Experimental Measurements and Surface Complexation Modeling of U(VI) Adsorption onto Multilayered Graphene Oxide: The Importance of Adsorbate-Adsorbent Ratios
Experimental Measurements and Surface Complexation Modeling of U(VI) Adsorption onto Multilayered Graphene Oxide: The Importance of Adsorbate-Adsorbent Ratios
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DOI：
10.1021/acs.est.6b05776
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发表时间：
2017-08-01
影响因子：
11.4
通讯作者：
Fein, Jeremy B.
中科院分区：
文献类型：
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作者：
Duster, Thomas A.;Szymanowski, Jennifer E. S.;Fein, Jeremy B.
表面络合模型使用实验吸附测量来计算稳定常数，量化吸附物质的热力学稳定性。然而，由于溶质从溶液中几乎完全去除和/或由于被测试的吸附剂：吸附剂的比例变化不够，这些常数通常限制得很差。利用量化U（VI）对多层氧化石墨烯（MLGO）吸附的数据集，我们测试了三种不同的U(VI):MLGO比例（3 ppm U; 20-210 mg L-1 MLGO）是否会影响非静电和扩散层模型在离子强度（1-100 mM）和pH（2-9.5）条件下预测U（VI）吸附行为的能力。模型公式假设在给定的pH范围内，离散MLGO表面位点与最丰富的水中U（VI）络合物（es）之间存在相互作用。我们确定了观察到的U（VI）结合程度需要吸附不止一种U（VI）物质(UO22+、氢氧化铀酰（s)和/或碳酸盐(s)），并计算了重要的U(VI)-MLGO表面配合物各自的稳定性常数。结果还明确表明，使用较高U(VI):MLGO比例处理的吸附数据的模型在整个实验条件测试范围内具有更好的拟合性，这意味着本文计算的U(VI)-MLGO稳定性常数可以自信地应用于一系列自然或工程系统。
Surface complexation models use experimental adsorption measurements to calculate stability constants that quantify the thermodynamic stability of adsorbed species. However, these constants are often poorly constrained due to nearly complete removal of the solute from solution and/or because the tested adsorbate:adsorbent ratios are not varied sufficiently. Using data sets that quantify the adsorption of U(VI) to multilayered graphene oxide (MLGO), we tested whether three different U(VI):MLGO ratios (3 ppm U; 20-210 mg L-1 MLGO) affect the ability of nonelectrostatic and diffuse layer models to predict U(VI) adsorption behaviors across a range of ionic strength (1-100 mM) and pH (2-9.5) conditions. Model formulations assumed interactions between discrete MLGO surfaces sites and the most abundant aqueous U(VI) complex(es) within a given pH range. We determined that the observed extents of U(VI) binding require adsorption of more than one U(VI) species (UO22+ and uranyl hydroxide(s) and/or carbonate(s)) and calculated the respective stability constants for the important U(VI)-MLGO surface complexes. The results also unequivocally illustrated that models using adsorption data from treatments with higher U(VI):MLGO ratios provide better fits throughout the tested range of experimental conditions, meaning that the U(VI)-MLGO stability constants calculated herein can be confidently applied to a range of natural or engineered systems.