Boosting the photoreduction activity of Cr(VI) in metal-organic frameworks by photosensitiser incorporation and framework ionization

It is necessary to decontaminate Cr(VI) species from wastewater due to their high toxicity. The photoreduction of hazardous Cr(VI) to nontoxic Cr(III) is a very promising approach to harness Cr(VI) pollution. Herein, cationic Ru-UiO-dmbpy(1) was synthesized by a sequential mix-and-match and ionization process. Driven by ion exchange, Ru-UiO-dmbpy(1) showed a larger Cr2O72- uptake capacity and higher adsorption rate than non-ionization counterpart. The presence of Ru(bpy)3 moieties makes Ru-UiO-dmbpy(1) an excellent visible-light harvester, which could adsorb visible light ranging from 420 to 780 nm. Thus, Ru-UiO-dmbpy(1) was used to reduce Cr2O72- under visible light. The Cr(VI) photoreduction rate could reached to 13.3 mgCr(VI)/gcatalyst/min, which was a recorded value among MOF-based photocatalysts. Remarkably, benzyl alcohol as hole scavenger was simultaneously oxidized by photogenerated holes into value-added benzaldehyde with high selectivity (> 99%). This work presented the first photocatalyst for Cr(VI) reduction coupled with the selective oxidation of benzyl alcohol under visible light, promoting us further to investigate for the improvement the utilization of visible light energy by simulations use of the energy of photogenerated electrons and holes in one process.