Effect of doping on the catalytic activity of materials based on TiO₂ for VOC degradation

Volatile organic compounds (VOCs), with boiling points below 250 °C, are atmospheric pollutants responsible for adverse effects such as climate change, depletion of the ozone layer and respiratory diseases. Traditional methods for their removal, such as absorption, condensation, membrane separation and thermal oxidation, present some limitations, including high cost, low efficiency or the generation of toxic byproducts. Therefore, more sustainable alternatives are needed, among which adsorption and photocatalytic oxidation stand out.

In this study, photocatalytic materials based on titanium dioxide (TiO₂) were synthesized and doped with nitrogen (N), nitrogen and boron (N-B), and nitrogen and sulfur (N-S) using a hydrothermal synthesis method, with the aim of degrading ethylene and toluene as model VOCs. The materials were obtained from a solution of titanium(IV) tert-butoxide and different doping agents, achieving a doping concentration of 2 wt%. After synthesis, the solids were washed, filtered and calcined. In addition, a sample of pure TiO₂ and several composites of the best-performing material with carbon xerogels doped with sulfur or nitrogen were also synthesized to enhance the performance.

The materials were characterized using complementary techniques such as SEM, XRD, XPS, DRUV and N₂ adsorption. The results showed an anatase crystalline structure with mesoporosity and a specific surface area of approximately 90 m²/g. The introduction of the carbon support increased these values and diminished the bandgap of the composite materials to 2.3 eV due to the formation of bonds between Ti and the heteroatoms. In photocatalytic tests under visible light and dynamic conditions, ethylene was easier to remove than toluene, and co-doped materials exhibited better performance, particularly under dry conditions. Notably, the SN-TiO₂ sample showed the highest activity and its combination with S- and N-doped xerogels significantly improved catalytic efficiency even under humid conditions due to an increase in hydrophobicity, achieving notable gains in terms of turnover frequency (TOF).