Bromate (BrO3–) is a carcinogenic substance introduced into drinking water in the process of ozonolysis, where naturally occurring bromide ions (Br–) get oxidized to bromate (BrO3–) by ozone (O3). Because of its toxic effects, including cancer, central nervous system depression, haemolytic anemia and pulmonary edema, the World Health Organization (WHO) has set the maximum contaminant level of bromate in drinking water to 10 μg L–1, or 10 ppb. Removal of BrO3– from drinking water has been investigated on three levels: (i) removal of precursors before ozonolysis, (ii) controlling the process of ozonolysis to minimize bromate formation, and (iii) bromate removal post ozonolysis, with post-treatment being largely understudied. In the current project, we utilized a cationic covalent organic framework (COF) material for bromate removal from water. The COF was synthesized using the Zincke reaction from a starting tetra-amino porphyrin derivative and the bipyridinium Zincke salt. The obtained material exhibited the morphology of uniform hollow spheres with an average diameter of 1.3 μm, which were used either as-synthesized, post-synthetically metallated with Zn, or had their cationic viologen subunits fully reduced to neutral. The three COFs were tested for removal of BrO3– from water at an industrially relevant concentration of 50 μg L–1. The as-synthesized COF performed best, removing over 95 % of BrO3– at a rate of 191.45 g mg–1 min–1, which is the fastest rate of adsorption reported till date, and bringing [BrO3–] down to well below the permitted drinking water concentration of 10 ppb. The same COF reached a maximum uptake capacity of 203.8 mg g–1, one of the highest values ever reported, and could be regenerated for several cycles.

Highly efficient carcinogenic bromate removal from water by a cationic covalent organic framework

2019 Fall National Meeting

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