Cellulose Membranes Embedded with Gold-Silver Bimetallic Nanoparticles for the Efficient Reduction of 4-Nitrophenol

Bimetallic nanoparticles (BNPs) have attracted much attention recently due to their improved properties compared to monometallic ones. Gold and silver nanoparticles (AuAgNPs) are among the most studied BNPs. Using these particles as powder or dispersion has drawbacks such as ease of aggregation and difficulty separating and recovering from the reaction medium. Therefore, immobilizing these nanoparticles in polymeric matrices, such as cellulose, is appealing. In this context, the present work focused on preparing unmodified cellulose membranes containing AuAgNPs for use as heterogeneous catalysts in reducing the pollutant 4-nitrophenol. Incorporating these nanoparticles into cellulose membranes represents a significant advancement in heterogeneous catalysis. In addition to being eco-friendly, cellulose membranes offer ease of handling and the potential for reusability, which are crucial factors in catalysis. The nanoparticles were prepared in an aqueous medium from the seeded growth of a silver shell around AuNP seeds. Images recorded by transmission electron microscopy showed that the particles have diameters smaller than 100 nm and are core-shell type. The cellulose membrane was prepared by dissolving microcrystalline cellulose in an ionic liquid, followed by a regeneration process using water. Next, the bimetallic nanoparticles were incorporated into the cellulose membrane. The analyses revealed that the membranes contain bimetallic nanoparticles homogeneously distributed in the matrix, and the inductively coupled plasma-optical emission spectroscopy (ICP-OES) showed that the membrane has 0.339 wt % in silver and 0.069% in gold. The membranes produced were efficient heterogeneous catalysts in reducing 4-nitrophenol, used for at least four cycles without loss of efficiency. This material can be easily isolated from the reaction medium, avoiding centrifugation or filtration processes for reuse. This study represents the first use of AuAgNPs supported on nonmodified cellulose membranes as heterogeneous catalysts, marking an advancement in catalysis and material science.