Preparation And Modification Of Supported Nanosized TiO₂ Photocatalyst By MOCVD And Its Application In Water Treatment

Nanosized TiO₂ has been extensively studied in the wastewater treatment because of its excellent photocatalytic activity. However, there are some drawbacks during the practical use of the nanosized TiO₂: (1) separation of powder TiO2 from water is difficult;(2) the suspended nanosized TiO₂ tends to aggregate;(3) the capacity to mineralize wastewater is low. In the present study, activated carbon (AC) supported TiO₂ photocatalysts were prepared by metal organic chemical vapor deposition (MOCVD) to overcome these drawbacks. In order to improve the photoactivity of supported TiO₂ photocatalysts, co-deposition or second deposition MOCVD methods were applied in the modification of them.TiO₂ was successfully supported on the surface of AC through MOCVD, and the deposition process was studied. When AC modified by HNO₃ was used as the support, the deposition rate and the concentration of TiO₂ on the external surface of AC were simultaneously enhanced.MOCVD was compared with sol-gel and MAD. It was found that the supported TiO₂ photocatalyst by MOCVD showed the best photocatalytic activity. The different supports supported TiO₂ photocatalytsts were compared, and we found that the decreasing order of photocatalytic activity of them was TiO₂/AC > TiO₂/Al₂O₃ >TiO₂/ACF.The conditions to obtain the best TiO₂/AC catalyst by MOCVD are the deposition temperature of 873 K, the source temperature of 423 K, the carrier gas flow rate of 400 ml/min, the calcination time of 2 h, the TiO₂ loading of 12 wt %. Anatsae TiO₂ particles were well dispersed with their sizes ranging from 10 to 50 nm. The TiO₂ photocatalyst so prepared behaves similarly to that of the commercial TiO₂ (Degussa P25). TiO₂/AC could be easily separated from water with its catalytic performance maintained even after 10 cycles. It was observed that TiO₂/AC showed a higher capacity to mineralize wastewater in comparison with P25.The second deposition MOCVD method was applied to the preparation of anAg-TiO2 photocatalyst on AC in order to enhance the photoactivity of the supported TiO2, i.e. improving the separation of electron-hole pair. Ag particles (1-5 run) were coated on the surface of the TiO2 layer. The photoactivity of the Ag-TiO2 photocatalyst with a proper Ag/Ti atomic ratio (0.0198-0.0595) was greatly higher than that of unmodified TiO2.To enhance the absorption in the visible region for supported TiC>2, Fe doped TiO2 coatings have been prepared in one step by a co-deposition process of MOCVD method. Iron exists as Fe3+ substituting Ti4+ in the TiC>2 lattice. Iron has a uniform distribution within Fe-TiC>2 coatings. The Fe doped TiC>2 samples exhibited good photocatalytic activities for the degradation of methyl orange under visible light irradiation.A kinetic study on the quantitative relationship between the specific reaction rate and the external concentration of TiC>2, the crystal size of TiO2, the light intensity and the loading of TiO2 was performed. A reactor with immobilized TiCVAC coatings was developed to avoid the recovery of catalysts, the kinetic of which was studied. The photodegradation pathway of methyl orange was studied on the base of the results of FTIR and GC-MS.