Dual path mechanism in the thermal reduction of graphene oxide

Visualizing Thermal Reduction in Graphene Oxide

The reduction of graphene oxide (GO) is critical for tuning its properties. This study integrates optical contrast analysis with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) to investigate the structural and optical evolution of GO in thermal reduction. For GO on 100 nm SiO2/Si, the R channel contrast exhibits superior sensitivity to structural changes, making it a reliable indicator of the reduction process. A theoretical model based on Fresnel equations reveals the role of SiO2 thickness in modulating optical contrast, providing guidelines for substrate optimization and channel selection.

Unveiling electron transfer and radical transformation pathways in coupled electrocatalysis and persulfate oxidation reactions for complex pollutant removal

The degradation of multiple organic pollutants in wastewater via advanced oxidation processes might involve different radicals, of which the types and concentrations vary upon interacting with different pollutants. In this study, electrochemical activation of peroxymonosulfate (E/PMS) using advanced activated carbon cloth (ACC) as electrode was applied for simultaneous degradation of mixed pollutants, e.g., metronidazole (MNZ) and p-chloroaniline (PCA). 92.5 % of MNZ and 91.4 % of PCA can be degraded at the cathode and anode at a low current density and PMS concentration, respectively. The rate constants for the simultaneous removal of MNZ and PCA in the E/PMS/MNZ(PCA) system were 118 times and 6 times higher than those in the sole PMS system, and 2.5 times and 1.6 times higher than those in the E/Na2SO4/MNZ(PCA) system, respectively. Different electrochemical characteristics, EPR spectra and radical quenching tests verified that the degradation of MNZ and PCA in the optimal system proceeded primarily through non-radical-dominated oxidation, involving electron transfer and 1O2 effect. The system also exhibited low energy consumption (0.215 kWh/m-3·order-1), broad operational pH range, excellent removal efficiency for water matrix, and low by-products toxicity, indicating its strong potential for practical applications. The ACC, with its super stable, low cost, and electrochemical activity, make it as a promising materials applicable in the E/PMS system for degradation of multiple pollutants. The study further elucidated the mechanism of pollutant interaction with electrode materials in terms of radical and non-radical transformation, providing fundamental insight into the application of this system for treatment of complex wastewater.

Hybridization of Sulfur-Defective MoS2 and Holey Expanded Graphite for a Long Cycling Lithium Oxygen Battery Cathode

The development of MoS2 as a cathode electrocatalyst for lithium-oxygen batteries (LOBs) has attracted considerable attention due to its natural abundance, excellent catalytic activity, and chemical stability. However, the sluggish and complicated kinetic of insulating and bulk discharge products on the electrode surface is one of major factors for MoS2 as a cathode for high performance LOBs. Defect engineering of an electrocatalyst and its hybridization with highly conductive frameworks are effective strategies to address this critical issue. Herein, we report a hybrid of rich sulfur-defective MoS2 (MoS2-x) nanosheets grown on highly conductive holey expanded graphite (hEG) with well-defined "worm-like" and holey structures (MoS2-x/hEG). Benefiting from rich sulfur defects of MoS2-x and the highly conductive nature and holey structures of hEG, the MoS2-x/hEG hybrid as a cathode for LOBs displays outstanding electrochemical performance with an extremely high discharge capacity of 19000.3 mAh g-1 at 500 mA g-1 and an ultralong cycling life of over 500 cycles at 1000 mA g-1 with a controlled specific capacity of 1000 mAh g-1.

Development of a one-pot synthesis of rGO in water by optimizing Tour's method parameters

Since its first synthesis in 2004, graphene has been widely studied and several different synthesis methods has been developed. Solvent exfoliation of graphite and the reduction of graphene oxide previously obtained through graphite oxidation are the most employed. In this work, we exploited synthesis conditions of a method usually employed for obtaining graphene oxide (the Tour's method) for directly obtaining a very poorly oxidised material with characteristics like reduced graphene oxide. For the first time, a one-pot synthesis of reduced graphene oxide (rGO) is reported avoiding the use of a post-synthesis chemical or thermal reduction of the graphene oxide that requires further reagents, heat and time.

Decisive role of electrostatic interaction in rheological evolution of graphene oxide under ultrasonic fragmentation

The aqueous dispersibility and processability of graphene oxide (GO) are pivotal for various applications, including the fluid assembly of macroscopic materials and nanofluidic systems. Despite the widespread utilization of ultrasonic treatment to achieve homogeneous dispersions, the rheological changes of GO during sonication have remained relatively unexplored, leading to conflicting research findings. In this study, we demonstrate that the viscoelastic evolution of GO can significantly differ under ultrasonic fragmentation depending on the balance between repulsion force and attraction force at the initial state before fragmentation. When electrostatic repulsion is in delicate equilibrium with attractive forces, gelation occurs under ultrasonic fragmentation, leading to increased viscosity under sonication. Conversely, when electrostatic repulsion predominates, viscosity decreases during sonication. This study reconciles conflicting observations on the rheological evolution of GO dispersions under ultrasonic fragmentation and provides valuable guidance and insights for the rheological engineering of GO colloidal systems.

MgH2 nanoparticles confined in reduced graphene oxide pillared with organosilica: a novel type of hydrogen storage material

Hydrogen is a promising alternative fuel that can push forward the energy transition because of its high energy density (142 MJ kg-1), variety of potential sources, low weight and low environmental impact, but its storage for automotive applications remains a formidable challenge. MgH2, with its high gravimetric and volumetric density, presents a compelling platform for hydrogen storage; however, its utilization is hindered by the sluggish kinetics of hydrogen uptake/release and high temperature operation. Herein we show that a novel layered heterostructure of reduced graphene oxide and organosilica with high specific surface area and narrow pore size distribution can serve as a scaffold to host MgH2 nanoparticles with a narrow diameter distribution around ∼2.5 nm and superior hydrogen storage properties to bulk MgH2. Desorption studies showed that hydrogen release starts at relatively low temperature, with a maximum at 348 °C and kinetics dependent on particle size. Reversibility tests demonstrated that the dehydrogenation kinetics and re-hydrogenation capacity of the system remains stable at 1.62 wt% over four cycles at 200 °C. Our results prove that MgH2 confinement in a nanoporous scaffold is an efficient way to constrain the size of the hydride particles, avoid aggregation and improve kinetics for hydrogen release and recharging.

