TiO2复合半导体及银硫化合物的制备及光催化活性研究
文献类型：学位论文
| 作者 | 常平静 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-09 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 中国科学院长春应用化学研究所 |
| 导师 | 赵凤玉 |
| 关键词 | 光催化 可见光 二氧化钛 复合半导体 金属硫化物 |
| 中文摘要 | TiO2半导体材料来源丰富、价格低廉、化学性质稳定、无毒无害，被广泛应用于光催化领域中，然而TiO2却存在两个不可忽视的缺点：一是光吸收范围窄，主要为紫外光区，对太阳光的利用率低；二是其产生的光生电子和空穴复合率高，造成光催化量子效率较低。另外，许多金属硫化物光吸收范围宽，能够吸收利用可见光，但是却容易被光腐蚀，因此如何提高TiO2基半导体的光催化活性和抑制金属硫化物的光腐蚀现象成为研究的热点。本文主要致力于设计合成TiO2基复合半导体材料以及高活性高稳定性的金属硫化物半导体材料，将所制备催化材料应用于光催化硝基化合物加氢及光降解染料的反应中，并取得了如下创新性的研究结果。 （1）采用双功能分子连接的方法制备了CdS量子点敏化的P25催化剂（CdS QDs-P25），与直接沉积-沉淀法制备的CdS-P25相比，在可见光下甲酸为牺牲剂的条件下还原邻-氯代硝基苯（o-CNB）的反应中表现出更佳的光催化活性。CdS QDs和P25之间的相互作用有利于光生载流子空间上的分离，能够有效地抑制光生电子-空穴的复合，而且由于量子效应CdS QDs相对于CdS能够提供更多的光生电荷；除此之外，光催化还原过程亦得到详细地研究，可见光照射下CdS QDs被激发，光生电子从CdS QDs的价带（VB）上跃迁至其导带（CB）上，随后迁移至未被激发的P25的导带上，同时，CdS QDs价带上产生的光生空穴能够氧化HCOOˉ，生成?CO2ˉ和H+，而o-CNB能够被上述光生电子和?CO2ˉ耦合H+还原成o-CAN。 （2）采用水热法制备了一系列电子结构不同的银硫化合物半导体，并对催化剂进行扫描电镜（SEM）、X射线衍射光谱（XRD）、紫外可见漫反射光谱（DRS UV-vis）表征。AgxS-c在光催化硝基苯加氢的反应中表现出最佳的光催化活性，在所制备的催化剂中AgxS-c具有粒径小，光吸收强度大，更重要的是其最大的价带和导带电势差值，导致其具有更强的氧化还原能力。另外，采用硫化钠作牺牲剂有效地抑制了AgxS-c的光腐蚀现象，在前三次循环实验中，AgxS-c仍保持较高的光催化活性。同时，详细地讨论了光催化过程，催化剂经光激发产生光生空穴与电子，光生空穴被硫化钠捕获，硫化钠本身会被氧化为多硫化物，光生电子会将硝基苯还原；除此之外，其它取代基的硝基化合物亦能够在硫化钠为牺牲剂的条件下，被AgxS-c光催化还原。 （3）分别采用水热法（Ag2S-H）和原位离子交换法（Ag2S-IE）制备了Ag2S晶体，对所制备的样品进行扫描电镜（SEM）、X射线衍射光谱（XRD）、紫外可见漫反射光谱（DRS UV-vis）表征。与Ag2S-IE相比，Ag2S-H具有较小的粒径、较大的光吸收强度及禁带宽度，使得其拥有更强的光催化活性。Ag2S-H在可见光催化甲基蓝降解的反应中具有很好的活性和稳定性，循环使用五次后仍能够保持较高的光催化活性。而且，提出了Ag2S晶体光催化降解甲基蓝的可能的路径，认为光生空穴及超氧自由基是催化降解甲基蓝的主要活性组分。 |
| 英文摘要 | TiO2 has been widely used as the catalyst in the photocatalysis due to its low cost, high stability and non toxic properties. However, TiO2 can only utilize the UV light in the sunlight. Moreover, the photogenerated holes and electrons of TiO2 can recombine rapidly, resulting in the low quantum efficiency, which limits its wide application. Metal sulfide semiconductors can utilize visible light, while are prone to be photo-corrosion, so how to improve the photocatalytic activity of TiO2 based semiconductors and suppress the photocorrosion phenomena of the metal sulfides become an important issue in the photocatalysis. In the present work, we focus on the design and synthesis of TiO2 based semiconductor and metal sulfide semiconductor materials with high active, high stability in photocatalysis. The prepared materials were evaluated for the photocatalytic hydrogenation of nitro compounds and the photodegradation of dyes, and the following innovative results are achieved. (1) The CdS quantum dots sensitized P25 (CdS QDs-P25) showed extremely enhanced activity in the reduction of o-chloronitrobenzene (o-CNB) by comparing to CdS-P25 in the presence of HCOOH. The synergistic effects between CdS QDs and P25 could benefit the separation of photogenerated carriers in space and thus the combination of photoelectrons