Green synthesis of TiO2/Ag@Eucalyptus globulus Labill nanocomposites: a comprehensive study and dual application in grape preservation and dye treatment

Abstract

This study presents the green synthesis of TiO₂/Ag@Eucalyptus globulus Labill (TiAgxPE) nanocomposites and their integration into chitosan (CS) active packaging films. Distinct from conventional chemically synthesized TiO₂/Ag and those utilizing standard plant extracts, the Eucalyptus extract provides unique phytochemicals that act as highly efficient reducing agents while imparting a synergistic capping layer. XRD analysis results confirmed nano TiO₂ formed in the anatase phase, with crystallite sizes increasing from 12.77 nm (TiPE) to 14.88 nm (TiAg0.33PE). UV-vis DRS revealed a narrowed bandgap induced by Ag surface plasmon resonance, while PL peaks at 510–520 nm indicated significantly suppressed electron–hole recombination. HR-TEM images and EDX mapping showed uniformly dispersed face-centered cubic Ag nanoparticles on porous TiO₂. Consequently, the TiAg0.33PE nanocomposite exhibited superior photocatalysis, nearly fully degrading RGB dye in 30 minutes at pH 4. Mechanistic studies revealed that superoxide radicals and photogenerated holes dominated the degradation process, facilitated by efficient unidirectional charge separation at the Ag–TiO₂ Schottky barrier. Furthermore, the TiAg1PE nanoparticles exhibited broad-spectrum antibacterial activity, effectively inhibiting E. coli, S. aureus, B. cereus, and P. stutzeri B27, yielding maximum inhibition zones of 12 mm. Incorporating these nanoparticles into CS films reduced the water vapor transmission rate by creating a tortuous diffusion path. Although mechanical flexibility slightly decreased, the CS + TiAg1PE film retained excellent bactericidal efficacy. Over a 9-day storage period, the CS + TiAg1PE formulation reduced moisture loss and microbial decay, limiting weight loss to 15% and confining decay incidence to 5%. Ultimately, these findings underscore the potential of the green synthesized TiAgxPE nanocomposites as a dual-functional platform for photocatalytic wastewater treatment and postharvest shelf-life extension of fresh agricultural produce.