Syntheses, Structures And Properties Of New Chalcogenide Semiconductor Photocatalysts

Chalcogenide semiconducting compounds have been well attractive because oftheir abundant structural features, distinctive physical and chemical properties. Thisdissertation deals with the syntheses, crystal and band structures, and propertycharacterizations of some new chalcogenide semiconducting compounds, and novelheterostructured TiO₂/ZnS_0.77Se_0.23and TiO₂/Co₄S_4.23Se_3.77catalysts were synthesizedby the combination of solid-state and sol-gel methods. Their photocatalytic activitywere evaluated by the degradation of methylene blue （MB）, this work provides a newapproach to the design and fabrication of heterostructured catalysts for the efficientdegradation of organic pollutants.1. Chalcogenide semiconducting compounds1) Mg₂Te₃O₈（1）：the crystal structure of1features a3D open-framework withspiroffite topology, the present compound is the firstly alkaline^-earth metalscompound with spiroffite topology, and its energy gap is4.23eV. The electronic bandstructure along with density of states （DOS） of1was calculated and analysed, and theoptical absorption of1was explained.2) ZnS_0.77Se_0.23（2）：the crystal structure of2features a3D framework withsphalerite topology, Se and S fill in the interspace of tetrahedron, ZnSe₄/ZnS₄tetrahedral concurrent connect to from a3D structure. And its energy gap is1.95eV.The electronic band structure along with density of states （DOS） of2was calculatedand analysed, and the optical absorption of2was explained.3) Co₄S_4.23Se_3.77（3）：the crystal structure of3features an octahedra structure withiron pyrites, and its energy gap is2.46eV.4) Mn_0.38Zn_0.63Te （4）：the crystal structure of4features the sphalerite topology,MnTe₄/ZnTe₄tetrahedral concurrent connect to from an octahedron structure. And itsenergy gap is3.52eV.5) ZnTe_0.95S_0.05（5）：the crystal structure of5features the sphalerite topology,ZnTe₄/ZnS₄tetrahedral concurrent connect to from a3D structure. And its energy gapis1.86eV. The electronic band structure along with density of states （DOS） of5wascalculated and analysed, and the optical absorption of5was explained.2. Heterostructured photocatalysts Compared with the single photocatalysts, the heterostructured photocatalystshave given much more attention due to the following two considerations. Firstly, theband gap of the heterostructured photocatalysts can be well controlled throughchanging the composition of the catalysts. Secondly, charge transferring from onesemiconductor to another can lead to efficient charge separation by reducing theelectron-hole pair recombination, which is an important reason that heterostructuredphotocatalysts have a higher photocatalytic activity than the single one. In this paper,novel heterostructured TiO₂/ZnS_0.77Se_0.23and TiO₂/Co₄S_4.23Se_3.77catalysts weresynthesized by the combination of solid-state and sol-gel methods. Theheterostructured TiO₂/ZnS_0.77Se_0.23and TiO₂/Co₄S_4.23Se_3.77were reported in the firsttime in the field of photocatalysis. All of samples were characterized by powder X-raydiffraction （XRD）, scanning electron microscope （SEM）, UV–vis diffuse reflectancespectroscopy （UV-Vis） and Roman spectroscopy. The results showed that the30%TiO₂/ZnS_0.77Se_0.23and30%TiO₂/Co₄S_4.23Se_3.77heterostructured photocatalystshave the best photocatalytic activity for methylene blue degradation than TiO₂,ZnS_0.77Se_0.23, Co₄S_4.23Se_3.77or other combination of them. Moreover, a newphotocatalytic mechanism of TiO₂/ZnS_0.77Se_0.23and TiO₂/Co₄S_4.23Se_3.77wereillustrated and confirmed for the first time.