities of the GO and AMPA-GO were obtained 151.06 and 178.67 mg g−1, respectively. Interestingly, GO and AMPA-GO both showed a higher preference for thorium over uranium so that the average “K d (Th)/K d (U)” for them was 52 and 44, respectively. This data suggests that chromatographic separation of thorium and uranium is feasible by these adsorbents.

Intercalated water mediated electromechanical response of graphene oxide films on flexible substrates

The confinement of water between sub-nanometer bounding walls of layered two-dimensional materials has generated tremendous interest. Here, we examined the influence of confined water on the mechanical and electromechanical response of graphene oxide films, prepared with variable oxidative states, casted on polydimethylsiloxane substrates. These films were subjected to uniaxial strain under controlled humid environments (5 to 90% RH), while dc transport studies were performed in tandem. Straining resulted in the formation of quasi-periodic linear crack arrays. The extent of water intercalation determined the density of cracks formed in the system thereby, governing the electrical conductance of the films under strain. The crack density at 5% strain, varied from 0 to 3.5 cracks mm^-1for hydrated films and 8 to 22 cracks mm^-1for dry films, across films with different high oxidative states. Correspondingly, the overall change in the electrical conductance at 5% strain was observed to be ∼5 to 20 folds for hydrated films and ∼20 to 35 folds for the dry films. The results were modeled with a decrease in the in-plane elastic modulus of the film upon water intercalation, which was attributed to the variation in the nature of hydrogen bonding network in graphene oxide lamellae.

In Situ Growth of Novel Graphene Nanostructures in Reduced Graphene Oxide Microspherical Assembly with Restacking-Resistance and Inter-Particle Contacts for Energy Storage Devices

Graphene is extensively investigated for various energy storage systems. However, the very low density (<0.01 g cm^-3 ) of graphene nanosheets has hindered its further applications. To solve this issue, a controlled assembly of 2D graphene building blocks should be developed into graphene microspheres with high packing density, and restacking of graphene should be prevented to ensure an electrochemically accessible surface area during the assembly. Furthermore, graphene microspheres should have multiple 1D external conductive architecture to promote contacts with the neighbors. This study reports in situ growth of novel graphene nanostructures in reduced graphene oxide microspherical assembly (denoted as GT/GnS@rGB) with restacking resistance and interparticle contacts, for electrochemical energy storage. The GT/GnS@rGB showed high gravimetric (231.8 F g^-1 ) and volumetric (181.5 F cm^-3 ) capacitances at 0.2 A g^-1 in organic electrolyte with excellent rate capabilities of 94.3% (@ 0.2 vs 10 Ag^-1 ). Furthermore, GT/GnS@rGB exhibited excellent cycling stability (96.1% of the initial capacitance after 100 000 charge/discharge cycles at 2 A g^-1 ). As demonstrated in the electrochemical evaluation as electrode materials for electrical double-layer capacitors, unique structural and textural features of the GT/GnS@rGB would be beneficial in the use of graphene assembly for energy storage applications.

Graphene-Based Hybrid Functional Materials

Graphene is a 2D material combining numerous outstanding physical properties, including high flexibility and strength, extremely high thermal conductivity and electron mobility, transparency, etc., which make it a unique testbed to explore fundamental physical phenomena. Such physical properties can be further tuned by combining graphene with other nanomaterials or (macro)molecules to form hybrid functional materials, which by design can display not only the properties of the individual components but also exhibit new properties and enhanced characteristics arising from the synergic interaction of the components. The implementation of the hybrid approach to graphene also allows boosting the performances in a multitude of technological applications. This review reports the hybrids formed by graphene combined with other low-dimensional nanomaterials of diverse dimensionality (0D, 1D, and 2D) and (macro)molecules, with emphasis on the synthetic methods. The most important applications of these hybrids in the fields of sensing, water purification, energy storage, biomedical, (photo)catalysis, and opto(electronics) are also reviewed, with a special focus on the superior performances of these hybrids compared to the individual, nonhybridized components.

