Fabrication of defective graphene oxide for efficient hydrogen production and enhanced 4-nitro-phenol reduction

Thermal conductivity of wrinkled graphene ring with defects

Graphene rings have great prospects in the fields of biological modulators, electrochemical biosensors, and resonators, but are prone to wrinkling which can affect their physical properties. This work establishes a theoretical model predicting the torsional wrinkling behavior of defective monolayer graphene rings, which provides direct understanding and reliable accuracy of the wrinkle levels. Then the thermal conductivity of wrinkled graphene rings is studied considering different wrinkle levels, defect concentrations and radii. It is found that with increased radius, defect concentration and torsional angle, the ratio of wrinkle amplitude to wavelength increases gradually. Vacancy defects and radii have more significant influences on the thermal conductivity than torsional wrinkles. The main influence mechanism of wrinkles and defects on thermal conductivity is revealed by phonon density of state. This work provides theoretical guidance for thermal manipulation based on the wrinkle-tuning approach.

Phonon thermal transport in ferroelectricα-In2Se3 via first-principles calculations

Two-dimensional (2D) ferroelectrics are promising candidates in the field of microelectronics due to their unique properties such as excellent photoelectric responsiveness. However, the thermal properties of 2D ferroelectrics are less investigated. Here, the thickness dependent thermal conductivity in ferroelectricα-In2Se3is systematically investigated by the first-principles method combined with the phonon Boltzmann transport equation. On this basis, the strain and oxidation effects on the thermal conductivity of monolayerα-In2Se3is further studied. The calculation results show that the thermal conductivity has a significant reduction with decreasing film thickness or increasing tensile strain, and the anharmonic phonon-phonon scattering rate is the intrinsic mechanism for the reduction in thermal conductivity. On the other hand, the replacement of Se atoms by O atoms can achieve a bidirectional and wide-range (12×) tuning of thermal conductivity. The increase in specific heat and phonon group velocity is responsible for the thermal conductivity enhancement at high doping levels while that in phonon-phonon scattering rate is responsible for the thermal conductivity reduction at low doping levels. In all cases, acoustic phonons dominate the in-plane thermal transport behavior. These findings broaden our understanding of phonon transport and its control in ferroelectric semiconductorα-In2Se3.

Titanium Carbide (Ti3C2Tx) MXene as Efficient Electron/Hole Transport Material for Perovskite Solar Cells and Electrode Material for Electrochemical Biosensors/Non-Biosensors Applications

Recently, two-dimensional (2D) MXenes materials have received enormous attention because of their excellent physiochemical properties such as high carrier mobility, metallic electrical conductivity, mechanical properties, transparency, and tunable work function. MXenes play a significant role as additives, charge transfer layers, and conductive electrodes for optoelectronic applications. Particularly, titanium carbide (Ti3C2Tx) MXene demonstrates excellent optoelectronic features, tunable work function, good electron affinity, and high conductivity. The Ti3C2Tx has been widely used as electron transport (ETL) or hole transport layers (HTL) in the development of perovskite solar cells (PSCs). Additionally, Ti3C2Tx has excellent electrochemical properties and has been widely explored as sensing material for the development of electrochemical biosensors. In this review article, we have summarized the recent advances in the development of the PSCs using Ti3C2Tx MXene as ETL and HTL. We have also compiled the recent progress in the fabrication of biosensors using Ti3C2Tx-based electrode materials. We believed that the present mini review article would be useful to provide a deep understanding, and comprehensive insight into the research status.

