Study On Synthesis And Surface Modification Of TiO₂Aerogels By Ambient Prusurs Drying

Titanium dioxide (TiO2) aerogels assembled by TiO2particles are nano-porous solid materials with network structure filled with gaseous dispersion medium. Combining catalytic activity, nontoxicity, good chemical stability of TiO2with high surface area and high porosity of aerogels, TiO2aerogels have various important application prospects. Now, the common drying method to prepare TiO2aerogels is supercritical drying that is good for preparing aerogels with high surface area, uniform particle size distribution and large pore volume. At the same time, it is so expensive, complex to operate and dangerous that application is restricted. However, ambient pressure drying can overcome these shortages.In this paper, after a retailed review of the present research status of aerogels and TiO2aerogels, TiO2aerogels were synthesized by the sol-gel process and ambient pressure drying. After analyzing some influencing factors on gelation time and aerogels property, the optimized parameters and process scheme were gotten. Based on this, surfactants were added for surface modification and the effects on gelation time and physicochemical characteristics were studied. At last, photocatalysis degradation performance of TiO2aerogels before and after surface modification was also discussed to lay an important foundation for research and application of TiO2aerogels.TiO2aerogels were synthesized by the sol-gel process and ambient pressure drying using tetrabutyl titanate (TBOT) as a precursor with suitable parameters as following TBOT:ethanol:water:acetic acid:formamide=1:24:6:1.8:0.5(molar ratio), dropping rate was one drop per second, the volume ratio of tetralthyl orthosilcate (TEOS)/ethanol as a surface modification agent was1:3and ethanol and n-hexane were low surface tension solvents. According to above process, low-density and porous aerogels with uniform network structure and nanoscale pores&framework were synthetized. The aerogels were0.818g/cm3in apparent density and79%in porosity. The specific surface area was416.6m2/g and the average pore size was8nm while samples still kept in anatase phase at900℃.Based on above process scheme, PEG2000and triblock copolymer F127as nonionic surfactants for surface modification were added to obtain modified TiO2aerogels with better property whose apparent density was as low as0.261g/cm3, porosity was93.3%and specific surface area was494.9m2/g. PEG2000and F127were found to contribut to improving specific surface area and decreasing apparent density respectively after investigating their effects on qualities of aerogels. Meanwhile, the effect of heat treatment on samples and mechanism of action of nonionic surfactants in system were also analyzed.Photocatalysis degradation performances of rhodamine B (RhB) using TiO2aerogels synthesized by ambient pressure drying were investigated and results indicated that their performances were quite good. The effects of heat treatment temperature, process scheme and surface modification on photocatalytic activity were discussed at the same time. Then, mechanism of photocatalytic degradation of RhB was also studied. There were two competitive processes during the photoreaction: N-deethylation and destruction of dye chromophore structure. The former occurred in early stage while the latter did in later stage.