Wang Zhoujie, Lu Qiuyi, Liu Chaopeng, Tian Huadong, Wang Jingyi, Xie Lei, Liu Qi, Zeng Hongbo
School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, P. R. China.
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.
Environ Sci Technol. 2024 Jan 22. doi: 10.1021/acs.est.3c08309.
The mobility and distribution of heavy metal ions (HMs) in aquatic environments are significantly influenced by humic acid (HA), which is ubiquitous. A quantitative understanding of the interaction mechanism underlying the adsorption and retention of HMs by HA is of vital significance but remains elusive. Herein, the interaction mechanism between HA and different types of HMs (i.e., Cd(II), Pb(II), arsenate, and chromate) was quantitatively investigated at the nanoscale. Based on quartz crystal microbalance with dissipation tests, the adsorption capacities of Pb(II), Cd(II), As(V), and Cr(VI) ionic species on the HA surface were measured as ∼0.40, ∼0.25, ∼0.12, and ∼0.02 nmol cm, respectively. Atomic force microscopy force results showed that the presence of Pb(II)/Cd(II) cations suppressed the electrostatic double-layer repulsion during the approach of two HA surfaces and the adhesion energy during separation was considerably enhanced from ∼2.18 to ∼5.05/∼4.18 mJ m. Such strong adhesion stems from the synergistic metal-HA complexation and cation-π interaction, as evidenced by spectroscopic analysis and theoretical simulation. In contrast, As(V)/Cr(VI) oxo-anions could form only weak hydrogen bonds with HA, resulting in similar adhesion energies for HA-HA (∼2.18 mJ m) and HA-As(V)/Cr(VI)-HA systems (∼2.26/∼1.96 mJ m). This work provides nanoscale insights into quantitative HM-HA interactions, improving the understanding of HMs biogeochemical cycling.
腐殖酸（HA）广泛存在于水生环境中，对重金属离子（HMs）的迁移性和分布有显著影响。定量了解HA对HMs的吸附和保留作用的相互作用机制至关重要，但仍不清楚。在此，在纳米尺度上定量研究了HA与不同类型的HMs（即Cd(II)、Pb(II)、砷酸盐和铬酸盐）之间的相互作用机制。基于具有耗散测试的石英晶体微天平，测量了Pb(II)、Cd(II)、As(V)和Cr(VI)离子物种在HA表面的吸附容量分别约为0.40、0.25、0.12和0.02 nmol/cm²。原子力显微镜力的结果表明，Pb(II)/Cd(II)阳离子的存在抑制了两个HA表面接近过程中的静电双层排斥，分离过程中的粘附能从约2.18显著提高到约5.05/约4.18 mJ/m²。光谱分析和理论模拟证明，这种强粘附源于金属-HA络合和阳离子-π相互作用的协同作用。相比之下，As(V)/Cr(VI)含氧阴离子只能与HA形成弱氢键，导致HA-HA（约2.18 mJ/m²）和HA-As(V)/Cr(VI)-HA系统（约2.26/约1.96 mJ/m²）具有相似的粘附能。这项工作提供了关于HM-HA定量相互作用的纳米级见解，增进了对HMs生物地球化学循环的理解。