Pd nanoparticles anchored Co-MOF for nitrophenol reduction

Three nitrophenols are among the 126 priority toxic pollutants identified by the US Environmental Protection Agency. Catalyzing hydrogenation is a simple way to convert these toxic nitrophenols into harmless aminophenols. Commercial PdC has excellent catalytic hydrogenation activity but has weaknesses such as high price and low reusability. Here, we fabricated a series of nano-Pd 2D Co-MOF heterostructures and filtered for optimal Co-MOF@Pd0.0012, which contain ultra-low Pd content (0.08 wt%) and recorded high catalytic efficiency for 4-nitrophenol among the reported non-single atom catalyst due to edge and size effects. The TOF value of Co-MOF@Pd0.0012 is 9800 h-1, ∼206 times higher than that of PdC (Pd content, 10 wt%). Furthermore, Co-MOF@Pd0.0012 has been widely applied to catalyze the reduction of various nitrophenol substrates with higher than 99% conversion efficiency and selectivity.

Hydrothermal Synthesis of a Magnesium Vanadate-Functionalized Reduced Graphene Oxide Nanocomposite for an Efficient Photocatalytic Hydrogen Production

Herein, we reported the fabrication of a magnesium vanadate-reduced graphene oxide (Mg3V2O8-rGO) composite. Further, the structural morphology of the as-prepared Mg3V2O8-rGO composite was studied by scanning electron microscopy. Powder X-ray diffraction and energy-dispersive X-ray spectroscopy techniques were also adopted to check the phase purity and elemental composition of the prepared Mg3V2O8-rGO composite. Mg3V2O8-rGO possesses a band gap of 2.98 eV, which prompted us to explore its photocatalytic activity for hydrogen (H2) evolution reaction. The Mg3V2O8-rGO composite demonstrated the generation of a reasonable amount of H2 evolution (97.45 μmol g-1), which is relatively higher than that of pristine Mg3V2O8 (17.45 μmol g-1). This may be attributed to the presence of synergism between Mg3V2O8 and rGO. In addition, Mg3V2O8-rGO also showed good stability and suggested its potential application for photocatalytic H2 evolution applications. So far, no report is available on the use of Mg3V2O8-rGO as a photocatalyst for H2 evolution. We propose the potential role of the Mg3V2O8-rGO composite for photocatalytic H2 evolution applications.

Ag NPs decorated on the magnetic rod-like hydroxyapatite/MIL-101(Fe) nanocomposite as an efficient catalyst for the reduction of some nitroaromatic compounds and as an effective antimicrobial agent

A rod-like magnetic nanocomposite was successfully synthesized in this work by loading Ag and Fe₃O₄ nanoparticles onto the surface of the hydroxyapatite/MIL-101(Fe) metal-organic framework. Various techniques were used to investigate the crystalline nature, size, morphology, and magnetic and structural properties of the HAP/MIL-101(Fe)/Ag/Fe₃O₄ nanocomposite, including X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), BET surface area measurements, and zeta potential analysis. The results indicate that the nanocomposite sample is composed of Ag and Fe₃O₄ nanoparticles adhered to rod-like hydroxyapatite/MIL-101(Fe). The catalytic and antibacterial abilities of the as-prepared HAP/MIL-101(Fe)/Ag/Fe₃O₄ were studied. This nanocomposite was utilized as a heterogeneous catalyst for the catalytic reduction of toxic pollutants, including 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), 2,4-dinitrophenol (2,4-NP), 4-nitroaniline (4-NA), and 2-nitroaniline (2-NA) by NaBH₄ in water and at room temperature. These compounds were converted to their amine derivatives within 8-18 min with rate constant values equal to 0.2, 0.3, 0.33, and 0.47 min^-1, respectively. This quaternary magnetic catalyst can be easily separated from the reaction medium using an external magnetic field and reused. The synthesized nanocomposite maintained its efficiency in reducing nitroaromatic compounds after 5 runs, showing the high stability of the catalyst. Besides, the antibacterial activity of the nanocomposite against Gram-negative and Gram-positive bacteria was evaluated using the disk diffusion method. The inhibition zone diameter of the nanocomposite against Staphylococcus aureus, Staphylococcus saprophyticus, and Escherichia coli was measured to be 17, 14, and 12 mm, respectively.

