N-doped TiO₂/sepiolite nanocomposites with enhanced visible-light catalysis: Role of N precursors

Several nitrogen-doped TiO₂/Sepiolite (N-TiO₂/Sep) photocatalysts were prepared via microwave-hydrothermal treatment using four different types of nitrogen sources: ammonium hydroxide, urea, ethylenediamine and triethylamine. The obtained nanocomposites were characterized by using XRD, TEM, BET, XPS and UV–vis techniques. The results revealed that the chemical and morphological properties of the nanocomposites were significantly dependent on the nitrogen source. The interstitial N doping occurred in the form of N-O-Ti-O and the surfaces of the samples were modified by carbon species from dopants. As compared to that of the undoped sample, N-doped samples exhibited a red shift in the band gap transition. The results of simulated solar light photocatalytic activities demonstrated that NTS-EDA exhibited better photocatalytic activity than singly N-doped (i.e., no carbon) or undoped TiO₂/Sep sample. The enhanced solar-light activity is attributed to the low band gap energy with N-doping, the high adsorption capacity and uniform distribution of titania nanoparticles with sepiolite as support, and the appropriate carbon content of the dopants.