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Copolymer-Templated Synthesis of Nitrogen-Doped Mesoporous Carbons for Enhanced Adsorption of Hexavalent Chromium and Uranium

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journal contribution
posted on 08.05.2018, 00:00 by Yang Song, Guoyu Wei, Maciej Kopeć, Linfeng Rao, Zhicheng Zhang, Eric Gottlieb, Zongyu Wang, Rui Yuan, Gang Ye, Jianchen Wang, Tomasz Kowalewski, Krzysztof Matyjaszewski
Polyacrylonitrile (PAN) homopolymer and polyacrylonitrile-block-poly­(n-butyl acrylate) (PAN-b-PBA) block copolymer were synthesized via supplemental activator reducing agent atom transfer radical polymerization and used as precursors to nitrogen-doped nanocarbons. Carbonization was performed at two different temperatures (500 and 800 °C) to fabricate nanocarbons with different structural properties and nitrogen contents. Copolymer-templated nitrogen-doped carbons (CTNCs) had larger surface area and higher mesoporosity than PAN homopolymer-templated nanocarbons (PANCs), due to the presence of PBA block acting as a sacrificial porogen. Adsorption performances of PANCs and CTNCs for Cr­(VI) and U­(VI) species were systematically studied. Due to the well-defined structure and larger surface area, CTNCs showed stronger adsorption ability than PANCs. The nitrogen atoms incorporated into the carbon framework led to higher electrostatic attraction for Cr­(VI) anions at low pH and complexation with U­(VI) cations at high pH. Theoretical maximum adsorption capacities of CTNC-500 on Cr­(VI) and U­(VI) were 333.3 mg/g (pH = 2) and 17.2 mg/g (pH= 5), respectively. CTNCs also showed preferential adsorption for U­(VI) compared to other ions, which might be explained by the hard and soft acids and bases theory. Thus, the copolymer-templated nitrogen-doped mesoporous carbons developed in this study represent a new class of nanocarbon sorbents with potential for removing heavy metal contaminants in either cationic or anionic form from aqueous media and thus mitigating environmental pollution.