Cr(VI) removal via anion exchange on a silver-triazolate MOF

Gram-scale synthesis of a silver-triazolato framework - {[Ag₈(tz)₆](NO₃)₂·6H₂O}_n (1-NO₃; tz^-=3,5-diphenyl-1,2,4-triazolate) - has been achieved, enabling the systematic investigation of its anion-exchange properties. Our experimental results show that the anion-exchange pattern of 1-NO₃ conforms to the so-called Hofmeister bias, which has been correlated to the hydrophobic nature of the MOF pores, and can be understood by considering the difference between the hydration energies of the exchanging anions. Furthermore, 1-NO₃ displays a fast, efficient, and reversible adsorption of HCrO₄^- (via anion-exchange) from Cr(VI)-containing aqueous solution (Q_max=37.0 Cr mg/g, 303K), rendering it a promising prototype of a recyclable MOF for Cr(VI) removal.