Bio-inspired synthesis of Strychnos potatorum-chitosan/zinc oxide nanocomposites for multifunctional water purification and photocatalytic degradation

Chitin-sourced, the natural biopolymer chitosan (CS) is a viable choice for eco-remediation due to its strong antibacterial, photocatalytic, and UV-protective properties, as well as its biodegradability. This research outlines Strychnos potatorum (SP)-mediated Zinc Oxide (ZnO) nanoparticles (SP-ZnONPs) and CS-conjugated nanocomposites (SP-CS/ZnONCs), followed by their physicochemical characterisation and functional assessment of their effectiveness in purifying river water, photocatalytic degradation of dyes, and radical-scavenging and bactericidal properties. SP-ZnONPs and SP-CS/ZnONCs were synthesised and characterised by UV–visible spectroscopy and visible colour transformation. XRD analysis confirmed the crystalline structure of SP-ZnONPs embedded within the SP-CS/ZnONCs. Scanning and transmission electron microscopy corroborated their spheroidal morphology. Dynamic light scattering measurements revealed particle sizes of 289.4 nm and 365.3 nm, polydispersity indices of 0.136 and 0.271, and zeta potential values of −21.1 mV and 14.2 mV for the nanoparticles and nanocomposites, respectively. DPPH and ABTS assays confirmed the substantial antioxidant potential of SP-ZnONPs and SP-CS/ZnONCs. Moreover, antibacterial assays demonstrated significant activity against selected pathogenic strains. After being exposed to light for 70 min, the SP-CS/ZnONCs performed better than the SP-ZnONPs (60%) and the SP extract alone (47%), achieving a high photocatalytic degradation rate of 93% for the bromophenol blue dye. Furthermore, river water treatment with SP-CS/ZnONCs reduced electrical conductivity (from 3998 to 2602 µS/cm), salinity (from 28.66 to 13.33 PSU), total dissolved solids (from 2099.67 to 1130.33 mg/L), and turbidity (from 4.95 to 1.63 NTU). In conclusion, SP-CS/ZnONCs demonstrated superior dye degradation, water purification, and bioactivity, highlighting their potential as an eco-friendly remediation material.