3.1. Chemical Fabrication of TiO2 Nanoparticles and N-Doped TiO2 Nanoparticles

In brief, TiO₂ nanoparticles were synthesized by a facile chemical method of co-precipitation. The reagents used were purchased from Sigma-Aldrich (St. Louis, MO, USA) and included titanium isopropoxide (97%), isopropyl alcohol (≥98%), nitric acid (70%) and ethanol (96%). The procedure of Shajudheen et al. [52] was followed after some modifications. Synthesis of undoped TiO₂ nanoparticles involved addition of 100 mL isopropyl alcohol to 15 mL titanium isopropoxide under continuous stirring for 30 min. 10 mL deionized water for hydrolysis was later added dropwise until white precipitates were obtained that were filtered and washed with deionized water and ethanol thrice. The precipitates were dried at 100 °C and grinded to a fine powder. Finally, calcination was done at 800 °C for 4 h.

In case of N-doped TiO₂ nanoparticles synthesis, 15 mL nitric acid as a nitrogen source was added to titanium isopropoxide mixture and it was vigorously stirred until dissolved. Later on, deionized water was added followed by the procedure similar to undoped synthesis of TiO₂ nanoparticles.