A facile and industrial method for synthesis of modified magnetic lipophilic graphene as a super oil additive

Friction and wear are the two major reasons for energy and material losses in mechanical processes. In this research, a simple, industrial and fast exfoliation technique for the production of graphene using sodium azide and graphite in a water solvent without the need for a specific device has been presented following by lipophilizing with octylamine and only with Fe (II). Magnetic nanoparticles were applied on graphene surface, and simultaneously the graphene surface was both lipophilic and magnetic. The method used for graphene production is unique up to now and also it does not oxidize in production procedure. Performed analyzes demonstrate non-destructive properties without any changes in surface functional groups.

A review of the recent progress on heterogeneous catalysts for Knoevenagel condensation

One of the most crucial attributes of synthetic organic chemistry is to design organic reactions under the facets of green chemistry for the sustainable production of chemicals. Thus, due to the intensified environmental and safety concern, the need for new technologies for conducting chemical transformation has grown. In this regard, there is enormous interest in the use of heterogeneous catalysts as they generally avoid the generation of waste, require fewer toxic reagents, as well as entail easier separation and recycling of the catalyst. α,β-Unsaturated acids have been widely used in various industrial applications and have been identified as one of the most promising chemicals obtained via the Knoevenagel condensation reaction. This review aims to discuss the most pertinent heterogeneous catalytic systems such as zeolites, mesoporous silica, ionic liquids, metal oxides, and graphitic carbon nitride-based catalysts in the Knoevenagel reaction. Ultimately, this review focuses not only on the catalyst but also provides an overall idea and guide for the preparation of new catalysts with outstanding properties by looking at the chemical and engineering aspects such as the reaction conditions and the mechanisms.

The Fabrication and Properties of a Bendable High-Temperature Resistance Conductive Pitch-Based Carbon/CNT Film Nanocomposite

This paper fabricates a carbon nanotube (CNT ) film-reinforced mesophase pitch-based carbon (CNTF/MPC) nanocomposite by using a hot-pressing carbonization method. During the carbonization, the stacked aromatic layers tended to rearrange into amorphous carbon, and subsequently generated crystalline carbon in the matrix. The continuous entangled CNT networks were efficiently densified by the carbon matrix though optimized external pressure to obtain the high-performance nanocomposites. The CNTF/MPC@1300 displayed a stable electrical conductivity up to 841 S/cm at RT-150 °C. Its thermal conductivity in the thickness direction was 1.89 W/m∙K, an order of magnitude higher than that of CNT film. Moreover, CNTF/MPC@1300 showed a mass retention of 99.3% at 1000 °C. Its tensile strength was 2.6 times the CNT film and the tensile modulus was two orders of magnitude higher. Though the CNTF/MPC nanocomposites exhibited brittle tensile failure mode, they resisted cyclic bending without damage. The results demonstrate that the CNTF/MPC nanocomposite has potential application in multi-functional temperature resistance aerospace structures.

Graphitic Carbon Nitride Quantum Dots Embedded in Carbon Nanosheets for Near-Infrared Imaging-Guided Combined Photo-Chemotherapy

Rational design of metal-free multifunctional therapeutic reagents offers great opportunities for cancer treatment in the clinic. Here, graphitic carbon nitride (g-C₃N₄) quantum dots embedded in carbon nanosheets (CNQD-CN) are in situ prepared via a one-pot hydrothermal approach with formamide as carbon and nitrogen source. The CNQD-CN not only serves as an excellent near-infrared (NIR) fluorescent marker but also acts as a pH-responsive nanocarrier. Moreover, the CNQD-CN possesses both light-to-heat conversion and singlet oxygen generation capabilities under a single NIR excitation wavelength. Further investigations show that systemic delivery of doxorubicin (DOX) using the multifunctional CNQD-CN nanocarrier under NIR irradiation was highly effective to cause cancer cell apoptosis in vitro and inhibit tumor growth in vivo. CNQD-CN represents a multifunctional therapeutic platform for synchronous cancer imaging and treatment through the synergistic effect of phototherapy and chemotherapy.

