Highly Efficient Photoelectrocatalytic Reduction of Hexavalent Chromium based on the Cascade Energy Transfer towards Using no Semiconducting Photocatalysts

•PEC reduction of Cr(VI) was realized with no semiconducting photocatalysts.•The citric acid, Ti anode, and Cr(VI) formed an energy-relay cascade structure.•PEC reduction of Cr(VI) with Ti anode was 4 times faster than PC reduction.•PEC reduction of Cr(VI) using Ti anode was 2 times faster than ITO/TiO2 anode.

Highly efficient photoelectrocatalytic (PEC) reduction of Cr(VI) has been realized in the absence of semiconducting photocatalysts. In the novel-configuration cell using Ti anode, Pt cathode, Cr(VI), and citric acid, the rate constant of the PEC reduction of Cr(VI) at a bias of 1.5 V was almost 3 times than that in the conventional-configuration cell using ITO/TiO2 anode, Ti cathode, Cr(VI), and citric acid. It was mostly because the citric acid, Ti anode, and Cr(VI) formed an energy-relay cascade structure, in which the photogenerated electrons in the citric acid were transferred to the positively biased Ti and then from anode to Cr(VI), leading to the very efficient Cr(VI) reduction. We develop a simple PEC method to reduce Cr(VI) over the Ti anode sensitized by photoexcited organic dye in no need of metal oxide photocatalysts, which can be considered as an important advance towards the cost-effective, environmentally friendly treatment of waste water.

Graphical abstractThe photoinduced cascade energy transfer between the citric acid, Ti anode, and Cr(VI) has been demonstrated. The photoelectrocatalytic (PEC) reduction of Cr(VI) using Ti anode was two times faster than using ITO/TiO2 anode. We provide a novel PEC concept of Cr(VI) removal towards using no semiconducting photocatalysts.Figure optionsDownload full-size imageDownload as PowerPoint slide