奈米光觸媒能夠有效分解污染物，然而奈米光觸媒顆粒由於粒徑太小，有不易自反應系統中分離回收再利用的問題，特别是在工業廢水的光催化處理，光催化劑的顆粒流失，限制了光催化反應在實廠上的應用。為了確保在較高光催化效率之前提下解决光觸媒顆粒的分離與回收這一關鍵問题，本研究旨在製備具有磁性的光觸媒顆粒，以期利用簡單的外加磁場來回收懸浮的二氧化鈦顆粒。採用共沉澱法制備出Fe3O4磁性奈米顆粒，以界面活性劑(SDS)控制磁性顆粒大小，再以溶膠-凝膠法合成奈米磁性二氧化鈦複合顆粒，並利用XRD、TEM、SQUID、ICP-AES和ASAP對其進行結構分析，以探討不同製備條件對於磁性二氧化鈦複合顆粒特性之影響。經由SQUID的分析結果顯示，酸洗步驟確實能將複合顆粒表面的鐵粉洗去，但結果仍然滿足磁性分離的要求；煅燒前後並不會對磁性二氧化鈦複合顆粒的飽和磁化率有所影響。另外，使用自製的TiO2 particles和magnetic TiO2 composite particles兩種光觸媒進行甲醇的分解實驗後，結果顯示，在光照期間，甲醛生成濃度皆隨時間有呈現線性增加的趨勢，其中TiO2 particles的甲醛生成速率明顯高於magnetic TiO2 composite particles的數值，但本研究所製備的磁性二氧化鈦，其產生自由基的速率優於文獻中包覆形之磁性二氧化鈦達2倍之多。

Photocatalysts assist decomposition of pollutants more effectively. However, particle size of nano-photocatalyst is usually too small to be separated and recycled from the reaction system, especially for wastewater treatment. These disadvantages lead to loss of photocatalyst particles and application of photocatalysis in scale-up is thus limited. The main objective of this research is to preparing magnetic TiO2 composite nanoparticles, which can be recycled by using external magnetic field. Magnetite nanoparticles were synthesized by chemical co-precipitation and the size was controlled by adding surfactant. The magnetic TiO2 composite nanoparticles were synthesized by sol-gel method. The composite nanoparticles were characterized by XRD, TEM, SQUID, ICP-AES and ASAP to understand the effects of preparation conditions on the properties of composite nanoparticles. The results of SQUID confirmed that acid-wash dissolved Fe3O4 nanoparticles on the surface of composite nanoparticles and the magnetic susceptibility was thus decreased. Still, the magnetic property of the particles is acceptable for magnetic separation. Calcination did not affect magnetic susceptibility of magnetic TiO2 composite particles. Decomposition of methanol by TiO2 nanoparticles and magnetic TiO2 composite nanoparticles were carried out to compare their photocatalytic ability. HCHO concentration displayed linear increase with reaction time. The formation rate of HCHO when pure TiO2 nanoparticles were used was higher than that when magnetic TiO2 composite nanoparticles were used as catalysts.

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