Star-shaped amino-functionalized poly(glycerol methacrylate)-stabilized gold nanoparticle composites with catalytic activity for reduction of 4-nitrophenol

Abstract

Polymers containing amine moieties reduce Au(III) and stabilize gold nanoparticles (AuNPs). Such polymers can be used to synthesize AuNPs with controlled sizes and shapes, providing high stability to the colloidal solutions. A star amino-functionalized poly(glycidyl methacrylate) (PGMA) can quickly be prepared by epoxide ring-opening reactions. We functionalized the β-cyclodextrin-(PGMA)7 with diethanolamine (DEA) to create a star polymer (β-CD-(PGDEA)7) by atom transfer radical polymerization (ATRP), using β-cyclodextrin (β-CD) as macroinitiator. We determined the tertiary amine content (-NR2 = 0.63 mmol/g; R = -CH2-CH2-OH) on the star polymer by gravimetric analysis. The material β-CD-(PGDEA)7 reduces Au(III) and stabilize AuNPs, following a strategy in-situ. AuNPs (7.8 nm) were created by controlling the tertiary amine content/Au(III) molar ratio. The ratio 5 at pH 5.2 supports protonated -NR2H+ (that binds [AuCl4]−) and -NR2 (that stabilize AuNPs) on the star polymer structure, providing colloidal stability over 70 days at room temperature due to the high Zeta potential (+30 mV). The catalytic activity of the colloidal suspension containing the star polymer-capped AuNPs was investigated in the conversion of 4-nitrophenol to 4-aminophenol, using sodium borohydride as a hydrogen donor agent. A high catalyst activity (knor = 65.11 L/min μmol) was obtained at 0.0043 μmol/L AuNPs. The result is assigned to the excellent AuNPs stability imparted by star polymer coatings, showing that the star polymer does not influence the catalytic activity of the covered AuNPs.