Transition metal-doped amorphous molybdenum sulfide/graphene ternary cocatalysts for excellent photocatalytic hydrogen evolution: Synergistic effect of transition metal and graphene

A GO/CoMo3S13 chalcogel heterostructure with rich catalytic Mo-S-Co bridge sites for the hydrogen evolution reaction

Molybdenum disulfide (MoS₂)-based materials are extensively studied as promising hydrogen evolution reaction (HER) catalysts. In order to bring out the full potential of chalcogenide chemistry, precise control over the active sulfur sites and enhancement of electronic conductivity need to be achieved. This study develops a highly active HER catalyst with an optimized active site-controlled cobalt molybdenum sulfide (CoMo₃S₁₃) chalcogel/graphene oxide aerogel heterostructure. The highly active CoMo₃S₁₃ chalcogel catalyst was achieved by the synergetic catalytic sites of [Mo₃S₁₃]^2- and the Mo-S-Co bridge. The optimized GO/CoMo₃S₁₃ chalcogel heterostructure catalyst exhibited high catalytic HER performance with an overvoltage of 130 mV, a current density of 10 mA cm^-2, a small Tafel slope of 40.1 mV dec^-1, and remarkable stability after 12 h of testing. This study presents a successful example of a synergistic heterostructure exploiting both the appealing electrical functionality of GO and catalytically active [Mo₃S₁₃]^2- sites.

Fabrication of visible light active Mn-doped Bi2WO6-GO/MoS2 heterostructure for enhanced photocatalytic degradation of methylene blue

The increase in environmental pollution has led to an increased investigation in the development of novel ternary photocatalytic systems for remediation. These photocatalytic systems exhibit superior photocatalytic action for the removal of pollutants because of their visible light active bandgaps. A highly effective visible light active ternary heterojunction was fabricated using a hydrothermal method assisted by ultrasonication. Herein, we report the in situ hydrothermal synthesis of Mn-doped Bi₂WO_6-GO/ MoS₂ photocatalyst, efficiently exhibiting greater photocatalytic activity for the wastewater treatment under solar light. The binary metal sulphide (MoS₂) used as a co-catalyst, acted as an electron collector and graphene oxide (GO) as a support material for interfacial electron transfer to and from bismuth tungstate and MoS₂. The as-prepared samples were characterized using SEM-EDX, FT-IR, XRD, XPS, BET, PL, and UV-Vis techniques. The bandgap of the novel photocatalyst was found in the visible region (2.2 eV) which helped in suppressing photoinduced electron-hole pairs recombination. The ternary Mn-doped Bi₂WO₆-GO/MoS₂ showed 99% methylene blue removal after 60 minutes of sunlight irradiation at the optimum conditions of pH 8, catalyst dose 50 mg/100ml, and initial MB concentration of 10ppm under sunlight irradiation. The doped ternary heterostructure has proved to be an effective sunlight-active photocatalyst that can be reused without substantial loss in photocatalytic efficiency.

An effective photocatalytic hydrogen evolution strategy based on tunable band gap (CuIn)xZn2(1−x)S2 combined with amorphous molybdenum sulfide

The combination of crystalline band-tunable (CuIn)_xZn_2(1−x)S₂ and amorphous a-MoS_x provides a good strategy for photocatalysts.

Novel Aggregation-Induced Emission Materials/Cadmium Sulfide Composite Photocatalyst for Efficient Hydrogen Evolution in Absence of Sacrificial Reagent

This work focuses on the development of a novel organic–inorganic photoactive material composited by aggregation-induced emission luminogens (AIE) and CdS. Tetraphenylethene-based AIE (TPE-Ca) is synthesized on CdS to form CdS/TPE-Ca electrode, due to its suitable band structure and potential capability of renewable energy production. The CdS/TPE-Ca electrode presents over three-fold improved photocurrent density and dramatically reduced interfacial resistance, compared with the pure CdS electrode. In addition, the engineering of the band alignment allows the holes to accumulate on the valance band of TPE-Ca, which would partially prevent the CdS from photo-corrosion, thus improving the stability of the sacrificial-free electrolyte photoelectrochemical cell.

