The photocatalytic efficiencies of bimetallic MOFs, namely STA-12-Mn–Fe, for the reductive removal of Cr(VI) were explored. The best effective variable values were obtained and correlation between the response and influential variables was optimized via experimental design methodology. Complete Cr(VI) removal was achieved under natural sunlight and fluorescent 40 W lamp radiation at pH 2, with an initial Cr(VI) concentration of 20 mg L−1, and 10 mg of photocatalyst within 30 min. A pseudo-first-order rate constant of 0.132 min−1 at T = 298 K was obtained for the Cr(VI) reduction reaction. The title catalysts revealed high performance in the visible region based on photoefficiency measurements, while improved activity was observed compared to the corresponding single-metal MOFs under natural sunlight, highlighting the synergistic effect between the two metal ions. Trapping experiment results proved that direct electron transfer is the main pathway during the photocatalytic Cr(VI) reduction process.