Diesel soot combustion in air-NO environment: Evolution of functional groups on soot surfaces

It is inevitable for NO to be involved in the soot combustion in diesel particulate filters (DPFs), so giving full play to the NO oxidation activity is one of the most effective means to improve the DPF regeneration performance. In this work, based on the results of programmed temperature oxidation (TPO) experiments, Fourier transfer inference spectroscopy, and X-ray photoelectron spectroscopy, the evolution of surface functional groups was seriously analyzed to explore the soot oxidation mechanism. The results revealed that with the presence of NO in the air atmosphere, the concentration of -ONO2 groups showed an increasing trend in the early oxidation stage of 0-20 % oxidation degree (OD) and then slowly decreased during 20-80 % OD, while the variations in CH functional group concentration were directly related to the concentration NO in the air atmosphere. COO functional group is easy to decompose, and NO promotes COO's generation and decomposition. The sp3/sp2 hybrid ratio is strongly correlated with CO (carbon‑oxygen double bond), but the content of CO is also affected by the desorption of COO functional groups. It is worth noting that when the soot oxidation degree is at 50 %-80 % OD, CO groups are converted to CO functional groups.

Structural Stability and Disorder Level of Moderately Reduced Paper-like Graphene Oxide Investigated with Micro-Raman Analysis

This paper discusses the results of the micro-Raman analysis performed on paper-like graphene oxide (GO) samples consisting of many functionalised graphene layers and annealed at moderate temperatures (≤500 °C) under vacuum conditions (p ≃ 10-4 mbar). The analysis of the standalone samples revealed that the obtained material is characterised by a noticeable disorder level but still stays below the commonly accepted threshold of high or total disorder. GO formed in a simple way showed two spectral bands above 1650 cm-1 recorded very rarely or not at all and their origin has been discussed in detail. The results also confirmed the metastable character of multilayer GO after the annealing process at moderate temperatures as the C/O ratio was kept between 2 and 3 and the spectral features were stable within the annealing temperature range.

A quantum mechanical approach to the oxidation mechanism of graphene oxide (GO)

Elucidation of the reaction mechanism concerning the oxidation above the face and at the edge of a large, oxidized graphene (GO) cluster, namely C80H22O, by molecular oxygen in the first excited state (1Δg) was achieved with quantum mechanical calculations using the ONIOM two-layer method. Oxidation on the face of the aforementioned cluster leads to the formation of an ozone molecule, whereas oxygen molecule attack at the edge of the oxidized graphene surface either launches an ozonide -a five-membered ring species- formation during its outward approach or an 1,3-dioxetane -a four-membered ring species- production along its inward invasion. A detailed examination of the proposed pathways suggests that the ozonide formation should overcome almost one and a half times an adiabatic energy barrier with respect to the ozone production and is strongly exergonic by up to -50.1 kcal mol-1, supporting the experimental findings that both compounds are critically involved in the explosive deoxygenation of GO. On the other hand, the 1,3-dioxetane alternative pathway is considered even more exergonic, although it requires an overwhelming adiabatic energy barrier of 29.8 kcal mol-1 to accomplish its target.

Rapid Yet Efficient Reduction of Graphene Oxide Triggered by Semi-Molten Metals

Reduced graphene oxide (rGO) has garnered extensive attention as electrodes, sensors, and membranes, necessitating the efficient reduction of graphene oxide (GO) for optimal performance. In this work, a swift reduction of GO that involves bringing GO foam in contact with semi-molten metals like tin (Sn) and lithium (Li) is presented. These findings reveal that the electrical resistance of GO foam is significantly diminished by its interaction with these metals, even in dry air. Taking inspiration from this technique, Sn foil is employed to encase the GO foam, followed by a calcination in 15 vol% H2 /Ar environment at 235 °C to fabricate the rGO, which demonstrates a remarkably lower electrical resistivity of 0.42 Ω cm when compared to the chemically reduced GO via hydrazine hydrate (650 Ω cm). The reduction mechanism entails the migration of Sn on GO and its subsequent reaction with oxygen functional groups. SnO/Sn(OH)2 formed from the reaction can be subsequently reversed through reduction by H2 to Sn. Utilizing this rGO as the host material for a sulfur cathode, a lithium-sulfur battery is constructed that displays a specific capacity of 1146 mAh g-1 and maintains a capacity retention of 68.4% after 300 cycles at a rate of 0.2 C.

Electrochemical Exfoliation of Graphene Oxide: Unveiling Structural Properties and Electrochemical Performance

An electrochemical exfoliation method for the production of graphene oxide and its characterization by electrochemical techniques are presented here. Graphite rods are used as working electrode in a three-electrode electrochemical cell, and electro-exfoliation is achieved by applying anodic polarization in a sulfuric acid solution. The electrochemical process involved two steps characterized by an intercalation at lower potential and an exfoliation at higher potential. The electrochemical behavior of the produced GO is studied through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). X ray Photoelectronic Spectroscopy (XPS), Raman spectroscopy, Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM) are employed to characterize the structural and chemical properties of the exfoliated GO. The results demonstrate that the electrochemical exfoliation method yields GO materials with varying degrees of oxidation, defect density, and crystallite size, depending on the applied potential and acid concentration. The graphene oxide samples exhibited distinct electrochemical properties, including charge transfer resistance, interfacial capacitance, and relaxation times for the charge transfer, as revealed by CV and EIS measurements with a specifically selected redox probe. The comprehensive characterization performed provides valuable insights into the structure-property relationships of the GO materials synthesized through electrochemical exfoliation of graphite.

