光觸媒是一種環保材料，也是一種催化劑，可以去除多數有害物質，應用範圍非常廣，可施作於地板、牆面、家具、跑道和污水中等。二氧化鈦因為能隙大且無毒性的優點，廣泛被使用為光觸媒的材料，且只需要紫外光，完全不需消耗其他能源，即可達到淨化空氣、純化水質和殺菌等功能。
由於奈米二氧化鈦顆粒小，分散性良好，在水中不易回收，本研究利用溶膠凝膠法製備鐵酸鎳-二氧化矽-二氧化鈦之磁性光觸媒複合粉末。溶膠凝膠法製備而得的奈米級鐵酸鎳，其磁性良好，熱穩定性佳，在外加磁場下，易回收；相同的，使用溶膠凝膠法製備奈米級二氧化矽鈍化層，均勻披覆在鐵酸鎳上，可提高顆粒比表面積，還可藉由二氧化矽之高能隙特性，避免光溶解現象。磁性光觸媒可回收並重複使用，其回收率高達90%以上，達到環保經濟兩方面之優點。
本研究擬合成鐵酸鎳-二氧化矽-二氧化鈦，其為具核殼結構之複合粉末，並利用XRD、FTIR、SEM確認複合層間之晶相與鍵結情形，BET、VSM分析其物理性質。在光催化降解亞甲基藍實驗中，在降解8小時後，鐵酸鎳-二氧化矽-二氧化鈦複合粉末具有好的光降解效能，接近市售P25光觸媒粉末，相較於P25粉末又具有磁性的優勢；且其優於鐵酸鎳-二氧化鈦之效能，證明二氧化矽鈍化層之高能隙特性，確實降低光溶解現象的發生。

Titanium dioxide nanoparticles have good dispersion and high surface area,but they are difficult to recover from water. The experiment of this study applies sol-gel method to synthesize NiFe2O4-SiO2-TiO2 magnetic photocatalyst. Nickel ferrite nanoparticles, has good magnetism, good thermal stability, and can easily be recovered when using an outer magnetic field using as magnetic core. NiFe2O4 was coated with a SiO2 passivation layer, which increases the surface area of the particles, and the passivation layer high energy gap helps avoiding photodissolution. Magenetic photocatalyst is retrievable and reusable, displaying environmental friendliness and economic effectiveness.

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