Carbohydrate-directed synthesis of silver and gold nanoparticles: effect of the structure of carbohydrates and reducing agents on the size and morphology of the composites

A monosaccharide (β-d-glucose) and polysaccharide (soluble starch) were used as structure directing and subsequently stabilizing agents for the synthesis of spherical nanoparticles (NPs) and nanowires of silver and gold. Homogeneous monodispersed Ag(0) nanoparticles (Ag NPs) of 15 nm diameter were obtained when 10−4 M AgNO3 precursor salt was reduced in starch (1 wt %)–water gel by 1 wt % β-d-glucose. For a second preparation the effect of reducing agents on the synthesis of Au(0) metallic nanoparticles (Au NPs) of 2 × 10−4 M concentration prepared in a β-d-glucose (0.03 M)–water dispersion was studied first in detail. Different equivalent amounts of NaBH4 and a number of pH values were evaluated for the reduction of the Au salt HAuCl4·3H2O to obtain Au NPs. The type and the amount of reducing agent, as well as the pH of the solution was shown to affect the size and morphology of the NPs. NaBH4 (4 equiv) produced the smallest (5.3 nm (σ 0.7)) metallic particles compared to larger particles (10.0 nm (σ 1.4)) when the salt was reduced by 1 equiv of NaBH4. Addition of excess NaBH4 caused the NPs to settle out as a precipitate forming a mesh or wire structure rather than monodispersed particles. Low pH (pH 6) resulted in incomplete reduction, while at pH 8 the salt was completely reduced. When the salt was reduced by NaOH at pH 8, the particles were larger (14.2 nm) and less homogeneous (σ 2.8) compared to those from NaBH4 reduction.

Graphical abstractCarbohydrates polysaccharide and monosaccharide have been used first to adjust the size and shape of silver and gold nanoparticles in green solvent medium of carbohydrate–water dispersions. The research has given a new directionality to apply biocompatible carbohydrates to synthesized nanomaterials from the viewpoints of catalysts to biomedical applications. (a) Preparation and TEM image of Au NPs when salt was reduced by 4 equiv of NaBH4 in glucose water dispersion, (b) same preparation as (a) but excess NaBH4 was added.Figure optionsDownload full-size imageDownload as PowerPoint slide