Preparation Of SO₄^2- Modified Co-TiO₂and Its Photocatalytic Activity Of Hydrogen Production For Water Splitting

Photocatalytic water splitting for hydrogen （H2） evolution by utilizing thesolar energy is considered to be one of the ideal means to solve energy andenvironmental problems. TiO₂has became one of the most commonphotocatalysts and drawn much attention duo to its various merits, such as low-cost, non-toxicity and chemical stability. However, because of the wide band gapof titanium dioxide（3.2eV）, only a small UV fraction of solar light（3-5%） can beutilized. The high recombination probability of photocarriers and poor solarefficiency has seriously impeded its development and application. In this work,TiO₂was doped with ion and modified to improve the photo efficiency as well asthe response into the visible part of the spectrum.In this paper, a cobalt （Co） doped titania （TiO₂） powder was prepared withby sol–gel method, then modified with SO₄^2-using an impregnation method. Theas-prepared powder was characterized by the techniques such as X-raydiffractometer, fourier transform infrared spectroscopy, scanning electronmicroscope and UV-vis Absorption Spectroscopy, and its photocatalytic activityfor water splitting was investigated in a water/methanol system. The impactmechanism to improve the photocatalytic activity by Co doping and SO₄^2-modification was discussed.The results show that Co doped in TiO₂can inhibit phase transition ofanatase to rutile. The doping of cobalt made the absorption threshold values ofTiO₂extending up to the visible light range but not reducing the absorption ofultraviolet. The results demonstrate that the photocatalytic activity of Co dopedTiO₂is significant higher than that of pure TiO₂. The rate of hydrogenproduction rate is up to151μmol·h-1under the conditions of the doping content of Co for2.0at%, calcination temperature of photocatalyst preparation at500℃,the amount of photocatalyst for0.5g, the volume fraction of methanol was10%and the pH of the system was7.The test of FT-IR argues that SO₄^2-is combined on surface of TiO₂bychelating bidentate, photogenerated electrons was induced to migrate to thesurface of the sample by the strong electronic inductive effect, which couldprohibit the recombination between active electrons and holes, and improve thephotocatalytic activity. The rate of hydrogen production is up to171.3μmol·h-1under the conditions of modifying content of SO₄^2-for8.0wt%, and calcinationtemperature of photocatalyst preparation at500℃, which was13.5%higher thanthat of Co-TiO₂. Furthermore, the stability of photocatalyst was demonstrated bykeeping the high photocatalytic activity after the photocatalytic reaction for20h.