Mechanistic Insights on Functionalization of Graphene with Ozone

The exposure of graphene to O3 results in functionalization of its lattice with epoxy, even at room temperature. This reaction is of fundamental interest for precise lattice patterning, however, is not well understood. Herein, using van der Waals density functional theory (vdW-DFT) incorporating spin-polarized calculations, we find that O3 strongly physisorbs on graphene with a binding energy of -0.46 eV. It configures in a tilted position with the two terminal O atoms centered above the neighboring graphene honeycombs. A dissociative chemisorption follows by surpassing an energy barrier of 0.75 eV and grafting an epoxy group on graphene reducing the energy of the system by 0.14 eV from the physisorbed state. Subsequent O3 chemisorption is preferred on the same honeycomb, yielding two epoxy groups separated by a single C-C bridge. We show that capturing the onset of spin in oxygen during chemisorption is crucial. We verify this finding with experiments where an exponential increase in the density of epoxy groups as a function of reaction temperature yields an energy barrier of 0.66 eV, in agreement with the DFT prediction. These insights will help efforts to obtain precise patterning of the graphene lattice.

Multi-Channel Hollow Carbon Nanofibers with Graphene-Like Shell-Structure and Ultrahigh Surface Area for High-Performance Zn-Ion Hybrid Capacitors

Porous carbon is the most promising cathode material for Zn-ion hybrid capacitors (ZIHCs), but is limited by insufficient active adsorption sites and slow ion diffusion kinetics during charge storage. Herein, a pore construction-pore expansion strategy for synthesizing multi-channel hollow carbon nanofibers (MCHCNF) is proposed, in which the sacrificial template-induced multi-channel structure eliminates the diffusion barrier for enhancing ion diffusion kinetics, and the generated ultrahigh surface area and high-density defective structures effectively increase the quantity of active sites for charge storage. Additionally, a graphene-like shell structure formed on the carbon nanofiber surface facilitates fast electron transport, and the highly matchable pore size of MCHCNF with electrolyte-ions favors the accommodation of charge carriers. These advantages lead to the optimized ZIHCs exhibit high capacity (191.4 mAh g-1 ), high energy (133.1 Wh kg-1 ), along with outstanding cycling stability (93.0% capacity retention over 15000 cycles). Systematic ex situ characterizations reveal that the dual-adsorption of anions and cations synergistically ensures the outstanding electrochemical performance, highlighting the importance of the highly-developed porous structure of MCHCNF. This work not only provides a promising strategy for improving the capacitive capability of porous materials but also sheds light on charge storage mechanisms and rational design for advanced energy storage devices.

Unraveling the Oxidation of a Graphitic Lattice: Structure Determination of Oxygen Clusters

Unraveling the oxidation of graphitic lattice is of great interest for atomic-scale lattice manipulation. Herein, we build epoxy cluster, atom by atom, using Van der Waals' density-functional theory aided by Clar's aromatic π-sextet rule. We predict the formation of cyclic epoxy trimers and its linear chains propagating along the armchair direction of the lattice to minimize the system's energy. Using low-temperature scanning tunneling microscopy on oxidized graphitic lattice, we identify linear chains as bright features that have a threefold symmetry, and which exclusively run along the armchair direction of the lattice confirming the theoretical predictions.

Transparent Electronics for Wearable Electronics Application

Recent advancements in wearable electronics offer seamless integration with the human body for extracting various biophysical and biochemical information for real-time health monitoring, clinical diagnostics, and augmented reality. Enormous efforts have been dedicated to imparting stretchability/flexibility and softness to electronic devices through materials science and structural modifications that enable stable and comfortable integration of these devices with the curvilinear and soft human body. However, the optical properties of these devices are still in the early stages of consideration. By incorporating transparency, visual information from interfacing biological systems can be preserved and utilized for comprehensive clinical diagnosis with image analysis techniques. Additionally, transparency provides optical imperceptibility, alleviating reluctance to wear the device on exposed skin. This review discusses the recent advancement of transparent wearable electronics in a comprehensive way that includes materials, processing, devices, and applications. Materials for transparent wearable electronics are discussed regarding their characteristics, synthesis, and engineering strategies for property enhancements. We also examine bridging techniques for stable integration with the soft human body. Building blocks for wearable electronic systems, including sensors, energy devices, actuators, and displays, are discussed with their mechanisms and performances. Lastly, we summarize the potential applications and conclude with the remaining challenges and prospects.

Photoelectrochemical C-H Activation Through a Quinacridone Dye Enabling Proton-Coupled Electron Transfer

Dye-sensitized photoanodes for C-H activation in organic substrates are assembled by vacuum sublimation of a commercially available quinacridone (QNC) dye in the form of nanosized rods onto fluorine-doped tin oxide (FTO), TiO₂ , and SnO₂ slides. The photoanodes display extended absorption in the visible range (450-600 nm) and ultrafast photoinduced electron injection (<1 ps, as revealed by transient absorption spectroscopy) of the QNC dye into the semiconductor. The proton-coupled electron-transfer reactivity of QNC is exploited for generating a nitrogen-based radical as its oxidized form, which is competent in C-H bond activation. The key reactivity parameter is the bond-dissociation free energy (BDFE) associated with the N⋅/N-H couple in QNC of 80.5±2.3 kcal mol^-1 , which enables hydrogen atom abstraction from allylic or benzylic C-H moieties. A photoelectrochemical response is indeed observed for organic substrates characterized by C-H bonds with BDFE below the 80.5 kcal mol^-1 threshold, such as γ-terpinene, xanthene, or dihydroanthracene. This work provides a rational, mechanistically oriented route to the design of dye-sensitized photoelectrodes for selective organic transformations.

From nanohole to ultralong straight nanochannel fabrication in graphene oxide with swift heavy ions

Porous architectures based on graphene oxide with precisely tailored nm-sized pores are attractive for biofluidic applications such as molecular sieving, DNA sequencing, and recognition-based sensing. However, the existing pore fabrication methods are complex, suffer from insufficient control over the pore density and uniformity, or are not scalable to large areas. Notably, creating vertical pores in multilayer films appears to be particularly difficult. Here, we show that uniform 6-7 nm-sized holes and straight, vertical nanochannels can be formed by simply irradiating graphene oxide (GO) films with high-energy heavy ions. Long penetration depths of energetic ions in combination with localized energy deposition and effective self-etching processes enable the creation of through pores even in 10 µm-thick GO films. This fully scalable fabrication provides a promising possibility for obtaining innovative GO track membranes.

