Preparation And Properties Of SiO 2 @TiO 2 Photocatalyst And N-doped Hollow Carbon Nanospheres

SiO₂ nanomaterials with various morphologies and microstructures are easily prepared by controlling the hydrolysis of silicate ester. These materials can be used as template to prepare functional materials with core-shell or hollow structure, but also as support to load catalyst nanoparticle. Among kinds of SiO₂ nanomaterials, mesoporous SiO₂ nanospheres have been successfully prepared in large scale, which pushes its application research in various fields.In this work, the application of mesoprous SiO₂ nanospheres with dimension size of 25 nm in the fields of catalyst and functional carbon are investigated, in which they are used as support and hard template, respectively. The major contents are as follows.?1? In the area of catalyst, there are some literature about loading TiO₂ nanoparticles in or on ordered mesoporous SiO₂ support, such as SBA-15. However, the type of support usually has large particle size and it is difficult to control their morphology, which results in a long route of mass transfer. To further improving the catalysis performance of TiO₂, one of possible means is reducing the particle size of SiO₂ support to increase specific surface area and shorten mass transfer route. Unluckily, the relative research is few, because it is difficult for simultaneously realizing the size control of TiO₂ nanoparticles and efficiently loading on SiO₂ support with smaller dimension. Therefore, it is necessary to explore new technique.In this work, a facile method is presented to load TiO₂ nanoparticles on and in monodispersed mesoporous SiO₂ nanospheres of-30 nm diameter, in which a vacuum-rotary evaporation procedure combined with subsequent calcination treatment make titanium precursor adsorb on or in SiO₂ support and then crystallize to anatase TiO₂. Characterization results suggest that tailoring the loading amount of TiO₂ could permit the formation of rutile phase outside of the pores of SiO₂ support, enabling the fabrication of hybrid TiO₂/SiO₂ nanomaterial with large specific surface area (247 cm²·g^-1) and highly dispersed anatase TiO₂ nanocrystals. No complicated process and expensive instrument is involved in this method, and thus it has potential applications in engineering. In addition, the photocatalytic activities of the samples with different TiO₂ loading amount were evaluated by the degradation of rhodamine B dye in aqueous solution under UV-light irradiation. It is found that photocatalytic efficiencies of these materials are better than commercial P25, and complete degradation of Rhodamine B can be realized under 40 min for the sample with TiO₂ loading of 43%, which is attributed to the balance of high surface area and suitable TiO₂ loading amount.?2? SiO₂ nanospheres with size up to hundreds nanometer are commonly used as hard template to prepare functional materials with hollow shell. But their dimension size reduces to 25 nm, it is difficult to obtain monodispersed materials due to severe aggregation.Here, the feasibility of preparation of nitrogen doped carbon nanospheres with hollow shell structure is carefully studied by using mesoporous SiO₂ nanoshpheres with dimension size of 25 nm as hard template and dopamine as nitrogen and carbon source. The influences of the polymerization parameters of dopamine, carbonization conditions and the mean of etching SiO₂ on the morphology of the products are systematically investigated. The results show that the main factor is pH value of reaction system. After optimizing the experiment parameters, nitrogen doped carbon nanospheres with hollow shell structure are successfully prepared and its specific surface area is up to 855m²/g. Moreover, this material possesses good electrochemical supercapacitive properties, and its specific capacitance is of 193 F/g at 0.5A/g.