Molecular Dynamics Simulation Study of the Early Stages of Nucleation of Iron Oxyhydroxide Nanoparticles in Aqueous Solutions

Abstract

Nucleation is a fundamental step in crystal growth. Of environmental and materials relevance are reactions that lead to nucleation of iron oxyhydroxides in aqueous solutions. These reactions are difficult to study experimentally due to their rapid kinetics. Here, we used classical molecular dynamics simulations to investigate nucleation of iron hydroxide /oxyhydroxide nanoparticles in aqueous solutions. Results show that in a solution containing ferric ions and hydroxyl groups, iron-hydroxyl molecular clusters form by merging ferric monomers, dimers and other oligomers, driven by strong affinity of ferric ions to hydroxyls.When deprotonation reactions are not considered in the simulations, these clusters aggregate to form small iron hydroxide nanocrystals with a six-member ring-like layered structure allomeric to gibbsite. By comparison, in a solution containing iron chloride and sodium hydroxide, the presence of chlorine drives cluster assembly along a different direction to form long molecular chains (rather than rings) composed of Fe-O octahedra linked by edge sharing. Further, in chlorine-free solutions, when deprotonation reactions are considered, the simulations predict ultimate formation of amorphous iron oxyhydroxide nanoparticles with local atomic structure similar to that of ferrihydrite nanoparticles. Overall, our simulation results reveal that nucleation of iron oxyhydroxide nanoparticles proceeds via a cluster aggregation-based non-classical pathway.

Colloidal FeIII, MnIII, CoIII, and CuII Hydroxides Stabilized by Starch as Catalysts of Water Oxidation Reaction with One Electron Oxidant Ru(bpy)33+

“…The catalyst prepared by method 3 provided a higher yield of O 2 (65 %) than the catalysts prepared by methods 1 and 2 (60 and 54 % of the stoichiometric yield, respectively). The results obtained can be understood based on the data reported by H. Zhang et al [27] who used the method of molecular dynamics for studying the process of the formation of primary particles of hydroxo compounds. The author established that disordered 1-2 nm hydroxide clusters are only formed at low concentrations of the hydrolyzed salts.…”

“…[35] Some literature data were used for modeling the iron hydroxide cluster. Zhang and co-authors [27] used centroid molecular dynamics with combined set of force fields [36,37] and additional central force model for water [38] for modeling the process of nucleation of Fe III hydroxide. These simulation results showed that during the early stages of hydrolysis there is occurs the coagulation processes and formation of amorphous primary hydroxide particles (1-2 nm).…”

“…where E 1 is the total energy of hydrated iron hydroxide cluster (Fe27 O 27 OH 27 + 1189 H 2 O); E 2 is the total energy of hydrated starch molecule ((C 6 H 10 O 5 ) 50 + 1189 H 2 O); E 3 is the total energy of hydrated hydroxide stabilized with starch molecule (Fe 27 O 27 OH 27 + (C 6 H 10 O 5 ) 50 + 1189 H 2 O)…”

Polyaspartic acid facilitates oxolation within iron(iii) oxide pre-nucleation clusters and drives the formation of organic-inorganic composites

“…In many experimental settings, cluster-and particle-based pathways have been observed for iron() oxide nucleation and growth. 2,[5][6][7] In the early stages of iron() hydrolysis, small species in the size range of 1-4 nm occur. Such polymeric clusters aggregate to form the different crystalline materials.…”

“…Such polymeric clusters aggregate to form the different crystalline materials. 2,5,6,8 It was recently proposed that iron() (oxyhydr)oxide precipitation in such cluster-based pathways can be described within the notions of the so-called pre-nucleation cluster (PNC) pathway. 9 In this model, in contrast to the classical nucleation picture, a) J. Konsek, J. Schwaderer, and S. M. Stadler contributed equally to this work.…”