In Situ Nucleation-Decoupled and Site-Specific Incorporation of Å-Scale Pores in Graphene Via Epoxidation

Generating pores in graphene by decoupled nucleation and expansion is desired to achieve a fine control over the porosity, and is desired to advance several applications. Herein, epoxidation is introduced, which is the formation of nanosized epoxy clusters on the graphitic lattice as nucleation sites without forming pores. In situ gasification of clusters inside a transmission electron microscope shows that pores are generated precisely at the site of the clusters by surpassing an energy barrier of 1.3 eV. Binding energy predictions using ab initio calculations combined with the cluster nucleation theory reveal the structure of the epoxy clusters and indicate that the critical cluster is an epoxy dimer. Finally, it is shown that the cluster gasification can be manipulated to form Å-scale pores which then effectively sieve gas molecules based on their size. This decoupled cluster nucleation and pore formation will likely pave the way for an independent control of pore size and density.

High-Throughput Preparation of Uncontaminated Graphene-Oxide Aqueous Dispersions with Antioxidant Properties by Semi-Automated Diffusion Dialysis

A semi-automated diffusion-dialysis purification procedure is proposed for the preparation of uncontaminated graphene oxide (GO) aqueous dispersions. The purification process is integrated with analytical-signal processing to control the purification degree online by several channels: oxidation-reduction potential, conductivity, and absorbance. This approach reduces the amounts of reagents for chemical treatment during dialysis. The total transition metal (Mn and Ti) content was reduced to a sub-ppb level (assessed by slurry nebulization in inductively coupled plasma optical atomic emission spectroscopy). Purified aqueous GO samples possess good stability for about a year with a zeta-potential of ca. -40 mV and a lateral size of ca. sub-µm. Purified GO samples showed increased antioxidant properties (up to five times compared to initial samples according to chemiluminometry by superoxide-radical (O₂^-) generated in situ from xanthine and xanthine oxidase with the lucigenin probe) and significantly decreased peroxidase-like activity (assessed by the H₂O₂-L-012 system).

Gas Separation Membranes with Atom-Thick Nanopores: The Potential of Nanoporous Single-Layer Graphene

Gas separation is one of the most important industrial processes and is poised to take a larger role in the transition to renewable energy, e.g., carbon capture and hydrogen purification. Conventional gas separation processes involving cryogenic distillation, solvents, and sorbents are energy intensive, and as a result, the energy footprint of gas separations in the chemical industry is extraordinarily high. This has motivated fundamental research toward the development of novel materials for high-performance membranes to improve the energy efficiency of gas separation. These novel materials are expected to overcome the intrinsic limitations of the conventional membrane material, i.e., polymers, where a longstanding trade-off between the separation selectivity and the permeance has motivated research into nanoporous materials as the selective layer for the membranes. In this context, atom-thick materials such as nanoporous single-layer graphene constitute the ultimate limit for the selective layer. Gas transport from atom-thick nanopores is extremely fast, dependent primarily on the energy barrier that the gas molecule experiences in translocating the nanopore. Consequently, the difference in the energy barriers for two gas molecules determines the gas pair selectivity. In this Account, we summarize the development in the field of nanoporous single-layer graphene membranes for gas separation. We start by discussing the mechanism for gas transport across atom-thick nanopores, which then yields the crucial design elements needed to achieve high-performance membranes: (i) nanopores with an adequate electron-density gap to sieve the desired gas component (e.g., smaller than 0.289, 0.33, 0.346, 0.362, and 0.38 nm for H₂, CO₂, O₂, N₂, and CH₄, respectively), (ii) narrow pore size distribution to limit the nonselective effusive transport from the tail end of the distribution, and (iii) high density of selective pores. We discuss and compare the state-of-the-art bottom-up and top-down routes for the synthesis of nanoporous graphene films. Mechanistic insights and parameters controlling the size, distribution, and density of nanopores are discussed. Fundamental insights are provided into the reaction of ozone with graphene, which has been successfully used by our group to develop membranes with record-high carbon capture performance. Postsynthetic modifications, which allow the tuning of the transport by (i) tailoring the relative contributions of adsorbed-phase and gas-phase transport, (ii) competitive adsorption, and (iii) molecular cutoff adjustment, are discussed. Finally, we discuss practical aspects that are crucial in successfully preparing practical membranes using atom-thick materials as the selective layer, allowing the eventual scale-up of these membranes. Crack- and tear-free preparation of membranes is discussed using the approach of mechanical reinforcement of graphene with nanoporous carbon and polymers, which led to the first reports of millimeter- and centimeter-scale gas-sieving membranes in the year 2018 and 2021, respectively. We conclude with insights and perspectives highlighting the key scientific and technological gaps that must be addressed in the future research.

Regulated dielectric loss based on core-sheath carbon-carbon hierarchical nanofibers toward the high-performance microwave absorption

As a response to stealth technology and electromagnetic pollution, microwave absorbing materials have attracted the attention of many research scholars. However, achieving effective absorption with a low filling level is still a challenge in the harsh environment. Here, an emerging carbon-carbon composite fiber with a core-sheath structure is cleverly tailored for high-performance microwave absorber by tuning the dielectric loss. Reasonable engineering heterogeneous interfaces and conductive paths give rise to a synergistic effect of the impedance matching, conductive loss, polarization loss and multiple scattering. The obtained CR-800 achieves the maximum reflection loss of -51.91 dB, effective absorbing bandwidth of 4.82 GHz, and radar cross section (RCS) reduction value of 41.5 dBm². Furthermore, the composites own superior environmental adaptation with stable absorbing properties in the harsh environment benefited from great environmental resistance of carbon materials. Given this, the core-sheath carbon-carbon composite fibers are expected to be a candidate for radar stealth technology and electromagnetic pollution.

