Photodegradation of ceftriaxone using g-C3N4-ZnO nanocomposite as an efficient photocatalyst

Abstract

The entrance of emerging contaminants (ECs) (hormones, dyes, pesticides, pharmaceuticals, etc.) into natural waters threatens public health and the ecosystem due to their longer half-life and low biodegradability. Particular interest is placed on antibiotics, whose presence in aqueous systems notoriously increased the recent COVID-19 pandemic and, thus, the risk for various organisms and other collateral implications. This work evaluates the photocatalytic activity of graphitic carbon nitride (g-C3N4)-zinc oxide (ZnO) composites (CNZO), compared to bare photocatalytic materials, to degrade Ceftriaxone (CEF) antibiotic. The synthesis methodology of materials comprised the obtention of bare photocatalysts using hydrothermal (ZnO) and thermal polymerization (g-C3N4) methods, whereas, for CNZO composites, wet impregnation methodology was employed. The impact of g-C3N4 wt% content (10, 25, 50, and 75%) in composites was investigated by correlating variations in their structural, morphological, chemical, and optical properties with their photocatalytic activity under UV and visible irradiation. The results showed an optimal relation between ZnO and g-C3N4 wt% content (CNZO (25–75) sample), resulting in complete molecule degradation in 60 min and 93 % of degradation in 180 min under UV and visible radiation, respectively. The reusability of the CNZO (25–75) sample was tested in five consecutive ceftriaxone-degradation cycles, where no deactivation phenomena in the sample (92% of degradation) was observed, suggesting its good stability and potential application in practical experiments. The enhanced photocatalytic activity is attributed to decreasing recombination of the charge carriers evidenced by PL spectra, which confirms the heterojunction formation between ZnO and g-C3N4. Based on the results, a schematic photocatalytic mechanism was proposed, which describes the enhanced electron-hole separation at the materials interface. These results provide a guideline for obtaining composites with superior photocatalytic activity. Additionally, their visible light-active feature might be helpful towards the use of sunlight, overcoming conventional photocatalysts (ZnO, TiO2, etc.) drawbacks.