Liquid-Phase Exfoliation and Functionalization of MoS2 Nanosheets for Effective Antibacterial Application

A lysozyme (Lys)-assisted liquid-phase exfoliation technique was designed to synthesize MoS₂ nanosheets (MoS₂-Lys NSs). As a novel nanozyme antibacterial agent with high peroxidase-like catalyst activity, MoS₂-Lys NSs showed good antibacterial efficacy against both Gram-negative ampicillin-resistant Escherichia coli (Amp^r E. coli) and Gram-positive Bacillus subtilis. A possible antibacterial mechanism is also proposed. This work provides an effective antibacterial strategy based on the MoS₂-Lys NSs antibacterial agent.     

Regulation of the Peroxidase-Like Activity of nGO,MoS2 and WS2 Nanozymes by Using Metal Cations

Two dimensional nanoparticles (2D-NPs) along with other nanoscale materials have been deemed to be the next generation of artificial enzymes (nanozymes). The low-cost bulk-scale production, ease of storage and modification of such nanomaterials have given nanozymes an advantage over traditional enzymes. Many studies have been aimed at developing methods to increase the performance of these nanozymes, and also identify interfering agents. To investigate the interference of a number of metal cations, we studied the effect of Ti²⁺, Fe²⁺, Ag⁺, Hg²⁺, Co²⁺, Cu²⁺, Ni²⁺, Pb²⁺, Ca²⁺, Zn²⁺ and Mn²⁺ in a nanozyme assays of 2D-NPs using ABTS radical formation. Ti²⁺, Co²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Zn²⁺ and Mn²⁺ ions did not display any notable effect on the peroxidase-like activity of nGO, MoS₂ and WS₂ 2D-NPs. However, Fe²⁺, Ag⁺, Hg²⁺ and Pb²⁺ ions’ effects on the overall ABTS reaction were significant enough to be visualised by partial least square discriminant analysis (PLSDA). We report that, similar to that of many natural enzymes, the nanozyme activity of 2D-NPs is regulated by a number of metal cations allowing their identification and discrimination by using a statistical analysis tool.     

Bimetallic CuCo2S4 Nanozymes with Enhanced Peroxidase Activity at Neutral pH for Combating Burn Infections

Peroxidase-mimicking nanozymes that can generate toxic hydroxyl radicals (^.OH) hold great promise as antibacterial alternatives. However, most of them display optimal performance under strongly acidic conditions (pH 3–4), and are thus not feasible for many medical uses, including burn infections with a wound pH close to neutral. Herein, we report a copper-based nanozyme (CuCo₂S₄) that exhibits intrinsic peroxidase-like activity and can convert H₂O₂ into ^.OH at neutral pH. In particular, bimetallic CuCo₂S₄ nanoparticles (NPs) exhibited enhanced peroxidase-like activity and antibacterial capacity, superior to that of the corresponding monometallic CuS and CoS NPs. The CuCo₂S₄ nanozymes possessed excellent ability to kill various bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, this CuCo₂S₄ nanozymes could effectively disrupt MRSA biofilms in vitro and accelerate MRSA-infected burn healing in vivo. This work provides a new peroxidase mimic to combat bacteria in neutral pH milieu and this CuCo₂S₄ nanozyme could be a promising antibacterial agent for the treatment of burn infections.     

Affinity‐tuned peroxidase‐like activity of hydrogel‐supported Fe3O4 nanozyme through alteration of crosslinking concentration

In this work, we evaluated the effect of crosslinking concentration on the affinity of poly (2‐acrylamido‐2‐methyl‐1‐propansulfonic acid) (PAMPS) hydrogel‐supported Fe₃O₄ nanozyme towards substrates (tetramethylbenzidine (TMB) and H₂O₂). The peroxidase‐like catalytic activity of PAMPS/Fe₃O₄ nanozyme was discussed with respect to crosslinking concentration of PAMPS hydrogel for the oxidation of TMB in the presence of H₂O₂ at room temperature. High catalytic activity was achieved due to good dispersion of Fe₃O₄ nanozyme in the hydrogel network and strong affinity of PAMPS hydrogel‐supported Fe₃O₄ nanozyme towards substrates. The affinity between the hydrogel‐supported Fe₃O₄ nanozyme and substrates can be improved by regulating the crosslinking concentration of PAMPS hydrogel without other trenchant experimental conditions. In addition, the result indicated that H₂O₂ can be detected even at a concentration as low as 1.5 × 10^?6 mol L^?1 with a linear detection range of 1.5–9.8 × 10^?6 mol L^?1. Such investigations not only showed a new approach to improve the affinity and peroxidase‐like activity of Fe₃O₄ nanozyme, but also verified its potential application in bio‐detection and environmental chemistry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43065.     

