Soil Chemistry and Chemical Soil Quality Group, Wageningen University & Research, 6708 PB, Wageningen, the Netherlands; State Environmental Protection Key Laboratory of Soil Health and Green Remediation, College of Resources and Environment, Huazhong Agricultural University, 430070, Wuhan, China.
Soil Chemistry and Chemical Soil Quality Group, Wageningen University & Research, 6708 PB, Wageningen, the Netherlands.
Chemosphere. 2022 Dec;308(Pt 1):136129. doi: 10.1016/j.chemosphere.2022.136129. Epub 2022 Aug 19.
Adsorption of natural organic matter (NOM) to mineral surfaces is an important process determining the environmental fate and biogeochemical cycling of many elements. Natural organic matter consists of a heterogeneous mixture of soft and flexible organic molecules. Upon adsorption, size fractionation may occur, as well as changes in molecular conformation. Although very important, these phenomena have been omitted in existing adsorption models. Filling this gap, a novel framework for NOM adsorption to metal (hydr)oxides is presented. Humic acid (HA) was used as an analog for studying experimentally the NOM adsorption to goethite and its size fractionation as a function of pH, ionic strength, and surface loading. Size fractionation was evaluated for adsorption isotherms collected at pH 4 and 6, showing HA molecules of low molar mass were preferentially adsorbed. This phenomenon was incorporated into the new model. Consistent description of the HA adsorption data over the entire range of pH (3-11), ionic strength (2-100 mM), and surface loading (0.1-3 mg m) indicated that the spatial distribution of HA molecules adsorbed in the interface is a trade-off between maximizing the interaction of the HA ligands with the oxide surface and minimizing the electrostatic repulsion between HA particles as a result of interfacial crowding. Our advanced consistent framework is able to quantify changes in molar mass and molecular conformation, thereby significantly contributing to an improved understanding of the competitive power of HA for interacting on oxides with other adsorbed small organic acids as well as environmentally important oxyanions, such as phosphate, arsenate, and others.
天然有机物 (NOM) 吸附到矿物表面是决定许多元素环境归宿和生物地球化学循环的重要过程。天然有机物由软而灵活的有机分子的不均匀混合物组成。在吸附过程中，可能会发生尺寸分级，以及分子构象的变化。尽管这些现象非常重要，但它们在现有的吸附模型中被忽略了。为了填补这一空白，提出了一种用于金属（水合）氧化物上 NOM 吸附的新框架。腐殖酸 (HA) 被用作研究针铁矿上 NOM 吸附及其随 pH、离子强度和表面负载变化的尺寸分级的实验模拟物。在 pH 4 和 6 下收集的吸附等温线上评估了尺寸分级，结果表明低摩尔质量的 HA 分子优先被吸附。这种现象被纳入了新模型。新模型能够一致描述整个 pH 范围 (3-11)、离子强度 (2-100 mM) 和表面负载 (0.1-3 mg m) 内的 HA 吸附数据，表明吸附在界面中的 HA 分子的空间分布是 HA 配体与氧化物表面相互作用最大化与由于界面拥挤导致 HA 颗粒之间的静电排斥最小化之间的权衡。我们先进的一致框架能够量化摩尔质量和分子构象的变化，从而显著促进对 HA 与其他吸附的小分子有机酸以及环境重要的含氧阴离子（如磷酸盐、砷酸盐等）在氧化物上相互作用的竞争能力的理解。
