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二维层状铁电铌酸盐SrBi2Nb2O9的合成、改性和光催化性能研究
张丙
学位类型硕士
导师李英宣
2017-05-28
学位授予单位中国科学院大学
学位授予地点北京
学位专业物理化学
关键词Srbi2nb2o9 熔盐合成法 二维层状钙钛矿 光催化
摘要

二维层状铌酸盐材料因原料来源广、合成工艺过程简单且成分和结构具有多样性等优点,从而在光催化合成新能源和治理环境污染等方面具有广泛的应用。然而,当前铌酸盐二维层状钙钛矿的合成方法主要依赖于传统的高温固相法和以水热法为代表的湿化学方法,这些方法普遍能耗高且工艺过程繁琐。为此,本文采用熔盐法制备出SrBi2Nb2O9二维层状钙钛矿。然后,通过自上而下的方法合成出H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片。在此基础上,通过自下而上的方法合成出Ni(III)-CH3CH2NH2/H1.78Sr0.78Bi0.22Nb2O7层状复合钙钛矿材料。然后研究了它们的光催化性能以及改性对光催化性能的微观物理化学影响机制。具体研究内容和结果如下:(1)以SrCO3、Bi2O3和Nb2O5为前驱体,NaCl和KCl为熔盐体系,采用熔盐法制备出铁电SrBi2Nb2O9二维层状钙钛矿。SrBi2Nb2O9的晶体结构是由(SrNb2O7)2?钙钛矿层和(Bi2O2)2+层沿垂直于(00l)晶面交替排列形成的二维层状钙钛矿结构,其中Sr2+位于NbO6八面体结构的间隙中。所合成的SrBi2Nb2O9为纳米板状结构并且结晶度高,其长度集中分布在2 μm~8 μm之间,厚度约为600 nm。光催化性能测试结果表明,所合成的SrBi2Nb2O9具有光催化分解水产氢和光热协同催化还原CO2产生CO的能力。(2)通过对SrBi2Nb2O9二维层状钙钛矿进行质子化(产物为H1.78Sr0.78Bi0.22Nb2O7纳米板)和化学液相剥离,得到厚度仅为2.6 nm的H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片。SrBi2Nb2O9、H1.78Sr0.78Bi0.22Nb2O7纳米板和H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片的带隙分别为3.12 eV、3.36 eV和3.43 eV。无任何助催化剂的条件下,三个样品的光催化分解水产氢速率分别为7.6 μmol?h?1、32.0 μmol?h?1和207.0 μmol?1。H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片光催化性能的提高是由于其厚度减小,从而导致其比表面积增加、光生载流子的分离效率提高所引起的。 (3)在H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片成功合成的基础上,引入Ni2+,通过化学反应诱导层层组装合成出Ni(III)-CH3CH2NH2/H1.78Sr0.78Bi0.22Nb2O7二维复合层状钙钛矿,然后研究了组装前后的催化剂光催化分解水产氢性能。和H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片相比,Ni(III)-CH3CH2NH2/ H1.78Sr0.78Bi0.22Nb2O7的比表面积增大,光生电子和空穴的分离效率提高,光催化分解水产氢性能也得到了提高。经优化后,0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7光催化分解水产氢速率最高,为372.67 μmol?h?1,相较于H1.78Sr0.78Bi0.22Nb2O7二维超薄纳米片光解水产氢速率提高了0.54倍,并且表现出良好的循环稳定性。此外,0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7还表现出与0.5% Pt/H1.78Sr0.78Bi0.22Nb2O7相当的光催化活性,0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7光催化分解水产氢速率约为0.5% Pt/H1.78Sr0.78Bi0.22Nb2O7的80.10%。

其他摘要

Due to the wide source of raw materials, simple synthesis process and diversity of composition and structure, niobate with two-dimensional (2D) layered structure has been widely used in photocatalytic production of new energy and environmental pollution control. However, the current synthesis methods of the niobate 2D layered perovskite are mainly dependent on the traditional high temperature solid state reaction method and wet chemical synthesis method represented by the hydrothermal method, which are high energy consumption and complex processes. Therefore, we had synthesized SrBi2Nb2O9 2D layered perovskite by molten salt method. Then, we had fabricated H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets through top-down method. Based on it, Ni(III)-CH3CH2NH2/HSN Ns layered composite perovskites were synthesized via the bottom-up method. Their photocatalytic properties and the micro-physics and chemistry influential mechanisms of modifications on the photocatalytic performance were studied. Specific research contents and results are as follows:(1) By using SrCO3, Bi2O3 and Nb2O5 as precursors, NaCl and KCl as molten salt system, SrBi2Nb2O9 2D layered perovskite was synthesized through molten salt method. The crystal structure of SrBi2Nb2O9 is formed by alternating arrangement of (Bi2O2)2+ layer and (SrNb2O7)2? perovskite layer perpendicular to the (00l) plane with the Sr2+ located in the gap of the NbO6 octahedron. The prepared SrBi2Nb2O9 shows platelete morphology with high crystallinity. The SrBi2Nb2O9 platelete with a length concentrated between 2 μm and 8 μm and a thickness of ~600 nm. Photocatalytic performance tests showed that the synthesized SrBi2Nb2O9 has the ability for hydrogen production and converting CO2 to CO by photo-thermal catalytic reduction. (2) H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets with a thickness of only about 2.6 nm were obtained through protonation of SrBi2Nb2O9 layered perovskite (the product is H1.78Sr0.78Bi0.22Nb2O7 platelete) and followed by chemical liquid phase exfoliation. The band gap of SrBi2Nb2O9, H1.78Sr0.78Bi0.22Nb2O7 platelete and H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets are 3.12 eV, 3.36 eV and 3.43 eV, respectively. Without any co-catalyst, the photocatalytic hydrogen evolution rate of the three samples are 7.6 μmol?h?1, 32.0 μmol?h?1 and 207.0 μmol?h?1, respectively. The enhanced photocatalytic performance of H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets can be ascribed to the decrease of its thickness, which results in its larger specific surface area and higher separation efficiency of photogenerated carriers. (3) Based on the successful synthesis of the H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets, Ni(III)-CH3CH2NH2/H1.78Sr0.78Bi0.22Nb2O7 layered composite perovskites were fabricated via the layer-by-layer (LbL) assembly method induced by the chemical reaction. The photocatalytic hydrogen production abilities of H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets and Ni(III)-CH3CH2NH2/ H1.78Sr0.78Bi0.22Nb2O7 were tested. Compared with H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets, Ni(III)-CH3CH2NH2/H1.78Sr0.78Bi0.22Nb2O7 has larger specific surface area and higher separation efficiency of photogenerated carriers, which results in the improved activity for photocatalytic hydrogen production. Through optimization, 0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7 exhibited the highest photocatalytic hydrogen production rate of 372.67 μmol?h?1, which is 0.54 times higher than that of H1.78Sr0.78Bi0.22Nb2O7 2D ultrathin nanosheets. Furthermore, 0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7 is also stable for photocatalytic hydrogen production. It is interesting to find that the photocatalytic activity for 0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7 is comparable to the 0.5% Pt/H1.78Sr0.78Bi0.22Nb2O7. The photocatalytic hydrogen production rate of 0.5% Ni/H1.78Sr0.78Bi0.22Nb2O7 Ns is about 80.10% to that of 0.5% Pt/H1.78Sr0.78Bi0.22Nb2O7.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4964
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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张丙. 二维层状铁电铌酸盐SrBi2Nb2O9的合成、改性和光催化性能研究[D]. 北京. 中国科学院大学,2017.
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