Enhanced Water Evaporation from Å-Scale Graphene Nanopores

Enhancing the kinetics of liquid-vapor transition from nanoscale confinements is an attractive strategy for developing evaporation and separation applications. The ultimate limit of confinement for evaporation is an atom thick interface hosting angstrom-scale nanopores. Herein, using a combined experimental/computational approach, we report highly enhanced water evaporation rates when angstrom sized oxygen-functionalized graphene nanopores are placed at the liquid-vapor interface. The evaporation flux increases for the smaller nanopores with an enhancement up to 35-fold with respect to the bare liquid-vapor interface. Molecular dynamics simulations reveal that oxygen-functionalized nanopores render rapid rotational and translational dynamics to the water molecules due to a reduced and short-lived water-water hydrogen bonding. The potential of mean force (PMF) reveals that the free energy barrier for water evaporation decreases in the presence of nanopores at the atomically thin interface, which further explains the enhancement in evaporation flux. These findings can enable the development of energy-efficient technologies relying on water evaporation.

Structure Evolution of Graphitic Surface upon Oxidation: Insights by Scanning Tunneling Microscopy

Oxidation of graphitic materials has been studied for more than a century to synthesize materials such as graphene oxide, nanoporous graphene, and to cut or unzip carbon nanotubes. However, the understanding of the early stages of oxidation is limited to theoretical studies, and experimental validation has been elusive. This is due to (i) challenging sample preparation for characterization because of the presence of highly mobile and reactive epoxy groups formed during oxidation, and (ii) gasification of the functional groups during imaging with atomic resolution, e.g., by transmission electron microscopy. Herein, we utilize a low-temperature scanning tunneling microscope (LT-STM) operating at 4 K to solve the structure of epoxy clusters form upon oxidation. Three distinct nanostructures corresponding to three stages of evolution of vacancy defects are found by quantitatively verifying the experimental data by the van der Waals density functional theory. The smallest cluster is a cyclic epoxy trimer. Their observation validates the theoretical prediction that epoxy trimers minimize the energy in the cyclic structure. The trimers grow into honeycomb superstructures to form larger clusters (1-3 nm). Vacancy defects evolve only in the larger clusters (2-3 nm) in the middle of the cluster, highlighting the role of lattice strain in the generation of vacancies. Semiquinone groups are also present and are assigned at the carbon edge in the vacancy defects. Upon heating to 800 °C, we observe cluster-free vacancy defects resulting from the loss of the entire epoxy population, indicating a reversible functionalization of epoxy groups.

In-situ detoxification of schedule-I chemical warfare agents utilizing Zr(OH)4@W-ACF functional material for the development of next generation NBC protective gears

Chemical warfare agents (CWAs) have become a pivotal concern for the global community and spurred a wide spectrum of research for the development of new generation protective materials. Herein, a highly effective self-detoxifying filter consisting of in-situ immobilized Zirconium hydroxide [Zr(OH)4] over woven activated carbon fabric [Zr(OH)4@W-ACF] is presented for the removal of CWAs. It was prepared to harness the synergistic effect of high surface area of W-ACF, leads to high dispersion of CWAs and high phosphilicity and reactivity of [Zr(OH)4]. The synthesized materials were characterized by ATR-FTIR, EDX, SEM, TEM, XPS, TGA, and BET surface area analyzer. The kinetics of  in-situ degradation of CWAs over Zr(OH)4@W-ACF were studied and found to be following the first-order reaction kinetics. The rate constant was found to be 0.244 min-1 and 2.31 × 10-2 min-1 for sarin and soman, respectively over Zr(OH)4@W-ACF. The potential practical applicability of this work was established by fabricating Zr(OH)4@W-ACF as reactive adsorbent layer for protective suit, and found to be meeting the specified criteria in terms of air permeability, tearing strength and nerve agent permeation as per TOP-08-2-501A:2013 and IS-17380:2020. The degradation products of CWAs were analyzed with NMR and GC-MS. The combined properties of dual functional textile with reactive material are expected to open up new exciting avenues in the field of CWAs protective clothing and thus find diverse application in defence and environmental sector.

Mechanisms of the Aggregation of Graphene Oxide at High pH: Roles of Oxidation Debris and Metal Adsorption

In this work, aggregation of graphene oxide (GO) in synthetic surface water at high pH was elaborated, and experimental characterizations and molecular dynamics simulations were employed to uncover the mechanisms. According to previous studies, aggregation of GO is supposed to be impossible at high pH considering the deprotonation of functional groups on GO and the increased electrostatic repulsions. However, significant aggregations and a reversed trend in zeta potential at high pH were observed. One of the mechanisms was that the promoted metal adsorption at high pH can offset the negative charges generated by the deprotonation. Additionally, the stripping of oxidation debris (OD) on GO also contributes to the unexpected trend in the aggregation behavior and zeta potential. GO consists of lightly oxidized functionalized graphene (FG) sheets and highly oxidized OD. Upon the increase of pH and the deprotonation of functional groups on FG and OD, OD was stripped from FG, which decreased the electrostatic repulsions between FG sheets and accelerated the aggregation. The stripped ODs may recombine to FG edges and bridged FG sheets, which also contribute to the aggregation. Upon the stripping of OD and microstructure transformation of FG, FG-water-OD aggregates formed. According to this study, the aggregation of GO was accompanied by deprotonation of functional groups, metal adsorption, and surface property transformation triggered by the stripping of ODs and should be considered during the development of GO-related nanomaterials and the evaluation of its environmental impact.

