Water-soluble natural organic acid for highly efficient photoreduction of hexavalent chromium

Successful studies have demonstrated that citric acid can significantly improve the photocatalytic reduction efficiency of Cr(VI) over semiconductor photocatalysts as a sacrificial donor. Here, we studied the Cr(VI) photoreduction performance of citric acid monohydrate (CAM) without any semiconductor photocatalysts. Water-soluble CAM displays extremely efficient photoreduction activity for Cr(VI), which is attributed to the synergism of H+, C5H7O5COO- and hv. Hence, the role of citric acid in photoreduction of Cr(VI) may be underestimated in the previous studies. This work may open a new perspective for the development of low-cost, high-efficient and green water-soluble materials applied in heavy metal ion wastewater treatment.