Photocatalytic Removal Of Gaseous Formaldehyde Over TiO₂Thin Film

Formaldehyde is a common air pollutant. Photocatalytic oxidation that can translate it into harmless CO2and H2O has extensive application prospects. TiO2has been widely researched as a photocatalyst for its chemical stability and non-toxic. TiO2thin film was deposited by atmospheric pressure dielectric barrier discharge chemical vapor deposition and its uniformity and quality were characterized. The degradation of ppm levels of formaldehyde in the simulated air by the film was carried out in a continuous flow flat-plate photocatalytic reactor under UV irradiation in this paper. Residence time, light intensity/source, initial concentration of formaldehyde and humidity were investigated as process variables. The photocatalytic reaction kinetic was analyzed. The results are as follows:3. UV-Vis absorption spectra of5testing points on surface of the TiO2film were in good agreement, which showed the uniformity of the TiO2thin film. Quantitative analysis showed that the film has a TiO2quality deposition of74μg·cm-22. Under the irradiation of254nm UV lamp for as-deposited film, overall rate was controlled by reaction when the linear velocity exceeded7.1cm-s-J. Under the control of reaction, the results are as follows:As0.72mW·cm-2<Ⅰ<1.78mW·cm-2,-ln(1-X)=kⅠτt, k=0.78cm2·mJ-1;In the range of the initial concentrations of HCHO investigated (23-56ppm), the reaction rate changed little with the initial concentration variation;In the range of the humidity from0.04vol%to1.06vol%, photocatalytic conversion of HCHO to CO2kept almost constant, while in the range of the humidity from1.06vol%to1.85vol%, photocatalytic conversion of HCHO to CO2decreased with increasing the humidity.3. Under the irradiation of254nm UV lamp for the film calcined at450℃for2hours, overall rate was controlled by reaction when the linear velocity exceeded9.1cm·s-1and under the control of reaction, the results are as follows:The effect of light intensity showed that-ln (1-X)=klτ:As0.21mW·cm-2<Ⅰ<0.98mW·cm-2, n=1, k=2.1cm2· mJ-1As0.98mW·cm-2<Ⅰ<1.78mW·cm-2,n=0.4, k=2.1cm0.8· mW-0.4·s-1;In the range of the humidity from0.04vol%to0.50vol%, photocatalytic conversion of HCHO to CO2increased with increasing the humidity, in the range of the humidity from0.50 vol%to1.10vol%, photocatalytic conversion of HCHO to CO2kept almost constant, in the range of the humidity from1.10vol%to1.63vol%, photocatalytic conversion of HCHO to CO2decreased with increasing the humidity.Under the irradiation of365nm UV lamp for the calcined film, overall rate was controlled by reaction within the scope of the inspection (linear velocity>3.3cm·s-1). In the range of the humidity from0.04vol%to0.80vol%, photocatalytic conversion of HCHO to CO2increased with increasing the humidity, while in the range of the humidity from0.80vol%to1.66vol%, photocatalytic conversion of HCHO to CO2kept almost constant.