Metal-free polymeric (SCN)n photocatalyst with adjustable bandgap for efficient organic pollutants degradation and Cr(VI) reduction under visible-light irradiation

The non-metal organic polymers have attracted increasing attentions in the photocatalysis field because of their low cost, metal-free, visible-light responsive, easy preparation and high stability. Herein, metal-free (SCN)(n) polymers with various polymerization degrees were prepared by a facile, low cost and environmentally friendly grinding method and presented excellent visible-light photocatalytic performance for organic pollutants degradation and Cr(VI) reduction. Owing to their pi conjugated structure, all the as-prepared (SCN)(n) polymers exhibited excellent visible-light absorption properties up to 550 nm, which were much better than that of bulk g-C3N4. Furthermore, both experiments and theoretical calculations unveiled that the peculiar chain structure, LUMO potential, charge separation and molecular oxygen motivation of (SCN)(n) polymers could be adjusted by tuning the polymerization degrees of samples. Therefore, the photocatalytic properties of (SCN)(n) polymers could be significantly improved by optimizing the polymerization degrees of samples. Besides, the possible photocatalytic degradation pathways of antibiotic Tetracycline (TC) over (SCN)(n) polymer was also studied based on liquid chromatography-tandem mass spectrometry (LC-MS) analysis. The developed metal-free (SCN)(n) polymer in this work proposed new thinking for the photocatalysis in water purification.