Structural regulation of amorphous molybdenum sulfide by atomic palladium doping for hydrogen evolution

Molybdenum sulfide materials have long been considered as attractive non-precious-metal electrocatalysts for the hydrogen evolution reaction (HER). However, comparing with the crystalline counterpart, amorphous MoSx has been less investigated previously. We here propose to increase the catalytical activity of a-MoSx by raising the reactant concentration at the catalytic interface via a chemical doping approach. The reconstruction of coordination structure of a-MoSx via Pd doping induces the formation of abundant unsaturated S atoms. Moreover, the reactant friendly catalytic interface is constructed through introducing hydrophilic groups to a-MoSx. The doped a-MoSx catalyst exhibits significantly enhanced HER activity in both acid and alkaline media.

Melamine-Ag with dual functions of electrochemiluminescence luminophore and coreactant accelerators: Construction of MIP/M-Ag@MoS2-QDs sensing platform for specific detection of thiabendazole

A novel self-enhancement molecularly imprinted electrochemiluminescence (ECL) sensor (MIP/M-Ag@MoS₂-QDs/GCE) was constructed to detect thiabendazole (TBZ) in food. Melamine was used as template to chelate Ag⁺ to prepare composite nanomaterials (M-Ag). M-Ag possesses both ECL properties and coreactant catalytic properties, which can realize the self-enhancement of ECL luminophore. MoS₂-QDs with excellent edge activity and electrochemical reaction catalytic activity were used to accelerate the reaction rate of the microsystem and further enhance the ECL intensity. The specific detection method of TBZ was established by investigating the ECL response mechanism and specific recognition mechanism of MIP/M-Ag@MoS₂-QDs/GCE. The ECL intensity was proportioned to the lg C_(TBZ) in the linear range 5 × 10^-8 mol L^-1-5 × 10^-5 mol L^-1 with a limit detection of 1.42 × 10^-8 mol L^-1. The satisfactory recovery rate (83.57%-101.03%) was obtained in sample analysis, which was in good agreement with the analysis result of HPLC.

Degradation of lomefloxacin by MoS2/MIL-53(Fe, Cu) catalyst in heterogeneous electro-Fenton process

A novel heterogeneous catalyst named MoS₂/MIL-53(Fe, Cu) (MMFC) was prepared by hydrothermal method and applied in a heterogeneous electro-Fenton (hetero-EF) system for lomefloxacin (LOM) degradation in this work. Under the optimal conditions of current density 3 mA/cm², catalyst dosage 0.100 g/L, and initial pH 6, 93.5% LOM (2 mg/L) removal efficiency was achieved in the MMFC hetero-EF system within 60 min, indicating an obvious improvement compared with the MIL-53(Fe, Cu) hetero-EF system. The good catalytic activity was attributed to more effective active sites of the catalyst and the conversion of Fe(II)/Fe(III) and Cu(I)/Cu(II) promoted by Mo(IV) in MoS₂, which could be inferred by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) characterizations. The reusability and stability of MMFC were explored based on five cyclic experiments, and the average degradation efficiency reached 73.9%. Furthermore, the hetero-EF system could achieve the total removal of moxifloxacin and tetracycline within 6 min and 40 min, respectively. Quenching experiments revealed that the hydroxyl radicals (·OH) were the main reactive radicals while superoxide radicals (·O₂^-) and singlet oxygen (¹O₂) played a certain part in LOM degradation. Finally, the possible mechanism of the hetero-EF process and LOM degradation pathways were proposed, including substitution, elimination, and cleavage of ring structures. Accounting for good catalytic performance, low preparation cost, and satisfactory versatility, the MMFC exhibited good potential to work as a hetero-EF catalyst for wastewater treatment.