Melt Rheology and Mechanical Characteristics of Poly(Lactic Acid)/Alkylated Graphene Oxide Nanocomposites

Poly(lactic acid) (PLA) nanocomposites were synthesized by a solution blending and coagulation method using alkylated graphene oxide (AGO) as a reinforcing agent. Turbiscan confirmed that the alkylation of GO led to enhanced compatibility between the matrix and the filler. The improved dispersity of the filler resulted in superior interfacial adhesion between the PLA chains and AGO basal plane, leading to enhanced mechanical and rheological properties compared to neat PLA. The tensile strength and elongation at break, i.e., ductility, increased by 38% and 42%, respectively, at the same filler content nanocomposite (PLA/AGO 1 wt %) compared to nonfiller PLA. Rheological analysis of the nanocomposites in the molten state of the samples was performed to understand the filler network formed inside the matrix. The storage modulus increased significantly from PLA/AGO 0.5 wt % (9.6 Pa) to PLA/AGO 1.0 wt % (908 Pa). This indicates a percolation threshold between the two filler contents. A steady shear test was performed to examine the melt flow characteristics of PLA/AGO nanocomposites at 170 °C, and the viscosity was predicted using the Carreau-Yasuda model.

Percolation Conduction of Carbon Nanocomposites

Carbon nanocomposites present a new class of nanomaterials in which conducting carbon nanoparticles are a small additive to a non-conducting matrix. A typical example of such composites is a polymer matrix doped with carbon nanotubes (CNT). Due to a high aspect ratio of CNTs, inserting rather low quantity of nanotubes (on the level of 0.01%) results in the percolation transition, which causes the enhancement in the conductivity of the material by 10-12 orders of magnitude. Another type of nanocarbon composite is a film produced as a result of reduction of graphene oxide (GO). Such a film is consisted of GO fragments whose conductivity is determined by the degree of reduction. A distinctive peculiarity of both types of nanocomposites relates to the dependence of the conductivity of those materials on the applied voltage. Such a behavior is caused by a non-ideal contact between neighboring carbon nanoparticles incorporated into the composite. The resistance of such a contact depends sharply on the electrical field strength and therefore on the distance between neighboring nanoparticles. Experiments demonstrating non-linear, non-Ohmic behavior of both above-mentioned types of carbon nanocomposites are considered in the present article. There has been a model description presented of such a behavior based on the quasi-classical approach to the problem of electron tunneling through the barrier formed by the electric field. The calculation results correspond qualitatively to the available experimental data.

Ultrafast and Highly Sensitive Chemically Functionalized Graphene Oxide-Based Humidity Sensors: Harnessing Device Performances via the Supramolecular Approach

Humidity sensors have been gaining increasing attention because of their relevance for well-being. To meet the ever-growing demand for new cost-efficient materials with superior performances, graphene oxide (GO)-based relative humidity sensors have emerged recently as low-cost and highly sensitive devices. However, current GO-based sensors suffer from important drawbacks including slow response and recovery, as well as poor stability. Interestingly, reduced GO (rGO) exhibits higher stability, yet accompanied by a lower sensitivity to humidity due to its hydrophobic nature. With the aim of improving the sensing performances of rGO, here we report on a novel generation of humidity sensors based on a simple chemical modification of rGO with hydrophilic moieties, i.e., triethylene glycol chains. Such a hybrid material exhibits an outstandingly improved sensing performance compared to pristine rGO such as high sensitivity (31% increase in electrical resistance when humidity is shifted from 2 to 97%), an ultrafast response (25 ms) and recovery in the subsecond timescale, low hysteresis (1.1%), excellent repeatability and stability, as well as high selectivity toward moisture. Such highest-key-performance indicators demonstrate the full potential of two-dimensional (2D) materials when decorated with suitably designed supramolecular receptors to develop the next generation of chemical sensors of any analyte of interest.

Structural-Defect-Mediated Grafting of Alkylamine on Few-Layer MoS2 and Its Potential for Enhancement of Tribological Properties

Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS₂ nanosheets comprising 4-10 molecular lamellae. A structural-defect-mediated route for grafting of octadecylamine (ODA) on MoS₂ nanosheets is outlined. The unsaturated d orbitals of Mo at the sulfur vacancies on the MoS₂ surface are coupled with the electron-rich nitrogen center of ODA and yield ODA-functionalized MoS₂ (MoS₂-ODA). The MoS₂-ODA nanosheets exhibit good dispersibility in lube base oil and are used as an additive (optimized dose: 0.1 mg·mL^-1) to mineral oil. It is shown that even at low concentration, MoS₂-ODA nanosheets significantly reduce the friction (48%) and wear (44%). Microscopy (field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM)) and spectroscopy (Raman and elemental mapping) analyses of worn scars revealed the formation of MoS₂-based protective thin films for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.

