Water/supercritical Co_2 Microemulsions With A Fluorinated Double-tail Surfactant For Syntheses Of Semiconductor Ultrafine Particles

摘要

A water/supercritical CO_2 microemulsion (W/scCO_2 μE) with a fluorinated double-tail surfactant bis (lH,lH,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2) was evaluated in terms of its nanoreactor performance for synthesizing semiconductor ultrafine particles of TiO_2, ZnS, and CdS. By the addition of tetraisopropylorthotitanate (TIP) in W/scCO_2 μE, TiO_2 ultrafine particles were successfully synthesized with a spherical shape and sizes of several tens of nanometers, which were similar to those synthesized in W/cyclohexane μE with a typical hydrocarbon double-tail surfactant AOT. Interestingly, in contrast to the μE system, TiO_2 particle syntheses in liquid-crystal-like (LC-like) surfactant precipitant phase yielded a dendritical morphology of TiO_2. For metal sulfide synthesis, the addition of metal nitrates as precursors in W/scCO_2 μE was found to lower the maximum W_0 value at which W/scCO_2 μE can form, which would result from the promoted aggregation and fusion between reverse micelles, i.e., LC formation. After mixing both the W/scCO_2 μEs containing metal nitrate and Na_2S, metal sulfide ultrafine particles were yielded with spherical shape and sizes of several tens of nanometers. These results suggested that W/scCO_2 (lE with 8FS (EO)_2 may become a valuable nanoreactor when further investigations reveal size-control techniques for the products.%二鎖型フッ素系界面活性剤により構築された水／超臨界CO_2マイクロエマルション（W／scCO_2μE）のナノリアクターとしてのrn性能を，TiO_2，ZnS，CdSの三種の微粒子合成系において評価した。アルコキシドからのTiO_2合成では，一般的なW／OμEによrnるものと同様に，数十nmに制御された球状TiO2微粒子が多く得られた。一方，液晶様析出物が存在する水／超臨界CO_2混合rn系でのTiO_2合成では，興味深いことに，数μmの放射状TiO_2微粒子が得られた。Na_2SとCd（NO_3）_2もしくはZn（NO3)_2を含む二rnつのW／scCO_2μEを混合し，金属硫化物を合成したところ，数十nmの球状微粒子が多く得られた。以上の結果は，W／scCO_2μErnが十分にナノリアクターとして働くことを示しており，圧力操作による簡易分離技術とサイズ制御技術が達成されれば，VOCrnフリーの有効な微粒子合成技術になり得ると考えられる。