Cationic Amorphous Metal–Organic Cage-Based Materials for the Removal of Oxo-Anions from Water

• Published in: ACS applied nano materials Vol. 2; no. 9; pp. 5824 - 5832
• Main Authors: Jin, Xia, Wang, Guang-Qing, Ma, Ding, Deng, Shu-Qi, Cai, Song-Liang, Fan, Jun, Zhang, Wei-Guang, Zheng, Sheng-Run
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27.09.2019
• Subjects: oxo-anion adsorption; high capacity; cationic framework; aMOC; rapid kinetics
• ISSN: 2574-0970; 2574-0970
• DOI: 10.1021/acsanm.9b01294

Oxo-anion pollutants pose a serious threat to natural water systems. It is highly necessary to develop cationic porous materials capable of removing oxo-anion from sewage. However, they are relatively rarely reported compared with anionic and neutral materials. Herein, two cationic amorphous metal–organic cage-based solids containing cages of different sizes, namely, aMOC-1 and aMOC-2, were constructed and use for removing oxo-anions from water. Because the cages in these materials have large cavities (with about 3.5 and 4.5 nm in diameter for aMOC-1 and aMOC-2, respectively) and high positive charges (positive +24 for both), both aMOC-1 and aMOC-2 exhibit rapid kinetics in carcinogenic chromate (CrO4 2– and Cr2O7 2–) and ReO4 – (a surrogate anion of radioactive isotope TcO4 –) adsorption. The adsorption equilibrium can be reached within only a few minutes. The adsorption capacities of aMOC-1 for CrO4 2–, Cr2O7 2–, and ReO4 – are 157.4, 203.8, and 350 mg/g, respectively. Because aMOC-2 contains larger metal–organic cage, the corresponding adsorption capacities are 242.0, 407.0, and 583.9 mg/g, respectively. The capacity of aMOC-2 for Cr­(VI) oxo-anion adsorption ranks the highest among all related materials ever reported. In addition, the oxo-anions can be released rapidly within several minutes from the oxo-anion-loaded aMOCs in 2 M NaNO3 solution, which allows these materials to exhibit good reusability. Finally, the aMOCs have a potential application in the removal of Cr­(VI) from electroplating bath wastewater, in which the concentration changes from 10 to 0.17 ppm after treatment with aMOCs.