College of Environmental Science and Engineering, Ocean University of China, Qingdao, 266100, China; Key Laboratory of Marine Environment and Ecology, Ministry of Education of China, Ocean University of China, Qingdao, 266100, China; Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, Ocean University of China, Qingdao, 266100, China.
College of Environmental Science and Engineering, Ocean University of China, Qingdao, 266100, China.
Chemosphere. 2023 Aug;331:138796. doi: 10.1016/j.chemosphere.2023.138796. Epub 2023 May 2.
Iron-modified biochar (Fe-biochar) has been widely developed to attenuate Cr(VI) pollution in both acid and alkaline environments. However, there are few comprehensive studies on how the iron speciation in Fe-biochar and chromium speciation in solution influencing the removal of Cr(VI) and Cr(III) under varying pH. Here, multiple Fe-biochar containing FeO or Fe(0) were prepared and applied to remove aqueous Cr(VI). Kinetics and isotherms suggested that all Fe-biochar could efficiently remove Cr(VI) and Cr(III) via adsorption-reduction-adsorption. The FeO-biochar immobilized Cr(III) by forming FeCrO, while amorphous Fe-Cr coprecipitate and Cr(OH) was formed when using Fe(0)-biochar. Density functional theory (DFT) analysis further indicated that pH increase caused more negative adsorption energies between Fe(0)-biochar and the pH-dependent Cr(VI)/Cr(III) species. Consequently, the adsorption and immobilization of Cr(VI) and Cr(III) species by Fe(0)-biochar was more favored at higher pH. In comparison, FeO-biochar exhibited weaker adsorption abilities for Cr(VI) and Cr(III), which were in consistent with their less negative adsorption energies. Nonetheless, Fe(0)-biochar merely reduced ∼70% of adsorbed Cr(VI), while ∼90% of adsorbed Cr(VI) was reduced by FeO-biochar. These results unveiled the importance of iron and chromium speciation for chromium removal under varying pH, and might guide the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.
铁改性生物炭（Fe-biochar）已被广泛开发用于减轻酸性和碱性环境中的 Cr(VI) 污染。然而，关于 Fe-biochar 中的铁形态和溶液中铬形态如何影响不同 pH 值下 Cr(VI) 和 Cr(III) 的去除，目前还鲜有综合研究。在此，制备了多种含有 FeO 或 Fe(0) 的 Fe-biochar 并用于去除水溶液中的 Cr(VI)。动力学和等温线研究表明，所有的 Fe-biochar 都可以通过吸附-还原-吸附的方式有效地去除 Cr(VI) 和 Cr(III)。FeO-biochar 通过形成 FeCrO 来固定 Cr(III)，而使用 Fe(0)-biochar 时则形成无定形的 Fe-Cr 共沉淀和 Cr(OH)。密度泛函理论（DFT）分析进一步表明，随着 pH 值的升高，Fe(0)-biochar 与 pH 依赖性的 Cr(VI)/Cr(III) 物种之间的吸附能变得更加负。因此，在较高 pH 值下，Fe(0)-biochar 对 Cr(VI)和 Cr(III)的吸附和固定更为有利。相比之下，FeO-biochar 对 Cr(VI)和 Cr(III)的吸附能力较弱，这与它们较弱的吸附能相一致。然而，Fe(0)-biochar 仅将约 70%的吸附 Cr(VI)还原，而 FeO-biochar 则将约 90%的吸附 Cr(VI)还原。这些结果揭示了铁和铬形态在不同 pH 值下去除铬的重要性，并可能指导多功能 Fe-biochar 的应用导向设计，以用于广泛的环境修复。
