Heterostructured BiOI@La(OH)_3 nanorods with enhanced visible light photocatalytic NO removal

BiOI@La(OH)_3纳米棒异质结制备及其增强可见光催化去除NO性能（英文）

Heterostructured BiOI@La（OH）3 nanorod photocatalysts were prepared by a facile chemical impregnation method.The enhanced visible light absorption and charge carrier separation can be simultaneously realized after the introduction of BiOI particles into La（OH）3 nanorods.The BiOI@La（OH）3 composites were applied for visible light photocatalytic oxidization of NO in air and exhibited an enhanced activity compared with BiOI and pure La（OH）3 nanorods.The results show that the energy levels between the La（OH）3 and BiOI phases matched well with each other,thus forming a heterojunctioned BiOI@La（OH）3 structure.This band structure matching could promote the separation and transfer of photoinduced electron-hole pairs at the interface,resulting in enhanced photocatalytic performance under visible light irradiation.The photocatalytic performance of BiOI@La（OH）3 is shown to be dependent on the mass ratio of BiOI to La（OH）3.The highest photocatalytic performance can be achieved when the mass ratio of BiOI to La（OH）3 is controlled at 1.5.A further increase of the mass ratio of BiOI weakened the redox abilities of the photogenerated charge carriers.A new photocatalytic mechanism for BiOI@La（OH）3 heterostructures is proposed,which is directly related to the efficient separation of photogenerated charge carriers by the heterojunction.Importantly,the as-prepared BiOI@La（OH）3 heterostructures exhibited a high photochemical stability after multiple reaction runs.Our findings demonstrate that BiOI is an effective component for the formation of a heterostructure with the properties of a wide bandgap semiconductor,which is of great importance for extending the light absorption and photocatalytic activity of wide bandgap semiconductors into visible light region.

一维La(OH)_3纳米棒具有特殊的电子结构和多功能特性,特别是作为半导体光催化剂引起了人们极大的兴趣.但La(OH)_3禁带宽度较大,且只能吸收紫外光,所以光催化效率较低,可见光利用能力较差,限制了La(OH)_3的实际应用.因此,需要开发一种高效的改进方法来提高La(OH)_3的可见光催化性能.本课题组发展了一种有效的改进La(OH)_3方法,通过简易的方法将BiOI纳米颗粒沉积在La(OH)_3纳米棒上,有效增强了对可见光的吸收能力和光生载流子的分离能力.本文采用X射线衍射(XRD)、透射电镜(TEM)、扫描电镜(SEM)、紫外-可见漫反射光谱(UV-Vis DRS)、荧光光谱(PL)、光电子能谱(XPS)、电子自旋共振(ESR)、N_2吸附和元素分析等手段研究了BiOI@La(OH)_3纳米棒异质结的构建原理及增强可见光催化性能的原因.XRD和XPS结果表明,通过简易化学沉积法原位构建了BiOI@La(OH)_3异质结,并且在异质结中没有杂相生成.由SEM图像可见,原始La(OH)_3由分散的一维纳米棒组成,平均直径为30-50 nm.通过BiOI与La(OH)_3表面的紧密接触成功构建异质结,但BiOI纳米颗粒未改变La(OH)_3纳米棒的形貌.由TEM和HRTEM图像可见,La(OH)_3纳米棒的平均长度为30-50 nm,并且在BiOI@La(OH)_3异质结中可以清晰看出BiOI和La(OH)_3之间紧密接触的界面和晶格间距.N_2物理吸附结果显示,随着BiOI量的增加,BiOI@La(OH)_3异质结的比表面积增加,但孔体积未现明显变化.UV-Vis DRS结果显示,引入BiOI后明显促进了La(OH)_3对可见光的吸收能力和利用效率,从而有利于增强可见光催化活性.通过理论计算分别得到BiOI和La(OH)_3的价带和导带位置,表明具有非常匹配的能带结构可以促进BiOI光生电子的有效转移.可见光催化去除NO测试结果表明,BiOI@La(OH)_3异质结的光催化活性高达50.5%,明显优于BiOI和La(OH)_3.ESR测试结果显示,BiOI@La(OH)_3异质结可见光催化活性中起主要作用的活性物种是~·OH.结合表征结果,BiOI@La(OH)_3纳米棒异质结可见光催化性能增强的原因主要有三个:(1)BiOI@La(OH)_3异质结增大的比表面积有利于反应物和产物在催化剂表面扩散,同时可提供更多活性位点参与光催化反应;(2)禁带宽度影响光催化效率,当BiOI与La(OH)_3达到合适比例时,既可以促进可见光吸收,也可以使光生电子具有较强还原能力;(3)BiOI@La(OH)_3异质结有利于光生载流子的分离,从而显著提高其光催化活性.