Correlation between X-ray diffraction and Raman spectra of 16 commercial graphene-based materials and their resulting classification

One-step synthesis of a core-shell structured biochar using algae (Chlorella) powder and ferric sulfate for immobilizing Hg(II)

Mercury (Hg) pollution poses a significant environmental challenge. One promising method for its removal is the sorption of mercuric ions using biochar. FeS-doped biochar (FBC) exhibits effective mercury adsorption, however may release excess iron into the surrounding water. To address this issue, a novel magnetic pyrrhotite/magnetite-doped biochar with a core-shell structure was synthesized for the adsorption of 2-valent mercury (Hg(II)). The proposed synthesis process involved the use of algae powder and ferric sulfate in a one-step method. By varying the ratio of ferric sulfate and alga powder (within the range of 0.18 - 2.5) had a notable impact on the composition of FBC. As the ferric sulfate content increased, the FBC exhibited a higher concentration of oxygen-containing groups. To assess the adsorption capacity, Langmuir and Freundlich adsorption models were applied to the experimental data. The most effective adsorption was achieved with FBC-4, reaching a maximum capacity (Qm) of 95.51 mg/g. In particular, at low Hg(II) concentrations, FBC-5 demonstrated the ability to reduce Hg(II) concentrations to less than 0.05 mg/L within 30 min. Additionally, the stability of FBC was confirmed within the pH range of 3.8 - 7.2. The study also introduced a model to analyze the adsorption preference for different Hg(II) species. Calomel was identified in the mercury saturated FBC, whereas the core-shell structure exhibited excellent conductivity, which most likely contributed to the minimal release of iron. In summary, this research presents a novel and promising method for synthesizing core-shell structured biochar and provides a novel approach to explore the adsorption contribution of different metal species.

An all-in-one FeOx-rGO sponge fabricated by solid-phase microwave thermal shock for water evaporation and purification

Developing high-efficiency photothermal seawater desalination devices is of significant importance in addressing the shortage of freshwater. Despite much effort made into photothermal materials, there is an urgent need to design a rapidly synthesized photothermal evaporator for the comprehensive purification of complex seawater. Therefore, we report on all-in-one FeOx-rGO photothermal sponges synthesized via solid-phase microwave thermal shock. The narrow band gap of the semiconductor material Fe3O4 greatly reduces the recombination of electron-hole pairs, enhancing non-radiative relaxation light absorption. The abundant π orbitals in rGO promote electron excitation and thermal vibration between the lattices. Control of the surface hydrophilicity and hydrophobicity promotes salt resistance while simultaneously achieving the purification of various complex polluted waters. The optimized GFM-3 sponge exhibitedan enhanced photothermal conversion rate of 97.3% and a water evaporation rate of 2.04 kg/(m2·hr), showing promising synergistic water purification properties. These findings provide a highly efficient photothermal sponge for practical applicationsof seawater desalination and purification,as well as develop a super-rapid processing methodology for evaporation devices.

Investigating the Performance of Lithium-Doped Bismuth Ferrite [BiFe1−xLixO3]-Graphene Nanocomposites as Cathode Catalyst for the Improved Power Output in Microbial Fuel Cells

In this study, multifunctional lithium-doped bismuth ferrite [BiFe1−xLixO3]-graphene nanocomposites (x = 0.00, 0.02, 0.04, 0.06) were synthesized by a sol-gel and ultrasonication assisted chemical reduction method. X-ray diffraction and FESEM electron microscopy techniques disclosed the nanocomposite phase and nanocrystalline nature of [BiFe1−xLixO3]-graphene nanocomposites. The FESEM images and the EDX elemental mapping revealed the characteristic integration of BiFe1−xLixO3 nanoparticles (with an average size of 95 nm) onto the 2D graphene layers. The Raman spectra of the [BiFe1−xLixO3]-graphene nanocomposites evidenced the BiFe1−xLixO3 and graphene nanostructures in the synthesized nanocomposites. The photocatalytic performances of the synthesized nanocomposites were assessed for ciprofloxacin (CIP) photooxidation under UV-visible light illumination. The photocatalytic efficiencies of [BiFe1−xLixO3]-graphene nanocomposites were measured to be 42%, 47%, 43%, and 10%, for x = 0.00, 0.02, 0.04, 0.06, respectively, within 120 min illumination, whereas the pure BiFeO3 nanoparticles were 21.0%. BiFe1−xLixO3 nanoparticles blended with graphene were explored as cathode material and tested in a microbial fuel cell (MFC). The linear sweep voltammetry (LSV) analysis showed that the high surface area of BiFeO3 was attributed to efficient oxygen reduction reaction (ORR) activity. The increasing loading rates of (0.5–2.5 mg/cm2) [BiFe1−xLixO3]-graphene composite on the cathode surface showed increasing power output, with 2.5 and 2 mg/cm2 achieving the maximum volumetric power density of 8.2 W/m3 and 8.1 W/m3, respectively. The electrochemical impedance spectroscopy (EIS) analysis showed that among the different loading rates used in this study, BiFeO3, with a loading rate of 2.5 mg/cm2, showed the lowest charge transfer resistance (Rct). The study results showed the potential of [BiFe1−xLixO3]-graphene composite as a cost-effective alternative for field-scale MFC applications.