Sea urchin shaped ZnO coupled with MoS2 and polyaniline as highly efficient photocatalysts for organic pollutant decomposition and hydrogen evolution

In this work, an attempt has been made to fabricate multifunctional composite photocatalysts by coupling sea urchin shaped ZnO with MoS₂ and polyaniline (PANI) sheets, and a significant improvement in photocatalytic activity was perceived with composites in comparison to pristine components. It was found that the ternary ZnO–MoS₂-PANI photocatalyst showed excellent adsorptive decomposition of organic pollutants natural sunlight irradiation. In addition, enhanced photocatalytic hydrogen evolution was also evidenced, which revealed the multifunctional nature of the photocatalysts. In the case of organic pollutant decomposition, the presence of MoS₂ in ZnO–MoS₂-PANI offers abundant catalytic active sites which result in adsorption of the pollutants and boost the photocatalytic activity. While for the photocatalytic hydrogen evolution, the binary ZnO-PANI composite showed the utmost activity in comparison to the pristine components and ZnO–MoS₂-PANI, which is due to the fact that the higher loading of MoS₂ in the composite increases the number of S atoms on the basal planes, which are inactive for H₂ evolution, and hence results in decreased photocatalytic activity. The results discussed in this work may pave the approach for the design and development of ZnO based multifunctional materials for diverse photocatalytic applications.     

Silica Gel-Supported, Metal-Promoted MoS2 Catalysts for HDS Reactions

Silica-supported, metal-promoted MoS₂ catalysts were prepared. Sol–gel method was used for providing the SiO₂ support as well as for including the catalyst precursors and promoter in one single step of preparation. The general idea in this approach is to obtain the promoted MoS₂ catalyst phase finely and uniformly distributed in the SiO₂ support. Scanning electron microscopy of the obtained catalysts shows a fine and homogeneous distribution of the metal-promoted MoS₂ particles on the SiO₂ matrix with surface area between 62 and 104m²/g. Metal promoter affects the surface area, pore size distribution and the hydrodesulfurization (HDS) activity and selectivity. When different promoters were used at the same amount, the highest selectivity for direct C–S bound cleavage is observed for Ru/MoS₂/SiO₂ catalyst, and at different amounts of Co the highest selectivity was occurred with Co/MoS₂/SiO₂ at 12% of Co/MoS₂, X-ray diffraction studies showed that the catalysts are poorly crystallized with a very weak intensity of the (002) line of 2H-MoS₂. Comparison on the catalytic activities of the catalysts with different metal promoters was made. Catalytic activity results showed the method of preparation used in this study is successful in producing very efficient catalysts for the HDS of dibenzothiophene (DBT). Silica-supported, cobalt-promoted MoS₂ catalyst showed the highest activity.     

Effect of Molybdenum Disulfide Layer on Surface Plasmon Resonance Biosensor for the Detection of Bacteria

In this study, a molybdenum disulfide (MoS₂) based surface plasmon resonance (SPR) biosensor is proposed. The reflectance curves for the proposed SPR biosensor are analyzed and compared with the graphene based and the conventional SPR biosensors. It is observed that the performance parameters of the proposed biosensor- sensitivity, detection accuracy, and the quality factor are enhanced by the utilization of the adsorption property of MoS₂ for monolayer and bi-layer MoS₂. Also, the effect of increasing the number of layers of MoS₂ on the reflectance curve is analyzed and compared.     

Electric-assisted strategy enhances the photocatalytic performance of mixed-dimensional CdS/MoS2 photocatalysts