and holes was prevented, and the CdS QDs could provide more photocharges than CdS due to the particle size effect. Furthermore, the process of the photocatalytic reduction in present system was investigated, under the irradiation of visible-light, the photogenerated electrons transferred from the valence band (VB) to the conduction band (CB) of CdS QDs, and injected into the CB of inactivated P25. Meanwhile, the holes generated in the VB of CdS QDs could oxidize HCOOˉ to ?CO2ˉ and H+. Then, o-CNB was reduced to o-chloroaniline (o-CAN) by the couple of eˉ and ?CO2ˉ with H+. (2) Silver sulfide semiconductors were synthesized via hydrothermal method. The prepared materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and diffuse reflectance UV–vis spectroscopy (DRS UV–vis). AgxS-c showed the highest activity in the reduction of nitrobenzene (NB), the reasons could be ascribed to the smaller particle size, stronger light absorbance and especially to the most anodic VB position and the most cathodic CB position, which means AgxS-c owned the strongest reduction and oxidation abilities. Moreover, Na2S was selected as a suitable sacrificial agent to prevent the photocrrosion of AgxS-c, therefore, AgxS-c showed good stability, it could be reused for three times without loss of photocatalytic activity. Furthermore, the process of the photocatalytic reduction in present system was investigated, under the irradiation of visible-light, the photogenerated holes oxidized sulfide ions to polysulfide, while photogenerated electrons reduced NB to aniline. In addition, AgxS-c could be used as an efficient photocatalyst in the reduction of nitroaromatics with various substituents. (3) Ag2S crystals were synthesized via hydrothermal (Ag2S-H) and in situ ion-exchange (Ag2S-IE) methods. The obtained samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and diffuse reflectance UV–vis spectroscopy (DRS UV–vis). The photocatalytic performance was investigated for the decomposition of methyl blue (MB) under visible light irradiation (λ ≥ 420 nm). The Ag2S-H had smaller particle size, larger light absorbance area and wider band gap compared to that of Ag2S-IE, resulting in higher photocatalytic activity of Ag2S-H than Ag2S-IE. Moreover, Ag2S-H showed good stability, it could be reused for five times without loss of photocatalytic activity. In addition, a possible pathway for the photocatalytic degradation of MB over Ag2S was proposed, that MB was oxidized by the superoxide radicals and the holes generated over Ag2S. |
| 语种 | 中文 |
| 公开日期 | 2016-05-03 |
| 源URL | [http://ir.ciac.jl.cn/handle/322003/64489]  |
| 专题 | 长春应用化学研究所_长春应用化学研究所知识产出_学位论文 |
| 推荐引用方式 GB/T 7714 | 常平静. TiO2复合半导体及银硫化合物的制备及光催化活性研究[D]. 中国科学院长春应用化学研究所. 中国科学院研究生院. 2014. |
入库方式： OAI收割
来源：长春应用化学研究所
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