Tailoring TiO₂through N doping and incorporation of amorphous carbon nanotubes via a microwave-assisted hydrothermal method

Nanohybrids consisting of titanium dioxide (TiO₂) and amorphous carbon nanotubes (aCNTs) or amorphous nitrogen-doped carbon nanotubes (aNCNTs) were synthesized using the microwave radiation-assisted hydrothermal method in order to investigate the effect of CNTs on the physicochemical, optical and photocatalytic properties of doped and undoped TiO₂. The synthesized nanohybrids consisted of titania-aCNT (TiO₂-aCNT), titania-aNCNT (TiO₂-aNCNT), and nitrogen doped titania-aNCNT (NTiO₂-aNCNT). Pristine NTiO₂was also synthesized as a control. It was observed that a small amount of aCNTs and aNCNTs (3wt.%) causes a significant difference in the physicochemical properties of the TiO₂nanohybrids such as particle size, particle size distribution, aggregation and optical properties. The presence of aNCNTs and aCNTs improves particle dispersion, reduces particle size and the size distribution for both TiO₂and NTiO₂. In addition, aCNTs or aNCNTs promote the formation of spherical TiO₂and cuboidal NTiO₂nanoparticles as opposed to the nanosheets in NTiO₂. Both carbonaceous materials also suppress electron-hole recombination, thus enhancing the photocatalytic activity of the nanohybrids. A strong correlation between the CNT loading and the physicochemical, optical properties and photodegradation of Congo Red dye of the nanohybrids was observed. For example, the nanohybrid TiO₂-aNCNT exhibited the smallest particle size and size distribution (6.18^_±1.25nm), the lowest energy band gap (3.02eV) the lowest PL intensity and thus the highest photocatalytic efficiency (99.2 % in 30min with ^{_{k1 app=41.2×10-3min-1}}) with TiO₂-aCNT being the second best in terms of particle size (7.06^_±1.48nm), energy band gap (3.04eV) and hence the CR removal rate at 30min (99.8 %). Furthermore, a comparison of the least performing photocatalyst NTiO₂and NTiO₂-aNCNT shows that while the incorporation of aNCNT into NTiO₂increases the energy band gap from (3.15-3.19)eV, it still enhances the NTiO₂particle dispersion and reduce the PL intensity. As a result, NTiO₂has less overall removal of CR 63.3 % than NTiO₂-aNCNT (82.6 %). Lastly, the incorporation of the carbonaceous materials promotes the second order adsorption kinetics and improves the photocatalytic performance of the nanohybrids.