製備高光催化活性之有機修飾中孔洞二氧化鈦

Abstract

本研究中首次以非水解性溶膠-凝膠法 (non-hydrolytic sol-gel)，使用三辛基氧化膦 (TOPO) 與1,3,5-三甲基苯 (TMB) 分別作為模板劑及擴張劑，以單一步驟製備有機修飾的中孔洞二氧化鈦 (TiO2) 結晶體。樣品比表面積介於2-103 m2/g，且數值隨TOPO濃度增加而減小，當TOPO/Ti = 0.05 (sample TP 1) 時，TiO2顆粒間隙可形成中孔洞結構，而當TOPO/Ti比例提升到0.1 (sample TP 2) 時，TOPO形成的微胞使樣品隨即轉變為微孔洞結構，進一步提高TOPO/Ti比例則製備出TOPO披覆的奈米顆粒。添加TMB之後，微孔洞與連續孔洞樣品皆呈現Type Ⅳ isotherm，並且大幅提升了比表面積與孔洞數量和孔洞尺寸，由此可知TMB擴大微胞尺寸並幫助TOPO形成微胞而驅使TiO¬2形成中孔洞材料。其中TMB/TOPO/Ti為0.12/0.1/1的條件下，可得到高比表面積236 m2/g，平均孔洞尺寸為3.6 nm的樣品，且未經鍛燒即得到高程度的anatase 晶體，晶粒大小約為4.4 nm。在紅外光光譜分析中可以清楚看到C-H的波峰出現在2760-3150 cm-1，且P-O-Ti的波峰出現在1100 cm-1，相對於原TOPO的P=O在1150 cm-1，此紅位移的結果顯示TOPO以化學鍵結修飾於二氧化鈦上。由X光光電子能譜儀分析顯示，樣品表面的Ti-O/(Ti + P)比例大約1.3~1.8，略小於二氧化鈦的理論值2，因此樣品表面有缺陷形成。並且，從元素分析結果得到約有45-70 %的TOPO會在合成的過程中遺失。有機修飾中孔洞二氧化鈦降解環境荷爾蒙-酚甲烷 (Bisphenol-A, BPA) 的光催化能力高於純TiO2。吸附結果顯示TOPO修飾的孔洞結構藉由疏水性物質間非特定性吸附與毛細作用力對BPA展現極高的吸附能力，因此除高比表面積外，孔洞結構與表面有機修飾物協同性的增進光催化活性。

In this study, an organically modified mesoporous TiO2 is prepared using a non-hydrolytic sol-gel method when trioctylphosphine oxide (TOPO) and 1,3,5-trimethylbenzene (TMB) are used as the template and auxiliary swelling agent, respectively. The specific surface areas of the samples ranged 2-103 m2/g and increased with decreasing the TOPO concentrations. The critical TOPO/Ti ratio for microporous structure was 0.1. Addition of TMB led micro- and continuous porous samples exhibiting Type Ⅳ isotherm. In addition, remarkable increases in specific surface areas, pore volumes and pore sizes were obtained. This finding indicates that TMB assists the formation of TOPO micelles and expands the size of the micelles to form mesoporous TiO2. The optimal TMB/TOPO/Ti ratio for the mesoporous TiO2 was 0.12/0.1/1, at which the TiO2 exhibited the largest surface area of 236 m2/g and an average mesopore size of 3.6 nm. Highly anatase structures with a mean crystallite size of 4.4 nm were obtained. The mesoporous TiO2 clearly shows C-H and P-O-Ti stretching absorptions at 2760-3150 and 1100 cm-1, respectively, in the FTIR spectra. Moreover, the red shift of the P=O peak from 1150 to 1100 cm-1 indicates that the TOPO is chemically bound to the surface through the formation of P-O-Ti bonds. Surface Ti-O/(Ti + P) ratios ranged 1.3-1.8, which were smaller than the theoretical ratio of 2 of TiO2. It suggested that many defects are introduced into the surface lattice. The mesoporous TiO2 shows higher photocatalytic activity than pure TiO2 for degradation of bisphenol-A (BPA). The TOPO-modified mesoporous TiO2 samples not only contained large surface areas but also surface hydrophobic property and proper porous structures that exhibit extraordinarily high affinity for BPA, thus synergistically enhancing the photoactivity.