As an effective semiconductor catalyst, cadmium sulfide (CdS) is used in the field of split water hydrogen evolution because of its suitable band gap (~2.4 eV), good photocatalysis activity. However, the rapid recombination of photogenerated electron–hole pairs limits the application of CdS in the field of catalytic hydrogen evolution. Here, we synthesize a CdS/MoS₂ mixed-dimensional heterojunction by a simple hydrothermal method. In this process, CdS nanoparticles were supported on MoS₂ nanosheets, where MoS₂ acts as a loading platform and co-catalyst to improve the photocatalytic performance of CdS. A series of characterizations confirmed that CdS nanoparticles with a size of approximately 130 nm were uniformly grown on the surface of MoS₂ nanosheets. Photoelectrochemical (PEC) tests show that this CdS/MoS₂ mixed-dimensional heterojunction has enhanced photocatalysis hydrogen evolution activity, which is due to the CdS/MoS₂ mixed-dimensional heterojunction can promote the separation of photogenerated electron–hole pairs and positive synergy of MoS₂ nanosheets as a co-catalyst. In addition, a new electrically assisted method is used to enhance the photocatalytic activity, and the photocatalytic performance of the CdS/MoS₂ mixed-dimensional heterojunction is improved by nearly four times when a voltage of 0.6 V is applied. This phenomenon is attributed to the fact that providing an appropriate voltage can further promote the separation of photogenerated electron–hole pairs and rapid carrier mobility, thereby effectively improve the photocatalytic activity of the photocatalyst. This work provides a good guiding significance for the design and construction of high-performance hydrogen evolution catalysts.     

On the structure of a nickel-molybdenum-alumina catalyst

TEM pictures show that the MoS₂ of a sulfided NiMo-alumina catalyst preferentially agglomerates at steps of the alumina support. Catalyst samples aged during direct coal liquefaction either 2 or 26 days show single MoS₂ layers at steps of the support, and the length of the agglomerates is about the same in the two catalysts. The data is not consistent with models for the catalyst structure that include multi-layers of MoS₂.     

Catalytic Activity of Exfoliated MoS2 in Hydrodesulfurization, Hydrodenitrogenation and Hydrogenation Reactions

The activity of exfoliated MoS₂ in the hydrodesulfurization (HDS) of dibenzothiophene, the hydrodenitrogenation (HDN) of carbazole and the hydrogenation of naphthalene has been determined. The catalytic activity was compared to MoS₂ prepared by the decomposition of molybdenum naphthenate (MoNaph). Exfoliated MoS₂ was found to give better overall HDS activity compared to MoNaph derived MoS₂ catalyst, whereas MoNaph derived MoS₂ was found to give higher hydrogenation and HDN activity. These results are discussed in terms of the morphology of the two catalysts. The relative activity of the two catalysts in the hydrotreating reactions is shown to be different to that obtained during Cold Lake bitumen hydrocracking.     

Study on atmospheric tribology performance of MoS2–W films with self-adaption to temperature

MoS₂ is easily oxidized into MoO₃ at elevated temperature, which leads to a sharp deterioration of lubricity and greatly limits the application. To improve the atmospheric tribology properties of MoS₂ at elevated temperature, the co-deposited MoS₂–W composite films are prepared by magnetron sputtering. Compared with pure MoS₂, the design of three kinds of MoS₂–W composite films not only maintains lower temperature-sensitivity, but also greatly improves the mechanical properties. In particular, the three MoS₂–W composite films embrace good tribology performance at all test temperature, especially 100 °C, at which physical adsorption of H₂O is prominently less than that of 25 °C and the oxidation is relatively slight, compared with that of the higher temperature. Individually, the MoS₂-8.2%W composite film maintains the optimal tribology performance at any test temperature and becomes self-adaptive to temperature variation, which originates from the optimized structure and good mechanical properties.     

Activity and thermal stability of sonochemically synthesized MoS2 and Ni-promoted MoS2 catalysts

Sonochemically synthesized MoS₂/Al₂O₃, which had a hydrodesulfurization (HDS) activity that was significantly greater than that of a catalyst prepared by impregnation, exhibited low thermal stability due to sintering of MoS₂ crystallites at high temperatures. The thermal stability was improved when the catalyst was promoted with Ni. In this study, we compared the activity and thermal stability of different Ni-promoted MoS₂ catalysts, which were prepared by addition of Ni to MoS₂ using either impregnation (IMP) or chemical vapor deposition (CVD). After use in the HDS of dibenzothiophene (DBT) at 673 K for 2 h, the initial activity of the un-promoted catalyst was partially lost, while that of the Ni-promoted catalysts was preserved. Ni added by CVD interacted more intimately with MoS₂ than Ni added by impregnation because CVD allowed selective deposition of Ni on the MoS₂ edge sites. Another advantage of the CVD method over the impregnation method is that Ni(CO)₄, which was used as the Ni precursor in the former method, could be decomposed at much lower temperatures than in the case of Ni(NO₃)₂, which was used in the impregnation method. As a result, Ni-promoted catalysts prepared using Ni-CVD showed superior HDS activity compared with those prepared using Ni-impregnation.     