Efficient removal of neonicotinoid by singlet oxygen dominated MoSx/ceramic membrane-integrated Fenton-like process

Removal of neonicotinoids (NEOs) from contaminated water is of great importance for both ecological environment and human health. However, conventional Fenton process might be insufficient for NEOs removal due to short lifetime for generated HO^• and limited Fe³⁺/Fe²⁺ redox cycle. Advancing Fenton process to produce singlet oxygen can be an effective route to improve its efficacy for NEOs removal. Herein, we developed a molybdenum sulfide modified ceramic membrane-integrated Fenton-like system to achieve efficient catalytic removal of NEOs. The reduced Mo⁰ and Mo⁴⁺ could promote the reduction process of Fe³⁺ to Fe²⁺, improving the activation efficiency of hydrogen peroxide (H₂O₂) and the generation of superoxide radical (O₂^•-). Consequently, the coexisting Mo⁶⁺ reacted with O₂^•- to generate ¹O₂. The membrane enabled the pollutants to adequately contact oxidants due to the enhanced convective mass transfer. The functionalized membrane exhibited stable catalytic performance for clothianidin (CLO, a kind of NEOs, 10 mg/L) removal (degradation efficiency > 85%). The presence of ¹O₂ enabled the dechlorination and hydroxylation of CLO and thus reduced the toxicity of wastewater. Our work sheds light on the use of functionalized ceramic membrane integrated catalytic Fenton system for effective environmental remediation.

Phosphorous-doped 1T-MoS2 decorated nitrogen-doped g-C3N4 nanosheets for enhanced photocatalytic nitrogen fixation

Herein, we report that the phosphorous-doped 1 T-MoS₂ as co-catalyst decorated nitrogen-doped g-C₃N₄ nanosheets (P-1 T-MoS₂@N-g-C₃N₄) are prepared by the hydrothermal and annealing process. The obtained P-1 T-MoS₂@N-g-C₃N₄ composite presents an enhanced photocatalytic N₂ reduction rate of 689.76 μmol L^-1 g^-1h^-1 in deionized water without sacrificial agent under simulated sunlight irradiation, which is higher than that of pure g-C₃N₄ (265.62 μmol L^-1 g^-1h^-1), 1 T-MoS₂@g-C₃N₄ (415.57 μmol L^-1 g^-1h^-1), 1 T-MoS₂@N doped g-C₃N₄ (469.84 μmol L^-1 g^-1h^-1), and P doped 1 T-MoS₂@g-C₃N₄ (531.24 μmol L^-1 g^-1h^-1). In addition, compared with pure g-C₃N₄ NSs (2.64 mmol L^-1 g^-1h^-1), 1 T-MoS₂@g-C₃N₄ (4.98 mmol L^-1 g^-1h^-1), 1 T-MoS₂@N doped g-C₃N₄ (6.21 mmol L^-1 g^-1h^-1), and P doped 1 T-MoS₂@g-C₃N₄ (9.78 mmol L^-1 g^-1h^-1), P-1 T-MoS₂@N-g-C₃N₄ (11.12 mmol L^-1 g^-1h^-1) composite also shows a significant improvement for photocatalytic N₂ fixation efficiency in the sacrificial agent (methanol). The improved photocatalytic activity of P-1 T-MoS₂@N-g-C₃N₄ composite is ascribed to the following advantages: 1) Compared to pure g-C₃N₄, P-1 T-MoS₂@N-g-C₃N₄ composite shows higher light absorption capacity, which can improve the utilization rate of the catalyst to light; 2) The P doping intercalation strategy can promote the conversion of 1 T phase MoS₂, which in turn in favor of photogenerated electron transfer and reduce the recombination rate of carriers; 3) A large number of active sites on the edge of 1 T-MoS₂ and the existence of N doping in g-C₃N₄ contribute to photocatalytic N₂ fixation.

