Photocatalytic removal of hexavalent chromium by newly designed and highly reductive TiO nanocrystals.

Hexavalent chromium Cr(VI), a highly toxic oxyanion, widely occurs in drinking water supplies. This study designed and synthesized a new type of highly reductive TiO nanocrystals for photochemical Cr(VI) removal, via the thermal hydrolysis of TiCl in the presence of diethylene glycol (DEG). Surface analyses and hydroxyl radical measurements suggested that DEG was chemically bonded on TiO surface that resulted in an internal hole-scavenging effect and a high electron-releasing capacity, making it advantageous to conventional TiO materials. Upon UV irradiation, the synthesized TiO photocatalyst exhibited fast Cr(VI) reduction kinetics in diverse water chemical conditions. Fast elimination of Cr(VI) was achieved on a time scale of seconds in drinking water matrices. The removal of Cr(VI) by reductive TiO exhibited a three-stage kinetic behavior: an initial fast-reaction phase, a lag phase resulting from surface precipitation of Cr(OH) and a final reaction phase due to surface regeneration from oxidation-reduction induced ripening process. The lag phase disappeared in acidic conditions that prevented the formation of Cr(OH). The catalyst exhibited extremely high electron-releasing capacity that can be reused for multiple cycles of Cr(VI) removal in drinking water treatment.