Electrochemical Exfoliation of Graphite to Graphene-Based Nanomaterials

Here, we report on a new automated electrochemical process for the production of graphene oxide (GO) from graphite though electrochemical exfoliation. The effects of the electrolyte and applied voltage were investigated and optimized. The morphology, structure and composition of the electrochemically exfoliated GO (EGO) were probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy and Raman spectroscopy. Important metrics such as the oxygen content (25.3 at.%), defect density (I_D/I_G = 0.85) and number of layers of the formed EGO were determined. The EGO was also compared with the GO prepared using the traditional chemical method, demonstrating the effectiveness of the automated electrochemical process. The electrochemical properties of the EGO, CGO and other carbon-based materials were further investigated and compared. The automated electrochemical exfoliation of natural graphite powder demonstrated in the present study does not require any binders; it is facile, cost-effective and easy to scale up for a large-scale production of graphene-based nanomaterials for various applications.

Development and Up-Scaling of Electrochemical Production and Mild Thermal Reduction of Graphene Oxide

To reduce the global emissions of CO2, the aviation industry largely relies on new light weight materials, which require multifunctional coatings. Graphene and its derivatives are particularly promising for combining light weight applications with functional coatings. Although they have proven to have outstanding properties, graphene and its precursor graphene oxide (GO) remain far from application at the industrial scale since a comprehensive protocol for mass production is still lacking. In this work, we develop and systematically describe a sustainable up-scaling process for the production of GO based on a three-step electrochemical exfoliation method. Surface characterization techniques (XRD, XPS and Raman) allow the understanding of the fast exfoliation rates obtained, and of high conductivities that are up to four orders of magnitude higher compared to GO produced via the commonly used modified Hummers method. Furthermore, we show that a newly developed mild thermal reduction at 250 °C is sufficient to increase conductivity by another order of magnitude, while limiting energy requirements. The proposed GO powder protocol suggests an up-scaling linear relation between the amount of educt surface and volume of electrolyte. This may support the mass production of GO-based coatings for the aviation industry, and address challenges such as low weight, fire, de-icing and lightning strike protection.

3D-printed NiFe-layered double hydroxide pyramid electrodes for enhanced electrocatalytic oxygen evolution reaction

Electrochemical water splitting has been considered one of the most promising methods of hydrogen production, which does not cause environmental pollution or greenhouse gas emissions. Oxygen evolution reaction (OER) is a significant step for highly efficient water splitting because OER involves the four electron transfer, overcoming the associated energy barrier that demands a potential greater than that required by hydrogen evolution reaction. Therefore, an OER electrocatalyst with large surface area and high conductivity is needed to increase the OER activity. In this work, we demonstrated an effective strategy to produce a highly active three-dimensional (3D)-printed NiFe-layered double hydroxide (LDH) pyramid electrode for OER using a three-step method, which involves direct-ink-writing of a graphene pyramid array and electrodeposition of a copper conducive layer and NiFe-LDH electrocatalyst layer on printed pyramids. The 3D pyramid structures with NiFe-LDH electrocatalyst layers increased the surface area and the active sites of the electrode and improved the OER activity. The overpotential (η) and exchange current density (i₀) of the NiFe-LDH pyramid electrode were further improved compared to that of the NiFe-LDH deposited Cu (NiFe-LDH/Cu) foil electrode with the same base area. The 3D-printed NiFe-LDH electrode also exhibited excellent durability without potential decay for 60 h. Our 3D printing strategy provides an effective approach for the fabrication of highly active, stable, and low-cost OER electrocatalyst electrodes.

