Green synthesis methods for nanoparticles: Principles, biological routes, and physicochemical approaches toward sustainable nanotechnology
Md. Rasel Ahmed, Kamrul Hasan Manik, Md. Shariful Islam, Asaduzzaman Rhine, Juhi Jannat Mim, Nayem Hossain
Abstract
The need to sustainably and scalably produce alternatives to conventional nanoparticle (NP) synthesis has been exacerbated by environmental, health, and regulatory issues surrounding conventional NP synthesis. This is a critical and comparative review of the strategy of green NP synthesis, grounded in the principles of green chemistry and sustainability measures. Biological pathways that use bacteria, fungi, algae, yeast, viruses, and plant extracts are discussed in terms of their biochemical reduction pathways, natural stabilisation routes, and major deficiencies in controlling morphology, batch-to-batch reproducibility, and scalability. Complementarily, solvent-free mechanochemistry, hydrothermal processing, and microwave- and ultrasound-assisted synthesis, among the green physicochemical methods, are evaluated as potentially capable of addressing the limitations of entirely biogenic methods without yet compromising environmental viability. In contrast to previous reviews, which are mainly descriptive, this article presents a standardised sustainability, scalability, and reproducibility (SUS-SCA-REP) benchmarking measurement system to enable transparent comparison of methodologies for biological, physicochemical, and hybrid syntheses. The framework transforms translation-critical metrics, such as particle controllability (size distribution/morphology), batch-to-batch consistency, process intensity/energy demand, waste penalty, and scale-readiness, into unswervingly reportable metrics. Lastly, significant obstacles to scale, such as biological variation, limitations in purification, and regulation, are also discussed, along with future solutions such as hybrid bio-physicochemical integration, ML-based process optimisation, and a more design-aware approach to the circular economy, to present a proactive vision of reproducible and industrially viable green nanomanufacturing.