Efficient visible light driven degradation of sulfamethazine and tetracycline by salicylic acid modified polymeric carbon nitride via charge transfer

Abstract

Photocatalysis has been widely studied as a promising technique for removal of organic pollutants in wastewater. A modified carbon nitride has been designed for this purpose. In this study, a facile method to synthesize distorted carbon nitride by simply copolymerizing urea and salicylic acid (SA) has been explored. The incorporation of SA induced the structure change from planar structure to distorted curls structure. Compared to pristine CN, the CN-SA shows wide light absorption, which is attributed to the n → π* transition at the nitrogen atoms with lone pair electrons of heptazine units. The photoelectrode of CN-SA exhibited higher photocurrent and lower charge resistance than that of pristine CN electrode, indicating that the photogenerated charge carriers of CN-SA are more efficiently separated. As a result, the optimal CN-SA shows 2-fold enhancement in degradation of tetracycline (TC) as compared to pristine CN. Furthermore, we found that the degradation rate of sulfamethazine (SMZ) was 0.0823 min−1 using the CN-SA photocatalyst, which is three times higher than that of pristine CN (0.0293 min−1). In addition, the CN-SA shows good stability without structural change or loss of photocatalytic performance after four cycles. According to the radical species trapping experiments and electron spin resonance analyses, O2− and h+ were the main active species involved in the degradation of organic pollutants. The developed strategy provides a novel approach to design the tunable band structure of organic semiconductor materials for various applications.