A probe-free electrochemical immunosensor for methyl jasmonate based on a Cu-MOF–carboxylated graphene oxide platform

A probe-free electrochemical immunosensor for methyl jasmonate has been developed based on a Cu-MOF-carboxylated graphene oxide platform.

Exploration of the Cs Trapping Phenomenon by Combining Graphene Oxide with α-K6P2W18O62 as Nanocomposite

A graphene oxide-based α-K₆P₂W₁₈O₆₂ (Dawson-type polyoxometalate) nanocomposite was formed by using two types of graphene oxide (GO) samples with different C/O compositions. Herein, based on the interaction of GO, polyoxometalates (POMs), and their nanocomposites with the Cs cation, quantitative data have been provided to explicate the morphology and Cs adsorption character. The morphology of the GO-POM nanocomposites was characterized by using TEM and SEM imaging. These results show that the POM particle successfully interacted above the surface of GO. The imaging also captured many small black spots on the surface of the nanocomposite after Cs adsorption. Furthermore, ICP-AES, the PXRD pattern, IR spectra, and Raman spectra all emphasized that the Cs adsorption occurred. The adsorption occurred by an aggregation process. Furthermore, the difference in the C/O ratio in each GO sample indicated that the ratio has significantly influenced the character of the GO-POM nanocomposite for the Cs adsorption. It was shown that the oxidized zone (sp²/sp³ hybrid carbon) of each nanocomposite sample was enlarged by forming the nanocomposite compared to the corresponding original GO sample. The Cs adsorption performance was also influenced after forming a composite. The present study also exhibited the fact that the sharp and intense diffractions in the PXRD were significantly reduced after the Cs adsorption. The result highlights that the interlayer distance was changed after Cs adsorption in all nanocomposite samples. This has a good correlation with the Raman spectra in which the second-order peaks changed after Cs adsorption.

Bamboo Charcoal/Poly(L-lactide) Fiber Webs Prepared Using Laser-Heated Melt Electrospinning

Although several studies have reported that the addition of bamboo charcoal (BC) to polylactide (PLA) enhances the properties of PLA, to date, no study has been reported on the fabrication of ultrafine BC/poly(L-lactide) (PLLA) webs via electrospinning. Therefore, ultrafine fiber webs of PLLA and BC/PLLA were prepared using PLLA and BC/PLLA raw fibers via a novel laser electrospinning method. Ultrafine PLLA and BC/PLLA fibers with average diameters of approximately 1 μm and coefficients of variation of 13–23 and 20–46% were obtained. Via wide-angle X-ray diffraction (WAXD) analysis, highly oriented crystals were detected in the raw fibers; however, WAXD patterns of both PLLA and BC/PLLA webs implied an amorphous structure of PLLA. Polarizing microscopy images revealed that the webs comprised ultrafine fibers with uniform diameters and wide variations in birefringence. Temperature-modulated differential scanning calorimetry measurements indicated that the degree of order of the crystals in the fibers was lower and the molecules in the fibers had higher mobilities than those in the raw fibers. Transmittance of BC/PLLA webs with an area density of 2.6 mg/cm² suggested that the addition of BC improved UV-shielding efficiencies.

Electrochemical detector based on a modified graphite electrode with phthalocyanine for the elemental analysis of actinides

The quantification of actinides in aqueous solutions involves complex and expensive separation processes. Electrochemical methods have been widely used for the quick and accurate identification and quantification of organic and inorganic compounds directly or indirectly. Therefore, this work proposes the use of modified graphite with phthalocyanine for electrochemical detection and quantification of Th, U, Pu, Am, and Cm, in aqueous media by cyclic voltammetry. The electrodes were characterized by Raman and infrared spectroscopy, and the cyclic voltammetry data were modeled with Aoki's model. The detection limits (DL) and the quantification limits (QL) reached by the electrochemical detection of these actinides were of the order of ppt. Aoki's model fitted perfectly with the experimental data. The functionalization of graphite electrodes promotes the formation of phthalic anhydride, and the phthalocyanine is anchored on the epoxy groups of the graphite. The electrochemical detection process of these actinides is indirect. This electrochemical detector is cheap and disposable and can be an alternative for an initial characterization of actinides in liquid waste.