Revealing the effect of electrocatalytic performance boost during hydrogen evolution reaction on free-standing SWCNT film electrode

Large-scale sustainable hydrogen production by water electrolysis requires a highly active yet low-cost hydrogen evolution reaction (HER) electrocatalyst. Conductive carbon nanomaterials with high surface areas are promising candidates for this purpose. In this contribution, single-walled carbon nanotubes (SWCNTs) are assembled into free-standing films and directly used as HER electrodes. During the initial 20 h of electrocatalytic performance in galvanostatic conditions, the films undergo activation, which results in a gradual overpotential decrease to the value of 225 mV. Transient physicochemical properties of the films at various activation stages are characterized to reveal the material features responsible for the activity boost. Results indicate that partial oxidation of iron nanoparticles encapsulated in SWCNTs is the major contributor to the activity enhancement. Furthermore, besides high activity, the material, composed of only earth-abundant elements, possesses exceptional performance stability, with no activity loss for 200 h of galvanostatic performance at − 10 mA cm⁻². In conclusion, the work presents the strategy of engineering a highly active HER electrode composed of widely available elements and provides new insights into the origins of electrocatalytic performance of SWCNT-based materials in alkaline HER.

Multipulsed Millisecond Ozone Gasification for Predictable Tuning of Nucleation and Nucleation-Decoupled Nanopore Expansion in Graphene for Carbon Capture

Predictable and tunable etching of angstrom-scale nanopores in single-layer graphene (SLG) can allow one to realize high-performance gas separation even from similar-sized molecules. We advance toward this goal by developing two etching regimes for SLG where the incorporation of angstrom-scale vacancy defects can be controlled. We screen several exposure profiles for the etchant, controlled by a multipulse millisecond treatment, using a mathematical model predicting the nucleation and pore expansion rates. The screened profiles yield a narrow pore-size-distribution (PSD) with a majority of defects smaller than missing 16 carbon atoms, suitable for CO₂/N₂ separation, attributing to the reduced pore expansion rate at a high pore density. Resulting nanoporous SLG (N-SLG) membranes yield attractive CO₂ permeance of 4400 ± 2070 GPU and CO₂/N₂ selectivity of 33.4 ± 7.9. In the second etching regime, by limiting the supply of the etchant, the nanopores are allowed to expand while suppressing the nucleation events. Extremely attractive carbon capture performance marked with CO₂ permeance of 8730 GPU, and CO₂/N₂ selectivity of 33.4 is obtained when CO₂-selective polymeric chains are functionalized on the expanded nanopores. We show that the etching strategy is uniform and scalable by successfully fabricating high-performance centimeter-scale membrane.

Graphitization with Suppressed Carbon Loss for High-Quality Reduced Graphene Oxide

An efficient reduction method to obtain high-quality graphene sheets from mass-producible graphene oxide is highly desirable for practical applications. Here, we report an in situ deoxidation and graphitization mechanism for graphene oxide that allows for high-quality reduced graphene oxide sheets under the low temperature condition (<300 °C) by utilizing a well-known Fischer-Tropsch reaction catalyst (CuFeO₂). By applying modified FTR conditions, where graphene oxide was reduced on the catalyst surface under the hydrogen-poor condition, deoxidation with much suppressed carbon loss was possible, resulting in high-quality graphene sheets. Our experimental data and density functional theory calculations proved that reduction which occurred on the CuFeO₂ surface preferentially removed adsorbed oxygen atoms in graphene oxide sheets, leaving dissociated carbon structures to be restored to a near-perfect few-layer graphene sheet. TGA-mass data revealed that GO with catalysts released 92.8% less carbon-containing gases than GO without catalysts during the reduction process, which suggests that this process suppressed carbon loss in graphene oxide sheets, leading to near-perfect graphene. The amount of oxygen related to the epoxide group in the basal plane of GO significantly decreased to near zero (from 43.84 to 0.48 at. %) in catalyst-assisted reduced graphene oxide (CA-rGO). The average domain size and the density of defects of CA-rGO were 4 times larger and 0.1 times lower than those for thermally reduced graphene oxide (TrGO), respectively. As a result, CA-rGO had a 246 and 8 times lower electrical resistance than TrGO and CVD-graphene. With these performances, CA-rGO coated paper connected to a coin-cell battery successfully lit an LED bulb, and CA-rGO itself acted as an efficient catalyst for both the hydrogen evolution reaction and the oxygen evolution reaction.

Molecular dynamics study of the pore formation in single layer graphene oxide by a thermal reduction process

Nanoporous graphene is considered the next-generation material for reverse osmosis water desalination providing both high water permeability and almost complete salt rejection. The main problem with graphene is the difficulty of synthesizing membranes with a consistent subnanometer pore size distribution. A recently proposed solution involves processing as-grown graphene oxide (GO) monolayers via a mild temperature annealing pre-treatment causing GO functional groups to cluster into small oxidized islands. A following harsh thermal reduction process creates pores only in the small oxidized regions. However, a suitable relationship between the area of the GO islands and the pore dimension is still missing. Here, we study in detail the effects of such a thermal reduction process on the graphene oxide sheet by means of molecular dynamics simulations, particularly highlighting and analysing the process parameters affecting the final pore area. Besides proving that epoxides represent the most suitable functional group to induce carbon removal and, thus, pore generation in reduced GO, we find a twofold way to achieve control over the pore size: tuning the dimension and shape of the initial clustered GO areas or changing the harsh reduction process temperature. An accurate balance of these parameters consistently gives rise to targeted pore dimensions in graphene membranes.

Self-assembled graphene-based microfibers with eclectic optical properties

The construction of graphene-based microfibers with reinforced mechanical and electrical properties has been the subject of numerous researches in recent years. However, the fabrication of graphene-based fibers with remarkable optical features still remains a challenge and has not been addressed so far. This paper aims to report a series of flexible self-assembled fibers, synthesized through a few-minute sonication of thermally oxidized graphene oxide nanosheets, so-called Nanoporous Over-Oxidized Graphene (NOG), in an acidic medium. These free-standing glassy fibers were classified into four distinct morphological structures and displayed a collection of intriguing optical properties comprising high transparency, strong birefringence, fixed body colorations (e.g. colorless, blue, green, and red), tunable interference marginal colorations, UV-visible-near IR fluorescence, and upconversion emissions. Moreover, they exhibited high chemical stability in strongly acidic, basic, and oxidizing media. The foregoing notable attributes introduce the NOG fiber as a promising candidate both for the construction of graphene-based photoluminescent textiles and the development of a wide variety of optical applications.

