Sunlight-induced photoreduction of Cr(VI) to Cr(III) in wastewater by nitrogen-phosphorus-doped carbon dots

Abstract Cr(VI) is a known toxic and non-biodegradable pollutant that results from multiple industrial processes, and can cause significant environmental damage if it is not removed from wastewater. However, it can be reduced to Cr(III), which is less toxic and can be readily precipitated out and removed. Here, a fast and facile single-step technique is reported for the synthesis of nitrogen–phosphorus doped fluorescent carbon dots (NP-CD) using a domestic microwave, as a potential photocatalytic material. Under natural sunlight, a simple photocatalytic experiment reveals that the NP-CD are highly efficient for the quantitative reduction of Cr(VI) to Cr(III) in synthetic contaminated water, in a linear range from 10 ppm (in approximately 10 min) to 2000 ppm (in approximately 320 min) by increasing the sunlight irradiation time followed by its removal by precipitation. NP-CD exhibit high recyclability of up to six cycles without any apparent loss in photocatalytic activity, demonstrating NP-CD as a potential photocatalyst material for Cr(VI) water treatment.