Fabrication of g-C3N4/N,Fe co-doped CQDs composites: in situ decoration of g-C3N4 with N-CQDs and Fe and efficient visible-light photocatalytic degradation of tetracycline

Abstract

Herein, for the first time, g-C3N4/N,Fe co-doped carbon quantum dots (CN/N,Fe-CQDs) composites were fabricated by a two-step fabrication route. N,Fe-CQDs were obtained via facile pyrolysis of ammonium ferric citrate. Through thermal condensation of the synthesized N,Fe-CQDs and urea, CN/N,Fe-CQDs composites were successfully fabricated for highly efficient photocatalytic degradation of tetracycline (TC). The optimized CN/N,Fe-CQDs composite obtained the degradation efficiency of 81.0% after 40 min visible-light illumination, and its apparent rate constant was 3.41 times higher than that of pure g-C3N4. The remarkable enhancement of photodegradation activity is mainly attributed to the synergetic effect of N-CQDs and Fe co-decoration in CN/N,Fe-CQDs arising from the incorporation of N,Fe-CQDs into the g-C3N4 matrix, which could increase the specific surface area, wide visible-light absorption range, and accelerate separation and transfer of interfacial charge. The active species capture experiments and electron spin resonance technique testified that ‧O2 −, ‧OH, 1O2 and h+ were all involved in the degradation of TC in the photocatalytic process. According to the result of mass spectrometry, TC underwent hydroxylation, demethylation, N-demethylation, deamination, dehydroxylation, ring opening processes, and was ultimately mineralized into CO2 and H2O. This research can provide a new understanding of the roles played by non-metal and metal ions co-doped CQDs in photocatalytic system and open up a new way to develop highly efficient photocatalysts for TC degradation.