Plasma Assisted Reduction of Graphene Oxide Films

The past decade has seen enormous efforts in the investigation and development of reduced graphene oxide (GO) and its applications. Reduced graphene oxide (rGO) derived from GO is known to have relatively inferior electronic characteristics when compared to pristine graphene. Yet, it has its significance attributed to high-yield production from inexpensive graphite, ease of fabrication with solution processing, and thus a high potential for large-scale applications and commercialization. Amongst several available approaches for GO reduction, the mature use of plasma technologies is noteworthy. Plasma technologies credited with unique merits are well established in the field of nanotechnology and find applications across several fields. The use of plasma techniques for GO development could speed up the pathway to commercialization. In this report, we review the state-of-the-art status of plasma techniques used for the reduction of GO-films. The strength of various techniques is highlighted with a summary of the main findings in the literature. An analysis is included through the prism of chemistry and plasma physics.

Building with graphene oxide: effect of graphite nature and oxidation methods on the graphene assembly

During nearly 2 centuries of history in graphene researches, numerous researches were reported to synthesize graphene oxide (GO) and build a proper graphene assembly. However, tons of research prevail without verifying the reproducibility of GO that can be sensitively attributed by the graphite nature, and chemical processes. Here, the structure and chemistry of GO products were analyzed by considering parent graphite sources, and three different oxidation methods based on Hummer's method and the addition of H3PO4. The oxidation level of GO was characterized by monitoring the C/O and sp2 carbon ratio from X-ray photoelectroscopy (XPS) spectra. It was observed that the oxidant intercalation behavior was dependent on the morphological differences of graphite; synthetic and natural flake graphite were compared based on their origins in shape and size from different suppliers. Thermal reduction and exfoliation were applied to GO powders to prepare thermally expanded graphene oxide (TEGO) as a graphene assembly. Gas releases from the reduction of oxygen functional groups split layered GO structure and build a porous structure that varied specific surface area regarding oxidation degrees of GO.

Nanoscale patterning at the Si/SiO2/graphene interface by focused He+ beam

We have studied the capability of He⁺ focused ion beam (He⁺-FIB) patterning to fabricate defect arrays on the Si/SiO₂/Graphene interface using a combination of atomic force microscopy (AFM) and Raman imaging to probe damage zones. In general, an amorphized 'blister' region of cylindrical symmetry results upon exposing the surface to the stationary focused He⁺ beam. The topography of the amorphized region depends strongly on the ion dose, D_S , (ranging from 10³ to 10⁷ions/spot) with craters and holes observed at higher doses. Furthermore, the surface morphology depends on the distance between adjacent irradiated spots, L_S . Increasing the dose leads to (enhanced) subsurface amorphization and a local height increase relative to the unexposed regions. At the highest areal ion dose, the average height of a patterned area also increases as ∼1/L_S . Correspondingly, in optical micrographs, the µm²-sized patterned surface regions change appearance. These phenomena can be explained by implantation of the He⁺ ions into the subsurface layers, formation of helium nanobubbles, expansion and modification of the dielectric constant of the patterned material. The corresponding modifications of the terminating graphene monolayer have been monitored by micro Raman imaging. At low ion doses, D_S , the graphene becomes modified by carbon atom defects which perturb the 2D lattice (as indicated by increasing D/G Raman mode ratio). Additional x-ray photoionization spectroscopy (XPS) measurements allow us to infer that for moderate ion doses, scattering of He⁺ ions by the subsurface results in the oxidation of the graphene network. For largest doses and smallest L_S values, the He⁺ beam activates extensive Si/SiO₂/C bond rearrangement and a multicomponent material possibly comprising SiC and silicon oxycarbides, SiOC, is observed. We also infer parameter ranges for He⁺-FIB patterning defect arrays of potential use for pinning transition metal nanoparticles in model studies of heterogeneous catalysis.

Laser photonic-reduction stamping for graphene-based micro-supercapacitors ultrafast fabrication

Micro-supercapacitors are promising miniaturized energy storage devices that have attracted considerable research interest. However, their widespread use is limited by inefficient microfabrication technologies and their low energy density. Here, a flexible, designable micro-supercapacitor can be fabricated by a single pulse laser photonic-reduction stamping. A thousand spatially shaped laser pulses can be generated in one second, and over 30,000 micro-supercapacitors are produced within 10 minutes. The micro-supercapacitor and narrow gaps were dozens of microns and 500 nm, respectively. With the unique three-dimensional structure of laser-induced graphene based electrode, a single micro-supercapacitor exhibits an ultra-high energy density (0.23 Wh cm⁻³), an ultra-small time constant (0.01 ms), outstanding specific capacitance (128 mF cm⁻² and 426.7 F cm⁻³) and a long-term cyclability. The unique technique is desirable for a broad range of applications, which surmounts current limitations of high-throughput fabrication and low energy density of micro-supercapacitors.

Microfabrication for cost-effective miniaturized energy storage devices remains a challenge. Here, the authors propose a spatially shaped femtosecond laser method, which is ultrafast, one-step, high resolution and large-scale, for use in patterning flexible high-performance micro-supercapacitors.

Oxidation of Arsenite by Epoxy Group on Reduced Graphene Oxide/Metal Oxide Composite Materials

Reduced graphene oxide/metal oxide (rGO/MO) hybrid has been widely used as a catalyst, while dissolved oxygen or radicals are generally recognized as the oxidant. This study finds that the adsorbed arsenite (As(III)) on rGO/MO is oxidized to arsenate (As(V)) in the absence of other oxidants or radicals. The oxidation of As(III) is observed on varying rGO/MOs, including rGO/MOs composited of different types of reduced graphene oxide (rGO) and metal oxide. The epoxy group on rGO acts as the oxidant, evidenced by the significant correlation between the consumption of epoxy group and oxidation of As(III). Meanwhile, metal oxide provides adsorption sites for As(III) during the adsorption-oxidation process. Based on a combination of spectroscopic measurements and computational calculation, a possible pathway for As(III) oxidation by rGO/MO is proposed: the oxygen atom in the epoxy group is bonded to the adsorbed AsIIIO3, which is consequently oxidized to AsVO4. Overall, this study proves the role of rGO/MO as an oxidant, which opens a new perspective on future studies using rGO/MO as a catalyst for the oxidation reaction.

