Synthesis of Highly Concentrated Silver Nanoparticle Dispersions and Their Integration into Cellulose Films for Catalytic and Antibacterial Applications

Abstract Silver nanoparticles (AgNPs) have attracted considerable attention due to their outstanding catalytic and antimicrobial properties. Nevertheless, most aqueous syntheses yield colloids with low metal concentrations and limited long-term stability, restricting their practical use. To address these challenges, highly concentrated and stable AgNP dispersions were prepared, reaching concentrations of up to 100 mM, by chemical reduction of AgBF4 with tetrabutylammonium borohydride in the presence of polyvinylpyrrolidone (PVP) as a stabilizer. The dispersions contained predominantly spherical nanoparticles with narrow size distributions and remained stable for at least 1 month. For improved reusability, the AgNPs were incorporated into regenerated cellulose films produced in 1-butyl-3-methylimidazolium chloride. Owing to its abundance, renewability, and biocompatibility, cellulose provides a sustainable and environmentally friendly platform for supporting metal nanoparticles, offering easy handling and potential for reuse. The resulting AgNP-cellulose composites contained up to 5 wt % of silver and preserved the cellulose type II structure. Structural, thermal, and morphological analyses confirmed the homogeneous distribution of PVP-stabilized AgNPs within the matrix. The hybrid films exhibited high catalytic activity toward 4-nitrophenol reduction and could be reused for at least five consecutive cycles with minimal loss of performance. In addition, antibacterial assays against Escherichia coli (ATCC 8739) and Staphylococcus aureus (ATCC 25923) showed antibacterial activity, with a statistically supported and concentration-dependent response that was more pronounced for the Gram-positive strain. This work demonstrates a straightforward strategy to combine concentrated AgNP dispersions and cellulose supports, yielding recyclable catalytic and antimicrobial materials.