Well-dispersed titanium dioxide and silver nanoparticles on external and internal surfaces of asymmetric alumina hollow fibers for enhanced chromium (VI) photoreductions

Abstract Silver (Ag)-decorated titanium dioxide (TiO2) catalysts were produced under ultrasound irradiation at different loadings of Ag nanoparticles (from 5 to 50 wt%). Then, the catalysts were supported on internal and external surfaces of alumina hollow fibers with asymmetric pore size distribution. The produced catalysts were considered for Cr(VI) photoreductions. The ultrasound-assisted process potentialized the distribution of Ag nanoparticles on the TiO2 surface. The loading of Ag nanoparticles at concentrations greater than 5 wt% was necessary to improve the TiO2 activity for Cr(VI) photoreduction. The loading of Ag nanoparticles at 30 wt% improved the Cr(VI) photoreduction of the single TiO2 catalyst from 40.49 ± 0.98 to 55.00 ± 0.83% after 180 min of reaction. Suspended and supported Ag-decorated TiO2 catalysts achieved total Cr(VI) photoreduction after 21 h of reaction. The adjusted reaction rate constant with the externally supported Ag-TiO2 catalyst was 3.57x10-3 ± 0.18 x10-3 min-1. Similar reaction rate constants were achieved with suspended and internally supported catalysts (approximately 2.70x10-3 min-1). After 10 sequential reuses, all catalysts presented similar Cr(VI) photoreductions of approximately 66%. Nevertheless, the use of the externally supported catalyst is suggested for Cr(VI) photoreductions due to its superior catalyst activity at least in the first reuse cycles.