Mesoporous sulfur-doped g-C3N4@attapulgite composite as an advanced photocatalyst for efficiently uranium(VI) recovery from aqueous solutions

Photocatalytic reduction of uranium(VI) is a promising and efficient method for the recovery of radioactive uranium contamination from wastewater. In this work, the mesoporous sulfur-functionalized g-C3N4@attapulgite composite was first synthesized via a two-step hydrothermal-roasting method with (NH4)2S2O8 as the sulfur source and attapulgite as the supporter, respectively. As expected, the recovery efficiency of uranium(VI) using S-doped g-C3N4 was 1.80 times higher than that of g-C3N4. Additionally, compared to S-doped g-C3N4, the mesoporous S-doped g-C3N4@attapulgite composite exhibited further improved photocatalytic efficiency and stability. The experimental results further showed the uranium(VI) was quickly eliminated within 20 minutes by mesoporous S-doped g-C3N4@attapulgite, and the recovery rate of which remained at 88.4% even after seven cycles. According to the XPS results and trapping experiments, the excellent uranium(VI) recovery and stability can be attributed to the adsorption capacity of attapulgite and the e- reduction from sulfur doping g-C3N4, respectively. This research contributes to understanding the enhanced photocatalytic reduction mechanism of uranium(VI) and to achieving the high-efficiency recovery of uranium from wastewater using the mesoporous S-doped g-C3N4@attapulgite composite.