Study On The Preparation And Photocatalytic Performance Of Sulfated TiO₂ And Ag-loaded TiO₂

As a kind of semiconductor material with high forbidden band, TiO₂ is anexcellent photocatalytic material with merits of steady chemical property, nontoxicity and low-cost. However, the low photon efficiency and the slow reactivevelocity make its photocatalytic activity poor. To improve its photocatalytic activityand develop its application in environmental management, surface modification isneeded, such as adulterating ion and light sensitization.Using industrial TiOSO₄ solution as raw materials, metatitanic acid prepared byhydrolysis of TiOSO₄ solution as a carrier with porous and high specific surface area,the mesoporous SO₄^2-/TiO₂ photocatalyst and Ag/TiO₂ photocatalyst were preparedby one-step process and photocatalytic reduction process, respectively. The catalystswere characterized by means of N₂ adsorption-desorption isotherms, X-raydiffraction, XPS, UV-Vis, FT-IR, Hammett indicator and Eschka. The photocatalyticperformance was examined by the photocatalytic degradation reaction of methyleneblue.The results show that:(1) The one-step process preparing SO₄^2-/TiO₂ catalyst through washing ofmetatitanic acid and roasting route, does not only simplify traditional two-step process which is firstly to prepare the porous carrier TiO₂, then to load the sulfuricacid, but also could obtain the materials easily and low-costly.(2) The adsorbed SO₄^2- links with free OH on the pore wall of metatitanic acidin roasting stage, which resists grain growth and transformation of TiO₂, andmaintains the pore structure as well as the high specific area of carrier TiO₂.Furthermore, the strong electron inducement effect from S=O bond makes theadjacent Ti atom as a superacid core, which accelerates the separation of photogenicelectron-hole pair and prolongs its life-span, so improves the photocatalyticperformance of TiO₂.(3) Under the optimal preparing conditions which are determined: thecalcination temperature and time are 500℃and 2 hours, respectively, the loadingdosage of SO₄^2- is 3.7ï¼…, SO₄^2-/TiO₂ with the steady mesoporous structure, highspecific surface area of 217.5 m²Â·g^-1, and superacid performance of H₀≦ -14.52,has the well photocatalytic performance on the photocatalytic degradation reactionof methylene blue, and the degradation rate is faster than that of P25.(4) Ag/TiO₂ photocatalyst prepared by photocatalytic reduction process is betterthan others prepared by pickling process, hydrothermal process and Ag₂CO₃precipitating process. The optimal preparing conditions are determined: Ag: TiO₂ is0.08:1.0, the pH value of reaction solution is 2, the calcination temperature and timeare 400℃and 2 hours, respectively. The prepared Ag/TiO₂ photocatalyst has theuniform grain, high specific surface area, fine dispersivity of Ag, and itsphotocatalytic performance is better than alone TiO₂.(5) Suitable amount of Ag effectively improves photocatalytic activity of TiO₂.The mechanism could be ascribed to that: The electron-hole pair separationefficiency of TiO₂ is improved by the introduction of Ag as a depletion layer. WhileAg is introduced, the increase of adsorbing -OH and H₂O on TiO₂ brings on theincrease of the concentration of hydroxide free radical -OH at the surface of TiO₂,which participates in photocatalytic redox reaction. The band-gap of TiO₂ is widened,which further improves its photocatalytic redox capability.