Photocatalytic Degradation of Dimethyl Sulfide under Visible Light Using Ce S Co-doped TiO2 Prepared by the Sol-gel Method

Abstract

The purpose of this study was to prepare different samples of Ce- and S-codoped TiO2 nanoparticles by the sol-gel method and to investigate the photocatalytic activity regarded to dimethyl sulfide degradation under visible-light irradiation The photocatalytic activity of the samples simulating indoor air was evaluated under various inlet DMS concentrations absolute humidities and residence times The DMS inlet concentration ranged from 0 65 to 2 4 ppm Absolute humidity varied from 5 to 35 g/kg The residence time was set from 35 to 180 second Characterization of TiO2 S/TiO2 and Ce/S/TiO2 were performed by various techniques such as XRD TGA BET SEM ICP-MS FTIR UV-visible and XPS The XRD results show that co-doped S- and Ce- TiO2 would reduce the crystalline size The UV-visible spectra analyses indicate that the absorbance in the visible region by S5/TiO2 and CenS5/TiO2 increases compared with TiO2 The XPS analyses of all photocatalysts show that Ti O and S exist as Ti4+ O2- and S6+ respectively and form Ti-O-S bonds in TiO2 The XPS spectra also prove that Ce3+ as Ce2O3 and Ce4+ as CeO2 exist in CenS5/TiO2 lattice and surface According to the results of activity test we chose S5/TiO2 for further study on the effects of operating parameters including residence time DMS inlet concentration and relative humidity The results show that the lower the DMS inlet concentration the higher degradation rate and carbon mineralization are while residence time ranged from 70 to 120 second The conversion of DMS is around 97 84 % and carbon mineralization is about 45 69 % under the best conditions The carbon recovery has been calculated The experimental condition was set at 7 83 ppm inlet DMS 35 s residence time 18 g/kg absolute humiditily and 45 oC The reactants DMS about 3 25 and 2 84 ppm were detected by GC-MS in the fifth and tenth minutes respectively after the white LED light turned on The intermediates DMDS about 0 55 and 0 47 ppm respectively were detected by GC-MS CO2 concentration was detected by a CO2 analyzer The CO2 concentration were 2 61 and 3 43 ppm respectively The carbon recoveries calculated were in the range of 81 9-86 0 % It’s suggested that some intermediates e g CO may account for around 15-20 % of carbon Two kinetic models the Mar & van Krevelen model and the Langmuir-Hinshelwood model were used to analyze the data The results show that the Langmuir-Hinshelwood model 2 may be feasible to describe the photocatalytic oxidation of DMS and the model is based on the assumption that reaction takes place with [VOC]i and water both adsorbed on photocatalyst surface Some reaction intermediates and products are detected in the gas phase and on the photocatalyst surface as SO2 H2SO4 CO2 DMDS DMSO DMSO2 CO and MSA by FTIR spectra Because the transmittance intensities of all species in the wet sample are stronger than that in the dry samples It can be found that ‧O2- and ‧OH are the key species for the dry sample and the wet sample respectively Besides the results are consistent with section 4-3 3 Water vapor and ‧OH may enhance the degradation of intermediates toward carbon mineralization and modify intermediate quantities A detailed photocatalytic DMS degradation pathways are proposed starting with O atom and C-S bond cleavage drives DMS oxidation in the dry sample and starting with ‧OH drives DMS oxidation C-S bond cleavage and S oxidation in the wet sample

Date of Award	2014 Aug 1
Original language	English
Supervisor	Hsin Chu (Supervisor)