Liu Bangwei,Zhou Yan,Zhang Yiwei,Chen Dandan,Liu Wenhui,Lu Ping,Su Xiaoyu,Xia Tian
A zero-valent iron-loaded corn straw char (ZVI-CSC) was synthesized in this study for the remediation of As(V) and Cd(II) contamination. The impact of ZVI-CSC on the adsorption performance of As(V) and Cd(II) in solution, as well as their migration properties in soil, was investigated through adsorption kinetics and soil column leaching experiments, respectively. The results showed that the adsorption capacity of As(V) by ZVI-CSC was significantly improved to 14.42 g·kg −1 at pH = 3, compared with unmodified corn straw char (CSC). However, the adsorption capacity of Cd(II) was not improved. In the leaching experiments, the addition of ZVI-CSC to As(V)-contaminated soil resulted in a significant reduction of cumulative As(V) release rate from 32.26 to 3.11%, compared with corn straw char (CSC). Moreover, the role of ZVI in As(V)/Cd(II) remediation was analyzed. nZVI forms ≡Fe-OH and ≡Fe-OOH due to oxidation, which can form monodentate and bidentate complexes with As(V) via ligand exchange, thus promoting As immobilization. Furthermore, to further improve the adsorption performance of Cd(II), the electrostatic potential (ESP) of biochars with different surface functional groups (C = O, C–O–C, –OH, and –COOH) and their bond dissociation enthalpy (BDE) with As(V) and Cd(II) were calculated based on density functional theory (DFT). The results showed that –OH was the most effective for As(V) adsorption, and C–O–C was the most effective for Cd(II) adsorption. C = O and –COOH can be used to the simultaneous adsorption of As(V) and Cd(II). Therefore, the surface functional groups of ZVI-CSC can be selectively modified to improve its adsorption performance of As(V) and Cd(II). Graphical
Pyrolytic reduction as an effective method is generally employed for synthesizing zero-valent iron @ biochar composite (ZVI@BC). However, it suffers from intractable obstacles, such as poor zero-valent iron (ZVI) dispersibility and low α-iron (α-Fe 0 ) content. Herein, we reported a possible way to target the dilemma for the first time, i.e., adding ammonium bicarbonate (NH 4 HCO 3 ) pretreatment step before pyrolytic reduction. In detail, the special NH 4 HCO 3 not only served as a precipitant to uniformly disperse ZVI over biochar by gradually releasing OH – , but also as a reductant to facilitate γ-Fe 0 transforming to α-Fe 0 in ZVI (∼71 %) via providing sufficient NH 3 . Besides, NH-ZVI@BC 3/1/5 exhibited outstanding oxytetracycline hydrochloride (OTC) removal ability (∼2869.1 mg/g), with the removal efficiency of 99.0 % at the dosage of 0.05 g/L. The removal mechanism was investigated which involved adsorption dominated by complexation, π-π electron donor acceptor interaction, hydrogen bonds, and electrostatic interactions. As well, OTC degradation was achieved by [H] and ·OH resulting from Fe-C micro-electrolysis and Fenton-like reaction during the corrosion of ZVI in ZVI@BC, respectively. In addition, four possible degradation pathways were proposed, and the contribution role in OTC removal followed the sequence: adsorption > degradation involved with [H] > degradation involved with ·OH. Moreover, N-ZVI@Biochar 3/1/5 exhibited easy separability, excellent reusability, and well practical applicability. Overall, this work not only opens a new avenue for the fabrication of ZVI@BC with high ZVI dispersibility and content of α-Fe 0 , but also shed light on the environmental remediation of antibiotics.
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