本論文係有關以聚丙烯酸溶膠凝膠法製備MgFe2O4奈米粉體及其吸附與光催化特性之研究。首先利用聚丙烯酸螯合Mg(II)與Fe(III)金屬陽離子產生交聯，然後將形成之溶膠乾燥製得凝膠，並於500℃下鍛燒，即可製得MgFe2O4奈米粉體。由X光繞射(XRD)與穿透式電子顯微鏡(TEM)分析得知，所得奈米粉體為平均粒徑20.5 ± 5.7 nm、具有尖晶石結構之MgFe2O4。由表面積及傅立葉轉換紅外線(FT-IR)光譜儀分析可知，其比表面積約45.43 m2/g，且表面具有-OH官能基。此外，由界面電位及磁性分析可確認所得MgFe2O4奈米粉體之等電點約在6.2附近，飽和磁化量為18.4 emu/g。因所得MgFe2O4奈米粉體在酸性溶液中表面帶有正電荷，且為在可見光範圍具有顯著吸收之半導體材料，可能作為磁性可操控之陰離子吸附劑與可見光光觸媒，故本研究進一步探討其吸附與光催化特性。
關於MgFe2O4奈米粉體吸附陰離子之特性研究，係以Cr(VI)為吸附對象。結果顯示，平衡所需時間約為45分鐘。pH越低時吸附量越大，此乃因pH值低於等電點時，MgFe2O4奈米粉體表面的-OH會傾向形成- OH2+，可藉由陰離子交換機制吸附Cr(VI)陰離子。又MgFe2O4奈米粉體吸附Cr(VI)遵守Langmuir恆溫吸附模式，在固定25℃、pH 4.5時其最大吸附容量和平衡常數分別為11.21 mg/g與0.07 L/mg。此外，在20~35℃範圍內，溫度效應並不顯著。關於MgFe2O4奈米粉體光催化特性之研究，係以分解玫瑰紅染料為例。結果顯示，MgFe2O4奈米粉體對玫瑰紅染料並無吸附能力，但可將玫瑰紅染料在可見光範圍之光分解速率常數顯著提升。

This thesis concerns the preparation of MgFe2O4 nano-powders by the polyacrylic acid-based sol-gel method and their adsorption and photocatalytic properties. At first, polyacrylic acid was used for the chelation of Mg(II) and Fe(III) ions to result in the crosslinking. Then, the sol was dried to form the gel. MgFe2O4 nano-powders could be obtained by calcining the gel at 500°C. From XRD and TEM analyses, it was found the resultant nano-powders were MgFe2O4 with a mean diameter of 20.5 ± 5.7nm and a spinel structure. By the analyses of surface area and FT-IR spectrum, their specific surface area was determined to be 45.43 m2/g and –OH group was found on their surface. In addition, the zeta potential and magnetic analyses revealed that they had an isoelectric point of 6.2 and a saturation magnetization of 18.4 emu/g. Because the resultant MgFe2O4 nano-powders were positively charged in acid solution and were the semiconductor material with significant absorption in visible range which made them useful as the magnetically controllable anion adsorbent and the visible light photocatalyst, their adsorption and photocatalytic properties were further examined in this study.
The adsorption capability of MgFe2O4 nano-powders for anions was examined using Cr(VI) ions as an example. It was found that the time required to achieve the equilibrium was about 45 min. As the pH decreased, the adsorption capacity increased. This could be attributed to the fact that, when the pH was less than their isoelectric point, the -OH group on the surface of MgFe2O4 nano-powders would be protonated to be - OH2+ group which could adsorb Cr(VI) ions via the anion exchange mechanism. The adsorption of Cr(VI) ions by MgFe2O4 nano-powders obeyed the Langmuir isotherm. At 25°C and pH 4.5, the maximum adsorption capacity and equilibrium constant were 11.21 mg/g and 0.07 L/mg, respectively. Moreover, in the range of 20-35°C, the temperature effect was not significant. The photocatalytic property of MgFe2O4 nano-powders was examined using the red dye rhodamine B as an example. It was found that MgFe2O4 nano-powders did not adsorb rhodamine B. However, the visible light photo-degradation rate of rhodamine B could be significantly enhanced by the presence of MgFe2O4 nano-powders.

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