Self-cleaning isotype g-C3N4 heterojunction for efficient photocatalytic reduction of hexavalent uranium under visible light.

Photocatalysis is a promising method to eliminate hexavalent uranium (U(Ⅵ)) and recycle it from wastewater. However, most of researched photocatalysts are metal-contained, inactive in visible light, and inconvenient to recycle, which unfortunately impedes the further utilization of photocatalytic technology in U(Ⅵ) pollution treatment. Herein, g-C3N4 isotype heterojunction with interpenetrated tri-s-triazine structure (ipCN) was prepared by inserting urea into the interlayer of tri-s-triazine planes of thiourea-derived g-C3N4 and in-site thermal treating. The synthesized nanocomposites were used to convert soluble U(Ⅵ) ions into U(Ⅳ) sediment under visible light. Experimental and characterization results reveal that ipCN possess larger BET surface area, more negative-charged surface, higher U(Ⅵ) adsorption capability, and more efficient mass diffusion and charges transfer properties. With these excellent characteristics, nearly 98% U(Ⅵ) could be removed within 20 min over ipCN5:1 and 92% photoreduction efficiency could also be kept after 7 cycle uses, which were equal to or even superior than most reported metal-based photocatalysts. It is also proven that the configuration of U(Ⅵ) and photogenerated ·O2- play a significant role in the photocatalytic U(Ⅵ) reduction process, with (UO2)x(OH)y2x-y are more prone to be adsorbed and the photoinduced process of ·O2- will steal electrons from photocatalysts. Furthermore, with the self-generated ·O2- and H2O2, a green and facile regeneration process of photocatalysts was proposed This work provides a promising scheme to extract U(Ⅵ) from the perspectives of photocatalysts exploitation, photocatalytic reduction, and photocatalysts regeneration, which is meaningful for the sustainable U(Ⅵ) resource recovery and U(Ⅵ) pollution purification.

Coordination-driven synthesis of perfected π-conjugated graphitic carbon nitride with efficient charge transfer for oxygen activation and gas purification.

Efficient yield of reactive-oxygen species (ROS) is greatly important for environmental purification and engineering. In this study, the perfected π-conjugated g-C3N4 (PNa-g-C3N4) photocatalysts were constructed by coordination between 3p orbits of Na and N 2p lone electron at vacancy structure of tri-s-triazine polymer for ROS evolution and elimination of HCHO and NO. The perfected π-conjugated structure enhances the visible-light capturing capability, enriches active sites for O2 activation, and promotes the directional charge transfer from N 2p of C3-N to Na and C. Therefore, the superior activities including the evolution of O2- (35 µmol.L-1h-1), and H2O2 (517 µmol.L-1h-1) have been achieved over PNa-g-C3N4 photocatalyst. As a result, PNa-g-C3N4 photocatalysts demonstrate high performances removal efficiency of NO (53% for 6 min), and HCHO (almost 100% for 55 min) in the elimination process. The results may provide the promising strategy to construct efficient photocatalytic system to yield ROS for environmental purification.