Metal nanoparticles on natural cellulose fibers: electrostatic assembly and in situ synthesis

The conformal deposition of metal nanoparticles (Au, Pd, and Pt) onto natural cellulose fibers using two chemical strategies is reported. The driven mechanism responsible for the high surface coverage of the substrates was identified as the electrostatic interactions between the positively charged cellulose and the either negatively charged nanoparticles or negative metal complex ions. The natural cellulose fibers were rendered cationic by grafting ammonium ions, using an epoxy substitution reaction, to the abundant hydroxyl groups present in cellulose molecules. The first method involved the electrostatic assembly of citrate-stabilized metal nanoparticles directly onto the cationic surfaces of cellulose. The second method involved the adsorption of negative metal complex ions onto the cationic cellulose followed by a reduction reaction. The attained metal nanoparticles bound with cellulose fibers were characterized by electron microscopy (TEM and SEM) and energy-dispersive X-ray spectroscopy (EDX). Both pathways generated metal nanoparticles with high packing densities on the cellulose substrates even when very dilute solutions of metal colloids or metal salts were used. Achieving high surface coverage with low-concentration precursor solutions may open an avenue for the production of flexible catalytic mantles or highly functionalized textile substrates.