Ocimum tenuiflorum leaf-mediated graphitic carbon nitride and ZnO/GCN nanohybrid: a sustainable approach for environmental applications

Abstract

Water contamination is a real concern, and safe water demand increases with the growing world population. The development of eco-friendly and cost-effective technologies that can clean water is necessary. This study investigates the bio-synthesis of pure graphitic carbon nitride nanoparticles (GCN-NPs), zinc oxide nanoparticles (ZnO-NPs), and ZnO-doped graphitic carbon nitride nanohybrids (ZnO/GCN-NHs) using Ocimum tenuiflorum (OT) leaf extract, with a focus on their potential applications in wastewater treatment, cytotoxicity assessment, and antibacterial activity. GCN synthesis using plant extract was never reported in previous studies. Under direct solar light photocatalytic performance of the synthesized NPs and NHs was tested on the degradation of methylene orange (MO) dye and compared. Among the samples, the ZnO/GCN-NHs (10 mg/100 mL) exhibits good photocatalytic activity, achieving up to 47.56% degradation in 150 min of MO dye. The cytotoxicity of the bio-synthesized NPs and NHs 50 µg/mL concentration was assessed against human dental pulp stem cells and these were found to be non-toxic, indicating their potential for biomedical applications. The antimicrobial properties were also assessed using well diffusion and disc diffusion tests against four bacterial strains, i.e., two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and two Gram-positive (Staphylococcus aureus and Streptococcus dysgalactiae). The tests demonstrate significant antibacterial activity with an excellent inhibition radius against Escherichia coli 17.5 ± 1 mm, Pseudomonas aeruginosa 15.04 ± 1 mm, Staphylococcus aureus 27.5 ± 1 mm, and Streptococcus dysgalactiae 25 ± 1 mm. The enhanced photocatalytic and antimicrobial properties of the ZnO/GCN-NHs are hypothesized to be due to the increased production of reactive oxygen species (ROS) through the combination of ZnO-NPs with biosynthesized GCN.

Graphical abstract