Nanobiocomposites of silver nanoparticles with polygalacturonic acid obtained by one-pot green synthesis: solid-state characterization

Abstract Silver nanoparticles (AgNP) were obtained by reduction of silver ions in alkaline solutions of polygalacturonic acid (PGA), the main chain of pectins. The growth of AgNP during the reaction was monitored by UV/Vis spectroscopy. The PGA solutions containing AgNPs were nanoprecipitated into an anti-solvent (ethanol) bath. Spherical particles of ca. 70 nm observed by atomic force microscopy embedded spherical AgNPs registered by transmission electron (TEM) and scanning electron (SEM) microscopies. The AgNP’s distribution determined both by TEM and SEM was Log-normal with the most probable AgNP’s size about 10 - 18 nm. The X-Ray diffraction (XRD) pattern of AgNPs was in accord with the face-centered cubic lattice of silver. The size of silver nanocrystals estimated by XRD was within the interval determined by TEM and SEM. Fourier-transform infrared spectra indicated ( i ) the bidentate bridging between carboxylate groups of PGA and silver atoms on AgNP surface; ( ii ) the strengthening of hydrogen bonds in the nanobiocomposites. The nanobioconjugation of PGA with the growing silver clusters during the synthesis was supposed to produce strip-like defects on AgNP surface that were observed by TEM.