Zhang Ling, Xu Min, Li Lingzhen
School of Environmental and Chemical Engineering, Shanghai University, 333 Nanchen Road, Shanghai 200444, PR China.
Langmuir. 2024 Mar 19;40(11):6016-6025. doi: 10.1021/acs.langmuir.4c00034. Epub 2024 Mar 6.
The development of low-cost, efficient, and environmentally friendly adsorbents is the key to highly toxic hexavalent chromium [Cr(VI)] removal by adsorption. In this paper, amino-functionalized lotus stem hydrochar (ALSHC) was prepared from an agricultural waste lotus stem (LS) for the adsorption removal of Cr(VI) from water. The effects of the initial Cr(VI) concentration, contact time, temperature, coexisting anions, and reusability of ALSHC on Cr(VI) removal were examined in detail. The adsorption mechanism was further discussed by investigating the impact of the solution's initial pH, the relation between the pH change in solution and Cr(VI) removal during the process, the changes of chromium (Cr) species in solution and on ALSHC during adsorption, and the XPS characterization. The results demonstrated that ALSHC effectively removed Cr(VI) from water with rapid adsorption (the removal rate reached 80.90% in only 10 min) and in situ detoxification. Most importantly, ALSHC still had better adsorption performance (adsorption capacity of 30.95 mg g) than commercially activated carbon, even at pH = 9.00. The adsorption of Cr(VI) by ALSHC accorded with the pseudo-second-order kinetic model and Langmuir isotherm model, indicating a monolayer chemisorption process. The adsorption process was shown to be spontaneous and endothermic based on the thermodynamic characteristics (Δ < 0, Δ > 0, and Δ > 0). The mechanism of Cr(VI) removal was mainly composed of three parts in sequence: Firstly, Cr(VI) in solution was quickly adsorbed onto ALSHC with protonated -NH through electrostatic attraction; subsequently, the adsorbed Cr(VI) on ALSHC was mostly detoxicated by in situ reduction; and finally, the reduced Cr(III) and the remaining Cr(VI) were fixed on the ALSHC surface by complexation. The prepared ALSHC displayed a certain superiority in Cr(VI) adsorption and had the prospect of further development.
开发低成本、高效且环保的吸附剂是通过吸附去除剧毒六价铬[Cr(VI)]的关键。本文以农业废弃物莲藕茎（LS）为原料制备了氨基官能化莲藕茎水炭（ALSHC），用于吸附去除水中的Cr(VI)。详细考察了初始Cr(VI)浓度、接触时间、温度、共存阴离子以及ALSHC的可重复使用性对Cr(VI)去除效果的影响。通过研究溶液初始pH值的影响、吸附过程中溶液pH变化与Cr(VI)去除的关系、吸附过程中溶液及ALSHC上铬（Cr）形态的变化以及XPS表征，进一步探讨了吸附机理。结果表明，ALSHC能快速有效地从水中去除Cr(VI)（仅10分钟去除率就达到80.90%）并实现原位解毒。最重要的是，即使在pH = 9.00时，ALSHC的吸附性能（吸附容量为30.95 mg/g）仍优于商业活性炭。ALSHC对Cr(VI)的吸附符合准二级动力学模型和朗缪尔等温线模型，表明是单分子层化学吸附过程。基于热力学特征（Δ < 0，Δ > 0，且Δ > 0），吸附过程是自发且吸热的。Cr(VI)的去除机理主要依次由三部分组成：首先，溶液中的Cr(VI)通过静电引力迅速吸附到带质子化 -NH的ALSHC上；随后，ALSHC上吸附的Cr(VI)大多通过原位还原解毒；最后，还原后的Cr(III)和剩余的Cr(VI)通过络合作用固定在ALSHC表面。所制备的ALSHC在Cr(VI)吸附方面表现出一定优势，具有进一步发展的前景。