Boosting the Catalytic Performance of AuAg Alloyed Nanoparticles Grafted on MoS2 Nanoflowers through NIR-Induced Light-to-Thermal Energy Conversion

MoS₂ nanoflowers (NFs) obtained through a hydrothermal approach were used as the substrate for the deposition of tiny spherical bimetallic AuAg or monometallic Au nanoparticles (NPs), leading to novel photothermal-assisted catalysts with different hybrid nanostructures and showing improved catalytic performance under NIR laser irradiation. The catalytic reduction of pollutant 4-nitrophenol (4-NF) to the valuable product 4-aminophenol (4-AF) was evaluated. The hydrothermal synthesis of MoS₂ NFs provides a material with a broad absorption in the Vis-NIR region of the electromagnetic spectrum. The in situ grafting of alloyed AuAg and Au NPs of very small size (2.0-2.5 nm) was possible through the decomposition of organometallic complexes [Au₂Ag₂(C₆F₅)₄(OEt₂)₂]_n and [Au(C₆F₅)(tht)] (tht = tetrahydrothiophene) using triisopropilsilane as reducing agent, leading to nanohybrids 1-4. The new nanohybrid materials display photothermal properties arising from NIR light absorption of the MoS₂ NFs component. The AuAg-MoS₂ nanohybrid 2 showed excellent photothermal-assisted catalytic activity for the reduction of 4-NF, which is better than that of the monometallic Au-MoS₂ nanohybrid 4. The obtained nanohybrids were characterised by transmission electron microscopy (TEM), High Angle Annular Dark Field-Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (HAADF-STEM-EDS), X-ray photoelectron spectroscopy and UV-Vis-NIR spectroscopy.

Microbial cellulase production and stability investigations via graphene like carbon nanostructure derived from paddy straw

Cellulases are among the most in-demand bioprocess enzymes, and the high cost of production, combined with their low enzymatic activity, is the main constraint, particularly in the biofuels industry. As a result, low-cost enzyme production modes with high activity and stability have emerged as the primary focus of research. Here, a method for producing a graphene like carbon nanostructure (GLCNs) has been investigated utilizing paddy straw (Ps), and its physicochemical characteristics have been examined using a variety of techniques including XRD, FT-IR, SEM and TEM. Further, the pretreatment of Ps feedstock for cellulase production was done using diluted waste KOH liquid collected during the preparation of the GLCNs. To increase the production and stability of the enzyme, newly prepared GLCNs is utilized as a nanocatalyst. Using 15 mg of GLCNs, 35 IU/gds FP activity was seen after 72 h, followed by 158 IU/gds EG and 114 IU/gds BGL activity in 96 h. This nanocatalyst supported enzyme was thermally stable at 70 °C up to 15 h and exhibited stability at pH 7.0 for 10 h by holding 66 % of its half-life.

Hydrothermal Synthesis of 1T-MoS2/Pelagic Clay Composite and Its Application in the Catalytic Reduction of 4-Nitrophenol

Pelagic clay is an emerging marine resource with strong hydrophilicity, fine particles and a large specific surface area. In this work, a 1T-MoS2/pelagic clay composite was fabricated by hydrothermal synthesis. In the composite, 1T-MoS2 nanosheets are evenly dispersed on the surface of the clay minerals, significantly reducing the agglomeration of MoS2. Compared with pure 1T-MoS2, the 1T-MoS2 nanosheets generated on the surface of pelagic clay have significantly smaller lateral dimensions and thicknesses. Moreover, the specific surface area is much larger than that of the pure 1T-MoS2 nanosheets fabricated by the same method, indicating that the active sites of the MoS2 sheets are fully exposed. In addition, the composite exhibited excellent hydrophilicity, leading to a high dispersibility in aqueous solutions. In this work, the composite was used as a catalyst in the reduction of 4-nitrophenol (4-NP), and the conversion of 4-NP reached up to 96.7%. This result shows that the 1T-MoS2/pelagic clay composite is a promising catalyst in a variety of reactions.