Synthesis And Photocatalytic Performance For Simulated Dye Wastewater Of Two-dimensional Transition Metal Sulfides

Two-dimensional transition metal sulfides（2D TMDs）and their heterostructures have by far stimulated growing research interests in the field of optoelectronics and photocatalysis due to their unique structure and superior properties than the bulk TMDs.On the one hand,scalable fabrication of 2D TMDs at an environmentally-benign and cost-effective manner via liquid phase exfoliation is a particularly fascinating concept.On the other hand,as a typical representative of two-dimensional layered transition metal sulfides,WS₂ and MoS₂ embrace strong visible-light absorption capacity,and the optical and chemical properties of 2D TMDs depend dramatically on their thickness,which make them ideal candidates as semiconductor material in photocatalysis.Herein,we present a facile and green strategy to produce few-layered WS₂ nanosheets、WS₂/MoS₂ heterostructure and WS₂/MoS₂-RGO composite by liquid phase exfoliation（LPE）、hydrothermal method and loading of graphene.the crystal form,morphology,chemical structure,energy band structure and optical properties of the as-prepared materials were characterized by X-ray diffraction analysis（XRD）,transmission electron microscopy（TEM）,field emission scanning electron microscope（FESEM）,atomic force microscopy（AFM）,X-ray photoelectron spectroscopy（XPS）,UV-Vis diffuse reflectance spectroscopy（DRS）,Raman spectroscopy（Raman）,etc.the photocatalytic activities of as-produced materials were evaluated in the photo-degradation of a model dye pollutant,rhodamine B（RhB）,methylene blue（MB）,Malachite green（MG）and methyl orange（MO）,under visible-light irradiation.Our work provides a new method and theoretical basis to fabricate 2D TMDs for photocatalytic functional applications.The main contents and conclusions are listed as below:（1）Study on the synthesis,characterisation and luminescent properties of few-layered WS₂ nanosheets:we present a facile strategy to produce few-layered WS₂ nanosheets at a large scale by a direct exfoliation in water-ethanol mixtures.The effects on the morphology and properties of the prepared WS₂nanosheets were investigated by adjusting the centrifugal speed and the volume ratios of ethanol/water.The results indicated that with the increase of centrifugal speed,the size of the nanosheets decreases gradually.Dispersant has a great influence on the exfoliation of WS₂,when the volume ratio of ethanol and water is7/3,leading to the highest concentration of exfoliated WS₂.In addition,few-layered WS₂ nanosheets were fabricated by this method and the size of nanosheets has great dispersibility.（2）Study on the synthesis,characterisation and photocatalytic performance of WS₂/MoS₂ heterostructure:a novel 2D WS₂/MoS₂ composite was constructed via an in-situ hydrothermal reaction.The effect on photocatalytic activity of WS₂/MoS₂ heterostructure was investigated by the addition of WS₂nanosheets suspensions.The results show that the volume ratios have a significant influence on the photocatalytic performances of WS₂/MoS₂,where the WS₂/MoS₂（7/3 S/W）sample displays the highest activity.Such a heterostructure mixture is superior to pristine 2D MoS₂,WS₂ and their physical mixtures in the photocatalysis of organic dye molecules.The enhancement of photocatalytic performance was associated with the heterogeneous junction effect between 2D WS₂/MoS₂.In addition,in this experiment,we compared the photocatalytic performances of our WS₂/Mo S₂ heterojunction with the two-dimensional TMD-based hybrid materials reported recently.The results indicated that the degradation efficiency of the heterojunction materials is significantly improved.（3）Study on the the synthesis,characterisation and photocatalytic performance of WS₂/MoS₂-RGO composite photocatalysts:The WS₂/Mo S₂-RGO composite photocatalysts was fabricated by loading RGO via hydrothermal reaction.The results indicated that the RGO content indeed exert a significant influence on the photocatalytic performances of WS₂/Mo S₂-RGO.When the RGO content is0.04 g,the composite photocatalysts exhibits the best photocatalytic performances.when the initial concentration of simulated dye wastewater by RhB is 20 mg/L and the dosage of WMG is 0.025 g,an advanced activity with the degradation efficiency of 95%can achieved under the irradiation of the simulated sunlight for 90 min.In addition,the WS₂/MoS₂ heterostructure distributed on the surface of graphene layer can be seen from electron microscopy,the characterization of Raman and XPS confirms that graphene was successfully reduced to RGO.