Li Wei, Wang Yan, Liu Fan, Xie Haijiao, Yin Hui, Yi Tian
Institute of Agricultural Quality Standards and Testing Technology Research, Hubei Academy of Agricultural Sciences Wuhan Hubei 430064 China
Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River) Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University Wuhan 430070 PR China
RSC Adv. 2023 Sep 7;13(38):26861-26868. doi: 10.1039/d3ra02945j. eCollection 2023 Sep 4.
Various exotic metal cations commonly coexist with ferrihydrite nanoparticles in natural environments. Lack of knowledge about the metal cations effects on ferrihydrite nucleation and growth greatly blights the deep understanding of ferrihydrite mineralogical properties and reactivities, and thus the fates of associated nutrients, heavy metals/metalloids, and organic pollutants. Here, the nucleation processes and mechanisms of ferrihydrite nanoparticles in the presence of Al or Cr were studied by combining visible spectroscopy, quick X-ray absorption fine structure spectroscopy and quantum chemical calculations. The formation of ferrihydrite can be divided into three stages. In stage 1, Fe(HO) forms μ-oxo Fe dimers, with the gradual increase of Fe-O bond length () and disappearance of Fe-O multiple scattering. In stage 2, ferrihydrite particles begin to form and grow slowly, during which continues to increase and edge- and corner-sharing Fe-Fe bonds appear. In stage 3, ferrihydrite growth rate increases significantly and continues to the end of the reaction, with the decreases of . The presence of metal cations at a molar ratio of 0.1 to Fe hinders the formation of μ-oxo dimers by affecting the Fe hydrolysis and polymerization at stage 1 and stage 2, but promotes the conversion of the μ-oxo dimer to the dihydroxo dimer with lower energy barrier and the creation of crystal growth sites and thus enhances the ferrihydrite nucleation and growth at stage 3.
在自然环境中，各种外来金属阳离子通常与水铁矿纳米颗粒共存。由于缺乏关于金属阳离子对水铁矿成核和生长影响的认识，严重阻碍了对水铁矿矿物学性质和反应活性的深入理解，进而影响了相关养分、重金属/类金属以及有机污染物的归宿。在此，通过结合可见光谱、快速X射线吸收精细结构光谱和量子化学计算，研究了在铝或铬存在下的水铁矿纳米颗粒的成核过程和机制。水铁矿的形成可分为三个阶段。在第一阶段，Fe(HO)形成μ-氧代铁二聚体，Fe-O键长（）逐渐增加，Fe-O多重散射消失。在第二阶段，水铁矿颗粒开始形成并缓慢生长，在此期间，继续增加，出现边共享和角共享的Fe-Fe键。在第三阶段，水铁矿生长速率显著增加并持续到反应结束，此时减小。金属阳离子与铁的摩尔比为0.1时，通过影响第一阶段和第二阶段的铁水解和聚合作用，阻碍了μ-氧代二聚体的形成，但促进了μ-氧代二聚体向能量势垒较低的二羟基二聚体的转化，并创造了晶体生长位点，从而增强了第三阶段水铁矿的成核和生长。
