Magnetic Field Effect On Photocatalytic Degradation Of Benzene Over Pt/TiO₂

To improve the quantum efficiency of the TiO2 photocatalytic process, the external fields involving electric field, microwave field, ultrasonic field and so on, have b een applied s uccessively i n t he p hotocatalytic d egradation s ystem. H owever, there is less study concerning the effect of magnetic field on the heterogeneous photocatalytic reactions,In this paper, the magnetic field effect (MFE) on heterogeneous photocatalytic degradation of benzene over Pt/TiO2 has been observed.Titanium dioxide sol was prepared by a sol-gel technique and platinized titania (Pt/TiO2) was synthesized by impregnation method. XRD characterized the dominant crystal phase and the average crystal size, while the BET specific surface areas of the platinized titania particles was got by nitrogen adsorption. On-line GC, DC photoconductivity, induced luminescence and in -situ FTIR were used to investigate the influence of magnetic field on the degradation reactivity, photogencrated charge carrier lifetime, surface hydroxy radical formation and the product distribution.The results showed that in the presence of the magnetic field the conversion reached to 18% from 15.5%, and the production of CO2 was increased to 175 ppm from 52 ppm. Accordingly, the mineralization of benzene was up to 52% from 19%. In addition, the magnetic field intensity influences the conversion of benzene and production of CO2 in different modes. To verify the magnetic field effect on the charge carrier dynamic and lifetime, photoconductivity was used to illustrate the MFE on the generation, recombination, trapping and interface charge transfer, and on the lifetime of the excess charge carriers. In the condition of external magnetic field (85.7 mT), the effective lifetime was prolonged to 5.67 ms from 2.11 ms without MF. And the lifetime was increased with the increase of the magnetic field intensity. The induced-luminescence technology was adopted to test the MFE on the rate of the hydroxy radical photo-formed on the surface of the catalyst, and the results showed that the application of the external magnetic field accelerated the production of the mentioned radical by 11.67%, compared to the reaction in the absence of MF. In situ FTIR spectroscopy was applied to investigate the MFE on the degradation route. The results revealed that the employment of magnetic field may not change the mechanism of photocatalytic degradation of benzene, however, after a period of application time, the integration area of benzene peak was down to 0.57 from 0.82,while CO2 was up to 42.78 from 28.3. Furthermore, the relative intensity of the two peaks ascribed to two major intermediates (quinone to phenol) was up to 1.05 from 0.96. The results indicated that the superimposition of magnetic field not only favor the conversion of benzene, but also facilitate the conversion of phenol to quinone, resulting in the formation rate of quinone is faster than that of phenol, and increasing the amount of CO2. That is, it greatly altered the distribution of the intermediates and products, resulting in improvement of the performance of the photocatalytic degradation.This work introduced the magnetic field i nto the heterogeneous photocatalytic degradation domain for the first time, and opened a new door to improve the quantum efficiency of the degradation of the pollutant.