超臨界二酸化炭素を溶媒とした酸化チタン粒子の表面改質

摘要

Surface modification of fine TiO_2 particles with various normal-chain alcohols was conducted in supercritical CO_2 (scCO_2) as a solvent using supercritical CO_2 method and immersion method. The modified fine TiO_2 particles were characterized by BET surface area, elemental analysis, FT-IR, XRD, particle size distribution, and dispersion test. The number of surface functional groups (N_R) on the samples was calculated from the results of elemental analysis and surface area. This value was available to evaluate the degree of the surface modification. Nr changed remarkably with reaction temperature, reaction pressure, and modification methods. Judging from the obtained results, the concentration of alcohol dissolved into (scCO_2) and the character of (scCO_2) affected on N_R. The effects of the use of (scCO_2) as a solvent were as follows : (l) promote dehydration between alcohol and hydroxyl groups on TiO_2 surface, and (2) suppress the agglomeration of modified particles. It was also found that the hydrophobicity of modified samples improved with an increase in the number of carbon chains. Consequently, a newly developed organic- free process which is environment-friendly has been proposed.%有機溶媒の代替溶楳として注目される超臨界二酸化炭素（scCO_2）を用いた酸化チタンの表面改質を行い，環境にやさしい表 面改質プロセスの構築を目指した。 改質剤として各種直鎖アルコール（C_4～C_(10)）を選択し，酸化チタン粒子の表面改質を行い，各種分析（BET表面積，元素分 析，分散嗜好性試験，IR測定，粒子径分布測定，XRD測定）結果より改質試料を評価した。 いずれの改質剤においても，酸化チタンの表面改質程度は温度・圧力に依存し，scCO_2中に溶解したアルコール濃度と，scCO_2 の溶解力と拡散性が改質程度に影響を及ぼすと考察した。また，scCO_2共存効果は，（1）酸化チタンの表面吸着水を除去し，ア ルコールと酸化チタンの脱水反応を促進する，（2）改質試料の凝集を抑制することであるとわかった。さらに，改質剤の炭素鎖 長の増加にともない，改質試料の疎水性が向上することもわかった。