Production and Properties of Molybdenum Disulfide/Graphene Oxide Hybrid Nanostructures for Catalytic Applications

Molybdenum disulfide (MoS₂) can be an excellent candidate for being combined with carbon nanomaterials to obtain new hybrid nanostructures with outstanding properties, including higher catalytic activity. The aim of the conducted research was to develop the novel production method of hybrid nanostructures formed from MoS₂ and graphene oxide (GO). The nanostructures were synthesized in different weight ratios and in two types of reactors (i.e., impinging jet and semi-batch reactors). Physicochemical analysis of the obtained materials was carried out, using various analytical techniques: particle size distribution (PSD), thermogravimetric analysis (TGA), FT-IR spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Due to the potential application of materials based on MoS₂ as the catalyst for hydrogen evolution reaction, linear sweep voltammetry (LSV) of the commercial MoS₂, synthesized MoS₂ and the obtained hybrid nanostructures was performed using a three-electrode system. The results show that the developed synthesis of hybrid MoS₂/GO nanostructures in continuous reactors is a novel and facile method for obtaining products with desired properties. The hybrid nanostructures have shown better electrochemical properties and higher onset potentials compared to MoS₂ nanoparticles. The results indicate that the addition of carbon nanomaterials during the synthesis improves the activity and stability of the MoS₂ nanoparticles.

Facile Fabrication of SrTiO3@MoS2 Composite Nanofibers for Excellent Photodetector Application

Molybdenum disulfide (MoS2), as a kind of transition metal dichalcogenide, has been widely studied for its excellent compatibility with most of inorganic nanomaterials. Nevertheless, its microscale and agglomeration limit the performance severely. Therefore, the special structure of V-MoS2 has drawn a lot of interest, which can not only reduce the size of MoS2 nanosheets but also improve the valence electron structure of the materials. In this work, SrTiO3@MoS2 composite nanofibers were synthesized by the simple electrospinning and hydrothermal method, and it was applied as a novel material for photodetector. SEM, TEM, EDX, XRD, I-T curves, and EIS analysis were used to study the structure and properties of the prepared SrTiO3@MoS2 composite nanofibers. Simulating under sunlight at a potential of 1.23 V, the prepared composite materials exhibited a superior photoelectric performance of photocurrent density of 21.4 μA and a resistance of 2.3 Ω. These results indicate that the composite of SrTiO3 nanofiber adhered with V-MoS2 has a stable composite structure, good electrical conductivity, and photoelectric sensitivity and is a suitable material for photodetectors. This work provides new ideas for the preparation of self-assembled materials and their application in photodetectors.

A novel hafnium-graphite oxide catalyst for the Meerwein-Ponndorf-Verley reaction and the activation effect of the solvent

Construction and application of novel hydrogenation catalysts is important for the conversion of carbonyl or aldehyde compounds into alcohols in the field of biomass utilization. In this work, a novel, efficient, and easily prepared hafnium-graphite oxide (Hf-GO) catalyst was constructed via the coordination between Hf4+ and the carboxylic groups in GO. The catalyst was applied into the hydrogenation of biomass derived carbonyl compounds via the Meerwein-Ponndorf-Verley (MPV) reaction. The catalyst gave high efficiency under mild conditions. An interesting phenomenon was found whereby the activity of the catalyst increased gradually in the initial stage during reaction. The solvent, isopropanol, was proved to have an activation effect on the catalyst, and the activation effect varied with different alcohols and temperatures. Further characterizations showed that isopropanol played the activation effect via replacing the residual solvent (DMF) in micro- and mesopores during the preparation process, which was hard to be completely removed by common drying process.

Recent Progress on Metal Sulfide Composite Nanomaterials for Photocatalytic Hydrogen Production

Metal sulfide-based photocatalysts have gained much attention due to their outstanding photocatalytic properties. This review paper discusses recent developments on metal sulfide-based nanomaterials for H2 production, acting as either photocatalysts or cocatalysts, especially in the last decade. Recent progress on key experimental parameters, in-situ characterization methods, and the performance of the metal sulfide photocatalysts are systematically discussed, including the forms of heterogeneous composite photocatalysts, immobilized photocatalysts, and magnetically separable photocatalysts. Some methods have been studied to solve the problem of rapid recombination of photoinduced carriers. The electronic density of photocatalysts can be investigated by in-situ C K-edge near edge X-ray absorption fine structure (NEXAFS) spectra to study the mechanism of the photocatalytic process. The effects of crystal properties, nanostructure, cocatalyst, sacrificial agent, electrically conductive materials, doping, calcination, crystal size, and pH on the performance of composite photocatalysts are presented. Moreover, the facet effect and light trapping (or light harvesting) effect, which can improve the photocatalytic activity, are also discussed.