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TiO_2作为一种光催化剂广泛应用于各种污染物的降解.但是它较大的宽禁带(~3.2 eV)导致其很难吸收可见光,因此寻找窄禁带的具有可见光响应的半导体光催化剂成为近年来光催化研究的热点.在众多窄禁带光催化剂中,纯Ag_2S在降解污染物方面并不出色,但是作为一种窄禁带的直接带隙半导体,它在加快电子迁移和提高光量子效率方面表现出色.目前有许多高催化活性的Ag_2S异质结复合半导体光催化剂的报道,如Ag_2Mo_3O_(10)-Ag_2S,TiO_2-Ag_2S,ZnS-Ag_2S和NiO-Ag_2S等.Ag_2WO_4是一种具有新颖物理化学性质的半导体材料,在催化、传感器、抗菌和光致发光等方面有着广泛应用.但是,Ag_2WO_4的理论带隙较宽,约为3.5 eV,而且光照下Ag_2WO_4很容易产生光化学腐蚀而分解出单质银,作为光催化剂存在太阳光利用率低和稳定性较差等缺点.声化学是一种特殊纳米材料的合成方法.它主要是利用超声空化产生特殊的物理化学环境来强化化学键的生成,同时实现半导体从无定形态到固定晶型转变.本文采用超声辅助共沉淀法制备了长为0.2-1μm、直径为20-30 nm的Ag_2S/Ag_2WO_4微米棒复合光催化剂.利用X射线衍射(XRD)、N_2物理吸附、扫描电镜、透射电镜、光电子能谱、光致发光谱(PL)和紫外-可见漫反射吸收光谱(UV-vis DRS)和光电流等手段对所制Ag_2S,Ag_2WO_4和Ag_2S/Ag_2WO_4进行了表征.结果表明,合成的样品比表面积较小(2.7-3.6 m~2/g).UV-vis DRS测试表明,声化学处理能有效拓宽Ag_2S/Ag_2WO_4在可见光区的吸收范围,提高其可见光响应性能.另外,PL和光电流测试结果证实,在声化学制备的Ag_2S/Ag_2WO_4体系中,光生电子(e~-)-空穴(h~+)的复合过程被极大地限制,具有较高的e~--h~+分离效率.以金卤灯为光源进行了光催化降解染料亚甲基蓝的性能测试.结果表明,声化学合成的Ag_2S/Ag_2WO_4的反应速率常数(0.150 min-1)分别为单纯Ag2WO4(0.031 min-1)和Ag2S(0.004 min-1)的4.7和29.8倍.自由基捕获实验表明,在Ag_2S/Ag_2WO_4光催化降解甲基橙过程中主要的活性物种为超氧自由基(·O_2~-)和光生空穴(h~+).此外,声化学合成的Ag_2S/Ag_2WO_4表现出很好的光催化稳定性.循环使用3次后,该样品对亚甲基蓝的光催化活性仍高达80.4%,而纯Ag_2WO_4几乎完全失活.Ag_2S/Ag_2WO_4具有很高的光催化活性的原因,一方面是声化学处理提高了催化剂的结晶度,同时生成了独特的棒状结构;另一方面是在超声作用下,Ag_2S和Ag_2WO_4两相紧密接触形成异质结,促进了可见光的吸收和光生e~-与h~+的分离.
As a photocatalyst, TiO_2 is widely used in the degradation of various pollutants, but its wide band gap (~ 3.2 eV) makes it difficult to absorb visible light. Therefore, looking for a narrow band gap semiconductor photocatalyst with visible light response becomes In many narrow bandgap photocatalysts, pure Ag_2S is not good at degrading pollutants, but as a kind of direct bandgap semiconductor with narrow bandgap, it accelerates electron transfer and enhances photon quantum efficiency There are many high catalytic activity of Ag_2S heterojunction composite semiconductor photocatalysts reported, such as Ag_2Mo_3O_ (10) -Ag_2S, TiO_2-Ag_2S, ZnS-Ag_2S and NiO-Ag_2S, etc. Ag_2WO_4 is a novel physical However, the theoretical bandgap of Ag_2WO_4 is about 3.5 eV, and Ag_2WO_4 is prone to photochemical corrosion in the light of the decomposition of elemental silver , As the photocatalyst there is the shortcomings of low utilization of sunlight and poor stability.Sound chemistry is a special method of synthesis of nanomaterials.It is mainly the use of ultra Cavitation produces a special physical and chemical environment to strengthen the chemical bond formation, and at the same time, the transition from amorphous state to fixed crystalline state is achieved.In this paper, Ag_2S with length of 0.2-1μm and diameter of 20-30 nm was prepared by ultrasonic assisted coprecipitation / Ag_2WO_4 microrods composite photocatalysts were synthesized and characterized by X-ray diffraction (XRD), N 2 physical adsorption, SEM, TEM, PL, PL and UV-vis DRS ) And photocurrent were used to characterize the prepared Ag_2S, Ag_2WO_4 and Ag_2S / Ag_2WO_4.The results showed that the specific surface area of the synthesized sample was small (2.7-3.6 m 2 / g) .UV-vis DRS test showed that the sonochemical treatment Which can effectively broaden the absorption range of Ag 2 S / Ag 2 WO 4 in the visible region and improve its visible light response.In addition, PL and photocurrent test results confirm that in the Ag 2 S / Ag 2 WO 4 system prepared by sonochemistry, photoelectron (e ~ h ~ +) was greatly limited, with high e ~ - h ~ + separation efficiency.The performance of photocatalytic degradation of methylene blue with a metal halide lamp as a light source was tested.The results showed that the Reaction rate of Ag_2S / Ag_2WO_4 The constants (0.150 min-1) were 4.7 and 29.8 times higher than that of Ag2WO4 (0.031 min-1) and Ag2S (0.004 min-1) respectively.Free radical trapping experiments showed that during the photocatalytic degradation of methyl orange by Ag_2S / Ag_2WO_4, Of the active species were superoxide radical (O_2 ~ -) and photogenerated holes (h ~ +). In addition, Ag_2S / Ag_2WO_4 synthesized by sonochemistry showed good photocatalytic stability. After three times of recycling The photocatalytic activity of methylene blue was still as high as 80.4%, while the pure Ag_2WO_4 was almost completely inactivated.The reason for the high photocatalytic activity of Ag_2S / Ag_2WO_4 was that the sonochemical treatment increased the crystallinity of the catalyst and the unique On the other hand, Ag2S and Ag2WO4 are in close contact with each other to form a heterojunction under the action of ultrasound, which promotes the absorption of visible light and the separation of photo-e ~ - and h ~ +.