Response of free-standing graphene monolayer exposed to ultrashort intense XUV pulse from free-electron laser

The response of a free-standing graphene monolayer exposed to a few tens of femtoseconds long extreme ultraviolet (XUV) pulse was studied theoretically in order to analyze and compare contributions of various mechanisms to the graphene damage, understood here as a global atomic disintegration. Our simulation results indicate that nonthermal disintegration of the atomic structure is the predominant damage mechanism for a free-standing graphene layer. Only at high absorbed doses, charge-induced disintegration of the graphene structure prevails. We also demonstrate that the progressing damage can be probed by femtosecond optical pulses in the soft UV regime (4 eV photon energy). The achieved quantitative understanding of the damage mechanisms may enable a better control of graphene-based devices when they are exposed to x-ray radiation, as well as an efficient processing of graphene layers with ultrashort intense XUV pulses.

Effect of KOH on the Energy Storage Performance of Molasses-Based Phosphorus and Nitrogen Co-Doped Carbon

In this study, we have evaluated the effect of potassium hydroxide (KOH) on the energy storage performance of metal-free carbon-based materials prepared from molasses. Molasses are a renewable-resource biomass and economical by-product of sugar refinement, used here as a carbon precursor. Two co-doped carbon materials using molasses were synthesized via a time and cost-efficient microwave carbonization process, with ammonium polyphosphate as a phosphorus and nitrogen doping agent. The phosphorus and nitrogen co-doped carbon (PNDC) samples were prepared in the presence and absence of a chemical activating agent (KOH), to study the role of chemical activation on PNDCs. Physical characterizations were performed to gain insight into the composition, pore size and topographical data of each material. Electrochemical characterization via cyclic voltammetry in 1 M sulfuric acid (H2SO4) as well as in 6 M KOH as electrolytes, revealed high current density and specific capacitance for the chemically activated material (PNDC2) compared to one without chemical activation (PNDC1). The capacitance value of 244 F/g in KOH electrolyte was obtained with PNDC2. It is concluded that addition of KOH prior to carbonization increases the surface functionality, which significantly enhances the electrochemical properties of the PNDC material such as current density, stability, and specific capacitance.

Superlow Wear Realizable Tribofilms from Lubricant Oil Containing Hydrothermally Synthesized Magnesium Silicate Hydroxide/Carbon Core-Shell Nanoplates

This paper reports on the hydrothermal synthesis of a novel 2D material, magnesium silicate hydroxide/carbon (MSH/C) core-shell nanoplate, in a graphite-MgO-SiO₂-NaOH system at 300 °C and 12 MPa for 48 h. Its significant potentials as an antiwear additive in lubricant oil were subsequently demonstrated. The 2D nanoplates consist of an MSH core and a 1-6 nm thick sp²-hybridized carbon shell with a layer spacing of 0.34 nm. In typical four-ball tests at a maximum Hertzian pressure of 3.4 GPa, the MSH/C core-shell nanoplates nearly eliminated wear, whether suspended in poly alpha-olefin oil or fully formulated lubricating oil, and the corresponding volume wear rates were reduced by 96.33% and 72%, respectively. The excellent antiwear performance was ascribed to the formation of a tribofilm consisting of diffusedly distributed Fe₃O₄ nanocrystals and carbon- and/or SiO_x-containing amorphous structures.

Synthesis and Electrochemical Study of Three-Dimensional Graphene-Based Nanomaterials for Energy Applications

Graphene is an attractive soft material for various applications due to its unique and exclusive properties. The processing and preservation of 2D graphene at large scales is challenging due to its inherent propensity for layer restacking. Three-dimensional graphene-based nanomaterials (3D-GNMs) preserve their structures while improving processability along with providing enhanced characteristics, which exhibit some notable advantages over 2D graphene. This feature article presents recent trends in the fabrication and characterization of 3D-GNMs toward the study of their morphologies, structures, functional groups, and chemical compositions using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Owing to the attractive properties of 3D-GNMs, which include high surface areas, porous structures, improved electrical conductivity, high mechanical strength, and robust structures, they have generated tremendous interest for various applications such as energy storage, sensors, and energy conversion. This article summarizes the most recent advances in electrochemical applications of 3D-GNMs, pertaining to energy storage, where they can serve as supercapacitor electrode materials and energy conversion as oxygen reduction reaction catalysts, along with an outlook.