Most suitable amino silane molecules for surface functionalization of graphene oxide toward hexavalent chromium adsorption

Adsorption is a simple and effective method for the removal of hexavalent chromium (Cr(VI)) from contaminated water. Several amino silane-graphene oxide (GO) composites with different species of amino groups (pN-GO, psN-GO, and pssN-GO; p: primary, s: secondary, N: amine) were evaluated to investigate their adsorption capacity and the effects of primary and secondary amines on Cr(VI) adsorption. We conducted a quantitative analysis to reveal the difference between primary and secondary amines in terms of Cr(VI) removal efficiency. A synergic effect was observed between the neighboring secondary amines in pssN-GO. From the Langmuir model prediction, we found that the composite with pssN-GO exhibited the highest maximum adsorption capacity (260.74 mg/g), followed by those with psN-GO (208.22 mg/g) and pN-GO (189.47 mg/g). Monolayer adsorption was more dominant when using pssN-GO, with the pseudo-second-order model best fitting the kinetic experiment results, whereas multilayer adsorption was dominant when using psN-GO and pN-GO.

Improved volatile cargo retention and mechanical properties of capsules via sediment-free in situ polymerization with cross-linked poly(vinyl alcohol) as an emulsifier

HYPOTHESIS

It is hypothesized that poly(vinyl alcohol) (PVOH) as an emulsifier destabilizes the insoluble molecular aggregates by increasing interparticle interactions and their tendency toward agglomeration into large particle aggregates during the encapsulation process of one-step in situ polymerization. Porosity of capsule shells is expected to decrease with reducing agglomeration tendency to allow dense packing of smaller insoluble aggregates. Cross-linking the polymer network further reduces shell permeability to improve the retention of volatile cargos. PVOH also modifies the short-range order of polymer network to bestow improved mechanical properties in addition to the shell thickening effect at appropriate synthesis conditions.

EXPERIMENTS

PVOH was used to stabilize a heptane-in-water emulsion as a template for producing capsules via one-step in situ polymerization. Shell morphologies at different PVOH concentrations were compared. Physical freeze-thawing and chemical cross-linking were adopted separately to synthesize capsules with a volatile cargo, and its retention was characterized qualitatively by a solvatochromism-based fluorescent method and quantitative payload calculation. Mechanical properties of capsules were tested with micromanipulation. The effect of graphene oxide (GO) impregnation into capsules was studied with various co-emulsifiers.

FINDINGS

When PVOH alone was used as the emulsifier for capsule synthesis, the higher its concentration, the more porous the shell structure was. At very low concentrations, visible pores were eliminated. Freeze-thaw cycles reduced the permeability of capsule shells when visible pores were absent. Chemical cross-linking with poly(acrylic acid) (PAA) significantly improved the retention of volatile cargo heptane. PVOH substantially reduced polymer sediment during capsule synthesis, which eliminated the tedious centrifugation procedure that normally would have followed. Superior mechanical strength of capsules was achieved with PAA cross-linked PVOH at appropriate conditions. The impregnation of aqueously dispersed GO into capsules was also promoted by using PVOH but not hydrocolloid emulsifiers.

Influence of Host-Guest Interaction between Chiral Selectors and Probes on the Enantioseparation Properties of Graphene Oxide Membranes

