Hierarchical synthesis of silver monoliths and their efficient catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol†
Abstract
A novel catalyst Ag/Triton X-705/SiNPs is synthesized by a modified sol–gel method without the use of an acid or a base as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of 0.1 M NaBH4 in aqueous media. The reduction time was found to be 30–35 seconds when the concentration of 4-NP was varied from 0.001 M to 0.009 M while maintaining a constant amount of the Ag/Triton X-705/SiNP catalyst at 0.006 g. Fe3O4NPs, dextran, and trimethylbenzene (TMB) were added separately to Ag/Triton X-705 hydrogels to modify their morphology and catalytic activities against the reduction of 4-NP to 4-AP. The as-synthesized monoliths were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area analysis. The pseudo first order rate constant (k), energy of activation (Ea), and thermodynamic parameters viz. activation enthalpy (ΔH‡), activation Gibbs free energy (ΔG‡) and entropy of activation (ΔS‡) have also been determined. The turnover frequency (TOF) of the Ag/Triton X-705/SiNP catalyst was 9.66 × 1020 molecules per s and the catalyst was used up to nine cycles successfully with greater efficiency, making it a potential and leading candidate for the industrial conversion of 4-NP to 4-AP. We claimed that the Ag/Triton X-705/SiNP catalyst took almost minimum time for the reduction of 4-NP to 4-AP.