Sustainable nanogold-cellulose composites: Green synthesis, emerging applications and future aspects

Sustainable Au NPs-cellulose composites fuse the renewable versatility of cellulose with the size-tunable plasmonic, catalytic, and biocompatible properties of Au nanoparticles (Au NPs) to create a class of lightweight, multifunctional materials engineered for real-world impact. This review synthesises recent progress in green synthesis routes, from cellulose-mediated and plant-extract reductions to plasma, hydrothermal, and ionic-liquid approaches, and contrasts in situ versus ex situ incorporation across nanocellulose, such as carboxylated cellulose nanocrystals (CNC, 3-10 nm diameter, 70-90% crystallinity), cellulose nanofiber (CNF, 4-20 nm diameter, >1000 nm length), and bacterial nanocellulose (BNC, 10-50 nm diameter, 60-80% crystallinity), alongside macroscopic fibre/paper platforms. We map the relationships between structural properties, such as nanoparticle size (typically 5-50 nm), shape, surface chemistry, and anchoring strategies, and various performance metrics, including thermal stability, mechanical improvements of up to 25%, mechanical modulus increases of 30-40%, optoelectronic conductivity gains of 2-3 orders of magnitude, catalytic conversion efficiencies exceeding 85-90%, and antimicrobial inhibition rates above 95%. Critical advances in scalable processing, retention control for papermaking lines, and closed-loop Au recovery (achieving >80% recovery efficiency) are evaluated alongside rigorous characterisation workflows using TEM/SEM, XRD/XPS, FTIR/UV-Vis, and performance assays. Life-cycle and regulatory perspectives identify hotspots in feedstock choice, nanoparticle leaching (<5% under aqueous conditions), and end-of-life recovery, and highlight safe-by-design strategies that balance efficacy with environmental stewardship. The review concludes by outlining translational pathways for high-value biomedical devices, water-treatment membranes, and flexible electronics. It prioritises standardised testing, pilot-scale demonstrations, and data-driven optimization to accelerate responsible commercialization.