Significant acceleration of Fe2+/ peroxydisulfate oxidation towards sulfisoxazole by addition of MoS2

Activation of peroxydisulfate (PDS) by Fe²⁺ has been considered as an effective activation method to generate reactive oxygen species (ROS). However, the process is limited for the low production yield of ROS owing to the inefficient Fe³⁺/Fe²⁺ cycle. Herein, we demonstrated that Fe²⁺/PDS system in the presence of molybdenum sulfide (MoS₂) was significantly efficient for the degradation of sulfisoxazole (SIX). As a co-catalyst in the Fe²⁺/PDS system, MoS₂ could greatly enhance the Fe³⁺/Fe²⁺ cycle by the exposed Mo⁴⁺ active sites, which could also improve the PDS decomposition efficiency. As a result, the degradation efficiency of SIX in the MoS₂/Fe²⁺/PDS system could reach to as high as 97.1% within 40 min, which was in distinct comparison with the 45.5% achieved by Fe²⁺/PDS system without MoS₂. Besides, effects of various reaction conditions on SIX degradation were also evaluated during the experiments, including the dosages of MoS₂, Fe²⁺, PDS and initial solution pH and the coexisting inorganic anions. In addition, both of sulfate radicals and hydroxyl radicals were identified as the dominant active species for SIX degradation by the radical scavenging experiments and verified by electron paramagnetic resonance (EPR). This study provides a promising idea for the degradation of organic contaminants in water treatment based on Fe²⁺/PDS process.

MoSx co-catalytic activation of H2O2 by heterogeneous hemin catalyst under visible light irradiation

The slow Fe³⁺/Fe²⁺ conversion and difficult reactants contact are the main challenges for H₂O₂ activation using heterogeneous iron-based catalysts. As a typical two-dimensional layered nanomaterial, molybdenum sulfide holds great promise for promoting such process as co-catalysts, but its combination with solid iron catalysts is rarely reported. In this work, we fabricated a novel heterogeneous photocatalyst by directly anchoring amorphous MoSx onto the PAN fibers with hemin via an adsorption and in-situ transformation method. The detailed characterizations show the successful assembly of hemin and MoSx with the fibrous support through axial coordination and electrostatic bonding, respectively. Taking the degradation of organic dyes as model reactions, the as-prepared catalyst achieved remarkably high and stable catalytic performance in the presence of H₂O₂ under visible light irradiation, which was much superior to that of the single hemin or MoSx supported fibrous catalyst. The enhanced photocatalytic activity is mainly attributed to (i) the excellent adsorption capability of MoSx, which allows the catalyst to easily capture the reactants and (ii) the accelerated rate-limiting step of Fe³⁺/Fe²⁺ conversion. In addition, we also explored the MoSx co-catalytic effect on the other iron-based heterogeneous H₂O₂ activation systems (such as supported Fe³⁺ or FePc), and similar enhancing effect was observed. Our findings provide a facile and promising strategy to rationally design the advanced oxidation processes for environmental remediation.

Molybdenum sulfide-based electrochemical platform for high sensitive detection of taxifolin in Chinese medicine

MoS₂ and nitrogen doped active carbon composite (MoS₂/ANC) is fabricated to detect taxifolin and exhibits superior redox current response and decreased redox potential difference. Further investigation reveals that the kinetic process of the redox reaction of taxifolin on MoS₂/ANC electrode is controlled by both adsorption and diffusion process. Under the optimum conditions, the redox peak currents linearly relate with the concentration of taxifolin in the range of 1 × 10^-9-1 × 10^-6 mol L^-1, accompanied by the low detection limit (3 × 10^-10 mol L^-1). Meanwhile, outstanding selectivity, stability and repeatability are also obtained at MoS₂/ANC electrode. At last, the proposed method is applied to quantitatively detect taxifolin in fructus polygoni orientalis and satisfactory results have been achieved.

Molybdenum sulfide Co-catalytic Fenton reaction for rapid and efficient inactivation of Escherichia coli

