二氧化矽/二氧化鈦中性水溶膠之製備與光催化活性研究

Abstract

二氧化鈦（TiO2）中性水溶膠因為不含有機溶劑，且所含的腐蝕性物質極少，可應用至各式建材，沒有揮發性有機氣體逸散或腐蝕現象。但TiO2在高溫下，容易轉變成金紅石晶型結構，降低光催化活性；且其高達2.52的折射率，使反射性過強，降低了光線的穿透率。為改善TiO2的熱穩定性與高折射率，並強化其光催化活性，本研究採用共沈澱解膠法，以四氯化鈦為前驅物，雙氧水為解膠劑，在加溫迴流階段，加入二氧化矽（SiO2），製備出SiO2/TiO2中性水溶膠，SiO2和TiO2形成的Ti-O-Si鍵結，具有較高的熱穩定性，在700℃的加熱條件下，不會轉變成金紅石晶型結構；同時，Ti-O-Si鍵結對水氣具有較佳的親和性，使SiO2/TiO2材料表面含有較高的氫氧官能基，電子電洞對產生時，容易與電洞形成氫氧自由基，大幅提高光催化的氧化能力。在中性條件下，SiO2和TiO2皆帶負電荷，可避免TiO2的聚集與成長，故SiO2/TiO2材料具有較小粒徑與較大的比表面積，也有助提高光催化活性。 光催化活性的氮氧化物去除性能測定結果顯示在SiO2/TiO2重量比為1.5時，具有最高的氮氧化物去除率和最低的二氧化氮選擇率；經700℃加熱後，其活性是市售的Degussa P25粉體及ONID TH中性水溶膠的兩倍。當SiO2/TiO2重量比達3以上時，所製備的SiO2/TiO2複合薄膜，具有抗反射性，可提高2%的穿透率，同時兼具暗處超親水性，可在暗處維持兩週以上的超親水性，並具備油酸分解和濕式亞甲基藍分解性能，具有優異的自我潔淨功效。 本研究製備的SiO2/TiO2中性水溶膠，經特性分析與各式光催化活性測定，證實具熱穩定性、抗反射性、暗處超親水性與高光催化活性，可以解決TiO2中性水溶膠的問題點，並擴大應用至採光玻璃等各式建材。

The neutral TiO2 photocatalytic hydrosol could be widely applied to various building materials without corrosion and emission of volatile organic compounds. However, the anatase TiO2 would transfer to the rutile phase and decrease the photocatalytic activity if the heating temperature is higher than 600℃. Besides, the high refractive index, n∼2.52, would cause high reflection and reduce the light transmission. In order to improve the thermostability and high reflection of TiO2, a neutral SiO2/TiO2 hydrosol was prepared in this study via a coprecipitation-peptization method using TiCl4 and SiO2 hydrosol as precursors and H2O2 as an oxidizing agent. The prepared SiO2/TiO2 composite hydrosol is an environmental benign material and maintains its good stability after keeping in ambient environment for more than two years. The additive SiO2 decreased the refractive index, suppressed the aggregation of TiO2 and formed Ti-O-Si bond with TiO2. The lower refractive index of SiO2/TiO2 thin film could increase the transmittance of visible light, and the Ti-O-Si bond could retard the transformation of TiO2 from anatase to rutile. In addition, SiO2 particles can separate TiO2 particles and suppress the growth of TiO2 particles; thus, the SiO2/TiO2 composite material has larger surface area after treating under high temperature. Simultaneously, the natural wettability of SiO2/TiO2 thin film contributed the persistent superhydrophilicity. While the SiO2/TiO2 weight ratio was 3, the prepared SiO2/TiO2 thin film exhibited antireflection, persistent superhydrophilicity and self-cleaning effect even after treated at 700 oC for 5 minutes for simulating the tempering process. The results showed the neutral SiO2/TiO2 composite hydrosol could be a good antireflective self-cleaning coating material for solar cells or building materials.