Liu Juanjuan, Louie Stacey M, Zhao Juntao, Gao Xubo, Hu Yandi
The Key Laboratory of Water and Sediment Sciences, Ministry of Education, State Environmental Protection Key Laboratory of All Material Fluxes in River Ecosystems, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; State Key Laboratory of Biogeology & Environmental Geology, School of Environmental Studies, China University of Geosciences, Wuhan, Hubei 430074, China.
Department of Civil & Environmental Engineering, University of Houston, Houston, TX 77004, United States.
Sci Total Environ. 2022 Jul 20;831:154976. doi: 10.1016/j.scitotenv.2022.154976. Epub 2022 Apr 2.
Magnetite nanoparticles (MNPs) with varied organic coatings (OCs) which improved their stability have broad environmental applications. However, the adsorbed amounts and layer thickness of varied OCs onto MNPs during the synthesis were generally not or poorly characterized, and their interactions with natural organic matter (NOM) were still in progress. In this study, acetic (HAc), citric (CA), and polyacrylic acid (PAA) were selected as model OCs, the adsorption behaviors of OCs on MNPs were characterized under varied aqueous C/Fe ratios, and the aggregation behaviors of MNPs with varied OCs (OC-MNPs) at neutral pH (7.0 ± 0.2) with NaCl (5-800 mM) in the presence/absence of NOM were systematically investigated. Under low aqueous C/Fe ratio, the adsorbed amounts of model OCs as -COOH/Fe ratio followed the order: CA ≈ PAA > > HAc. With high aqueous C/Fe ratio, the maximum adsorbed masses of OC-MNPs were similar. The adsorbed layer thicknesses of OC-MNPs were thoroughly characterized using three different methods, all showing that the adsorbed layer of PAA was thicker than that of CA and HAc. Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (EDLVO) calculations showed that electrostatic and van der Waals forces were dominant for CA-MNPs and HAc-MNPs stabilization; while steric repulsion played major roles in stabilizing PAA-MNPs, probably due to a thicker PAA layer. In the presence of NOM, stability behaviors of all OC-MNPs were similar, ascribing to the much greater amounts of NOM adsorbed than the OCs, causing greater steric repulsion. This study provides new mechanistic insights which could help better understand the effects of varied OCs on MNPs' colloidal stability.
具有不同有机涂层（OCs）且稳定性得到改善的磁铁矿纳米颗粒（MNPs）在环境领域有广泛应用。然而，合成过程中不同OCs在MNPs上的吸附量和层厚度通常未得到充分表征或表征不佳，并且它们与天然有机物（NOM）的相互作用仍在研究中。在本研究中，选择乙酸（HAc）、柠檬酸（CA）和聚丙烯酸（PAA）作为模型OCs，在不同水相C/Fe比下表征OCs在MNPs上的吸附行为，并系统研究了在存在/不存在NOM的情况下，不同OCs（OC-MNPs）在中性pH（7.0±0.2）和NaCl（5 - 800 mM）条件下的聚集行为。在低水相C/Fe比下，模型OCs的吸附量以-COOH/Fe比计遵循以下顺序：CA≈PAA >> HAc。在高水相C/Fe比下，OC-MNPs的最大吸附质量相似。使用三种不同方法对OC-MNPs的吸附层厚度进行了全面表征，结果均表明PAA的吸附层比CA和HAc的厚。Derjaguin-Landau-Verwey-Overbeek（DLVO）和扩展DLVO（EDLVO）计算表明，静电和范德华力对CA-MNPs和HAc-MNPs的稳定性起主导作用；而空间排斥在稳定PAA-MNPs中起主要作用，这可能是由于PAA层更厚。在存在NOM的情况下，所有OC-MNPs的稳定性行为相似，这归因于NOM的吸附量远大于OCs，从而导致更大的空间排斥。本研究提供了新的机理见解，有助于更好地理解不同OCs对MNPs胶体稳定性的影响。
