Preparation, Characterization And Photocatalytic Activity Of Zinc Sulfide - Based Photocatalyst

ZnS is a kind of II-VI important direct bandgap semiconductor, the band gap is about3.6～3.8eV, as a kind of wide band gap n-type semiconductor compound, ZnS mainly used as electroluminace, gas sensor and optical materials, such as the photoluminescence and electroluminescence, phosphor, sensor and infrared window, etc. However, there are few researches for its photo catalytic properties at present.In view of the research status of ZnS photocatalyst, a series of ZnS, Al3+/ZnS and WO3/ZnS photocatalysts were prepared by a solvothermal and precipitation-calcination method. The obtained samples were characterized by N2physical adsorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (UV-vis DRS), fourier transform infrared (FT-IR) spectrophotometer and photoluminescence (PL) spectroscopy. The different pollutant of acid orange II, methylene blue, and rhodamine B was used to photocatalytic activity test. The relation of the composition, physical structure and photo catalytic properties of catalyst and its photocatalysis mechanism was also discussed. The details works were shown as the following:1. A series of ZnS photocatalysts were prepared by a solvothermal method with ethylene glyclo as the reaction medium and zninc acetate (Zn(CH3COO)2-2H2O) and thiourea ((NH2)2CS) as the precursors. The effects of reaction temperature and time on the crystallnity, surface area, optic adsorption and photocatalytic performance of the ZnS were investigated. The photocatalytic activity of the prepared samples was evaluated by photocatalytic degradation of different dyes under UV light (λ=254nn) irradiation. The experimental results show that these photocatalysts prepared under solvothermal condition have good crystallinity and spherical morphology. ZnS photocatalyst prepared at140℃for16h shows the highest photocatalytic activity in decomposition of the dyes. This high photocatalytic activity is mainly attributed to the good crystallnity, big surface area, and less crystal defects of the ZnS prepared under the optimal condition.2. A series of Al3+doped ZnS nanocrystals were prepared by a solvothermal method with ethylene glycol as the reaction medium and aluminum nitrate nonahydrate (A1(NO3)3) as the precursors based on the experiment of spherical morphology ZnS nano crystal which prepared by the solvothermal. method. The effects of Al3+doping with different content on the crystallinity, surface area, surface groups, light adsorption and photocatalytic performance in degradation of different dyes were investigated. Results show that at the mild temperature of140℃, the prepared spherical Al3+doped ZnS nanocrystals show high crystallinity. Al3+doping results in an increase in surface area and a higher level of surface hydroxyl groups. A lower recombination rate of photogenerated hole-electron (e-/h+) pairs was also observed over Al3+doped ZnS. Doping optimum content of Al3+(6%mol) brings about3.5,1and0.9times increase in degradation rates of the dyes of acid orange Ⅱ, methylene blue, and rhodamine B, respectively.3. A series of WO3/ZnS composite photocatalysts with different WO3concentrations were prepared by a precipitation-calcination method. The effects of WO3composite with different content on the structure, surface property, the separation efficiency of the photogenerated hole-electron (e-/h+) pairs, and photocatalytic performance in degradation of acid orange Ⅱ were investigated. Results show that the increase in the photocatalytic activity could be attributed to the coupling of small amount of WO3, which suppressed the growth of ZnS particles, increase of the surface area and increased amount of surface OH groups of the sample. The presence of WO3also restrained the recombination rate of photogenerated hole-electron (e-/h+) pairs.The research results indicated that ZnS with good crystallinity and spherical morphology could be prepared by a solvothermal method; besides, the control of the reaction temperature and time, and the doping of suitable metal, the formation of semiconductou he teroj unction could effectively improve the photocatalytic properties of ZnS.