Titanium dioxide/carbon nanotube composite for photoreactive membrane filtration.

摘要

The ultimate goal of this research is to fabricate a highly reactive photocatalyst composed of TiO2 and carbon nanotubes (CNTs) and to apply TiO 2 photocatalysis in a rotating filtration system for water purification. We synthesized nanostructured assemblies composed of different proportions of anatase (5 or 100 nm) or rutile (1.2 mum), and either single- or multi-walled CNTs, using a simple low temperature process. The nanostructured composite assembled from the 100 nm anatase and single-walled CNTs (SWCNTs) exhibited enhanced and selective photocatalytic oxidation of phenol in comparison to both pure anatase and Degussa P25. A mechanism for the enhanced reactivity is proposed in which electrons are shuttled from TiO2 particles to the SWCNTs as a result of an optimal TiO2/CNT arrangement that stabilizes charge separation and reduces charge recombination. SWCNTs can also substantially improve the uniformity and coverage of TiO2 coatings on porous ZrO2 membranes. The TiO2/SWCNT composite forms a complete and uniform coating on ZrO2 membranes at pH 5 (∼100% coverage). We also created a rutile/SWCNT composite that exhibits enhanced photocatalytic reactivity compared to pure rutile for phenol oxidation. The rutile/SWCNT composites, P25, and anatase/SWCNT compostes were deposited on alumina membranes and used for membrane filtration. The membranes deposited with anatase/SWCNT composites show the highest photocatalytic reactivity for phenol oxidation. The optimum density for the deposition of the anatase/SWCNT composite on porous membranes for reactive filtration is 0.33 mg/cm2. Three generations of rotating filtration systems were designed and fabricated for bio-fouling formation tests. Cylindrical ceramic (ZrO2/TiO2) porous filters (1.4 mum pore size) were coated with several types of TiO2 and TiO2/SWCNT composites and were tested in a 195-hour long bio-fouling test using the latest generation system, a 6-filter rotating filtration system. Results indicate that the anatase/SWCNT 100:1 composite holds potential for bio-fouling control.