以鐵改質二氧化鈦光催化降解酸性紅27之研究

Abstract

本研究利用光沉積法製備由TiO2和Fe改質成的光觸媒，克服純TiO2高電子電洞再結合率的問題，大幅提升處理偶氮染料Acid Red 27 (AR27) 的效率。實驗先由貴金屬Ag (k=0.0047min-1)、過度金屬Fe (k=0.0419min-1)、稀土金屬Ce (k=0.0018min-1)三種金屬中，選定Fe為最佳披覆二氧化鈦的金屬，在調整製作光觸媒的操作參數披覆Fe量和Fe0-TiO2的鍛燒溫度，並做SEM-EDX和UV-vis分析Fe0-TiO2的表面特性和測染料、觸媒之最大吸收波長、AR27脫色率，最後找出最佳光降解AR27之實驗環境如UV光種類、觸媒劑量、pH、曝氣種類，探討其中的反應機制。 由SEM-EDX結果可知，Fe在TiO2上的披覆量為重量百分比0.71%左右，觸媒粒徑約為34 nm，Fe0-TiO2¬鍛燒溫度達450度，其晶型主要為銳鈦礦，能有效降解AR27，繼續升溫至550度，銳鈦礦慢慢轉變成晶紅石，效率反而降低。披覆金屬量對於AR27的脫色效率，隨著披覆量的上升而上升直到1 wt%，之後由於遮蔽效應和燒結現象披覆過多Fe反而影響脫色效率，因此選定披覆1 wt%的鐵以450度鍛燒作為光沉積法的最佳操作條件。 本研究的處理的目標汙染為10 ppm之AR27，選用8 W、254 nm之UV光為效益最高之燈管，加入最佳劑量0.5 g的Fe0-TiO2，在25度的恆溫水域中，經過兩小時的光降解，AR27幾乎完全去除，其中在酸性條件下，水中的AR27容易和Fe0-TiO2吸附做進一步的降解反應，因此降解效率pH 3 > pH 7 > pH 9，在曝氣情形下，因氧氣幫助超氧自由基和過氧化氫等強氧化劑的生成，曝氧氣的效率比曝氮氣佳，加入氧化劑0.5 mM H2O2和Na2S2O8能幫助光催化反應的進行，加入抑制劑5 % C2H5OH則反之。

This study presents photocatalytic activity of Fe0-TiO2 toward AR27 degradation in aqueous solution. Photocatalyst powders were analyzed for surface composition by scanning electron microscopy (SEM) and crystal composition by energy dispersive X-ray spectrometer (EDX). The SEM image showed that the particle size distribution of Fe0-TiO2 was narrow and the average particle size was approaching 34 nm. EDX result showed that 0.71 wt% Fe was coating on the TiO2. AR27 is detected by UV-Vis spectrometer to find maximum absorption wavelength of AR27 and catalysts. In 25°C, choosing 8W, 254 nm UV light irradiation, AR27 completely photodegradated in the present of the best cost-effective 0.5 g Fe0-TiO2 (1 wt%) photocatalyst after 120 min. Fe0-TiO2 with higher dye photodegradation efficiency was found to prepare with synthesis temperature 450°C than 350°C and 550°C, due to increasing of anatase TiO2 phase. Decolorization capacity of Fe0-TiO2 would increase with increasing coating weight until 1 wt% and decrease with increasing coating weight over 1 wt% of Fe0: 1 wt% > 2 wt% > 10 wt% > 0.5 wt%. The effect of pH on color removal was studied, acidic conditions were more favorable than alkaline condition. In the other hand, aeration is a significant factor for photodegradation. The result showed as follow: O2 > N2. Hydrogen peroxide and persulfate trapped photogenerated electrons and inhibited the recombination of electron/hole pairs in UV/Fe0-TiO2, thereby accelerating decolorization rate. On the contraty, the addition of ethanol inhibited decolorization. And a comparative investigation between Fe0-TiO2, Ag0-TiO2 and Ce0-TiO2 was carried out. The decomposition of AR27 could be well simulated with pseudo first-order kinetics, and the rate constants (kobs) were 0.0419 min-1, 0.0047 min-1, 0.0018 min-1. Fe0-TiO2 particles led to an enhanced photoactivity because of the rapid transfer of the photo-generated electrons from the semiconductors to the dopant. Experimental results indicated that synthesis temperature, coating weight, pH, aeration, oxidants, inhibitors would significantly affect the photo-decolorization capacity.