Facile Synthesis of Phosphate-Functionalized MWCNT-TiO2 Nanocomposites as Efficient Photocatalysts and Insights into the Roles of Nanostructured Carbon

Abstract

Effectively contacted multiwalled carbon nanotube (MWCNT)-titanium dioxide nanocomposites and phosphate-functionalized MWCNT-TiO₂ composites have been successfully synthesized by simple one-pot phase-separated hydrolysis-solvothermal processes. The key to this synthetic strategy is to disperse MWCNTs uniformly in Ti(OBu)₄ in advance and then to put them into the toluene organic phase. The as-prepared nanocomposites between TiO₂ and the correct amount of MWCNT exhibits higher activity in the photocatalytic degradation of rhodamine B than that with the resulting TiO₂ , although the activity in the photocatalytic degradation of gas-phase aldehyde and liquid-phase phenol is lower. Interestingly, the functionalization of MWCNTs with an appropriate amount of phosphoric acids prior to the synthesis could greatly improve the activity of the MWCNT-TiO₂ nanocomposites for the degradation of aldehyde and phenol, even superior to that of commercial P25 TiO₂ . Based on the measurements of atmosphere-controlled surface photovoltage spectra and O₂ temperature-programmed desorption, it is suggested that MWCNTs are favorable to increase rhodamine B adsorption on the composite to promote the photosensitization oxidation reactions, whereas it is unfavorable for the adsorption of O₂ and responsible for the low photocatalytic activity for the degradation of colorless pollutants. Phosphate functionalization greatly enhances the amount of O₂ adsorbed on the MWCNT, which leads to significant charge separation, and thus, to significant photoactivity for the degradation of colored and colorless pollutants of the nanocomposites.

Keywords: charge separation; nanotubes; oxygen; photochemistry; titanium.