Plant-based Nanoparticle Synthesis: A Critical Comparison of Green and Conventional Chemical Approaches

Abstract

Plant-mediated nanoparticle synthesis is widely presented as a sustainable alternative to conventional chemical fabrication, yet the label "green" often rests on the substitution of a synthetic reducing or capping reagent with a crude biological extract rather than on demonstrated reductions in hazard, energy demand, waste generation or life-cycle burden. This critical narrative review compares plant-based and conventional chemical approaches for the synthesis of metallic and metal-oxide nanoparticles, with emphasis on reaction mechanisms, process control, characterisation, reproducibility, environmental performance, safety and translation. Literature published from 2003 to 1 June 2026 was examined, while seminal pre-2003 studies on solution-phase nucleation and chemical reduction were retained to establish mechanistic context. Plant extracts can simultaneously provide reducing, complexing and stabilising functions through polyphenols, flavonoids, terpenoids, sugars, proteins and organic acids. These multicomponent reaction environments may enable aqueous, moderate-temperature synthesis and generate biologically active surface coronas. However, the same compositional complexity produces batch variability, uncertain active-agent concentrations, difficult purification, incomplete mass balances and weak control over particle size, morphology, oxidation state and surface chemistry. Conventional routes generally offer superior kinetic control, compositional definition, scale-up predictability and structure-property tuning, but may rely on hazardous reagents, organic solvents, high temperatures or energy-intensive unit operations. Comparative life-cycle evidence shows that neither route is intrinsically sustainable: precursor production, extraction, heating, drying, purification, solvent recovery, yield and the functional performance of the nanoparticle can dominate environmental outcomes. Across the literature, overreliance on colour change, ultraviolet-visible spectra and nominal particle size remains a major limitation, while inadequate ionic controls and residual-extract controls confound antimicrobial and cytotoxicity claims. A defensible green synthesis claim therefore requires quantified inputs and outputs, fit-for-purpose characterisation, benchmarked performance, safety assessment and life-cycle reasoning. Plant-based synthesis is most compelling where locally available low-value biomass can replace hazardous reagents without sacrificing reproducibility, purification efficiency or application performance.