Preparation And Microstructure Of Tungsten Disulfide/Sepiolite Composites

Two-dimensional tungsten disulfide（WS₂）with the layered structure has the merits of large surface area,appropriate energy gap and considerable photocatalytic active edge sites,so WS₂ has a good application prospect in photocatalytic degradation of organic dyes.However,characteristic of agglomerated WS₂ restricts the application of WS₂ in photocatalysis.The natural mineral sepiolite with the merits of large surface area,distinguished thermal stability and outstanding adsorption property can be adopted as a carrier for assisting the growth of WS₂,which can improve the dispersion of WS₂ and thus exposing more photocatalytic active sites.In this work,tungsten disulfide/sepiolite composites were synthesized via solvothermal-roasting method with ammonium tetrathiotungstate as tungsten and sulfur source and were also synthesized via hydrothermal-roasting method with ammonium metatungstate,thioacetamide and oxalate as tungsten source,sulfur source and reductant,respectively.The influences of synthesis temperature and time,sepiolite additional content on microstructure of the composite were systematically explored with the support of some technologies including XRD and SEM.Besides,the degradation of RhB was adopted as a probe reaction to assess the photocatalytic activities of the composites.At last,the explanations for the improved photocatalytic properties of tungsten disulfide/sepiolite,as well as the photocatalytic mechanism were further studied.The main research results were as follows.The optimal parameters for fabricating composites via solvothermal-roasting method were 24 h of solvothermal time,220℃of solvothermal temperature and 3.0 wt.%of sepiolite additional content.Compared with WS₂,the photodegradation rate of RhB over the optimal composites reached 82.3%after 2.5 h lighting,which was about 2.1 times improved.The best parameters for preparing the composites via hydrothermal-roasting method were 24 h of hydrothermal time,220℃of hydrothermal temperature and 10.0 wt.%of sepiolite additional content.Compared with WS₂,the photodegradation rate of RhB over the optimal composites reached 88.5%after 2.5 h lighting,which was about 7.4 times improved.The better photocatalytic activity of tungsten disulfide/sepiolite composites prepared via solvothermal-roasting method and hydrothermal-roasting method than pristine WS₂,which could mainly because of the improved dispersion of WS₂ and thus exposuring more photocatalytic active sites after WS₂ dispersed on sepiolite.Compared with the solvothermal-roasting method,the composites prepared via hydrothermal-roasting method had better dispersion of WS₂ on the surface of sepiolite.Active species capture experiments could further explore the active species of composites in the photocatalytic process and reaction mechanism.The result showed that photo-generated holes（h⁺）played a dominant part during photocatalysis,while superoxide radical（·O₂^-）and hydroxyl radicals（·OH）played ancillary part.Except for the improved dispersion of WS₂,the synergies effects between sepiolite and WS₂ could also jointly promote the progress of photocatalytic reaction The excellent adsorption of sepiolite could not only transfer RhB to the catalytic active site of WS₂ to promote the degradation of RhB,but also transferred dissolved oxygen to the surface of WS₂ to promote the generation of·O₂^-.In addition,the surface of sepiolite was rich in hydroxyl and water molecules,which was conducive to the formation of·OH.Synergies as mentioned above improved the utilization efficiency of photogenerated holes and photogenerated electron pairs and inhibited their recombination,thus further improving the photocatalytic performance of the composites.In this work,the natural mineral sepiolite was used as the functional carrier and the tungsten disulfide/sepiolite composites had giantly development potential in the domain of photocatalytic degradation of organic dye.