Synthesis and characterization of nano-gold composite using Cylindrocladium floridanum and its heterogeneous catalysis in the degradation of 4-nitrophenol

Abstract

Greener synthesis of nanogold-biocomposite by fungus, Cylindrocladium floridanum was reported in this study. Results revealed that when cultured in static condition for a period of 7 d, the fungus accumulated gold nanoparticles on the surface of the mycelia. Bionanocomposites with Au nanocrystals were characterized by UV–Vis spectroscopy, XRD, SEM, EDX and high-resolution TEM. The SPR band of UV–Vis spectrum at 540 nm confirmed the presence of gold nanoparticles on the surface of the fungal mycelia. The fcc (1 1 1)-oriented crystalline nature of particles was identified by XRD pattern. The synthesized particles are spherical in shape as evidenced by TEM image. The biocomposites with Au nanoparticles function as an efficient heterogeneous catalyst in the degradation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), in the presence of reducing agent, sodium borohydride which was reflected by UV–Vis spectra of the catalytic reaction kinetics. The reduction of 4-nitrophenol follows pseudo-first-order kinetic model with the reaction rate constant of 2.67 × 10 −2 min −1 with 5.07 × 10 −6 mol/dm 3 of gold at ca. 25 nm. The rate of the reaction was increased by increasing the concentration of gold nanoparticles from 2.54 × 10 −6 to 12.67 × 10 −6 mol/dm 3 (∼25 nm) and with reduced size from 53.2 to 18.9 nm respectively. This is the first report on fungal-matrixed gold(0) nanocomposites heterogeneously catalyzing the reduction of the toxic organic pollutant, 4-nitrophenol that enable the recovery and recycling of AuNPs catalysts.