Graphene oxide (GO)-based membranes have displayed superior performances in the chiral resolution compared with conventional polymer-based and inorganic membranes. However, the effect of the host-guest interaction between chiral selectors and probes on the enantioseparation properties of GO-based membranes remains to be established. In this work, l-phenylalanine (l-Phe, as the chiral selector)-modified GO-based (l-Phe-GO) membranes were fabricated, and their enantioseparation performances toward various enantiomers, that is, d- and l-phenylalanine (d- and l-Phe), d- and l-methionine (d- and l-Met), N-acyl-d-phenylalanine (N-acyl-d-Phe) and N-acyl-l-phenylalanine (N-acyl-l-Phe), and N-acyl-d-methionine (N-acyl-d-Met) and N-acyl-l-methionine (N-acyl-l-Met), were detected. Results show that (i) l-Phe is preferential to transport d-enantiomers relative to l-enantiomers; (ii) as far as d-enantiomers are concerned, the d-Phe-like enantiomers move faster than d-Met-like ones through the l-Phe-GO membrane owing to their different host-guest interactions. The strength of interactions between chiral selectors and probes was further confirmed from both experimental and theoretical standpoints. In the former case, the enantioselective adsorption of l-Phe-GO nanosheets toward the aforementioned enantiomers demonstrates that l-Phe delivers a higher adsorption capacity to d-enantiomers relative to l-enantiomers, and meanwhile, d-Phe-like enantiomers are better than d-Met-like enantiomers in the adsorption capacity. In the latter case, the chiral separation mechanism is clarified using the periodical density functional theory (DFT) calculation, indicating that l-Phe interacts with d-enantiomers more strongly than l-enantiomers. Especially, our calculations unveil that the difference in the interaction strength is principally dominated by the nonstereoselective interactions between chiral probes and the GO surface. Therefore, our findings suggest that the nonstereoselective weak interaction can be employed to improve the enantioselectivity of GO-based membranes.

Novel Unsaturated Polyester Nanocomposites via Hybrid 3D POSS-Modified Graphene Oxide Reinforcement: Electro-Technical Application Perspective

The latest trends in technologies has shifted the focus to developing innovative methods for comprehensive property enhancement of the polymer composites with facile and undemanding experimental techniques. This work reports an elementary technique to fabricate high-performance unsaturated polyester-based nanocomposites. It focuses on the interactive effect of polyhedral oligomeric silsesquioxanes (POSS)-functionalized graphene oxide (GO) within the unsaturated polymermatrix. The hybrid framework of POSS-functionalized graphene oxide has been configured via peptide bonding between the aminopropyl isobutyl POSS and graphene oxide. The synergistic effect of POSS and graphene oxide paved the way for a mechanism to inculcate a hybrid framework within the unsaturated polyester (UP) via in situ polymerization to develop UP/GO-POSS nanocomposites. The surface-appended POSS within the graphene oxide boosted its dispersion in the UP matrix, furnishing an enhancement in tensile strength of the UP/GO-POSS composites by 61.9%, thermal decomposition temperature (10% mass loss) by 69.8 °C and electrical conductivity by 10⁸ S/m, in contrast to pure UP. In particular, the homogenous influence of the POSS-modified GO could be vindicated in the surging of the limiting oxygen index (%) in the as-prepared nanocomposites. The inclusive property amelioration vindicates the use of fabricated nanocomposites as high-performance nanomaterials in electrotechnical applications.

Designing multifunctional gels with electrical conductivity, mechanical toughness and self-oscillating performance

Self-oscillating polymer gels driven by the Belousov–Zhabotinsky (BZ) oscillating chemical reaction are a new class of functional gels that have potential applications in autonomously functioning membranes and as artificial muscle actuators.

Nickel-molybdenum nitride nanoplate electrocatalysts for concurrent electrolytic hydrogen and formate productions

Hydrogen production by electrocatalytic water splitting is an efficient and economical technology, however, is severely impeded by the kinetic-sluggish and low value-added anodic oxygen evolution reaction. Here we report the nickel-molybdenum-nitride nanoplates loaded on carbon fiber cloth (Ni-Mo-N/CFC), for the concurrent electrolytic productions of high-purity hydrogen at the cathode and value-added formate at the anode in low-cost alkaline glycerol solutions. Especially, when equipped with Ni-Mo-N/CFC at both anode and cathode, the established electrolyzer requires as low as 1.36 V of cell voltage to achieve 10 mA cm^-2, which is 260 mV lower than that in alkaline aqueous solution. Moreover, high Faraday efficiencies of 99.7% for H₂ evolution and 95.0% for formate production have been obtained. Based on the excellent electrochemical performances of Ni-Mo-N/CFC, electrolytic H₂ and formate productions from the alkaline glycerol solutions are an energy-efficient and promising technology for the renewable and clean energy supply in the future.

