FORMATION OF FERRIC OXIDES FROM AQUEOUS-SOLUTIONS - A POLYHEDRAL APPROACH BY X-RAY ABSORPTION-SPECTROSCOPY .1. HYDROLYSIS AND FORMATION OF FERRIC GELS
FORMATION OF FERRIC OXIDES FROM AQUEOUS-SOLUTIONS - A POLYHEDRAL APPROACH BY X-RAY ABSORPTION-SPECTROSCOPY .1. HYDROLYSIS AND FORMATION OF FERRIC GELS
复制标题
DOI：
10.1016/0016-7037(89)90001-x
复制
发表时间：
1989-03-01
影响因子：
5
通讯作者：
BOTTERO, JY
中科院分区：
文献类型：
--
作者：
COMBES, JM;MANCEAU, A;BOTTERO, JY
X 射线吸收光谱 (XAS) 用于跟踪从 1 M 氯化物和 0.1 M 硝酸盐溶液形成三水合氧化铁凝胶过程中铁离子周围局部结构环境的演变。 Fe K-XANES 和 EXAFS 证实三价铁离子在此演化过程中保持 6 倍配位。在部分水解的三氯化铁溶液上获得的 EXAFS 光谱表明存在高达 OH Fe= 2.2 的水氯铁络合物。当溶液中OH Fe<1时，铁主要以反式[FeCl 2 (H 2 O) 4] 2+ 八面体形式存在，Fe-Cl和Fe-O距离分别为2.31和2.01 Å。随着溶液中 OH 可用性的增加，Cl− 阴离子倾向于逐渐交换为 (O, OH, OH 2) 配体。低于 OH Fe= 1，在第一配位层之外没有检测到结构顺序。高于此比率，可观察到 3.05 Å 和 3.44 Å 处的两个 Fe-Fe 距离，这对应于共享边和顶点的 Fe 八面体的存在。 XAS 结果表明，铁凝胶和高度聚合的水性物质是短程有序的。凝胶无序的主要贡献在于小尺寸的相干散射域，这也是其 X 射线“无定形”特征的原因。从水解的最初阶段到最后阶段，对于由氯化物和硝酸盐溶液形成的聚合物，颗粒具有接近球形的形状，最小平均直径范围为 10-30 Å。随着聚合的进行，局部有序度扩展到几十埃，颗粒结构逐渐接近赤铁矿 (β-FeOOH) 或针铁矿 (α-FeOOH)。 This local structure is distinct from that of the lepidocrocite (γ-FeOOH)-like structure of ferric gels precipitated after oxidation of divalent Fe solutions.晶体 Fe-羟基氧化物从凝胶中的生长是通过三价铁聚合物中渐进的长程有序而发生的，而不改变 Fe 周围的短程有序。
X-ray absorption spectroscopy (XAS) was used to follow the evolution of local structural environments around ferric ions during the formation of ferric hydrous oxide gels from 1 M chloride and 0.1 M nitrate solutions. Fe K-XANES and EXAFS confirm that ferric ions remain 6-fold coordinated during this evolution. EXAFS spectra obtained on partially hydrolyzed ferric chloride solutions indicate the presence of aqua-chloro ferric complexes up to OH Fe= 2.2. When OH Fe< 1 in the solution, iron mainly occurs in trans-[FeCl 2 (H 2 O) 4] 2+ octahedra with Fe-Cl and Fe-O distances of 2.31 and 2.01 Å, respectively. With increasing OH availability in the solution, Cl− anions tend gradually to be exchanged for (O, OH, OH 2) ligands. Below OH Fe= 1, no structural order is detected beyond the first coordination sphere. Above this ratio, two Fe-Fe distances at 3.05 Å and 3.44 Å are observed and correspond to the presence of edge-and vertex-sharing Fe-octahedra. XAS results show that ferric gels and highly polymerized aqueous species are short-range ordered. The main contribution to disorder in the gels arises from the small size of coherently scattering domains also responsible for their X-ray ‘amorphous’ character. From the initial to the final stage of hydrolysis, particles possess a nearly spherical shape with a minimum average diameter ranging from 10–30 Å for polymers formed from chloride and nitrate solutions. As polymerization proceeds, the local order extends to several tens of angströms and the particle structures becomes progressively closer to that of akaganeite (β-FeOOH) or goethite (α-FeOOH). This local structure is distinct from that of the lepidocrocite (γ-FeOOH)-like structure of ferric gels precipitated after oxidation of divalent Fe solutions. The growth of the crystalline Fe-oxyhydroxides from gels takes place by the progressive long-range ordering in the ferric polymers without modifying the short-range order around Fe.