奈米金粒子對反蛋白石結構二氧化鈦光電化學特性之影響

Abstract

二氧化鈦為一種N型半導體，由於製作成本低、無毒性對環境很友善、化學穩定度高等特點，是最常見的光催化材料，然而其照光產生之電子電洞對容易再結合，且其能隙 (3.2 eV) 較大無法有效利用可見光，使得光催化效率不高，仍有很大的改善空間。有許多文獻指出具有高表面積多孔洞的結構可增加二氧化鈦與電解液的接觸面積，提高其光電催化之效能，而添加惰性金屬可增加二氧化鈦照光產生之電子電洞分離的效率，並可利用金屬表面電漿共振的特性增加可見光下之催化活性。 本研究利用自組裝成規則排列的聚苯乙烯球作為模板，以溶膠凝膠法製備出反蛋白石結構之二氧化鈦，並進一步在其表面添加金奈米粒子。當二氧化鈦薄膜所浸泡之金氯酸溶液濃度越高，製備出之樣品金含量也越高，且金奈米粒子擁有較大的粒徑。之後利用量測光電流來分別探討添加不同含量的金奈米粒子對二氧化鈦電極在紫外光及可見光下光催化活性的影響。此外，本研究利用SEM、TEM、XRD及Raman等方式探討樣品之形貌結構，使用XPS分析樣品表面之元素化學組成，並利用吸收光譜量測樣品的光學特性。實驗結果發現不論在紫外光或可見光下，皆可藉由添加金奈米粒子增加二氧化鈦的光催化活性，得到較大的光電流值。在含有紫外光的光源下，以Au/Ti比為2.4 %，金奈米粒子平均粒徑為7 nm之樣品擁有最好的光轉換效率2.03 %；而在可見光下之光電流，以Au/Ti比為3.5 %，金奈米粒子平均粒徑為11 nm之樣品擁有最大的光電流值2.05 □A/cm2，為原本二氧化鈦的六倍。

Titanium dioxide, an n-type semiconductor, is the most widely used photocatalytic material due to its high chemical stability, low cost and environmental friendliness. However, the photocatalytic efficiency of TiO2 is limited by the large band gap (3.2 eV) that can only utilize UV light (about 5 % of total sunlight) and fast charge recombination. Loading noble metals has been reported to enhance the photocatalytic efficiency of TiO2 by improving the separation of charge carriers and absorbing visible light due to surface plasmon resonance (SPR) effect. In this study, hierarchical macroporous titania was produced through a sol-gel method using ordered polystyrene (PS) spheres as the templates to form inversed opal structures. We futher loaded different quantity of gold nanoparticles by immersing the inversed opal TiO2 film into HAuCl4 solutions. The loading quantity and particle size of Au increased as the HAuCl4 concentration was increased. The photocatalytic activity of the as-prepared TiO2 was investigated by the photocurrent generated under UV-Vis and visible light irradiations, respectively. Furthermore, we determined the morphology and crystal structure of samples by SEM, TEM, XRD and Raman. Also, we analyzed the surface chemical composition by XPS and measured the optical properties by UV-Vis absorption spectra. Under UV-Vis light irradiations, the sample with Au/Ti ratio of 2.4 % and Au particle size of 7 nm exhibited the best photoconversion of 2.03% which was 1.3 times higher than pristine TiO2; under visible light irradiation, the sample with Au/Ti ratio of 3.5 % and Au particle size of 11 nm displayed the maximum pototcurrent 1.19 □A/cm2 a 6-fold increase relative to priatine TiO2.