Biomediated nanosized ZnS using Ulva fasciata and Citrus japonica : A new bio-photocatalyst for textile wastewater treatment

The aquatic ecosystems face excessive stress and depletion due to many pollutants impacting water quality. Biosynthesis of nanoparticles (NPs) using the green route represents a cost-effectively and eco-friendly approach, with significant applicability in various fields. In this regard, ZnS-NPs with improved photocatalytic and antimicrobial activities were biosynthesized for the first time from Ulva fasciata and Citrus japonica aqueous extracts . Biosynthesized ZnS-NPs were characterized and compared with chemically synthesized ones using UV–Vis spectroscopy, FTIR, TEM, XRD, and EDAX. TEM micrographs and XRD confirmed the formation of polygonal and spherical-shaped ZnS blend sphalerite nanocrystals with an average diameter between 7 and 31 nm. The optical properties of the produced ZnS-NPs showed higher band-gap energy of 5.63 eV and 4.76 eV for chemically and biosynthesized ZnS-NPs, respectively, as compared to ZnS macromolecules (3.77 eV). Biosynthesized ZnS-NPs showed excellent photocatalytic activity toward textile wastewater and two organic dyes (crystal violet and safranin), with significant degradation efficiency of 82–96.8, 82.5–98.12, and 84–95.9%, respectively. Biosynthesized ZnS-NPs showed high stability up to three subsequent cycles of photodegradation and exhibited promising antimicrobial activity against different Gram-positive and Gram-negative bacteria and Candida albicans. Biosynthesized ZnS-NPs have a less cytotoxic effect (IC 50 > 300 μg/mL) than chemically synthesized ZnS-NPs (IC 50 88 μg/mL) on human skin fibroblast normal cell lines. The photocatalytic efficiency of the biosynthesized ZnS-NPs has some advantages, such as non-toxic products, cost-effectiveness, and antimicrobial activity, which give them superiority to be used as a safe bio-photocatalyst for water treatment. Graphical abstract