Atomic Force Microscopy and Surface Characteristics of Iron Oxides Formed in Citrate Solutions

Abstract

Surface geometry of minerals greatly influences the physical, chemical, and biological processes occurring on the surface. However, a quantitative or even a qualitative description of the surface geometry of minerals has proven to be extremely difficult. In our study, the fine‐scale morphology (1 by 1 µm scale) and surface geometry described by mean surface roughness and surface fractal dimension of Fe oxides formed at various concentrations of citrate, which is common in terrestrial and aquatic environments, were investigated by atomic force microscopy (AFM). Specific surface area and Point of Zero Salt Effect (PZSE) of the Fe oxides, as well as P adsorption, were also studied. Citrate present during the formation of Fe oxides significantly altered the fine‐scale morphology, surface geometry, and other surface characteristics of the products. The mean surface roughness and surface fractal dimension determined by AFM measured the degree of the disorder of surface structure of Fe oxides. The modification of the surface characteristics of the Fe oxides by coprecipitated citrate through fundamental structural changes and the blocking of P‐adsorption sites by citrate affected the P adsorption. Due to the hindrance of the crystallization process, P adsorption per unit weight of the Fe oxides formed at 10‐3 M citrate was very significantly enhanced. The fine‐scale morphology, surface geometry, and related surface characteristics of Fe oxides formed under the influence of organic acids merit close attention as we advance our understanding of their surface chemistry pertaining to dynamics and transformations of nutrients and pollutants in terrestrial and aquatic environments.

Kinetics of phosphate adsorption on iron oxides formed under the influence of citrate

“…III, Digital Instruments, Santa Barbara, CA) as described by Liu and Huang (1999). After a height image was captured, the computer automatically recorded all the three-dimensional data of the surface.…”

“…Further, the Fe oxides formed at the initial citrate/Fe(II) MR of 0.1 had the lowest PZSE values and, thus, the least net positive charges at pH of 4.0 (Liu and Huang 1999), and the largest micropore surface areas (Table 1). The negative charges on the Fe oxides would result in an electrostatic repulsion of phosphate anions and make it difficult for phosphate to approach the Fe oxide surface.…”

“…However, pure Fe oxides seldom occur in natural environments, since other ions present in the environment can influence their formation (Krishnamurti and Huang 1990;Cornell and Schwertmann 1996). The presence of low-molecular-weight organic acids such as citric acid during the formation of Fe oxides can greatly modify the surface prop-erties of the Fe oxides formed, such as surface structure, surface geometry, specific surface area, surface porosity, surface charge, and PZSE, through fundamental structural modifications (Liu and Huang 1999). Ainsworth and Sumner (1985) found that Al substitution in goethite affected the pseudo-first-order rate constant of phosphate adsorption by the goethite at all pH levels and lower phosphate concentrations.…”

Ultraviolet Sensors Based on Two-Dimensional Zinc Oxide Structures

“…The citrate is used, as it adsorbs strongly on mineral surfaces and significantly alters the mineral growth behaviour [38]. Using this method, Tian et al [34] succeeded in growing 2D ZnO with plate (nanoplates) shapes.…”

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…[311] Hydrophilic and negatively charged nanoparticles are consequently resulted due to, at least, one carboxylic acid group exposed to the solvent. [312] However, this method suffers from labile carboxylic functions which can be easily broken by due to elevation of temperature or presence of carboxylic compounds with higher affinities to the surface. [308] Organophosphorus molecules, such as phosphonic acid, alkylphosphoric acid, and their salts, phosphates and phosphonates have been investigated as promising stabilizing Figure 25.…”