非晶态镍硼酸盐结构的EXAFS研究

摘要

由摩尔比分别为1：2和1：8的NiCl2∙6H2O和Na2B4O7∙10H2O作为反应物,合成两种非晶态镍硼酸盐,同时通过水热法合成β-Ni(OH)2.化学分析和热重-微商热重法(TG-DTG)分析结果确定两种非晶态镍硼酸盐的分子组成分别为NiO∙0.8B2O3∙4.5H2O和NiO∙B2O3∙3H2O.激光拉曼(Raman)实验结果表明镍硼酸盐样品中主要存在的硼氧阴离子为B3O3(OH)52-和B2O(OH)62-.同步辐射扩展X射线吸收精细结构(EXAFS)方法对样品进行结构解析,通过数据拟合给出样品中Ni原子周围近邻配位原子种类、配位数以及原子间距离.用不同晶体结构作为标准对两种非晶态镍硼酸盐进行拟合的结果表明,样品中Ni原子周围局域结构与Ni3B2O6晶体(ICSD No.31387)中的吻合较好. Ni原子周围配位原子为O、B和Ni,对于NiO∙0.8B2O3∙4.5H2O,配位数分别为5.7、3.8和3.8,配位距离分别为0.208、0.263和0.311 nm；对于NiO∙B2O3∙3H2O,配位数分别为6.0、4.0和4.0,配位距离分别为0.207、0.262和0.310 nm.%In this work, two amorphous hydrated nickel borates were synthesized with nickel chloride hexahydrate and borax as reactants at mole ratios of 1:2 and 1:8, respectively. The chemical compositions of these nickel borates were determined to be NiO∙0.8B2O3∙4.5H2O and NiO∙B2O3∙3H2O through thermogravimetry-derivative thermogravimetry (TG-DTG) and chemical analysis, in which the main anions were determined to be B3O3(OH)52-and B2O(OH)62-, respectively, by Raman spectroscopy. The local structure of these samples was studied by synchrotron radiation extended X-ray absorption fine structure (EXAFS). Based on the processing and fitting of the EXAFS experimental data, the neighboring coordination atoms type, the interatomic distances, and the atom-pair numbers of Ni were determined. The fitting results of the amorphous nickel borate show that the local structure around the Ni atom has a similar structure to that of the Ni3B2O6 crystal. The neighboring coordination atoms of Ni in these amorphous nickel borates are O, B, and Ni. For NiO∙0.8B2O3∙4.5H2O, the interatomic distances for Ni―O, Ni―B, and Ni―Ni are 0.208, 0.263, and 0.311 nm, and the atom-pair numbers are 5.7, 3.8, and 3.8, respectively. The interatomic distances of NiO∙B2O3∙3H2O are 0.207, 0.262, and 0.310 nm, and the atom-pair numbers are 6.0, 4.0, and 4.0, respectively. The first shel s of Ni2+in NiO∙0.8B2O3∙4.5H2O and NiO∙B2O3∙3H2O are octahedral with six oxygen atoms.