A novel piezocatalytic active membrane based on mixed matrix of exfoliated multi-flaw MoS 2 (E-MoS 2 ) nanosheets and polyvinylidene fluoride (PVDF) was synthesized by electrospinning technique. The composition and structure of the obtained E-MoS 2 /PVDF electrospun fiber membranes (EFMs) were characterized via FESEM, HR-TEM, XRD, FTIR and XPS techniques. The piezocatalytic activity of the EFMs was evaluated by the degradation of antibiotic oxytetracycline (OTC) under ultrasonic irradiation in the dark. The 10.0 wt% E-MoS 2 /PVDF EFMs exhibited superior OTC degradation efficiency of 93.08% within 24 min with pseudo-first-order kinetic constant ( k ) of 0.09124 min −1 , which was 21.1 times higher than that of the pure PVDF EFMs. The superior performance was attributed to the synergetic effect of the embedded E-MoS 2 nanosheets and a high proportion of PVDF β -phase (94.1%) to effectively improve the piezoelectric property of composite. In addition, the ultrathin multi-flaw structure of E-MoS 2 provided abundant catalytic active edge sites and increased the surface charge density, promoting the generation of more ∙OH and ∙O 2 – radicals to degrade OTC pollutants. The degradation intermediates of OTC over 10 wt% E-MoS 2 /PVDF EFMs were detected by HPLC–MS and two main degradation pathways were reasonably proposed. The piezocatalytic activity of 10 wt% E-MoS 2 /PVDF EFMs remained stable after five consecutive cycles. This study is meaningful for exploring the composite membrane piezocatalysts for largescale applications in wastewater treatment.
2D transition-metal dichalcogenides (TMDs) have attracted much attention for promising application in gas sensors. Edges of the layered nanostructures are well known as highly reactive sites, besides the low working temperature. However, TMD sensors still suffer from the bottlenecks of low response and slow reaction kinetics. We propose an innovative use of porous carbon nanostructures originated from zeolitic imidazolate frameworks. In this work, multi-layered MoS2 nanoplates are confined in nanoscale porous carbon nanocages (PCNCs) by a facile hydrothermal technique. The carefully designed MoS2/PCNC sensor exhibits good triethylamine (TEA) sensing performances. Compared with pure MoS2, the response (Ra/Rg) of the MoS2/PCNC composite sensor to 100 ppm TEA is as high as 53. The theoretical TEA detection limit is estimated to be as low as 12 ppb. In addition, the investigation proves good stability and reproducibility. The possible sensing mechanism for the improved performances is discussed too. The innovative strategy for the controlled design of MoS2/PCNC nanostructures may provide valuable application in designing high-performance TEA sensors.
The phase transition of multilayer MoS2 nanosheets from semiconducting 2H to metallic 1T (2H/1T) has been realized mainly by chemical methods (e.g., Li intercalation). Here, we develop a simple yet effective method, cyclic voltammetry, to successfully tune the 2H/1T phase transition of multilayer MoS2 nanosheets without using intercalation species. The phase transition is triggered by the electrochemical incorporation of S vacancies (obtained by electrochemical etching), which on the one hand injects electrons into the framework of S–Mo–S and on the other hand facilitates the sliding of S planes. Density functional theory calculations show that O doping in the framework of S–Mo–S decreases the energy barrier for forming S vacancies and stabilizes the 1T-phase by occupying the 4d orbital of Mo. Our calculations further show that the presence of S vacancies and O incorporation not only reduces the bandgap of MoS2, indicating an increased conductivity, but also decreases the hydrogen adsorption free energy, implying significant improvement of hydrogen evolution reaction (HER) activity. Indeed, the overpotential and Tafel plot of the electrochemically treated MoS2 nanosheets are decreased respectively by 174 mV and 25 mV/dec at a cathodic current density of 10 mA cm–2 compared with pristine 2H-MoS2 nanosheets. The HER experiment also reveals the order of catalytical activity for the studied phases and structural defects: 1T-MoS2 > S vacancies > O doping >2H-MoS2. Our study has provided a new route to control the phase transition of multilayer MoS2 nanosheets with promising applications potentially in catalysis and optoelectronics.
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