Surface chemistry of graphene and graphene oxide: A versatile route for their dispersion and tribological applications

Graphene, the most promising material of the decade, has attracted immense interest in a diversified range of applications. The weak van der Waals interaction between adjacent atomic-thick lamellae, excellent mechanical strength, remarkable thermal conductivity, and high surface area, make graphene a potential candidate for tribological applications. However, the use of graphene as an additive to liquid lubricants has been a major challenge because of poor dispersibility. Herein, a thorough review is presented on preparation, structural models, chemical functionalization, and dispersibility of graphene, graphene oxide, chemically-functionalized graphene, and graphene-derived nanocomposites. The graphene-based materials as additives to water and lubricating oils improved the lubrication properties by reducing the friction, protecting the contact interfaces against the wear, dissipating the heat from tribo-interfaces, and mitigating the corrosion by forming the protecting thin film. The dispersion stability, structural features, and dosage of graphene-based dispersoids, along with contact geometry, play important roles and govern the tribological properties. The chemistry of lubricated surfaces is critically reviewed by emphasizing the graphene-based thin film formation under the tribo-stress, which minimizes the wear. The comprehensive review provides variable approaches for the development of high-performance lubricant systems and accentuates the lubrication mechanisms by highlighting the role of graphene-based materials for enhancement of tribological properties.

New fabrication method for producing reduced graphene oxide flexible electrodes by using a low-power visible laser diode engraving system

The fabrication of bendable electronic devices is a scientific-technological area of very rapid advance in which new materials and fabrication techniques are being continuously developed. In these kinds of devices, the fabrication of flexible conductive electrodes adherent to the substrate is a key factor. Further, eco-friendliness, low cost and fast production are essential requirements for the successful progress of new technologies. In this work, a novel method for obtaining graphene-based flexible electrodes is presented. Conductive films were obtained by means of the visible laser irradiation of graphene oxide layers deposited on polyethylene terephthalate substrates and self-standing membranes sandwiched between glass slides. Despite the low power of the laser system, the numerical simulations indicate the development of temperatures over 1000 K throughout the irradiated material. The laser-induced spatially confined heating leads to the reduction of the graphene oxide material, whereas the glass-based sandwich assembly avoids reoxidation from the surrounding air. By scanning and pixelated modes, reduced graphene oxide electrodes, up to 100 μm in thickness, and with a resistivity as low as 6 × 10^-4 Ωm, were obtained in an easy and versatile way. Proof-of-concept microsupercapacitors and electrochemical sensors were fabricated with this technique, showing promising performance.

Customizing the reduction of individual graphene oxide flakes for precise work function tuning with meV precision

Being able to precisely control the reduction of two-dimensional graphene oxide films will open exciting opportunities for tailor-making the functionality of nanodevices with on-demand properties. Here we report the meticulously controlled reduction of individual graphene oxide flakes ranging from single to seven layers through controlled laser irradiation. It is found that the reduction can be customized in such a precise way that the film thickness can be accurately thinned with sub-nanometer resolution, facilitated by extraordinary temperature gradients >102 K nm-1 across the interlayers of graphene oxide films. Such precisely controlled reduction provides important pathways towards precision nanotechnology with custom-designed electrical, thermal, optical and chemical properties. We demonstrate that this can be exploited to fine tune the work function of graphene oxide films with unprecedented precision of only a few milli electronvolts.

Comprehensive Review on Graphene Oxide for Use in Drug Delivery System

Motivated by the accomplishment of carbon nanotubes (CNTs), graphene and graphene oxide (GO) has been widely investigated in the previous studies as an innovative medication nanocarrier for the loading of a variety of therapeutics as well as anti-cancer medications, poor dissolvable medications, antibiotics, antibodies, peptides, DNA, RNA and genes. Graphene provides the ultra-high drug-loading efficiency due to the wide surface area. Graphene and graphene oxide have been widely investigated for biomedical applications due to their exceptional qualities: twodimensional planar structure, wide surface area, chemical and mechanical constancy, sublime conductivity and excellent biocompatibility. Due to these unique qualities, GO applications provide advanced drug transports frameworks and transports of a broad range of therapeutics. In this review, we discussed the latest advances and improvements in the uses of graphene and GO for drug transport and nanomedicine. Initially, we have described what is graphene and graphene oxide. After that, we discussed the qualities of GO as a drug carrier, utilization of GO in drug transport applications, targeted drug transport, transport of anticancer medications, chemical control medicine releasee, co-transport of different medications, comparison of GO with CNTs, nano-graphene for drug transport and at last, we have discussed the graphene toxicity. Finally, we draw a conclusion of current expansion and the potential outlook for the future.

Antibacterial Character of Cationic Polymers Attached to Carbon-Based Nanomaterials

The preparation of hybrid polymeric systems based on carbon derivatives with a cationic polymer is described. The polymer used is a copolymer of a quaternizable methacrylic monomer with another dopamine-based monomer capable of anchoring to carbon compounds. Graphene oxide and graphene as well as hybrid polymeric systems were widely characterized by infrared, Raman and photoemission X-ray spectroscopies, electron scanning microscopy, zeta potential and thermal degradation. These allowed confirming the attachment of copolymer onto carbonaceous materials. Besides, the antimicrobial activity of hybrid polymeric systems was tested against Gram positive Staphylococcus aureus and Staphylococcus epidermidis and Gram negative Escherichia coli and Pseudomonas aeruginosa bacteria. The results showed the antibacterial character of these hybrid systems.