本研究係利用紫外光-二氧化鈦/氧化鋅光催化處理含六價鉻水溶液，利用紫外光催化光觸媒二氧化鈦/氧化鋅而產生電子電洞分離，藉由電洞捕抓劑移除帶正電的電洞(h+)，讓電子(e－)有效導引至催化劑表面，處理含六價鉻水溶液。
在實驗中分別添加 甲酸、檸檬酸、水楊酸鈉、及EDTA二鈉塩等4種電洞捕捉劑於反應中，在電洞捕捉劑的選擇中，二氧化鈦光催化效果以EDTA最好，氧化鋅光催化效果以甲酸的最好。氧化鋅及二氧化鈦對六價鉻之光催化效果隨其添加劑量增加而增高，但隨著溶液pH值增高而遞減。隨後在光觸媒電洞捕抓劑之不同添加劑量試驗中，發現光催化活性與電洞捕抓劑濃度之間並無顯著關係，在本實驗中最佳濃度為0.01 M。
在本實驗反應機制部分，有添加氧化鋅的試驗中發現反應後總鉻濃度，都較初始濃度為低，經研判氧化鋅處理六價鉻機制主要還是以吸附反應為主，且在反應過程因紫外光照射強度及pH值影響，在反應過程析出鋅離子。而在二氧化鈦部分，因其總鉻濃度，都接近初始濃度，推估有部分的六價鉻被TiO2還原為三價鉻，因此TiO2機制主要還是以還原反應為主。 The photocatalysis application of TiO2 or ZnO catalyst by UV on treatment of chromium (VI) aqueous solution was investigated. The utilization of UV could photocatalyticlly generate electrons and holes on surface of TiO2 or ZnO powder. The addition of hole scavengers could attract and catch electric hole (h+) and reduce the recombination rate of photogenerated electrons and holes. The accumulation of photogenerated electrons on surface of catalysts, TiO2 and ZnO powder, could improve the removal of chromium (VI) contaminant in aqueous solution.
Electric hole scavengers such as formic acid, citric acid, sodium salicylate, and disodium ethylenediaminetetraacetic were evaluated in batch photocatalytic experiment. The enhancement of photocatalytic activity of TiO2 with disodium ethylenediaminetetraacetic was higher than other hole scavengers. The enhancement of photocatalytic activity of ZnO with formic acid was higher than others. The photocatalytic efficiency of chromium (VI) decontamination increased with the additive amount of TiO2 or ZnO catalyst, however, reduced with the increase of aqueous pH values. The photocatalytic activity of ZnO and TiO2 did not have significant correlations with the additive concentration of electric hole scavengers. The optimal concentration of electric hole scavengers were 0.01M founded.
Because of the reduction of total chromium ions concentration comparing with initial chromium (VI) addition, the principal photocatalytic reaction mechanism of chromium (VI) decontamination with ZnO was chemisorption. The dissociation of Zn(II) was due to UV light intensity and pH change in solution. However, the total concentration of chromium did not change significantly after the photocatalytic action of TiO2. Some of the Cr(Ⅵ) reduced into Cr(III) with photogenerated electrons on surface of TiO2 was expressed. The decontamination mechanism of Cr(Ⅵ) with TiO2 was reduction reaction.
