Solar-light-driven photocatalytic degradation and detoxification of ciprofloxacin using sodium niobate nanocubes decorated g-C3N4 with built-in electric field

Abstract

Simultaneous degradation and detoxification during pharmaceutical and personal care product removal are important for water treatment. In this study, sodium niobate nanocubes decorated with graphitic carbon nitride (NbNC/g-C3N4) were fabricated to achieve the efficient photocatalytic degradation and detoxification of ciprofloxacin (CIP) under simulated solar light. NaNbO3 nanocubes were in-situ transformed from Na2Nb2O6•H2O via thermal dehydration at the interface of g-C3N4. The optimized NbNC/g-C3N4-1 was a type-I heterojunction, which showed a high conduction band (CB) level of −1.68 eV, leading to the efficient transfer of photogenerated electrons to O2 to produce primary reactive species, •O2−. Density functional theory (DFT) calculations of the density of states indicated that C 2p and Nb 3d contributed to the CB, and 0.37 e– transferred from NaNbO3 to g-C3N4 in NbNC/g-C3N4 based on the Mulliken population analysis of the built-in electric field intensity. NbNC/g-C3N4-1 had 3.3- and 2.3-fold of CIP degradation rate constants (k1 = 0.173 min−1) compared with those of pristine g-C3N4 and NaNbO3, respectively. In addition, N24, N19, and C5 in CIP with a high Fukui index were reactive sites for electrophilic attack by •O2−, resulting in the defluorination and ring-opening of the piperazine moiety of the dominant degradation pathways. Intermediate/product identification, integrated with computational toxicity evaluation, further indicated a substantial detoxification effect during CIP degradation in the photocatalysis system.