Feng Haotian, Li Xiong, Xing Yuhang, Xie Liangchen, Zhen Shuai, Chang Wenqian, Zhang Jianguo
College of Natural Resources and Environment, Northwest A & F University, Yangling 712100, Shaanxi, China.
Taklimakan Desert Research Station, Xinjiang Institute of Ecology and Geography Chinese Academy of Sciences, Korla 841000, China.
Phys Chem Chem Phys. 2023 Mar 15;25(11):7951-7964. doi: 10.1039/d2cp05234b.
Soluble inorganic carbon is an important component of a soil carbon pool, and its fate in soils, sediments, and underground water environments has great effects on many physiochemical and geological processes. However, the dynamical processes, behaviors and mechanism of their adsorption by soil active components, such as quartz, are still unclear. The aim of this work is to systematically address the anchoring mechanism of CO and HCO on a quartz surface at different pH values. Three pH values (pH 7.5, pH 9.5 and pH 11) and three carbonate salt concentrations (0.07, 0.14 and 0.28 M) are considered, and molecular dynamics methods are used. The results indicate that the pH value regulates the adsorption behavior of CO and HCO on the quartz surface by affecting the CO/HCO ratio and the surface charge of quartz. In general, both HCO and CO ions were able to adsorb on the quartz surface and the adsorption capacity of CO is higher than that of HCO. HCO ions tended to uniformly distribute in an aqueous solution and contact the quartz surface in the form of single molecules instead of clusters. In contrast, CO ions were mainly adsorbed as clusters which became larger as the concentration increased. Na ions were essential for the adsorption of HCO and CO, because some of the Na and CO ions spontaneously associated together to form clusters, promoting the clusters to be adsorbed on the quartz surface through cationic bridges. The local structures and dynamics trajectory of CO and HCO showed that the anchoring mechanism of carbonate solvates on quartz involved H-bonds and cationic bridges, which changed in relation to the concentration and pH values. However, the HCO ions mainly adsorbed on the quartz surface H-bonds while the CO ions tended to be adsorbed through cationic bridges. These results may help in understanding the geochemical behavior of soil inorganic carbon and further the processes of the Earth's carbon chemical cycle.
可溶性无机碳是土壤碳库的重要组成部分，其在土壤、沉积物和地下水环境中的归宿对许多物理化学和地质过程具有重大影响。然而，其被土壤活性成分（如石英）吸附的动力学过程、行为和机制仍不清楚。这项工作的目的是系统地研究不同pH值下CO₃²⁻和HCO₃⁻在石英表面的锚定机制。考虑了三个pH值（pH 7.5、pH 9.5和pH 11）和三个碳酸盐浓度（0.07、0.14和0.28 M），并使用了分子动力学方法。结果表明，pH值通过影响CO₃²⁻/HCO₃⁻比例和石英表面电荷来调节CO₃²⁻和HCO₃⁻在石英表面的吸附行为。一般来说，HCO₃⁻和CO₃²⁻离子都能够吸附在石英表面，且CO₃²⁻的吸附能力高于HCO₃⁻。HCO₃⁻离子倾向于均匀分布在水溶液中，并以单分子形式而非簇状形式与石英表面接触。相比之下，CO₃²⁻离子主要以簇状形式吸附，且随着浓度增加簇变得更大。Na⁺离子对于HCO₃⁻和CO₃²⁻的吸附至关重要，因为一些Na⁺和CO₃²⁻离子会自发结合形成簇，通过阳离子桥促进这些簇吸附在石英表面。CO₃²⁻和HCO₃⁻的局部结构和动力学轨迹表明，碳酸盐溶剂化物在石英表面的锚定机制涉及氢键和阳离子桥，它们会随浓度和pH值而变化。然而，HCO₃⁻离子主要通过氢键吸附在石英表面，而CO₃²⁻离子倾向于通过阳离子桥吸附。这些结果可能有助于理解土壤无机碳的地球化学行为以及地球碳化学循环的过程。
