UV/TiO2程序光催化降解水中單氯苯之研究

Photocatalytic degradation of monochlorobenzene in water by UV/TiO2 process

黃欣栩(Hsin-Hsu Huang)

指導教授 ： 曾迪華

國立中央大學/工學院/環境工程研究所/博士(2008年)

摘要

本研究使用四種具不同表面特性之二氧化鈦(TiO2)作為光觸媒，用以探討單氯苯(MCB)於UV/TiO2程序中的吸附、降解以及礦化反應行為。氣相吸附實驗結果指出，MCB於TiO2表面之單位面積吸附容量不受晶相影響，液相吸附結果則顯示，MCB於TiO2表面的吸附行為，明顯受到水分子存在的抑制，理論最大MCB吸附量介於0.164至2.071 ?mol MCB/m2 of TiO2之間。
光催化降解結果顯示，相較於直接光解以及UV/H2O2程序，UV/TiO2程序能有效降解MCB，且具高表面積或高表面位置密度之光觸媒，有較佳之光催化活性。實驗結果顯示MCB的降解反應與初始濃度、入射光強度以及光觸媒劑量有關。MCB的降解可以Langmuir-Hinshelwood反應動力式描述，由光強度與降解速率的低關聯性，可知電子-電洞再結合效應明顯，而最適光觸媒劑量介於1.0至2.0 g/L。溶液pH值會影響MCB的吸附以及氫氧自由基(•OH)的產生，進而影響光催化降解效率，一般而言，中性環境下，有較佳之MCB降解效果，而較佳之礦化效率發生於酸性環境。
溶氧的存在被證實有助於光催化降解反應，降解及礦化效率機會隨溶氧濃度增加而增加。H2O2由於同時具有捕捉電子與•OH自由基的能力，在適量的添加下，有助於MCB的降解與礦化。礦化過程中，有機中間產物的生成與降解可以簡易二階段反應動力式描述。
MCB光催化降解過程中，同時伴隨著礦化及脫氯反應，然根據水中氯離子濃度以及反應後TiO2表面分析，證實MCB經脫氯反應所形成之氯離子，會與TiO2表面結合。

關鍵字

礦化 ； 降解 ； 二氧化鈦 ； 單氯苯 ； 吸附

並列摘要

In this investigation, the reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO2 process, including substrate adsorption, degradation, and mineralization, was studied. Four commercial powder TiO2 with different characteristics were used as photocatalyst. The gaseous adsorption results illustrated that the adsorption capacity of MCB vapor on the base of the same surface area, was independent of crystalline. Moreover, the adsorption of MCB onto TiO2 surface was suppressed in aqueous solution obviously. For isotherm adsorption in aqueous phase, the theoretical maximum adsorption capacity of MCB onto TiO2 surface was in the range of 0.164 to 2.071 ?mol MCB/m2 of TiO2.
As compared with direct photolysis and H2O2-assisted photocatalysis, UV/TiO2 process was proven to be an effective method for the degradation of MCB. Large surface area and higher surface sites capacity of TiO2 photocatalyst and higher relative surface coverage of MCB were favor for the photocatalytic degradation. In accordance with the experimental results, the degradation of MCB was a function of the initial substrate concentration, incident light intensity, and TiO2 dosage. Langmuir-Hinshelwood kinetic model was applied to simulate the degradation of MCB. In addition, the low dependency of the initial degradation rate on the light intensity revealed the considerable adverse effect of e–-h+ pair recombination. In this study, the optimum photocatalyst dosage was in the range of 1.0 to 2.0 g/L. The influence of the solution pH on the degradation of MCB can be explained by the generation of hydroxyl radicals (•OH) and the potential for the adsorption. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition.
Oxygen was proven to be a determining parameter for improving the photocatalytic degradation. Both degradation and mineralization efficiencies were improved with increasing DO concentration. Owing to H2O2 acted as electron and •OH radicals scavenger, the addition of H2O2 should in a proper dosage range to promote the degradation and mineralization of MCB. A simplified two-step consecutive kinetic model was used to model the mineralization of MCB.
Mineralization and dechlorination were both occurred during the photocatalytic degradation of MCB. Nevertheless, an analysis of Cl– ion concentration in the bulk solution and the characteristics of used TiO2 concluded that the Cl– ions reacted with TiO2 particles.

並列關鍵字

Titanium dioxide ； Monochlorobenzene ； Adsorption ； Degradation ； Mineralization

參考文獻

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