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

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.