A1-xZnxSn(OH)6(A=Ca,Mn,Co)晶面及表界面调控提高光催化CO2还原性能研究

Photocatalytic reduction of CO2 into hydrocarbon fuels by utilizing solar energy holds promise to address the current and future demand of energy supply. However, the photocatalytic efficiency of single photocatalyst is still very low. Therefore, one of the promising strategies is to improve the separation efficiency of photoinduced charges and the adsorption ability of CO2 onto the surfaces of photocatalysts. Metal hydroxystannate will be prepared by hydrothermal method, vapor deposition and other controllably synthetic avenues. And photocatalysts with two different kinds of crystal facets and different properties of surface and interface will be obtained by controlling the preparation parameters in detail. The high efficiency of the efficiently spatial separation and migration of photoinduced charges is attributed to the potential difference between the two different kinds of crystal facets and the high adsorption capacity of CO2 is attributed to the alkaline surface, surface defects and so on. The effect of the crystal facet and surface and interface on separation and migration of photoinduced charges, adsorption of CO2 and photocatalytic reaction will be studied systematically, in order to drawing out the meaning of photocatalytic reduction of CO2 in the presence of metal hydroxystannate. The investigations provide some scientific and experimental bases for research on novel, high efficient photocatalysts to photocatalytic reduction of CO2 and will favor the development of researches on physical chemistry process.

光催化剂的光生电荷分离效率低以及CO2分子的化学惰性，是导致光催化CO2还原效率不高的两个关键问题。本课题拟以羟基锡酸盐A1-xZnxSn(OH)6(A=Ca，Mn，Co)为研究对象，通过模板或表面配体调控各晶面的生长速度，获得两种不同晶面裸露的光催化剂，利用不同裸露晶面间的电势差，促进光生电荷的有效分离，同时通过对酸碱活性位等表界面性质的调控，提高光催化剂对CO2分子的吸附与活化。揭示晶面、表界面性质对光生电荷传输特性的调控规律；阐明晶面及表界面调控对CO2分子的吸附与活化以及光生电荷分离的促进作用规律和机制；并利用理论计算与光催化CO2还原反应相结合的方法，揭示光催化剂与CO2分子间的相互作用模式及电子转移机制，阐明CO2光催化还原反应机理，获得高活性的光催化剂。本课题的实施为研发新型、高效光催化CO2还原催化剂提供新思路，对光催化过程中物理化学机制的研究具有促进作用。

光催化剂的光生电荷分离效率低以及CO2分子的化学惰性，是导致光催化CO2还原效率不高的两个关键问题。本课题通过模板或者表面配体调控各晶面的生长速度，获得了不同晶面裸露的{100}和{111}晶面ZnSn(OH)6、{100}及{110}晶面共暴露BiOCl/ZnCr-LDH同质-异质结、能带结构可调的ZnxCd1-xS固溶体、以及BiWO4-Bi2S3异质结。十四面体ZnSn(OH)6单晶中的{111}和{100}晶面由于晶面间的电势差，光生电子和空穴可分别有效地迁移至{111}和{100}晶面，实现了光生电荷的分离。DFT计算表明，二氧化碳分子更易于在ZnSn(OH)6的{111}还原晶面上发生离解反应，这可能是{111}晶面具有比{100}晶面更大的表面羟基密度。由于晶面间的电势差，光生电子和空穴可分别有效地迁移至BiOCl纳米单晶{100}和{110}晶面；同时由于BiOCl与ZnCr-LDH之间的能带匹配，可驱使聚集在{100}晶面上的光生电子进一步迁移至ZnCr-LDH表面，实现了光生电荷的有效空间分离。BiOCl与ZnCr-LDH间的二维接触提高了电子传输的通道面积，适度量的ZnCr-LDH薄片也可作为高催化活性位点，提升了载流子分离动力学，也有效提高了光生电子的寿命。ZnxCd1-xS固溶体的导带与价带随着Zn2+离子含量的增加，分别往更负与更正位置移动。相比纯的CdS，ZnxCd1-xS固溶体不仅具有可调的禁带宽度，同时具有可见光还原CO2能力，其中Zn0.8Cd0.2S可以在可见光下将CO2还原为乙醇。由于BiVO4与Bi2S3之间的能带匹配，可驱使光生电子和空穴分别向BiVO4及Bi2S3迁移，实现了光生电荷的有效空间分离。本课题的实施为研发新型、高效光催化CO2还原催化剂提供新思路，对光催化过程中物理化学机制的研究具有促进作用。