Amorphous carbon nanotube residue modification of solgel-synthesized C-, N-doped TiO 2 for photocatalytic applications

The work reports an investigation into the role played by the carbon residue from low-quality amorphous carbon nanotubes (aCNTs) and nitrogen doped aCNTs (aNCNTs) in the properties of solgel-synthesized TiO2 and NTiO2. The resutant modified nanohybrids are compared to nitrogen-doped TiO2 where the N is sourced from an ethylenediamine as an organic C and N precursor. The presence of carbon originating from ethylenediamine was confirmed by TGA and DTA while additional C doping originating from aCNT and aNCNT residues was confirmed by EDS and XRD spectroscopic techniques. XRD spectroscopy further demonstrated that the carbonaceous material residues resulted in the formation of TiC in TiO2–aCNT nanohybrids, and carbon nitride in NTiO2–aCNT nanohybrids. The TiC promoted photocatalytic performance of TiO2–aCNT nanohybrids while the carbon nitride residue increased charge recombination and thereby hampering the photocatalytic performance of NTiO2. A strong correlation exists between the optical properties and the photocatalytic performance in that NTiO2 has the lowest Eg (2.84 eV), second lowest charge recombination rate, and a high 2nd-order rate constant for the kinetics for CR dye removal. The TiO2–aCNT nanohybrids have the best overall performance in terms of dye adsorption, color removal through chemisorption, and UVA 254 TOC removal due to its low charge recombination. Therefore, the introduction of the carbonaceous materials into TiO2 significantly increases the adsorption capacity. Lastly, the presence of N in the carbonaceous materials further impedes the photocatalytic activity as observed by the low photocatalytic performance of NTiO2–aNCNT and TiO2–aNCNT nanohybrids.