CNTs/TiO2奈米複合材料去除水中鉻金屬可行性之研究

Combining CNTs and TiO2 nano-materials to remove chromium metal from water

吳映潔(Ying-Jie Wu)

指導教授 ： 蔡勇斌

國立暨南國際大學/科技學院/土木工程學系/碩士(2010年)

摘要

本研究分別利用硫酸改質之多壁奈米碳管(multi-walled carbon nanotubes, MWCNTs)、二氧化鈦(titanium dioxide, TiO2)光觸媒與CNTs/TiO2 複合材料去除水中重金屬鉻離子，並探討在光催化實驗中以水楊酸(Salicylic acid, SA)作為電洞清除劑時對Cr(VI)還原之影響。
由Sulfuric Acid MWCNTs 長時間吸附Cr(VI)實驗得知，Cr(VI)吸附平衡時間受起始濃度影響，且對於Cr(VI)之吸附效率不佳，而XPS 分析證實Cr(VI)以Cr(VI)與Cr(III)型式附著於奈米碳管上。在光催化還原Cr(VI)實驗中，市售二氧化鈦Hombikat UV100 因粒徑小易團聚的特性，造成對Cr(VI)的還原能力不如P25。而從CNTs/TiO2 複合材料光催化還原Cr(VI)實驗得知，本研究製備之CNTs/TiO2 複合材料可能因光催化過程中生成較多的·OH 而不利於Cr(VI)之還原。
而於光催化還原Cr(VI)實驗中添加電洞清除劑(SA)能有效提高Cr(VI)還原速率及效率，然而光降解SA 生成的中間產物可能與Cr 形成複合物並造成失活現象(deactivation)。此外，Cr(VI)之還原效率受光照波長與溶氧影響，實驗結果顯示Cr(VI)還原效率隨光照波長減短與能量提高而提升，但供給過高的能量反而不利Cr(VI)還原；另外，由於溶氧不僅能與Cr(VI)競爭光生電子亦可扮演傳遞電子的角色，故實
驗中也發現適當曝入氮氣或空氣能提升Cr(VI)還原速率。
在水楊酸降解方面，使用CNTs/TiO2 複合材料做為催化劑的礦化程度較P25高，而添加適當的Cr 離子做為電子清除劑，以及提高光照能量與增加溶氧皆能提升其降解速率與礦化程度。

關鍵字

鉻 ； 吸附 ； 光催化 ； 奈米碳管 ； 二氧化鈦 ； 複合材料 ； 電洞清除劑

並列摘要

In this study three ways were used to remove chromium metal ions from water. One is the use of multi-walled carbon nanotubes (MWCNTs), the others are the photocatalyst
titanium dioxide (TiO2) and CNTs/TiO2 composites. And, we study the influence of using salicylic acid as a hole scavenger on the photocatalytic reduction of Cr(VI) as well.
By means of the carbon nanotube which was modified by sulfuric acid (Sulfuric Acid MWCNTs) to adsorb the Cr(VI) in a long term, the experimental results indicated that the adsorption equilibrium time was influenced by the initial Cr(VI) concentration, and the XPS analysis proved that the adsorbed Cr on MWCNTs presented as Cr(III) and Cr(VI) forms. In the photocatalytic reduction of Cr(VI) experiments, the Cr(VI) reduction capacity of commercially available titanium dioxide Hombikat UV100 was smaller than
P25 because of the characteristic of small grain size and being agglomerated easily. The CNTs/TiO2 composites prepared in this study were not good for Cr(VI) reduction because that using CNTs/TiO2 composites as catalysts might produce more hydroxyl radicals during the photocatalytic process.
By adding salicylic acid (SA) as a hole scavenger in the experiment of Cr(VI) reduction could increase the reduction rate and the efficiency. However, the intermediate
photodegradation products of salicylic acid might produce certain Cr-complexes andresult in deactivation process. Besides, the reduction rate of Cr(VI) was affected by
illumination wavelength and dissolved oxygen. The experimental results demonstrated that the reduction efficiency increased with the decrease of illumination wavelength and the increase of the illumination energy, but decreased with the excessive illumination energy. In addition, oxygen could compete with Cr(VI) not only for photogenerated electrons, but also could serve as an electron-transfer mediator. Therefore, the experimental results also found that the reduction efficiency was increased by purging nitrogen or air appropriately.
In the aspect of salicylic acid degradation, using CNTs/TiO2 composites as the catalysts had a higher degree of mineralization than P25. Besides, the degradation rate and the degree of mineralization of salicylic acid were increased by adding the appropriate amount of Cr ions as the electron scavenger, increasing illumination energy and the dissolved oxygen concentration.

並列關鍵字

chromium ； adsorption ； photocatalysis ； carbon nanotube ； titanium dioxide ； composites ； hole scavenger

參考文獻

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