A novel g-C3N4 modified biosynthetic Fe(III)-hydroxysulfate for efficient photoreduction of Cr(VI) in wastewater treatment under visible light irradiation

Rational design of catalyst and reduction process are significant for the treatment of Cr(VI)-containing wastewater. In this work, for the first time, g-C3N4-modified biosynthetic Fe(III)-hydroxysulfate (g-C3N4@bio-Fe(III)hydroxysulfate) composites were developed to achieve efficient Cr(VI) reduction under visible irradiation with the assistance of citric acid. By simple addition of g-C3N4 to cultivation medium of Acidithiobacillus ferrooxidans (A. ferrooxidans), g-C3N4@bio-Fe(III)-hydroxysulfate composites were obtained with improved productivities and surface properties. Compared with pure g-C3N4 and bio-Fe(III)-hydroxysulfate, the prepared composite exhibited higher photocatalytic activity in catalyst/citric acid/light system. Under optimized conditions (catalyst = 0.5 g L-1, citric acid = 1.0 mM and temperature = 25 degrees C), 100% reduction of 20 mg L-1 Cr(VI) could be achieved in 20 min without pH adjustment (initial pH = 3.13). The enhanced photocatalytic activity of g-C3N4@bio-Fe(III)-hydroxysulfate in the presence of citric acid mainly results from abundant reducing species (Fe(II), e- and center dot O-2(-)), accelerated electron-hole separation efficiency and enhanced Fe(II)/Fe(III) cycle. The strategy developed in this study provides new insights into the modification of bio-synthesized Fe(III)-hydroxysulfate and design of reductive system for the treatment of toxic Cr(VI)-containing wastewater.