以微波水熱法合成硫化鋅觸媒光催化降解水中染劑

Abstract

使用UV/光觸媒系統來去除水中污染物，為近年來許多學者的研究課題。本研究利用微波水熱法製備光觸媒(ZnS)，此方法較傳統水熱法加熱迅速且易準確的控制溫度，在製備過程中利用poly N-vinyl-2-pyrrolidone (PVP)作為穩定劑，並以偶氮染劑甲基橙（MO）及甲基紅（MR）作為目標污染物進行光催化反應，探討合成溶劑、鋅硫比例、微波功率、反應時間對光觸媒活性的影響。 本實驗中發現，以乙醇為溶劑時可合成出粒徑最小的ZnS，而PVP的添加可改善ZnS的凝聚現象，增加可吸收波長的範圍。當PVP添加過量時，觸媒活性反而降低。隨著硫鋅比例增加( S2-/Zn2+大於1時)， ZnS粒徑尺寸亦隨之增加。合成功率增加至800 W，所合成的ZnS其光催化能力最強。合成時微波加熱的時間增加，其所生成的ZnS粒徑尺寸也隨之增加，進而使材料之反應活性減小。 光催化反應實驗中， pH=7~12時，由於MO及MR表面帶負電而與ZnS表面相斥，隨著pH值上升，ZnS對MO及MR的降解率反而降低。當污染物之初始濃度增加時，由於光線的穿透量減少，造成電子電洞對的生成量下降，使光催化反應受到抑制，ZnS對MO及MR的降解率也隨之下降。此外，溫度同樣在光催化反應中扮演重要角色，根據實驗本材料對於MO與MR的最佳光催化反應溫度為25℃。

UV / Photocatalyst systems removing contaminants from water have been widely reported in recent years. Photocatalyst ZnS were prepared via a microwave hydrothermal, which is faster than the traditional hydrothermal method and control temperature apt to be accurate. In the preparation process, poly(N-vinyl-2-pyrrolidone) (PVP) was added as a stablelizer, the azo dyes, content methyl orange (MO) and methyl red (MR), were used as a target contaminants in the photocatalytic reaction to discuss the effects of synthetic solvent, the ratio of sulfur/zinc, microwave power, reaction time on the photocatalytic activity. The synthesis of ZnS has minimum size in ethanol solution. ZnS agglomeration can be improved by adding PVP to increase the absorption wavelength range. As the proportion of sulfur/zinc increases (S2-/Zn2+ is greater than 1), the particle size of ZnS increase. When synthesis power increase up to 800 W, photocatalytic ability of synthesized ZnS is the strongest than other power. As synthesis of microwave heating time increasing, it generated ZnS particle size has increased. However, the ZnS ability was decreased. In the photocatalytic reaction, the surface of target contaminants, MO and MR, are both negative charges which would lead to repulsion between the contaminants and ZnS at pH=7~12. As the pH value increases, the degradation rate of MO and MR using ZnS would decrease. When initial concentration increases, the formation of electron hole pairs would decline because of less light penetration. Thus, photocatalytic reaction was inhibited. Besides, temperature also plays an important role in the photocatalytic reaction. According to the experiment, the best temperature of photocatalytic reaction for ZnS is 25°C.