A systematic study on the growth of molybdenum disulfide with the carbon disulfide as the sulfurizing source

In this work, the growth of molybdenum disulfide (MoS₂) was systematically investigated. Firstly, the stepwise investigation of dual source precursor approach was determined by energy dispersive X-ray, non-resonant Raman spectroscopy and Fourier transform Infrared. The spin-coated MoS-based films were transformed into MoS₂ thin films via thermal vapour sulfurization with carbon disulfide as the sulfurizing source. The extension of sulfurization duration provides the better homogeneity and compactness of MoS₂ thin films. However, the deformation of MoS₂ nanostructure was observed beyond 40 min of sulfurization duration. X-ray photoelectron spectroscopy detects the present of Mo⁴⁺ 3d and S²⁻ 2p chemical states, which proves the highly formation of 2H-MoS₂. Next, absorption features of MoS₂ were discovered at ∼668 nm, ∼617 nm, and ∼447 nm. Resonant Raman (RR) spectroscopy shows multilayers of MoS₂ are grown. However, multilayers wall of MoS₂ nanoparticles was observed by the high-resolution transmission electron spectroscopy (HRTEM). The deviation of these observations (RR and HRTEM) is due to the rotational stacking fault of MoS₂ layers.     

Electrospinning and hydrothermal synthesis of recyclable MoS2/CNFs hybrid with enhanced visible-light photocatalytic performance

In this work, a two-step synthesis route combining an electrospinning method and a hydrothermal process was used to prepare MoS₂/CNFs hybrid. CNFs was applied as the matrix for the nucleation and growth of MoS₂ nanosheets. In this hybrid, the crisscrossed MoS₂ nanosheets were randomly aligned and densely packed over the surface of CNFs. We probed the photocatalytic activity of MoS₂/CNFs hybrid to degrade rhodamine B (Rh B) in an aqueous solution under visible light irradiation. The hybrid displayed higher photodegradation performance relative to MoS₂ and mechanical mixture of MoS₂ with CNFs, with 67% Rh B completely degraded over 5 h-period. We attributed such enhancement in photocatalytic activity to the enhanced absorption property and electrical conductivity due to the synergy between MoS₂ and CNFs. The hybrid can furthermore be easily separated from the solution and reused for the subsequent photodegradation cycles. We verified the negligible loss in the photodegradation activity of MoS₂/CNFs hybrid towards Rh B during the three subsequent cycles. The high photocatalytic activity and recyclability of the hybrid render its practical application to degrade organic pollutants (i.e., dye compounds) in industrial wastewater.     

Properties of unsupported MoS<Subscript>2</Subscript> species produced in the preparation of MoS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> using a sonochemical method

Unsupported MoS₂ particles, which were produced in the preparation of MoS₂/Al₂O₃ using a sonochemical method, were successfully separated from the prepared sample catalyst by adding oleylamine as an agent for dispersing the unsupported particles. The fraction of the unsupported MoS₂, which was estimated based on Mo balance, varied between 0.03 and 0.4, independent of the Mo loading levels investigated (6–54 wt% of Mo). The activity of the unsupported MoS₂ for the hydrodesulfurization of dibenzothiophene was nearly the same as that of the Al₂O₃-supported MoS₂, indicating that the activity of the prepared catalyst was not affected by the presence of the unsupported MoS₂ particles.     

Preparation of g-C3N4/MoS2 Composite Material and Its Visible Light Catalytic Performance

The g-C₃N₄ nanosheet was prepared by calcination method, the MoS₂ nanosheet was prepared by hydrothermal method. The g-C₃N₄/MoS₂ composites were prepared by ultrasonic composite in anhydrous ethanol. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and photoluminescence techniques were used to characterize the materials. The photocatalytic degradation of Rhodamine B (Rh B) by g-C₃N₄/MoS₂ composites with different mass ratios was investigated under visible light. The results show that a small amount of MoS₂ combined with g-C₃N₄ can significantly improve photocatalytic activity. The g-C₃N₄/MoS₂ composite with a mass ratio of 1:8 has the highest photocatalytic activity, and the degradation rate of Rh B increases from 50 to 99.6%. The main reason is that MoS₂ and g-C₃N₄ have a matching band structure. The separation rate of photogenerated electron–hole pairs is enhanced. So the g-C₃N₄/MoS₂ composite can improve the photocatalytic activity. Through the active material capture experiment, it is found that the main active material in the photocatalytic reaction process is holes, followed by superoxide radicals.

