Plant extracts-mediated green synthesis of zinc oxide/carbon nanofiber nanocomposites with highly efficient photocatalytic and antimicrobial properties for wastewater treatment

Abstract

In the present study, a novel biosynthesis method for the preparation of zinc oxide/carbon nanofiber nanocomposite (ZnO-CNFs) is proposed along with evaluated their photocatalytic and antimicrobial properties for wastewater treatment. For biosynthesis of ZnO-CNFs, plant extracts of Thymus daenensis (TD) and Stachys pilifera Benth (SB) were used as both green-reducing agents and aqueous carbon-rich sources. The photocatalytic activity of the synthesized ZnO-CNFs was studied in the photodegradation of tetracycline antibiotic residues in contaminated water. The photocatalytic test (UVA irradiation, λ = 365 nm) results showed that the photodegradation efficiency of tetracycline by ZnO-CNFTD was 93.65 ± 2.1 %, 73.58 ± 1.5 %, 67.41 ± 1.7 %, and 81.28 ± 2.1 % in ultrapure water, infectious disease hospital 1, infectious disease hospital 2, and general hospital influents, respectively. Furthermore, the antimicrobial activity was examined against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) bacteria and Candida albicans (C. albicans) fungus. To this end, the antibacterial behaviors of ZnO-CNFs were studied based on minimal inhibitory concentration (MIC) ranges and diameter of inhibition zone, which indicated that the ZnO-CNFs exhibited superior antibacterial activity against Gram-positive (B. subtilis) and Gram-negative (E. coli) bacteria compared to ZnO nanoparticles. Also, the antifungal activity of ZnO-CNFTD with MIC range of 156.25–625 μg mL−1 was more potent than ZnO nanoparticles with MIC range of 156.25–2500 μg mL−1. Overall, our findings indicate that the synthesized ZnO-CNFTD exhibits excellent photocatalytic and antimicrobial potential compared to ZnO nanoparticles and therefore can be a promising candidate for effective treatment of water contaminated with microorganisms and organic compounds.