Visible-light-induced reduction of hexavalent chromium utilizing cobalt phosphate (Co-Pi) sensitized inverse opal TiO2 as a photocatalyst

Spurred by the threat of hexavalent chromium (Cr(VI)), the idea of reducing Cr(VI) into less toxic Cr(III) has been commonly studied. Here, we used a facile photodeposition method to modify inverse opal TiO2 (i.o.TiO2) with cobalt phosphate (Co-Pi), and the resulting composite was applied for photocatalytic reduction of Cr(VI). This is the first time that an inverse opal structure as well as a Co-Pi catalyst is applied in the photocatalytic reduction of Cr(VI). In addition, the combination of i.o.TiO2 and Co-Pi achieves high visible-light-driven photocatalytic activity, which is better than that of the pure Co-Pi catalyst and unmodified i.o.TiO2. Experimental results demonstrated that the Co-Pi in the composite could absorb a large amount of visible light and then inject electrons into the conduction band of i.o.TiO2 which subsequently participate in the reduction reaction of Cr(VI). Moreover, the inverse opal structure of the catalyst possesses the advantages of having a large surface area and efficient light harvesting ability, leading to the better catalytic activity of Co-Pi/i.o.TiO2 than Co-Pi/bulk TiO2 and Co-Pi/P25. It's also proved that this Co-Pi/i.o.TiO2 photocatalyst can efficiently remove organic pollutants together with Cr(VI). This study provides new insights into the design and fabrication of efficient photocatalysts for the removal of environmental pollutants under visible light.