Sunlight removal of diclofenac using g-C3N4, g-C3N4/Cl, g-C3N4/Nb2O5 and g-C3N4/TiO2 photocatalysts

Abstract

This study aimed to investigate four photocatalysts, whether element-doped (g-C3N4/Cl) or through heterojunctions (g-C3N4/Nb2O5 and g-C3N4/TiO2), and compare against unmodified (bare) g-C3N4 for diclofenac removal under artificial sunlight. The synthesis methodologies were deliberately chosen for simplicity to enable practical applications. Additionally, the potential phytotoxicity of the products was investigated. In this sense, the main novelty of the present work is to contribute to elucidate the performance of photocatalysts commonly employed in photocatalysis (such as Nb2O5 and TiO2), but combined with a material that allows them to be photoactive under visible irradiation. Under the experimental conditions of this study (C0= 20 mgL-1; Ccat. = 600 mgL-1; pH = 6.0; artificial sunlight: 40 Wm-2 UVA, 245 Wm-2 VIS), the four photocatalysts displayed no statistically significant differences in diclofenac removal over the 240-minute evaluation period. However, the specific constant rate normalized by SBET indicated that bare g-C3N4 demonstrated statistically superior efficacy in diclofenac removal. When exposed to natural sunlight, bare g-C3N4 achieved a 68-minute normalized illumination time (t30w) to remove over 67% of diclofenac. Assessing phytotoxicity involved 14 assays using the four photocatalysts and two seed types (cucumber and lettuce). With a few exceptions (g-C3N4, g-C3N4/Cl, and g-C3N4/TiO2, limited to cucumber seeds), experiments revealed non-phytotoxic byproducts after diclofenac photocatalysis, as indicated by germination indices exceeding 80%.