Efficient photoelectrocatalytic reduction of Cr(VI) using TiO2 nanotube arrays as the photoanode and a large-area titanium mesh as the photocathode

We report the efficient photoelectrocatalytic (PEC) reduction of Cr(VI) using TiO2 nanotubes (TNTs) as the photoanode and a large-area Ti mesh as the photocathode. Short-length TNTs (S-TNTs) show much greater PEC activity than either long-length TNTs (L-TNTs) or sol–gel-prepared TiO2 film, due to the fact that the TNT structure is advantageous of trapping light energy over the thin-film structure and the S-TNTs enable the more efficient electron transfer into the substrate than L-TNTs. More importantly, increasing the surface area of the photocathode (Ti mesh) can greatly accelerate the PEC reduction of Cr(VI), presumably due to the increased number of the active reduction sites on the larger-surface Ti mesh. In the PEC reduction of Cr(VI), Cr(V) is identified as a reaction intermediate using the electroparamagnetic resonance technique, whereby the process for the Cr(VI) evolution is proposed. The S-TNTs have been confirmed to be stable over many repetitive cycles of use, indicating their suitability for wide-scale use.

Graphical abstractNearly complete PEC reduction of Cr(VI) to Cr(III) was achieved using TNTs photoanode and large-area Ti mesh photocathode.Figure optionsDownload full-size imageDownload high-quality image (198 K)Download as PowerPoint slideResearch highlights▶ TNT arrays photoanode combine with Ti mesh photocathode for PEC reduction of Cr(VI). ▶ The complete PEC reduction of Cr(VI) to Cr(III) is achieved. ▶ Large-area Ti mesh photocathode is essential for the efficient reduction of Cr(VI).