Hybrid surfaces active in catalysis based on gold nanoparticles modified with redox-active pendants and polymer brushes

We present hybrid systems bearing both plasmonic colloids and redox-active molecules that have demonstrated excellent performances in the catalytic reduction of nitrophenol (Nip) to aminophenol (Amp) in the presence of sodium borohydride. First, amino-functionalized spherical and triangular gold nanoparticles (AuNSs and AuNTs, respectively) were covalently incorporated onto polyacrylic acid (PAA) brushes attached to silicon surfaces. Next, a redox-active anthraquinone derivative (AQ-COOH) was immobilized onto the AuNPs surface by amidation reactions. The AuNP concentrations were varied to increase the incorporation and distribution of gold onto the PAA brushes. The catalytic activity in the reduction of 3-Nip and 4-Nip to Amp by NaBH4 was evaluated by 1H NMR spectroscopy. Colloidal size and morphology are analyzed by transmission electron microscopy (TEM) and UV–visible spectroscopy. Particle distribution on the silicon wafer was analyzed by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The presence of bonded cysteamine (Cys) and anthraquinone (AQ) derivatives on the gold surface was confirmed by X-ray photoelectron spectroscopy (XPS) and surface-enhanced Raman spectroscopy (SERS). The hybrid system could perform seven consecutive catalytic runs without loss of catalytic activity with conversions higher than 80%.