Study On Photocatalytic And Electrocatalytic Properties Of Titanium Dioxide/Molybdenum Disulfide(Copper Sulfide)Heterostructures

Photocatalysis and electrocatalysis have important applications in the field of environment and energy.Photocatalysis is a green and environmental means of pollutant degradation.And electrocatalysis can convert electric energy into hydrogen,which is an important way to realize the conversion,storage and transportation of renewable energy.Therefore,the study on high efficiency photocatalytic and electrocatalytic materials has important practical value and wide application prospect.Titanium dioxide(TiO₂)is a kind of non-toxic and environment-friendly material with excellent photocatalytic performance.However,the application of TiO₂ in the field of photocatalysis is trapped by its inherent defects of wide band gap and low quantum efficiency.And the conductivity of TiO₂is poor and its electrocatalytic activity is not high,which limit its application in the field of electrocatalytic.In order to enhance the photocatalytic and electrocatalytic efficiency of TiO₂,to combine TiO₂ with other semiconductor materials to construct heterostructures is an important way.In this dissertation,TiO₂ is the main research object.Narrow band gap semiconductor molybdenum disulfide(Mo S₂)and copper sulfide(CuS)are selected to be composited with TiO₂ to produce new heterostructure composites.The properties of photocatalysis and electrocatalysis are discussed,and the mechanisms of growth and catalysis are explored.Some progresses have been obtained:TiO₂ nanoparticles(P25)and TiO₂ nanobelts were synthesized with Mo S₂ by hydrothermal method,respectively.Then,two heterostructures,TiO₂ nanoparticles(P25)/two-dimensional Mo S₂ nanosheets and TiO₂ nanobelts/two-dimensional Mo S₂nanosheets,were produced.The composition,morphology and structure of the these heterostructures were analyzed and characterized,and the photocatalytic and electrocatalytic performances were investigated.The enhanced photocatalytic property should be attributed to widened range of light absorption,increased light absorption capacity,matched energy levels of TiO₂ and Mo S₂ to improve the separation efficiency of photogenerated electron-hole pairs,the built-in electric field at the interface of heterostructure promoting the separation of photogenerated electrons/holes and inhibits recombination of migration.The improved electrocatalytic property is related to Mo S₂ morphology of discrete nanosheets structure to expose more active sites and the built-in electric field at the interface of heterostructure promotes the carrier transport ability.TiO₂ nanobelt/CuS heterostructures were synthesized by hydrothermal method,and their photocatalytic and electrocatalytic properties were studied.The improved photodegradation property implies that enhanced absorption,matched energy levels,blue-in electric field at the interface are main factors.In the experiment of hydrogen evolution reaction,the electrocatalytic properties were obviously different with different ratios of TiO₂ to CuS,which imply that the ratio can significant effect the electrocatalytic property.It showed that the TiO₂ nanobelts/CuS composite with mass ratio of 1:1 has the lowest overpotential and Tafel slope.The improvement of electrocatalytic performance is related to the exposure of more active sites increasing the number of active sites and the built-in electric field at the heterostructure interface improving the carrier transport ability.Electrospinning and hydrothermal methods were used to prepare the 2D Mo S₂nanosheets on TiO₂/polyvinylidene fluoride(PVDF)fibers at low temperature without acid.The samples were prepared by using two different growth substrates with three different solution concentrations.The growth mechanism of Mo S ₂ on the fiber surface was explained.The improved photocatalytic performance of TiO₂/PVDF@Mo S₂ fiber should be attributed to the matched energy levels,increased specific surface area and the built-in electric field at the interface.The flexibility of the fiber has not be damaged at low temperature to be prepared.Different morphologies of CuS were designed to grow on TiO₂/PVDF fiber,controlled by adjusting the amount of Cu source and cetyltrimethylammonium bromide(CTAB).The growth mechanism of CuS and the effect of the morphology on the photocatalytic performance were proposed.The results showed the degradation efficiency of CuS was high with loose,small and thin morphology.This is because the interface of heterostructure is an important area for the separation and transfer of photogenerated carriers.Large and thick CuS will increase the distance from the photogenerated carriers to the interface,greatly increase the probability of photogenerated carriers recombination,and reduce the contact area between catalyst and solution,all which will extremely lower the efficiency of photocatalysis.Therefore,the thin and small CuS on fiber surface is more conducive to the improvement of the photocatalytic ability of TiO₂/PVDF@CuS.