Preparation Of Carbon Doped TiO₂ Photocatalyst And Its Application In Photodegradation Of VOCs

Carbon doped TiO₂ photocatalyst was prepared by propane/air flame (CVD) method, andcharacterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD),EPMA pattern and UV-spectrophotometer. The photocatalytic degradation of VOCs vapor,such as benzene, toluene, methanol, acetone and 1-heptane, over TiO₂ nanofilm was studiedby using a tubular photoreactor. Effects of relative humidity, initial concentration, gasflowrate or residence time and wavelength or light intensity on photocatalytic degradationwere investigated experimentally, and comparisons on degradation rate with Degussa P25were also made. The results showed that (1) The grain size of nanometer YiO₂ was40～80nm.The wavelength corresponding to the maximum absorbency values were observedin the 200～320nm range.The crystal structure of carbon doped TiO₂ photocatalyst is primarilyanatase(22.43% rutile), and the content of carbon is about 4.6%. (2) The relative humidityvaring from 8% to 80%, the photocatalytic degradation degree of benzene increased withincreasing relative humidity; and to toluene, degradation rate was hanced by relative humidityup to 60%, and more or less inhibited above 60%. (3) Scheme and results of orthogonal testswere used by evaluating the photocatalytic performance of the gas phase methanol, acetoneand 1-heptane.The results revealed that their degradation degree reached 84.5%, 93.39% and93.45%, respectively. (4) The 254nm UV lamp showed higher photocatalytic degradation rate.For methanol, acetone and 1-heptane, it was found that photocatalytic degradation reactionoccurs with the light strength of daylight lamp. (5) Under the the same conditions, 15%degradation degree has been obtained for benzene, whilst about 10% degradation degree wasattained by Degussa P25; During the initial phases, the toluene revealed higher photocatalyticactivity, comparing with Degussa P25, the degradation degree of methanol, acetone and1-heptane were slightly lower.In theory, the photocatalytic reaction kinetics was discussed. The reaction- diffusionmodel for the tubular photocatalytic reactor was established, which simulated theconcentration distribution of the reactor. (1) The photocatalytic reaction of VOCs matchedwell with the Langmuir-Hinshelwood kinetic equation. (2) At low VOCs concentration, thephotocatalytic kinetics approached 1st order. (3) By modifying 1st order rate constant k', theconcentration distribution in the reactor had been well described. Five kinds of VOCs photocatalytic experiments and photocatalyst activity and stabilitytests were achieved. The results indicated that the degradation degree of methanol 74.62%,toluene 23.19%, 1-heptane 19.75%, benzene 14.47% and acetone 12.67% were obtained.During 43 hours reaction, carbon doped TiO₂ photocatalyst showed high activity and stability.