Adsorption performance and physicochemical mechanism of MnO 2 -polyethylenimine-tannic acid composites for the removal o
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RESEARCH ARTICLE
Adsorption performance and physicochemical mechanism of MnO2-polyethylenimine-tannic acid composites for the removal of Cu(II) and Cr(VI) from aqueous solution Xiaoyan Deng1, Luxing Wang1, Qihui Xiu2, Ying Wang2, Hong Han2, Dongmei Dai2, Yongji Xu2, Hongtao Gao (✉)2, Xien Liu2
1 College of Environment and Safety Engineering, State Key Laboratory Base of Eco-Chemical Engineering, Qingdao University of Science & Technology, Qingdao 266042, China 2 College of Chemistry and Molecular Engineering, State Key Laboratory Base of Eco-Chemical Engineering, Qingdao University of Science & Technology, Qingdao 266042, China
© Higher Education Press 2020
Abstract In this work, an adsorbent, which we call MnPT, was prepared by combining MnO2, polyethylenimine and tannic acid, and exhibited efficient performance for Cu(II) and Cr(VI) removal from aqueous solution. The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation. The maximum adsorption capacities of MnPT for Cu(II) and Cr(VI) were 121.5 and 790.2 mg$g–1, respectively. The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(II) and Cr(VI) co-adsorption on MnPT. Electrostatic force, solvation action, adsorbate–adsorbate lateral interaction, and complexation were involved in the spontaneous adsorption process. Physical electrostatic action was dominant in the initial stage, whereas chemical action was the driving force leading to adsorption equilibrium. It should be noted that after adsorption on the surface of MnPT, Cr(VI) reacted with some reducing functional groups (hydroxylamine-NH2) and was converted into Cr(III). The adsorption capacity declined by 12% after recycling five times. Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents. This MnPT nanocomposite has been proven to be a low-cost, efficient, and promising adsorbent for removing heavy metal ions from wastewater. Keywords MnO2-polyethylenimine-tannic acid composite, surface complexation formation model, Cu(II), Cr(VI), physicochemical mechanism Received February 15, 2020; accepted May 11, 2020 E-mail: [email protected]
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Introduction
Heavy metals, such as cooper and chromium, pose a serious worldwide threat not only to public health but also to the whole food chain due to their non-biodegradability [1,2] and high carcinogenicities [3]. Under natural environmental conditions, chromium exists stably in the states of Cr(III) and Cr(VI) [4–6]. Cr(VI) is more toxic and carcinogenic than Cr(III). Cu(II) usually exists in cationic form, and high concentrations of Cu(II) in the body stimulate the digestive system, causing pain, vomiting, and death [7,8]. Hence, the World Health Organization suggests that the maximum concentrations of Cr and Cu in drinking water should not exceed 0.05 and 2.0 mg$L–1, respectively [5,6,9]. These regulations have greatly stimulated the development of heavy metal remova
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