ZnIn2S4可見光光觸媒之合成與鑑定

Abstract

本研究以微波水熱法在不含模板及有機溶劑的條件下，成功於低溫80oC下持溫一小時製備ZnIn2S4粉體。第一部分研究反應溫度及前驅溶液酸鹼值對ZnIn2S4合成之影響。在pH值1 - 3時成功合成單相六方晶系ZnIn2S4，pH值增加，粉體結晶性下降。以穿透式電子顯微鏡觀察，發現顆粒表面均帶有奈米片狀物。當pH值為1時，由於硫代乙醯胺分解速率快，反應初期生成之硫化氫氣體較多，導致顆粒呈不規則連續狀。當pH值為2 – 3時，形成微球體。其中pH值為2時，產物顆粒粒徑均一且孔洞較大。反應溫度65oC時，尚未形成ZnIn2S4粉體，當溫度增加至95oC時，成功合成ZnIn2S4粉體，且顆粒表面粗糙化。持續增溫後顆粒表面生成奈米片狀物。隨著反應溫度持續增加，表面之奈米片狀物厚度增加，並生成花瓣狀。於紫外光及可見光範圍觀察到一高吸收度之峰值，且吸收邊界陡峭，顯示粉體不含雜質。 第二部分研究退火溫度對ZnIn2S4粉體之影響。當退火溫度≦400oC時，粉體結晶性及平均微晶粒徑隨退火溫度的增加而增加。並於400oC的退火條件下達到較佳結晶性。推斷由於結晶性增加，缺陷減少，電子在傳輸過程損失之能量較小，且因晶體不規則排列造成之漫反射較少，使得400oC退火後之粉體於可見光之吸收率增加。退火對粉體能隙無明顯改變，約2.40 eV。當退火溫度超過500oC時，粉體氧化生成氧化銦。當退火溫度增加時，表面奈米片狀物逐漸消失、凝團現象增加，導致表面積以及粉體之孔洞體積減小。為研究ZnIn2S4粉體之熱穩定性以及退火溫度對光觸媒活性之影響，以亞甲基藍水溶液之降解作為指標。隨著退火溫度增加，以可見光為光源，分解40%亞甲基藍所需的時間，亦隨之增加，顯示隨著退火溫度增加，粉體之光觸媒活性下降。本研究發現隨著前驅溶液pH值及反應溫度的不同，ZnIn2S4顆粒型態隨之改變。而未經熱處理之ZnIn2S4具備最佳光觸媒活性。

In the present study, ZnIn2S4 powder was successfully synthesized via a rapid, template-, surfactant-, and organic solvent-free microwave-hydrothermal route merely at 80°C. The effect of pH value and synthesis temperature was investigated in details. Single phased ZnIn2S4 was obtained via changing the pH value from 1 to 3. Transmission electron microscopic (TEM) studies exhibited the formation of nanosheets on the surface of ZnIn2S4 particles. With the increase in pH value of the precursor solution, the crystallinity of the obtained powders was observed to decrease. When the pH was approximated to 1, large amount of H2S gases arose owing to the increased decomposition of thioacetamide. The evolution of gases might be responsible for the irregular morphology of ZnIn2S4 particles. With the increment in pH value to 2 and 3, the microspherical morphology of ZnIn2S4 particles was observed. However, relatively uniform and large porous microspheres were observed with the pH value equal to 2. The obtained samples exhibited a strong absorption with steep edge in the visible region. The bandgap increased from 2.25 eV to 2.43 eV as the pH value was increased. Furthermore, increased reaction temperature thickened the nanosheets, and led to the formation of floriated particles. The post annealing treatment on the synthesized ZnIn2S4 was also investigated. When the annealing temperature was lower than 400oC, the crystallinity and average crystallite size enlarged as a function of increasing annealing temperature. The crystallinity of the sample annealed at 400 oC was observed to be superior. The post annealing treatment led to an increment in the absorption capability of the sample owing to the reduction of defects, which were responsible for the energy loss during electron transport. Furthermore, improved crystallinity diminished the reflectance and scattering from the irregular arrangement of the crystallites. When annealing temperature rose over 500oC, ZnIn2S4 powder was transformed into indium oxide via oxidation. The band gap of the samples was found to be independent of the annealing temperature, and estimated to be around 2.40 eV. The nanosheets on the surface agglomerated and disappeared with the increase in temperature. Photocatalytic activity was evaluated based on the degradation of methylene blue. Annealing effect resulted in the decay of photocatalytic activities owing to the decrease in specific surface area as well as pore volume. The morphology of ZnIn2S4 particles was changed with the variation in the pH value of the precursor solution and reaction temperature. The sample without post heat treatment was observed to have best photocatalytic activity.