利用三辛基氧化膦包覆之二氧化鈦奈米晶粒光降解內分泌干擾物質研究

Abstract

近年來，利用異相光催化反應分解內分泌干擾物質之議題備受矚目，其中，加強光觸媒中電子-電洞對轉移能力與促進污染物吸附於光觸媒上，於提升光催化反應過中污染物分解之效率有著十分重要的貢獻。本研究利用非水解性溶膠-凝膠法合成三辛基氧化膦包覆之二氧化鈦奈米晶粒(TOPO-capped TiO2)，並探討此光觸媒對三種不同親疏水性的環境荷爾蒙：酚(log K¬ow = 1.46)、丙二酚(log K¬ow = 2.2)與雌酮(log K¬ow = 3.13)的光催化分解特性。結果證明有機修飾光觸媒對於內分泌干擾物質有優越的吸附能力，具有最高log Kow的雌酮於TOPO-capped TiO2的分配係數最高為28.64 l/g，其次為丙二酚，其分配係數為 3.09 l/g，最低為酚，其分配係數為0.15 l/g，反之，P25對於水中內分泌干擾物質之分配能力則是十分微弱。光催化結果可以Langmuir-Hinshelwood反應動力式描述，發現TOPO-capped TiO2分解酚與丙二酚的速率分別優於商用觸媒P25的1.4和3.2倍;動力速率常數分別為7.3□10-2和1.4□10-1 ppm□g□min-1□m-2，為P25之0.9與2.7倍 (8.2□10-2和5.2□10-2 ppm□g□min-1□m-2)，由於表面修飾的有機物會佔據二氧化鈦表面的活性位置，因此於降解酚的過程中，其速率常數略低於P25的表現，而TOPO-capped TiO2對酚與丙二酚的吸附常數分別為2.2□10-2 and 6.4□10-2 l/mg，為P25之2.2與5.8倍 (1.0□10-2 and 1.1□10-2 l/mg)。由此可知TOPO-capped TiO2促進酚與丙二酚吸附於TiO2，因此大幅提高其對環境荷爾蒙降解能力。此外，EPR結果發現在TOPO-capped TiO2系統中，光催化反應產生的氫氧自由基含量低，可知環境荷爾蒙主要利用電子電洞對進行直接光催化降解，且TOPO-capped TiO2中捕捉住的電子與電洞量明顯大於P25，可知TOPO-capped TiO2能有效抑制電荷再結合，以致於增進有效電荷利用率。總而言之，本研究合成有機物修飾之光觸媒具有良好有機物吸附能力與電子電洞對分離能力，因而大幅提升對環境荷爾蒙分解的光催化活性。與商用光觸媒 P25 相比，在處理不同親疏水性的環境汙染物上TOPO-capped TiO2對於催化極高疏水性的汙染物展現出優越的吸附與光催化能力，此種利用有機修飾光觸媒表面的材料為未來的環境汙染物降解議題提供了新的可行方案。

Heterogeneous photocatalytic reaction for decomposition of endocrine disrupting chemicals (EDCs) has attracted much attention. The efficiency of photodecomposition is limited by the recombination of electrons and holes and the adsorption ability between catalysts and target compounds. In this study, modification of titanium dioxide (TiO2) with trioctylphosphine oxide (TOPO) was prepared by a non-hydrolytic sol-gel method. The TOPO-capped TiO2 exhibited high adsorption ability for EDCs. The partition coefficients of phenol, BPA and estrone in the presence TOPO-capped TiO2 are 0.15, 3.09, and 28.64 l/g, respectively. In contrast, Degussa P25 adsorbs EDCs inefficiently. In the case of photocatalytic reaction, photocatalysis of EDCs follows Langmuir-Hinshelwood model. The initial rates for decomposition of phenol and bisphenol A (BPA) by TOPO-capped TiO2 are 1.4 and 3.2 times, respectively, higher than those by Degussa P25. The kinetic rate constants of phenol and bisphenol A are 7.3□10-2 and 1.4□10-1 ppm□g□min-1□m-2, respectively, in the presence of TOPO-capped TiO2, which are 0.9 and 2.7 times, respectively, higher than those in the P25 slurry (8.2□10-2 and 5.2□10-2 ppm□g□min-1□m-2). The smaller rate constant of TOPO-capped TiO2 for decomposition of phenol is due to that the modifier occupied active sites. The adsorption coefficients of phenol and bisphenol A are 2.2□10-2 and 6.4□10-2 l/mg, respectively, in the presence of TOPO-capped TiO2, which are 2.2 and 5.8 times, respectively, higher than those in the P25 slurry (1.0□10-2 and 1.1□10-2 l/mg). The photocatalytic mechanism of TOPO-capped TiO2 mainly involves direct photodecomposition of these adsorbed EDCs by photo-generated charges rather by hydroxyl radicals which is normally occurred in the P25-based system. In addition, the intensity of trapped holes and electrons in TOPO-capped TiO2 are much higher than that in P25. These results reveal that TOPO-capped TiO2 improved interfacial charge transfer. In summary, the TOPO assists partition of EDCs onto the TiO2 surface and facilitates interfacial charge transfer. These contributions improve photocatalytic activity of TOPO-capped TiO2.