| 摘要: | 光催化技術可有效應用於廢水處理；於光觸媒中，又以二氧化鈦(TiO2)最具光催化效能；然而氧化鋅(ZnO)具備價格便宜、可吸收可見光範圍大、對特定染劑光催化效果佳等眾多優點，因此有其潛力取代傳統TiO2光觸媒。對於氧化鋅光觸媒之合成技術一般包含氣相冷凝法、物理粉碎法、沉積法、沉澱法、水熱合成法、溶膠凝膠法及微乳液法。本研究利用不同天然多醣進行改質以製備奈米氧化鋅，其具成本低、低污染、廢棄物再利用及製備容易等優點。因海藻酸鈉、幾丁聚醣、玉米澱粉及纖維素於自然界中含量豐富，故被選擇為製備ZnO之前驅物。
本研究利用上述四種天然多醣體於不同製備條件探討ZnO之製備及其表面理化特性，並進一步測試其對甲烯藍、結晶紫與剛果紅等三種染劑的吸附作用及光催化反應。由XRD結果顯示四種天然多醣體所合成光觸媒皆為ZnO結構，且隨鍛燒溫度增加，光觸媒於XRD有較強散射波峰。另外；由SEM圖及BET分析結果顯示光觸媒ZnO於較高鍛燒溫度條件會產生燒結現象，導致比表面積下降。光觸媒於三種染劑(甲烯藍、結晶紫及剛果紅)催化結果顯示利用玉米澱粉與海藻酸鈉製備ZnO對三種染劑催化降解效率相當，特別於結晶紫催化，兩者觸媒於第3小時即可完全降解結晶紫；反之，幾丁聚醣合成氧化鋅對染劑催化降解效果最差。儘管不同製備條件影響ZnO光觸媒對染劑催化性能，本研究亦發現溫度、染劑濃度、觸媒含量及pH值皆會影響氧化鋅的催化性能。大致而言，本研究利用改質多醣體可成功合成ZnO且應用於廢水處理。;Photocatalytic technology is considered as one effective way for wastewater treatment. Among various photocatalysts, TiO2 is most effective catalyst for wastewater treatment. Nevertheless, ZnO has potential to substitute traditional TiO2 due to low cost, large visible light range, and good photocatalytic performance. Generally, synthetic methods for ZnO preparation include vapor condensation, physical crushing, deposition, precipitation, hydrothermal synthesis, sol-gel and microemulsion.
This study attempted to use natural polysaccharides, such as sodium alginate, chitosan, corn starch and cellulose as precursors for ZnO preparation with various conditions. Various ZnO prepared were characterized by XRD, SEM, BET and TGA, respectively. Further performances of ZnO prepared were evaluated for the removal of various pollutants including methylene blue, crystal violet and congo red. The XRD results indicated that ZnO prepared by 4 polysaccharides as precursors mainly present diffraction peaks of ZnO. It was also observed that diffraction peaks of ZnO enhance with increasing calcination temperature. In addition, SEM and BET results indicated that ZnO would present sintering as photocatalyst was calcined with a higher temperature, resulting in lower BET specific surface area. Further lower BET specific surface area may influence performance of photocatalyst. For photocatalytic test, the results indicated that ZnO prepared by sodium alginate and corn starch revealed good photocatalytic activity for removal of various pollutants. Especially, removal efficiency of crystal violet achieved with ZnO prepared by sodium alginate and corn starch could 100% after 3hr. On the contrary, ZnO prepared by chitosan revealed the lowest activity for removal of various pollutants. In addition, various preparation processes for ZnO synthesis significantly influence their characteristics and catalytic performances. Also, various operating conditions influence catalytic performance for removals of methylene blue, crystal violet and congo red. Overall, ZnO developed by this study revealed good activity and potential for wastewater treatment. |
