Preparation And Performances Of Hierarchically Macro-mesoporous TiO₂Composites

Hierarchically macro-mesoporous TiO2has great advantages in photocatalysis and adsorption applications because of its large specific surface area and small molecular diffusion resistance. However, the photocatalytic activity of this kind of TiO2has been restricted due to poor utilization ratio of visible light and easy recombination of photogenerated electronic-hole pairs. Furthermore, TiO2has a small adsorption capacity to dyes and other organic pollutants. Therefore, in this paper, for the hierarchically macro-mesoporous TiO2synthesized by the surfactant self-assembly technology, several modification methods, such as Zirconium ion doping, noble metal Au deposition and grapheme decoration were put forward to improve the photocatalytic activity and adsorption capacity of TiO2.In order to improve the photocatalytic activity of hierarchically macro-mesoporousTiO2, hierarchically macro-mesoporous ZrO2-TiO2composites were successfully synthesized by the surfactant self-assembly technology. The photocatalytic activities of ZrO2-TiO2composites were evaluated by the decomposition of Rhodamine B under UV light irradiation. XPS analysis showed that a hybridized ZrO2TiO2matrix with the [=Zr-O-Ti=] bonding structure was formed in the composite. It was demonstrated that ZrO2-TiO2composites exhibited remarkably higher photocatalytic activities than pure TiO2and ZrO2materials. Especially, ZrO2-TiO2(6.9%) was proved to be the most efficient catalyst. It can degrade87%of Rhodamine B under UV light irradiation for3hours and its degradation kinetic constant was2.0times larger than that of pure TiO2-The degradation of Rhodamine B followed pseudo-first-order kinetic model. ESR measurements showed the direct evidence that the active radicals (OH· and O2·) were responsible for the photodecomposition of Rhodamine B.Aimed at enhancing photocatalysis through intensifying light harvesting, a new photocatalyst was fabricated by infiltrating Au nanoparticles into hierarchically macro-mesoporous TiO2via in situ hydrothermal reduction approach. The photocatalytic activities of AU-TiO2composites were evaluated by the decomposition of Rhodamine B under UV and visible light irradiation. The absorption spectra of AU-TiO2composites were extended to the visible region of400-800nm. Au-TiO2composites were found to exhibit remarkably higher photocatalytic activities than pure TiO2under both UV and visible light irradiation. Especially, Au-TiO2-1.9was proved to be the most efficient photocatalyst. It can degrade84%of Rhodamine B under UV light irradiation for3hours and its apparent rate constant was1.8times larger than that of TiO2. The dye degradation followed pseudo-first-order kinetic model and photogenerated holes were the main active species under UV light irradiation. Au-TiO2-1.9can degrade94%of Rhodamine B under visible light irradiation for2hours, which was2.4times larger than that of pure TiO2.In order to improve the adsorption ability of hierarchically macro-mesoporous TiO2, hierarchically macro-mesoporous GS-TiO2composites were successfully synthesized based on the surfactant self-assembly technology. For GS-TiO2composites, XRD patterns and FTIR spectra both demonstrated that graphene oxide had been reduced to graphene under calcination at high temperature. The equilibrium adsorption rate of GS-TiO2composites to Rhodamine B and methylene blue were88%and99%, respectively, which was3.9and0.6times larger than that of pure TiO2, indicating the significantly enhanced adsorption capacity of GS-TiO2composites The dye adsorption kinetics of GS-TiO2composites were in accordance with the pseudo second-order kinetic model.