Gold Nanoparticles Grafted Mesoporous Silica: A Highly Efficient and Recyclable Heterogeneous Catalyst for Reduction of 4-Nitrophenol.

Synthesis of gold nanoparticles dispersed uniformly on mesoporous silica (mAu/SiO2) by homogeneous deposition-precipitation (HDP) method is used as an effective catalyst for reduction of 4-nitrophenol to 4-aminophenol. Silica provides support and surface area to increase the catalytic activity of gold. X-ray photon spectroscopy revealed binding energy of Au 4 (84.0eV) and Au 4 (87.7eV) which support the formation of Au0 on SiO2 surface. Au/SiO2 showed Langmuir type-IV isotherms which are the characteristic features of mesoporous materials furthermore, pore size decreases with incorporation of Au NP's on SiO2 surface. The enhancement is due to the strong interaction of Au0 with silica support. The catalytic conversion was studied by UV-Visible spectroscopy and high performance liquid chromatography (HPLC) quantification method, which shows conversion of nitro group into amino group. In addition, the catalyst was easily separated and reused. The reusability of the catalyst exhibited better reduction of the 4-nitrophenol to 4-aminophenol even after 10 consecutive cycles. In comparison to trisodium citrate capped pure gold nanoparticles mAu/SiO2 catalysts showed very good catalytic activity toward nitrophenol reduction. Here we conclude that embedment of metal catalysts like Au into high surface area support like silica is a positive step toward development of novel heterogeneous catalysts. This study demonstrates the synthesis of silica-embedded Au nanocomposites and their catalytic in.uence on the reduction of 4-nitrophenol to 4-aminophenol. Higher loading of Au (4wt%) resulted in the better catalytic performance. [ABSTRACT FROM AUTHOR]