| In recent years, semiconductor function materials have attracted significant interest. Especially, nano-sized TiO2 are paid the extensive attention because of its various merits, such as nontoxicity, long-term stability and high photocatalytic activity. Therefore, it has several promising applications in the photoelectric chemistry and photocatalysis. Generally, the catalytic activities mainly depend on the anatase phase, high crystallinity, small size and large surface area. However, there is contradiction among these influential factors, which is difficult to further improve its photocatalytic performance. The high thermal stability is the key point to resolve this question. Recently, titania has been synthesized with ammonia or amine to increase thermal stability. But the synthetic method is complex and the analysis of mechanism is not clear, which would bring much discommodity to the work. Based on the above discussion, in this work we present a novel simple approach to the preparation of the thermal stability and highly photocatalytic activity of anatase TiO2 with amine, and deeply search for the mechanism.TiO2 nanoparticles synthesized by a sol-hydrothermal process were modified with amine by a simple method. The effects of amine modification on the thermal stability and photocatalytic activity of anatase TiO2 were mainly investigated, by means of XRD, XPS, TEM, SPS and other techniques. The results show that the amine modification obviously enhances the thermal stability of nanosized anatase TiO2, extending the anatase to rutile phase transformation by 250℃compared to the unmodified sample. Thermal stability has been raised mainly due to:ammonia molecules produced by hydrolysis of amine and nitrogen impurities generated by high temperature thermal treatment can effectively prevent direct contact of anatase particles. During the processes of photocatalytic degradation RhB, the as-prepared amine modified TiO2 by thermal treatment at 750℃exhibit higher activity, and even close to P25-TiO2. It is revealed that excellent photocatalytic performance is mainly ascribed to high anatase crystallinity and a small amount of nitrogen impurities. The work provides a guideline for the design of high thermal stability and high activity of nano-anatase TiO2 photocatalytic materials, and is bound to develop nano-TiO2 used in ceramics, coatings and other fields.The rutile phase TiO2 with lower photocatalytic activity were obtained at high temperature by a heat treatment method. To prove the rutile TiO2 can show high activity, TiO2 nanopowders with different phase composition were directly obtained via a sol-hydrothermal process, using hydrochloric acid solution. The relationship between the rutile phase content and surface photovoltage (SPV) characteristic, along with the photocatalytic activities degradation of dye pollutant under the visible-light., were mainly investigated in detail. The results show that TiO2 nanopowders with different rutile phase composition can be synthesized from the hydrochloric acid solution. It is found that chlorine ionic play a very important role in control of crystal phase, crystallite size and shape. The SPS response of the directly obtained TiO2 is different from the samples accepted by post-thermal treatments at different temperature. With the rutile phase content increasing, the SPS response intensity of the directly obtained samples gradually increased. The SPS response relating to intrinsic defects of the rutile TiO2 did not appear, indicating that it contains less intrinsic defects, which also explains why the samples showed a higher response peak resulting from band-to-band transitions. As-synthesized rutile sample showed a high activity under visible light, which is better than the P25-TiO2. The excellent photocatalytic performance is mainly related to the large surface area and high photogenerated charge separation rate. This provides a novel method to design and synthesize the high efficiency photocatalyst. |
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