As a typical advanced oxidation technology, the Fenton reaction has been employed for the disinfection, owing to the strong oxidizability of hydroxyl radicals (·OH). However, the conventional Fenton system always exhibits a low H₂O₂ decomposition efficiency, leading to a low production yield of ·OH, which makes the disinfection effect unsatisfactory. Herein, we develop a molybdenum sulfide (MoS₂) co-catalytic Fenton reaction for rapid and highly efficient inactivation of Escherichia coli K-12 (E. coli) and Staphylococcus aureus (S. aureus). As a co-catalyst in the Fe(II)/H₂O₂ Fenton system, MoS₂ can greatly facilitate the Fe(III)/Fe(II) cycle reaction by the exposed Mo⁴⁺ active sites, which significantly improves the H₂O₂ decomposition efficiency for the ·OH production. As a result, the MoS₂ co-catalytic Fenton system can reach up to 83.37% of inactivation rate of E. coli just in 1 min and 100% of inactivation rate within 30 min, which increased by 2.5 times than that of the conventional Fenton reaction. Furthermore, the ·OH as the primary reactive oxygen species (ROS) in MoS₂ co-catalytic Fenton reaction was measured and verified by electron paramagnetic resonance (EPR) and photoluminescence (PL). It is demonstrated an increased amount of ·OH generated from the decomposition of H₂O₂ in the presence of MoS₂, which is responsible for the rapid and efficient inactivation of E. coli and S. aureus. This study provides a new perspective for rapid and highly efficient inactivation of bacteria in environmental remediation.

Recent advances in unveiling active sites in molybdenum sulfide-based electrocatalysts for the hydrogen evolution reaction

Hydrogen has received significant attention as a promising future energy carrier due to its high energy density and environmentally friendly nature. In particular, the electrocatalytic generation of hydrogen fuel is highly desirable to replace current fossil fuel-dependent hydrogen production methods. However, to achieve widespread implementation of electrocatalytic hydrogen production technology, the development of highly active and durable electrocatalysts based on Earth-abundant elements is of prime importance. In this context, nanostructured molybdenum sulfides (MoS _x ) have received a great deal of attention as promising alternatives to precious metal-based catalysts. In this focus review, we summarize recent efforts towards identification of the active sites in MoS _x -based electrocatalysts for the hydrogen evolution reaction (HER). We also discuss recent synthetic strategies for the engineering of catalyst structures to achieve high active site densities. Finally, we suggest ongoing and future research challenges in the design of advanced MoS _x -based HER electrocatalysts.

Disulfide-Bridged (Mo3S11) Cluster Polymer: Molecular Dynamics and Application as Electrode Material for a Rechargeable Magnesium Battery

Exploring novel electrode materials is critical for the development of a next-generation rechargeable magnesium battery with high volumetric capacity. Here, we showed that a distinct amorphous molybdenum sulfide, being a coordination polymer of disulfide-bridged (Mo3S11) clusters, has great potential as a rechargeable magnesium battery cathode. This material provided good reversible capacity, attributed to its unique structure with high flexibility and capability of deformation upon Mg insertion. Free-terminal disulfide moiety may act as the active site for reversible insertion and extraction of magnesium.

MoS2/reduced graphene oxide hybrid with CdS nanoparticles as a visible light-driven photocatalyst for the reduction of 4-nitrophenol

Photocatalytic reduction of nitroaromatic compounds to aromatic amines using visible light is an attractive process that utilizes sunlight as the energy source for the chemical conversions. Herewith we synthesized a composite material consisting of CdS nanoparticles grown on the surface of MoS2/reduced graphene oxide (rGO) hybrid as a novel photocatalyst for the reduction of 4-nitrophenol (4-NP). The CdS-MoS2/rGO composite is shown as a high-performance visible light-driven photocatalyst. Even without a noble-metal cocatalyst, the catalyst exhibited a great activity under visible light irradiation for the reduction of 4-NP to much less toxic 4-aminophenol (4-AP) with ammonium formate as the sacrificial agent. Composite CdS-0.03(MoS2/0.01rGO) was found to be the most effective photocatalyst for 4-NP reduction. The high photocatalytic performance is apparently resulted from the synergetic functions of MoS2 and graphene in the composite, i.e. the cocatalysts serve as both the active adsorption sites for 4-NP and electron collectors for the separation of electron-hole pairs generated by CdS nanoparticles. The laboratory results show that the CdS-MoS2/rGO composite is a low-cost and stable photocatalyst for effective reduction and detoxification of nitroaromatic compounds using solar energy.