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The preparation of Hydrophobic TiO2 by the wet coupling treatment method was investigated using compounds of the alkyltrimethoxysilane series. Additionally, wet treatment of TiO2 using preliminarily treated n-PTMS and n-BTMS solutions was examined for the effectiveness of the use of preliminarily treated silane coupling agent in the wet process. The main results obtained are as follows : (1) The adsorption amount of n-PTMS dissolved in pure water onto TiO2 treated by the wet method was negligibly small, resulting in an M value that indicated the degree of hydrophobicity was zero. In contrast, M values of TiO2 treated by the wet method using i-BTMS, n-BTMS and n-HTMS increased with the increase in elapsed time. However the increase in carbon number resulted in the acceleration of increase of M values, causing an increase in maximum M value. A large amount of fixed ATMS does not necessarily signify maximum M value. (2) The maximum M value of TiO2 treated by the wet method using different pH solutions containing n-BTMS appeared to be 60%. Retention time required to increase of M value was shortened according to the sequence of pure water, pH 9.0, pH 4.0 and pH 3.3, and this finding suggested that the sequence was directly related to hydrolysis and condensation reaction rates of n-BTMS in those solutions. The amount of n-BTMS required to provide sufficient hydrohobicity to TiO2 at pH value, under which coupling treatment proceeds quickly, is larger than for slower treatment. The minimum amount of fixed n-BTMS providing maximum M value to TiO2 was found to be about 1 mg per 1 g TiO2, which was 27% of the theoretical amount of n-BTMS addition. In aqueous ammonia solution of pH 10.0, n-BTMS exhibits white turbidity to form an emulsion. Using this emulsion, wet coupling treatment of TiO2 proceeds quickly compared to those at lower pHs. (3) Wet treatment of TiO2 using preliminarily treated n-PTMS or n-BTMS was able to provide hydrophobicity faster than that using n-BTMS solution without preliminary treatment. |
