Immobilizing Au-nanocolloids in co-branched polymer molecules in presence of gluconic acid in poly(vinyl alcohol) in hot water

It is explored that in hot water (50–70 °C) polymer molecules of poly(vinyl alcohol) (PVA) induce Au3+ → Au reaction and serve as an Au-stabilizer by immobilizing the Au-particles capping in part of the polymer molecules. Adding gluconic acid (GA) inhibits Au3+ coalescence in small groups in process to the reaction capping in surface stabilized PVA–GA polymer molecules. Tetrachloroauric acid HAuCl4·3H2O (supplies Au3+) in reaction with PVA molecules (with as much GA as twice the PVA in molar ratio) demonstrates the experiments. A robust shell comprises Au-nanoparticles of a thin polymer surface layer characterized by light absorption (450–750 nm) in the Au-surface plasmon bands. In general, GA affects the formation of Au-nanoparticles, with a blue shift (smaller size) of the absorption, e.g., from 565 nm in 1.0 wt% Au in reaction in PVA to that of 540 nm in PVA–GA, with an order of improved value of absorbance. X-ray diffraction of the films or thin plates (2–5 mm thickness) has well-defined lattice reflections (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2) and (4 0 0) in fcc-Au crystallites (∼25 nm average size). Microstructure reveals non-agglomerated particles of near cuboids or prismatic shapes of 35–70 nm widths.