Single walled carbon nanotubes (SWNTs) as templates for the growth of TiO2: the effect of silicon in coverage and the positive and negative synergies for the photocatalytic degradation of Congo red dye

Abstract

Single walled carbon nanotubes (SWNTs) are used as scaffolds to grow titania (TiO₂) under a range of different growth conditions. It is found that the titania growth occurring on SWNTs is significantly different in the presence of silica; this is contrary to prior reports, the important controlling factor for obtaining good coverage is not “nanoscopic HF bubbles”. The silica is either sourced from the reaction vessel if made from glass or may be added in the form of fumed silica: the greater the silicon content the greater the coverage of the SWNT. The adsorption and photocatalysis of organic Congo red dye on these hybrid titania covered SWNT materials are studied; while the adsorption of the dye onto the catalyst may be high, it is only in certain cases wherein it results in superior catalytic performance. The synergy between TiO₂ and SWNTs with regard to photocatalysis is not always positive. The addition of silica promotes the complete coating of SWNT with TiO₂, the resulting materials show very high absorption of Congo red but essentially no catalytic activity. In order to promote catalytic activity, it is necessary to have less full coverage of the SWNTs and the smallest average particle size of the grown titania. Intimate contact between the SWNT and the TiO₂ is needed (rather than a physical mixture) for any catalysis, and the electronic properties of the SWNTs are clearly important since multiwalled carbon nanotubes appear to have little effect on altering the photocatalytic activity.