     

Cold Lake Bitumen Upgrading Using Exfoliated MoS2

Exfoliated MoS₂ has been investigated as a dispersed catalyst for Cold Lake bitumen upgrading. The results are compared with MoS₂ prepared in situ by the decomposition of molybdenum naphthenate. Although liquid yield and coke suppression were similar among the catalysts, better hydrogenation activity, especially hydrodenitrogenation, and asphaltene and microcarbon residue (MCR) removal, were obtained with the exfoliated MoS₂. The improved hydrogenation is suggested to be a consequence of increased rim-edge sites associated with the exfoliated MoS₂. The potential for recycle of the exfoliated MoS₂ is also reported.     

Boosting flame retardancy of thermoplastic polyurethane: Synergistic effect of nickel phosphide nanoparticles and molybdenum disulfide nanosheets

For the first time, a novel nanohybrid based on nickel phosphide (Ni₂P) nanoparticles and molybdenum disulfide (MoS₂) nanosheets was facilely synthesized for enhancing flame retardancy and smoke suppression of thermoplastic polyurethane (TPU). The synergistic effect on flame retardancy is proposed. TPU composite with 2 wt% Ni₂P/MoS₂ hybrid exhibits the best overall flame retardancy, while TPU composites with the same amount of individual Ni₂P nanoparticles and MoS₂ nanosheets are average in performance. Specifically, the 41.2% reduction of peak heat release rate (PHRR) is achieved for TPU/Ni₂P/MoS₂ composite, which is only 16.8% and 26.4% for TPU/Ni₂P and TPU/MoS₂ composites, respectively. In addition, a more intact protective char layer of TPU/Ni₂P/MoS₂ composite can be observed. These results clearly suggest the synergistic effect between Ni₂P nanoparticles and MoS₂ nanosheets. It is hypothesized that physical barrier effect and chemical catalytic ability of Ni₂P/MoS₂ hybrid contribute to the dramatic reduction of heat release and smoke production. The strategy proposed here is a simple yet efficient approach to fabricate high-performance MoS₂-based flame retardants.     

Behaviors of oil-soluble molybdenum complexes to form very fine MoS2 particles in vacuum residue

Dispersion and thermal behaviors of oil-soluble Mo-dithiocarbamate (Mo-DTC) and Mo-dithiophosphate (Mo-DTP) as the MoS₂ catalyst precursors were studied in petroleum vacuum residue (VR) using FT-Far IR, XRD and TEM. FT-Far IR was proved to detect the Mo complexes and their derived MoS₂ in VR without the interference of the complicated organic matrix. Their transformation into MoS₂ was identified by detecting the changes in the ligand bonds and crystal structure. These complexes were found to be distributed in asphaltene (or maltene) by fractionation with hexane due to their solubility in the heavy oil, ruling out any chemical interaction of the complex with asphaltene. Mo-DTC was found to be decomposed at 350 °C to form definite MoS₂ in VR. Mo-DTP started its decomposition around 200 °C, and however, no definite formation of MoS₂ was confirmed by heating up to 500 °C. Dispersion of the complexes in VR and asphalthene was always good as indicated by TEM. Both complexes in VR at 380 °C under hydrogenation (HYD) conditions provided more or less MoS₂. H₂S and reactive sulfur species were assumed to accelerate the transformation of the Mo complex to MoS₂ during HYD reaction. Some difficulty of Mo-DTP to be transformed quantitatively into definite MoS₂ in VR may explain its poor activity for up-grading VR.     

Ultra-deep hydrodesulfurization on MoS2 and Co0.1MoS2: Intrinsic vs. environmental factors

A hydrogenation index (HI), measured in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), is used to estimate the intrinsic hydrogenation selectivities of MoS₂, Co_0.1MoS₂, and two supported HDS catalysts. The HI and catalyst activity for desulfurizing 4,6-diethyl-DBT follow the same trend: MoS₂ ? Co_0.1MoS₂ ? supported catalysts. For desulfurizing a petroleum fraction rich in 4,6-alkyl-DBTs and 4-alkyl-DBTs, the activity decreases as follows: Co_0.1MoS₂ > supported catalysts ? MoS₂. These results introduce an apparent conundrum: MoS₂ has such a high hydrogenation power and activity for desulfurizing 4,6-diethyl-DBT, why does it perform poorly in real-feed tests? This conundrum is resolved by showing that an ultra-deep HDS catalyst requires an optimum balance between an intrinsic factor (hydrogenation function) and an environmental factor (tolerance of organonitrogen). Incorporating Co into MoS₂ lowers the hydrogenation function of MoS₂ and hence improves tolerance of organonitrogen. This conclusion corroborates the prediction of an early modeling study.