Temperature regulated adsorption and desorption of heavy metals to A-MIL-121: Mechanisms and the role of exchangeable protons.

Chenghan Ji, Daowen Wu, Junhe Lu, Chao Shan, Yi Ren, Ting Li, Lu Lv, Bingcai Pan, Weiming Zhang

Water research 2021 Feb 01

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Adsorption is a viable technology to remove trace heavy metals from wastewater, but regeneration of adsorbents in an economic and environmentally friendly manner often represents a limiting factor of its application. Compared with traditional strong acid desorption, developing a chemical-free method is of great significance to both economic and the environmental welfare. Herein, we synthesized a novel thermoresponsive absorbent, A-MIL-121, which could effectively remove trace Cu(II) (> 95 %) from a high-salinity ([Na+]/[Cu2+] = 20000) water at normal temperature. At elevated temperature, A-MIL-121 could quickly and efficiently desorb Cu(II), with over 90% desorption rate at 80°C within 3 h. Fourier transform infrared spectroscopy (FTIR) analysis revealed that two types of -COOH groups existed in the material. One was in free form and acted as the sites for Cu(II) adsorption; the other was in dimer connected by two H-bonds, which cleaved at elevated temperature. As a result, massive exchangeable protons were released to the solution, which caused the desorption of Cu(II). Similar temperature dependent adsorption-desorption behavior was also found to other heavy metals, such as Cd2+, Pb2+, Ni2+. No significant capacity loss was observed after 10 successive adsorption-desorption cycles. Finally, Column experiments using a real copper electroplating wastewater showed that a total of ~ 1650 mL of clean water was generated before breakthrough (Cu2+ < 0.5 mg/L), while less than 45 mL of 80°C water was used for regeneration. This study indicates the potential of A-MIL-121 as a novel green adsorbent to address trace heavy metals in wastewater. Copyright © 2020 Elsevier Ltd. All rights reserved.

Citation

Chenghan Ji, Daowen Wu, Junhe Lu, Chao Shan, Yi Ren, Ting Li, Lu Lv, Bingcai Pan, Weiming Zhang. Temperature regulated adsorption and desorption of heavy metals to A-MIL-121: Mechanisms and the role of exchangeable protons. Water research. 2021 Feb 01;189:116599