Ag@AgBr/Ni薄膜光催化降解罗丹明B及其机理

Photocatalytic Degradation of Rhodamine B by Ag@AgBr/Ni Thin Film and Reaction Mechanism

用电化学方法制备Ag@AgBr/Ni表面等离子体薄膜光催化剂。对薄膜的表面形貌、晶相结构、光吸收特性进行了表征,用罗丹明B(RhB)作为模拟污染物对薄膜的光催化活性和稳定性进行了测定,探索了薄膜光催化降解机理。结果表明:Ag@AgBr/Ni的优化制备工艺为:电解液中NaBr和(NH_4)_3PO_4的浓度分别为0.3和1 mol/L,pH值为8.0,电解电流密度为2.5mA/cm^2,时间为18min,并在140℃后处理1 h。优化工艺下制备的Ag@AgBr/Ni薄膜表面是由附着少量Ag粒子的AgBr纳米晶构成。薄膜表现出明显的表面等离子共振效应、优异的光催化活性和良好的稳定性:可见光辐照15 min,薄膜光催化RhB的降解率(81.0%)是Ag_3PO_4/Ni薄膜的6倍,是P25 TiO_2/ITO薄膜的14倍;光照射1 h对RhB的降解率为99.5%,循环使用4次后的降解率仍为91.6%。薄膜的高光催化活性是由AgBr晶体在(111)晶面产生择优取向和薄膜表面纳米Ag发生等离子体共振效应引起的。讨论了可见光下薄膜光催化降解RhB的反应机理。

Ag@AgBr/Ni thin films were prepared by an electrochemical method. The surface morphology, phase structure, optical characteristics of the thin films were characterized. The photocatalytic properties and stability were evaluated with Rhodamine B （i.e., RhB） as a model compound. The mechanism of photocatalytic degradation of the films was investigated. The results show that the Ag@AgBr/Ni thin films can be obtained under the optimized preparation conditions （i.e., concentrations of NaBr and （NH4）3PO4 in the electrolyte of 0.3 and 1 mol/L, respectively, the pH value of the electrolyte of 8, the electrolytic current density of 2.5 mA/cm2, the deposition time of 18 min, and the films heat treated at 140 ℃ for 1 h）. The Ag@AgBr/Ni thin films prepared under the optimized preparation conditions are composed of AgBr micron-sized particles coated with Ag nanocrystals, which have a significant surface plasmon resonance （SPR） effect. The thin film exhibits a maximum photocatalytic activity and a superior photocatalytic stability to decompose RhB. The photodegradation rate of the Ag@AgBr/Ni thin films under the visible light irradiation 15 min （i.e., 81.0%） is 6 times greater than that of Ag3PO4/Ni thin film, and 14 times greater than that of P25TiO2/ITO thin film. The degradation rate of the Ag@AgBr/Ni thin film for RhB under the visible light irradiation for 1 h is 99.5%, and is still 91.6% after reused for four times. The improvement in photocatalytic activity for Ag@AgBr/Ni thin films could be mainly attributed to the AgBr crystal （111） preferred orientation and the plasmon resonance effect of Ag nanocrystals on the AgBr particles. In addition, the photodegradation mechanism of the films for RhB under the visible light was also discussed.