Surface Chemistry and Phase Transformation of Nanoscale Zero-Valent Iron (nZVI) in Aquatic Media

Abstract

The unique "core-shell" structure endows nanoscale zero-valent iron (nZVI) rich aquatic surface chemistry properties. Transformation of surface chemistry and crystal phase of nZVI affect its reactivity and environmental transport and fate. Recent advances on the surface chemistry and phase transformation of nZVI in aqueous media are highlighted in this paper focusing on a basic theory of nZVI for pollution control and environmental application. Surface chemistry and phase of both fresh and reacted nZVI are presented. The structure, composition and properties of nanoparticles are determined not only by reaction time but also by environmental conditions. Specifically, the influences of dissolved oxygen, hydraulic conditions (static and stirring), types and concentrations of heavy metals (U(VI), Cr(VI), Se(IV)) and anions (HPO − and 3 HCO − ) are investigated. In addition, the effect of surface modification with polyelectrolytes, including anionic polyacrylamide (APAM) and carboxymethylcellulose sodium (CMC), on microstructure, morphology and composition of nanoparticles in aqueous phase was discussed. Results demonstrate that environmental conditions have significant impacts on particles structure, composition and properties, consequently on nZVI performance for pollutant removal. After corrosion under different aqueous conditions, the core-shell structured nZVI are distorted and the metallic iron core is transformed into different iron oxides/hydroxides, such as γ-Fe 2 O 3 , Fe 3 O 4 and γ-FeOOH. These iron (hydr)oxides exhibit different surface complexation and affinity proprieties, thus eventually affecting the pollutant removal performance and the environmental fate of reaction products. More research on the effect of dynamic structure transformation by different types of pollutants, and a reaction model between the surface chemistry/phase transformation and removal performance are needed to deepen our understanding on nZVI surface chemistry, and develop more effective technologies of environmental applications. Keywords nanoscale zero-valent iron; aquatic media; surface chemistry; crystal phase; transformation 1 引言 铁的标准氧化还原电位为-0.44 V, 零价铁材料 (Zero-Valent Iron, ZVI)因其强还原能力、良好的电化学 和配位化学特性 [1～4] , 在环境修复领域被广泛应用. 纳 米零价铁(nanoscale Zero-Valent Iron, nZVI)不但具有零

Aging of zero‐valent iron‐based nanoparticles in aqueous environment and the consequent effects on their reactivity and toxicity

“…To date, many researchers have put great efforts into answering to the above questions. There have been some reviews summarizing the transformations of nZVI in aqueous environment (Bae, Collins, Waite, & Hanna, ; Lei, Sun, Tsang, & Lin, ; Liu, Gu, Wang, Liu, & Zhang, ). However, these reviews mainly focused on the nZVI particles, without much attention given to the transformations of the other modified nZVI particles (e.g., sulfide‐modified nZVI, nZVI‐based bimetallic particles, surface‐coated nZVI), especially for the consequent impacts of the transformations on their reactivity and toxicity.…”

Effective removal of Cd(ii) by sludge biochar supported nanoscale zero-valent iron from aqueous solution: characterization, adsorption properties and mechanism

“…This shows that the Fe 0 particles on the surface of SBC are composed of polycrystalline particles with smaller particle sizes. 34 There are characteristic diffraction peaks of g-FeOOH and Fe 3 O 4 /g-Fe 2 O 3 at 2y = 18.391, 33.521, and 47.051, indicating that part of nZVI was oxidized during the material preparation. After the adsorption of Cd(II), the dispersion of the diffraction peaks of the material increases.…”