Faculty of Engineering and IT, University of Technology Sydney (UTS), Sydney, Australia.
Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh, 700000, Viet Nam; Faculty of Environmental and Chemical Engineering, Duy Tan University, Da Nang, 550000, Viet Nam.
Chemosphere. 2022 May;295:133370. doi: 10.1016/j.chemosphere.2021.133370. Epub 2021 Dec 29.
This study developed a layered double hydroxides (Mn/Mg/Fe-LDH) material through a simple co-precipitation method. The Mn/Mg/Fe-LDH oxidized arsenite [As(III)] ions into arsenate [As(V)] anions. The As(III) and oxidized As(V) were then adsorbed onto Mn/Mg/Fe-LDH. The adsorption process of arseniate [As(V)] oxyanions by Mn/Mg/Fe-LDH was simultaneously conducted for comparison. Characterization results indicated that (i) the best Mg/Mn/Fe molar ratio was 1/1/1, (ii) Mn/Mg/Fe-LDH structure was similar to that of hydrotalcite, (iii) Mn/Mg/Fe-LDH possessed a positively charged surface (pH of 10.15) and low Brunauer-Emmett-Teller surface area (S = 75.2 m/g), and (iv) Fe/Fe and Mn/Mn/Mn coexisted in Mn/Mg/Fe-LDH. The As(III) adsorption process by Mn/Mg/Fe-LDH was similar to that of As(V) under different experimental conditions (initial solutions pH, coexisting foreign anions, contact times, initial As concentrations, temperatures, and desorbing agents). The Langmuir maximum adsorption capacity of Mn/Mg/Fe-LDH to As(III) (56.1 mg/g) was higher than that of As(V) (32.2 mg/g) at pH 7.0 and 25 °C. X-ray photoelectron spectroscopy was applied to identify the oxidation states of As in laden Mn/Mg/Fe-LDH. The key removal mechanism of As(III) by Mn/Mg/Fe-LDH was oxidation-coupled adsorption, and that of As(V) was reduction-coupled adsorption. The As(V) mechanism adsorption mainly involved: (1) the inner-sphere and outer-sphere complexation with OH groups of Mn/Mg/Fe-LDH and (2) anion exchange with host anions (NO) in its interlayer. The primary mechanism adsorption of As(III) was the inner-sphere complexation. The redox reactions made Mn/Mg/Fe-LDH lose its original layer structure after adsorbing As(V) or As(III). The adsorption process was highly irreversible. Mn/Mg/Fe-LDH can decontaminate As from real groundwater samples from 45-92 ppb to 0.35-7.9 ppb (using 1.0 g/L). Therefore, Mn/Mg/Fe-LDH has great potential as a material for removing As.
本研究通过简单共沉淀法制备了层状双氢氧化物（Mn/Mg/Fe-LDH）材料。Mn/Mg/Fe-LDH 将亚砷酸盐[As(III)]离子氧化为砷酸盐[As(V)]阴离子。然后，将 As(III)和氧化的 As(V)吸附到 Mn/Mg/Fe-LDH 上。同时进行了砷酸盐[As(V)]阴离子在 Mn/Mg/Fe-LDH 上的吸附过程比较。表征结果表明：(i)最佳 Mg/Mn/Fe 摩尔比为 1/1/1；(ii) Mn/Mg/Fe-LDH 结构类似于水滑石；(iii) Mn/Mg/Fe-LDH 表面带正电荷(pH 值为 10.15)，BET 表面积较低(S = 75.2 m/g)；(iv)Fe/Fe 和 Mn/Mn/Mn 共存于 Mn/Mg/Fe-LDH 中。在不同实验条件下（初始溶液 pH 值、共存的外来阴离子、接触时间、初始 As 浓度、温度和洗脱剂），Mn/Mg/Fe-LDH 对 As(III)的吸附过程与 As(V)相似。在 pH 7.0 和 25°C 时，Mn/Mg/Fe-LDH 对 As(III)的最大吸附容量(56.1mg/g)高于 As(V)的最大吸附容量(32.2mg/g)。X 射线光电子能谱用于鉴定负载 Mn/Mg/Fe-LDH 中 As 的氧化态。Mn/Mg/Fe-LDH 去除 As(III)的主要去除机制是氧化偶联吸附，去除 As(V)的主要机制是还原偶联吸附。As(V)的吸附机制主要涉及：(1)Mn/Mg/Fe-LDH 与 OH 基团的内球和外球络合；(2)层间与主体阴离子(NO)的阴离子交换。As(III)的主要吸附机制是内球络合。氧化还原反应使 Mn/Mg/Fe-LDH 在吸附 As(V)或 As(III)后失去原有的层状结构。吸附过程高度不可逆。Mn/Mg/Fe-LDH 可以将实际地下水中的 As 从 45-92 ppb 降低到 0.35-7.9 ppb(使用 1.0 g/L)。因此，Mn/Mg/Fe-LDH 作为一种去除 As 的材料具有很大的潜力。
