Study On The Strategy And Photocatalytic Performance Of Nano - TiO 2 + Addition Charge Separation

Among numerous semiconductor photocatalysis, nano-TiO₂ has got a lot of public attention due to its unique physical and chemical character. Among the three kinds of crystal phase composition of TiO₂, anatase has been widely studied due to its high efficiency of photocharge separation. Compared with anatase, rutile is always ignored owing to its small specific surface area and then poor photoactivity. However, it possesses several features, involved with high chemical stability, high hardness and narrow band gap, etc. As is well known, the capture of electrons by the adsorbed O₂ on TiO₂ surfaces is the key issue during the process of photocatalytic degradation of pollution. However, during the process of photocatalytic reduction of CO₂, the O₂ production is a four-hole process and is considered to be the rate-determining step, thus,trapping holes by introducing negative field is the key step. Based on the above consideration, this work would improve the photocatalytic activity of nanosized rutile TiO₂ by surface acids modification, introducing negative field, construction of composite to trap the photogenerated electrons and photogenerated holes respectively.Details are as follows:Nano-rutile TiO₂ nanorods that has residual Cl on its surface have been prepared by a low-temperature hydrothermal process in the presence of 2.0 M HCl, and then targeted co-modified with phosphoric and boric acids. The results show that phosphoric was modified on TiO₂ surfaces by the dehydration condensation of –P–OH and–Ti–OH–, boric acids was modified on TiO₂ surfaces by the vacancy atomic orbits in the B of H3BO3 and the lone-pair electrons exist in the Cl of residual chloride, therefore, we have realize the goal of the targeted co-modification with phosphoric and boric acids.The targeted co-modification could greatly promote the photogenerated electrons being captured, compared to the phosphate modification and borate one alone. This is attributed to the increased amount of adsorbed O₂, further leading to the enhanced separation of photogenerated charges and then the amount of produced hydroxyl radicals. This is well responsible for the obviously-enhanced photocatalytic activities for degrading pollutant of TiO₂ nanorods.The prepared rutile TiO₂ nanorods that has residual Cl on its surface were modifiedwith phosphate, and then coupled with CNTs. The modified chloride could trap photogenerated holes. The modified phosphate groups could not only dissociate in water to form the surface negative field to trap holes, but also take as the bridges between TiO₂ and CNTs so as to promote the charge transfer. The coupled CNTs could accept photogenerated electrons from TiO₂ and favor the charge transportation. These effects lead to the greatly-enhanced charge separation and then the obviously-improved photocatalytic activities for CO₂ conversion to solar fuels.This work would help us deep understand the process mechanism of semiconductor photocatalysis, and provide a much feasible route to synthesize efficient nanosized TiO₂-based photocatalysts for degrading pollutant and CO₂ reduction.