Efficient removal of parabens from real water matrices by a metal-free carbon nitride photocatalyst

Raquel A Fernandes; Maria J Sampaio; Goran Dražić; Joaquim L Faria; Cláudia G Silva

doi:10.1016/j.scitotenv.2019.135346

Efficient removal of parabens from real water matrices by a metal-free carbon nitride photocatalyst

Sci Total Environ. 2020 May 10:716:135346. doi: 10.1016/j.scitotenv.2019.135346. Epub 2019 Nov 21.

Authors

Raquel A Fernandes¹, Maria J Sampaio¹, Goran Dražić², Joaquim L Faria¹, Cláudia G Silva³

Affiliations

¹ Laboratory of Separation and Reaction Engineering - Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal.
² Department of Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, Ljubljana, Slovenia.
³ Laboratory of Separation and Reaction Engineering - Laboratory of Catalysis and Materials (LSRE-LCM), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal. Electronic address: cgsilva@fe.up.pt.

PMID: 31843308
DOI: 10.1016/j.scitotenv.2019.135346

Abstract

Metal-free graphite-like carbon nitride (GCN-500) was obtained by thermal post-treatment of bulk polymeric carbon nitride at 500 °C. The catalyst was thoroughly characterized by morphological, optical and textural analysis techniques. The efficiency of GCN-500 was evaluated under visible (λ_exc = 417 nm) LED excitation for the photocatalytic degradation of methyl-, ethyl- and propyl-paraben in different water matrices either isolated or in a mixture of the three compounds. The GCN-500 proved to be more efficient than the benchmark TiO₂ P25, with complete conversion of the individual parabens within 20 min of irradiation, contrasting with 120 min needed for total degradation using TiO₂. Experiments in the presence of selected scavengers confirmed the high importance of superoxide radicals in the photocatalytic oxidation of parabens using GCN-500. The effect of the nature of the aqueous matrix in the kinetics of the photocatalytic process was assessed using ultrapure, tap and river waters spiked with a mixture of the three parabens. Although still very efficient, the complexity of the real water samples turned the degradation process slower due to the presence of other components such as ions and dissolved organic matter. GCN-500 proved to be stable in a continuous-flow system using GCN-500 coated glass rings (GCN-500-GR) to remove MP, EP and PP from real water matrices.

Keywords: Carbon nitride; Degradation; Parabens; Photocatalysis; Visible light; Water matrices.