Metal-Organic Complexes@Melamine Foam Template Strategy to Prepare Three-Dimensional Porous Carbon with Hollow Spheres Structures for Efficient Organic Vapor and Small Molecule Gas Adsorption

Three-dimensional (3D) porous carbon materials have received substantial attention owing to their unique structural features. However, the synthesis of 3D porous carbon, especially 3D porous carbon with hollow spheres structures at the connection points, still pose challenges. Herein, we first develop a metal-organic complexes@melamine foam (MOC@MF) template strategy, by using hot-pressing and carbonization method to synthesize 3D porous carbon with hollow spheres structures (denoted as NOPCs). The formation mechanism of NOPCs can be attributed to the difference in Laplace pressure and surface energy gradient between the carbonized MOC and carbonized MF. These rare 3D porous carbons exhibit high BET surface area (2453.8 m² g^-1), N contents (10.5%), and O contents (16.3%). Moreover, NOPCs show significant amounts of toluene and methanol at room temperature, reaching as high as 1360 and 1140 mg g^-1. The adsorption amounts of SO₂ and CO₂ for NOPCs are up to 93.1 and 445 mg g^-1. Theoretical calculation indicates surfaces of porous carbon with N and O coexistence could strongly enhance adsorption with high adsorption energy of -65.83 kJ mol g^-1.

High-Sulfur-Content Graphene-Based Composite through Ethanol Evaporation for High-Energy Lithium-Sulfur Battery

Lithium-sulfur batteries are the most promising candidates for next-generation energy storage devices owing to their high theoretical specific capacity of 1675 mAh g^-1 and high theoretical energy density of approximately 3500 Wh kg^-1 . However, the lack of cathode active materials with appropriate electrical conductivities and stability coupled with an inexpensive and industrially compatible production process has so far hindered the development of practical devices. Here, a facile preparation pathway is reported for the production of a sulfur-carbon composite active material by drying a mixture of highly conductive few-layer graphene (FLG) flakes (produced by exploiting an innovative wet jet milling process with a yield of ≈100 % and production capability of ≈23.5 g h^-1 ) with elemental sulfur, using ethanol as an environmentally friendly solvent. The designed sulfur-FLG composite shows excellent electrochemical results. The assembled lithium-sulfur battery exhibits a stable rate capability up to a current rate of 2C, a coulombic efficiency approaching 100 % for 300 cycles at the current rate of C/4 (420 mA g^-1 ), and a long cycle life up to 500 cycles delivering around 600 mAh g^-1 at 2C (3350 mA g^-1 ).

Self-assembly of graphene oxide/PEDOT:PSS nanocomposite as a novel adsorbent for uranium immobilization from wastewater

In recent years, water pollution caused by radionuclides has become a rising concern, among which uranium is a representative class of actinide element. Since hexavalent uranium, i.e. U(VI), is biologically hazardous with high migration, it's essential to develop efficient adsorbents to minimize the impact on the environment. Towards this end, we have synthesized a novel material (GO/PEDOT:PSS) by direct assembling graphene oxide (GO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through a facile ball milling method, which shows impressing performance for the immobilization of U(VI). On the basis of the batch experiments, GO/PEDOT:PSS exhibits ionic strength-independent sorption edges and temperature-promoted sorption isotherms, revealing an inner-sphere complexation with endothermic nature. The sorption kinetics can be illustrated by the pseudo-second-order model, yielding a rate constant of 1.09. × 10^-2 g mg^-1∙min^-1, while the sorption isotherms are in coincidence with the Langmuir model, according to which the maximum sorption capacity is measured to be 384.51 mg g^-1 at pH 4.5 under 298 K, indicating a monolayer sorption mechanism. In the light of the FT-IR and XPS investigations, the surface carboxyl/sulfonate group is responsible to the chelation of U(VI), indicating that the enhanced sorption capacity may be ascribed to the PSS moiety. These findings can greatly contribute to the design strategy for developing highly efficient adsorbents in the field of radioactive wastewater treatment.