Tailoring TiO2 through N doping and incorporation of amorphous carbon nanotubes via a microwave-assisted hydrothermal method. Issue 5 (October 2020) - Zikalala, Sithembela A.
Highlights: Titania-amorphous carbon nanotube nanohybrids and their doped counterparts were fabricated. Amorphous carbon nanotubes enable carbon doping of nanohybrids. Microwave irradiation hydrothermal synthesis enables size and optical properties control. Nanohybrid with small particle size and narrow size distribution has highest photocatalytic activity. Abstract: Nanohybrids consisting of titanium dioxide (TiO2 ) and amorphous carbon nanotubes ( a CNTs) or amorphous nitrogen-doped carbon nanotubes ( a NCNTs) 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– a CNT (TiO2 – a CNT), titania– a NCNT (TiO2 – a NCNT), and nitrogen doped titania– a NCNT (NTiO2 – a NCNT). Pristine NTiO2 was also synthesized as a control. It was observed that a small amount of a CNTs and a NCNTs (3 wt.%) causes a significant difference in the physicochemical properties of the TiO2 nanohybrids such as particle size, particle size distribution, aggregation and optical properties. The presence of a NCNTs and a CNTs improves particle dispersion, reduces particle size and the size distribution for both TiO2 and NTiO2 . In addition, a CNTs or a NCNTs promote the formation of spherical TiO2 and cuboidal NTiO2 nanoparticles 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 – a NCNT exhibited the smallest particle size and size distribution (6.18 ± 1.25 nm), the lowest energy band gap (3.02 eV) the lowest PL intensity and thus the highest photocatalytic efficiency (99.2 % in 30 min with k 1 a p p = 41.2 × 10 - 3 m i n - 1 ) with TiO2 – a CNT being the second best in terms of particle size (7.06 ± 1.48 nm), energy band gap (3.04 eV) and hence the CR removal rate at 30 min (99.8 %). Furthermore, a comparison of the least performing photocatalyst NTiO2 and NTiO2 – a NCNT shows that while the incorporation of a NCNT into NTiO2 increases the energy band gap from (3.15–3.19) eV, it still enhances the NTiO2 particle dispersion and reduce the PL intensity. As a result, NTiO2 has less overall removal of CR 63.3 % than NTiO2 – a NCNT (82.6 %). Lastly, the incorporation of the carbonaceous materials promotes the second order adsorption kinetics and improves the photocatalytic performance of the nanohybrids.