Durable Antipilling Modification of Cotton Fabric with Chloropyrimidine Compounds

Cotton fabric, a natural cellulose material, is widely used in the textile industry for its excellent properties. However, its application in some fields are seriously restricted because of its poor antipilling behavior. In this study, cotton fabrics were modified with 2,4,6-trichloropyrimidine (TLP), 2,4-dichloro-5-methoxypyrimidine (DMP), and 2-amino-4,6-dichloropyridine (ADP). The surface morphology and chemical structure of the modified cotton fabric were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Furthermore, the antipilling behavior, dyeing properties, thermal properties, and mechanical properties of modified cotton fabric were evaluated. The results showed that chloropyrimidine compounds were successfully grafted onto the surface of the cotton fabric, leading to excellent and durable antipilling activity of grade 3-4 even after 10 washes. Moreover, compared with control cotton fabric, the heat release rate (HRR) and total heat release (THR) of TLP-modified cotton fabric decreased to 173.2 W/g (42.3% reduction) and 11.3 KJ/g (13.7% reduction), respectively. In addition, the increased K/S value of modified cotton fabrics dyed with reactive dyes indicated that the modification can enhance the dyability of cotton fabric. This technique provides a simple and versatile method for improving the antipilling behavior of cellulosic materials and supports further preparation of functional textiles.

Fabrication and Characterization of Modified Graphene Oxide/PAN Hybrid Nanofiber Membrane

In this study, a series of novel modified graphene oxide (MGO)/polyacrylonitrile (PAN) hybrid nanofiber membranes were fabricated by electrospinning a PAN solution containing up to 1.0 wt.% MGO. The GO was initially prepared by a time-saving improved Hummer’s method. Subsequently, the formation of GO was confirmed by scanning electron microscopy (SEM), AFM, Fourier-transform infrared spectroscopy (FT–IR), and Raman spectroscopy. This study also prepared the modified GO with polydiallyldimethylammonium chloride (GP) by using a simple surface post-treatment method to improve its dispersion. Varying amounts of GP were incorporated into PAN nanofibers for the better properties of GP/PAN nanofibers, such as hydrophilicity, mechanical properties, and so on. The resulting GP/PAN hybrid nanofiber membranes were characterized by SEM, FTIR, contact angle, and thermal and mechanical properties. These results showed that the hydrophilic and mechanical properties of GP/PAN hybrid nanofiber membranes were dramatically improved, i.e., 50% improvement for hydrophilicity and 3–4 times higher strength for mechanical property, which indicated the possibility for water treatment application. In addition, the notably improved thermal stability results showed that the hybrid nanofiber membranes could also be a potential candidate for the secondary battery separator.

γ-Aminobutyric acid-modified graphene oxide as a highly selective and low-toxic fluorescent nanoprobe for relay recognition of copper(II) and cysteine

A sensitive and selective graphene oxide (GO)-based fluorescent nanoprobe has been developed for the relay recognition of Cu²⁺ and cysteine (Cys) by covalently grafting γ-aminobutyric acid (GABA) onto GO. The fluorescence of the probe (with excitation/emission maxima at 360/445 nm) is selectively quenched by Cu²⁺ via static fluorescence quenching. Fluorescence drops linearly as the concentration of Cu²⁺ is increased from 50 nM to 1.0 µM, and the detection limit for Cu²⁺ is calculated as 15 nM. By virtue of the strong interaction between Cys and Cu²⁺, the GO-GABA/Cu²⁺ complex can further sensitively recognize Cys in a "switch-on" mode. The linear range for Cys detection is from 50 nM to 1.0 µM, and the detection limit is 38 nM. The probe has low cytotoxicity, and it works well inside living cells, which is verified by the successful application in imaging of LLC-PK1 cells. Graphical abstract Gamma-Aminobutyric Acid (GABA) modified graphene oxide (GO) is a highly selective nanoprobe for the fluorometric relay recognition of Cu²⁺ and Cys.

Preparation of graphene/Au aerogel film through the hydrothermal process and application for H2O2 detection

In this paper, one-step preparation of graphene/gold nanoparticle hydrogel film through the hydrothermal method is reported. The hydrogel film could be formed on a glass substrate under hydrothermal conditions, and upon freeze-drying, the aerogel film of 40 μm thickness with satisfying flexibility and strength is obtained. The aerogel composite film is characterized by scanning/transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. Moreover, the aerogel film is directly used as the electrochemical electrode for sensing H2O2, and exhibits good performance with a broad linear range, low detection limit and excellent selectivity. This work provides a route for the fabrication of graphene film material with wide potential in various aspects.