Photoreductive elimination of heavy metal ions and radionuclides by g-C3N4-based materials: A review

It is urgent to treat the heavy metal ions and radionuclides in water as they cause serious damage to the water environment and living beings. Graphitic carbon nitride (g-C3N4) has been deeply studied and used for water treatment owing to its superior chemical resistance, medium bandgap, variable morphology, facile synthesis, non-toxicity, etc. Different from previous reviews mainly focused on removing pollutants by oxidation over gC3N4-based materials, this review systematically summarized and analyzed the recent progress in the photocatalytic reduction of heavy metal ions (e.g., Hg(II), Cr(VI), and Cu(II)) and radionuclides (e.g., U(VI)) over gC3N4-based materials. Starting from the brief introduction of environmental pollution issues, photocatalysis and the g-C3N4 material, the mechanisms about reducing heavy metal ions or radionuclides, effects of experimental conditions on the photoreduction efficiency, as well as the roles and design strategies of the aforementioned gC3N4-based materials, are sequentially discussed and emphasized. Besides, the achievements of the reported gC3N4-based photocatalysts for eliminating heavy metal ions or radionuclides are compared and summarized. Finally, the opportunities and challenges for photo-reducing heavy metal ions and radionuclides using g-C3N4based materials have also been proposed and discussed.