Flexible hierarchical Pd/SiO2-TiO2 nanofibrous catalytic membrane for complete and continuous reduction of p-nitrophenol

Abstract

Flexible and hierarchical nanostructured Pd/SiO2-TiO2 nanofibrous catalytic membranes were fabricated via combining electrospinning technique and a two-step hydrothermal method. The size and distribution of TiO2 nanorods immobilised on SiO2 nanofibrous membranes can be regulated via adjusting the dosage of TiCl3 solution in the first step hydrothermal process. When using an optimal TiCl3 solution dosage of 0.2 mL, a hierarchical structured Pd/SiO2-TiO2-0.2 nanofibrous catalytic membrane with uniformly dense TiO2 nanorods loaded on SiO2 nanofibers is obtained, and still shows good tensile strength and flexibility. The catalytic activity of Pd/SiO2-TiO2-0.2 increases 5 times as compared to Pd/SiO2-TiO2-0 in the reduction of p-nitrophenol (PNP) to p-aminophenol (PAP). The modification with TiO2 nanorods can provide more surface areas for loading the Pd nanoparticles, thereby increased active sites. The three-dimensional open-cell network stacked and assembled by thousands of SiO2 nanofibers and TiO2 nanorods enhances the contact between the reactants and Pd nanoparticles. Both aspects contribute the superior catalytic activity of Pd/SiO2-TiO2-0.2. Furthermore, a continuous and complete conversion of PNP to PAP can be stably operated over 240 min in a gravity-driven catalytic membrane reactor constructed by Pd/SiO2-TiO2-0.2.