Eco-synthesis of chitosan-panchagavya-ZnO nanocomposites: Bridging green chemistry and sustainable agriculture for enhanced plant growth

The present research focuses on developing chitosan-based zinc oxide nanocomposites (CS/ZnONCs) as sustainable, eco-friendly plant growth promoters for agricultural practices. The incorporation of Panchagavya -functionalized zinc oxide nanoparticles ( PG -ZnONPs) into the CS matrix at the nanoscale promotes the production of more effective alternatives to chemical treatments while minimising chemical consumption. PG -ZnONPs and CS/ PG -ZnONCs were synthesised and characterised using UV-Vis, XRD, FESEM, and HRTEM, revealing their unique nanomaterial properties. SEM showed that PG -ZnONPs possessed a hexagonal morphology consistent with the wurtzite crystal structure, while CS/ PG -ZnONCs exhibited an apparent oval rod-like morphology due to chitosan coating, with the hexagonal wurtzite crystal structure remaining unchanged, as confirmed by XRD. TEM confirmed the nanoparticle sizes and matrix formation. Particle size and zeta potential (ZP) analysis of PG -ZnONPs (PS, 234.4 nm, ZP, −20mV) and CS/ PG -ZnONCs (PS, 496.5 nm, ZP + 1.11 mV) showed stable nanocomposite formation. The CS/ PG -ZnONCs exhibited the strongest antibacterial activity against pathogens, with lower MICs and larger inhibition zones than the individual components, particularly against Staphylococcus epidermidis and Escherichia coli . Seed germination and pot studies on mung bean plants revealed that PG- ZnONPs performed optimally at 125 mg/L, whereas CS/ PG -ZnONCs were most effective at 62.5 mg/L. The metal nanocomposites significantly enhanced root/shoot length and improved morphological traits, as well as chlorophyll and phenolic content. The superior performance of CS/ PG -ZnONCs improved the plant absorption of PG -ZnONPs through the CS matrix. Mung seedlings treated with PG -ZnONPs and CS/ PG -ZnONCs had a root/shoot length of 2.42 cm and 5.20 cm, respectively. In comparison, foliar spray treatments with PG -ZnONPs and CS/ PG -ZnONCs resulted in root and shoot lengths of 2.48 cm and 10.17 cm, respectively. In the pot study, the CS/ PG -ZnONCs plant growth promoter outperformed the other treatments. Therefore, research highlights the importance of sustainable and eco-friendly agriculture.