Preparation And Its Photocatalytic Performance Of Titania Nanomaterials Modified With Fuller Carbon

Due to its well optical and thermal stability and innoxious property, titania (TiO2) nano-materials is the most common photocatalyst used in the field of photocatalytic hydrogen production and environmental photocatalysis. However, TiO2 can only absorb UV light (wavelength less than 387nm) due to its wide energy gap (3.2 eV), which greatly limited its application in the visible-light photocatalysis. In addition, the reaction mechanisms of photocatalytic degradation of organic compounds are not well understood, which limits the practical application of the photocatalysis in the wastewater treatment. Herein, photocatalytic degradation intermediates and mechanisms of methamidophos and phoxime were investigated in the suspension containing TiO2 and La-TiO2, respectively. Three types of fuller carbon modified TiO2 nanocomposites (MWNT-TiO2, SWNT-TiO2, C60-TiO2) were prepared by hydrothermal method and their photocatalytic activities under visible-light irradiation were evaluated by photocatalytic hydrogen production and photocatalytic degradation of pirimicarb. The formation mechanism of the nanocomposites and the mechanism of photocatalytic hydrogen production were discussed, respectively. The detail researchs and conclusions are as follows:1. By using various types of chromatographic technique, the photocatalytic mineralization products and degradation intermediates of methamidophos and phoxime were investigated in the suspension containing TiO2 and La-TiO2, respectively. The photocatalytic degradation mechanisms of methamidophos and phoxime were discussed. The experiment result shows that methamidophos was adsorbed on m-TiO2 surfaces through C7-O-Ti bond in the initial degradation process. The cleavage of P-N, P-N, and P-N bond were dominated by the electron transfer process. Afterward, methamidophos was degraded by the hydroxylation process. There were three types of intermediates found in the photocatalytic degradation of phoxime, i.e. one methylated product of the hydrolysate from phoxim and two products from the electron transfer process. In addition, in the present system, all organic compounds in the commercial emulsion can be decomposed unselectively without generation of any long-life compound, which could be useful in view of the practical application. 2. MWNT-TiO2 and SWNT-TiO2 nanocomposites were prepared through a hydrothermal process and characterized. Their photocatalytic activities were evaluated and their formation mechanism was discussed. The inter-particle mesopores are existed in the TiO2 nanoparticles, which have intimate contact with CNT. MWNT and SWNT after functionalization were well dispersed in the nanocomposites, which could hinder the grain growth and elevate the transforming temperature of anatase TiO2 to rutile TiO2. CNT-TiO2 nanocomposites with different CNT content possess similar porosity and relative large surface area. MWNT-TiO2 exhibited visible-light activity and enhanced full spectra activity upon photocatalytic degradation of pirimicarb, which can be attributed to the suppressed electron-hole recombination resulted from the quick transfer of electron on MWNT. However, SWNT-TiO2 did not exhibit any visible-light activity although a relative good full spectra activity was obtained over SWNT-TiO2 with 1.25 and 2.5 wt% SWNT.3. The photocatalytic activities of MWNT-TiO2 and SWNT-TiO2 nanocomposites were evaluated by photocatalytic hydrogen production. The effects of functionalization treatment, CNT content, hydrothermal temperature, and light source on the rate of hydrogen evolution were investigated. The mechanism of photocatalytic hydrogen production was also discussed. The experiment result showed that a simple mixture of MWNT and TiO2 did not have visible-light activity. The treatment in boiled nitrate solution can produce functional groups on the MWNT surface and avoid destroying MWNT structure due to the excessive oxidation reaction. MWNT content have a large influence on the photocatalytic activitiy of MWNT-TiO2 and the optimal content is 5 wt%.5 wt% MWNT-TiO2 derived from hydrothermal process at 140℃showed the best visible-light activity with a hydrogen evolution rate of 15.1μmol/h whereas 5 wt% MWNT-TiO2 at 100℃performed the best full spectra activity. MWNT-TiO2 showed a wide photoresponse under monochromatic light of wavelength changing from 350 to 475 nm with quantum efficiencies of 4.4% and 3.7% upon irradiation with wavelength of 420 and 475 nm, respectively. However, SWNT-TiO2 did not exhibit any visible-light activity, which could be related to the nature of SWNT. Furthermore, a weak full spectra activity was observed over SWNT-TiO2 in comparison with pure TiO2, which possibly can be attributed to the formation of recombination centre on SWNT. 4. C60-TiO2 nanocomposites were prepared through a hydrothermal process and characterized. The photocatalytic activities were also evaluated. C6o after functionalization was well dispersed in the nanocomposites, which could hinder the grain growth and elevate the transforming temperature of anatase TiO2 to rutile TiO2. TiO2 nanoparticles in the C60-TiO2 have inter-particle mesopores, and a relative uniform distribution of particle size, which is in the range of 20-75 nm with the mean particle size of 48 nm. C60-TiO2 also have relative large surface area and good adsorption in the visible-light spectra (λ>420 nm). C60-TiO2 exhibited visible-light activity and enhanced full spectra activity upon photocatalytic degradation of pirimicarb.5. The photocatalytic activities of C60-TiO2 nanocomposite was evaluated by photocatalytic hydrogen production. The effects of C60 content, preparation method, and light source on the rate of hydrogen evolution were investigated. The mechanism of photocatalytic hydrogen production was also discussed. C60-TiO2 nanocomposite demonstrates excellent stability of both visible-light photoactivity and chemical composition after working for a long time. In comparison with photocatalytic hydrogen production over dye sensitized TiO2, C60-TiO2 possess a efficient and stable photocatalytic activity on hydrogen production. C60-TiO2 shows a wide photoresponse under monochromatic light of wavelength changing from 350 to 550 nm with quantum efficiencies of 4.2% and 8.3% upon irradiation with wavelength of 420 and 475 nm, respectively.