The limitations of TiO₂ as a photocatalyst such as the larger bandgap energy, which only activates under the UV region, give a lower photocatalytic activity. This study reports the role of the N and Pt co-dopant on the modification of the TiO₂ photocatalyst for photocatalytic degradation of methylene blue dye under different mode preparations, i.e., sequential and vice-versa modes. The sequential mode preparation of the N and Pt co-dopant TiO₂ photocatalyst consisted of the initial preparation of the N-doped TiO₂ (N-TiO₂) under the calcination method, which was then further doped with platinum (Pt) through the photodeposition process labeled as NP_seq-TiO₂, while the vice-versa mode was labeled as PN_rev-TiO₂. About 1.58 wt.% of N element was found in the NP_seq-TiO₂ photocatalyst, while there was no presence of N element detected in PN_rev-TiO₂, confirmed through an elemental analyzer (CHNS-O) and (EDX) analysis. The optimum weight percentage of Pt for both modes was detected at about ±2.0 wt.%, which was confirmed by inductively coupled plasma-emission spectroscopy (ICP-OES). The photoactivity under methylene blue (MB) dye degradation of the NP_seq-TiO₂ photocatalyst was 2 and 1.5 times faster compared to the unmodified TiO₂ and PN_rev-TiO₂, where the photodegradation rates were, ca., 0.065 min⁻¹ and 0.078 min⁻¹, respectively. This was due to the N elements being incorporated with the TiO₂ lattice, which was proven by UV-Vis/DRS where the bandgap energy of NP_seq-TiO₂ was reduced from 3.2 eV to 2.9 eV. In addition, the N generated a stronger PL signal due to the formation of oxygen vacancies defects on the surface of the NP_seq-TiO₂ photocatalyst. The higher specific surface area as well as higher pore volume for the NP_seq-TiO₂ photocatalyst enhanced its photocatalytic activity. Moreover, the NP_seq-TiO₂ showed the lowest COD value, and it was completely mineralized after 7 h of light irradiation. The preparation order did not affect the Pt dopant but did for the N element. Therefore, it is significant to investigate different mode preparations of the N and Pt co-dopant for the modification of TiO₂ to produce a good-quality photocatalyst for photocatalytic study under the photodegradation of MB dye.

Modification has been made to TiO₂ thin film to improve the wettability and the absorption of light. The sol-gel spin coating method was successfully used to synthesize GO/TiO₂ thin films using a titanium (IV) isopropoxide (TTIP) as a precursor. Different amounts of polyethylene glycol (PEG) (20 to 100 mg) were added into the parent sol solution to improve the optical properties and wettability of the GO/TiO₂ thin film. The effect of different amounts of PEG was characterized using X-ray diffraction (XRD) for the phase composition, scanning electron microscopy (SEM) for microstructure observation, atomic force microscopy (AFM) for the surface topography, ultraviolet–visible spectrophotometry (UV-VIS) for the optical properties and wettability of the thin films by measuring the water contact angle. The XRD analysis showed the amorphous phase. The SEM and AFM images revealed that the particles were less agglomerated and surface roughness increases from 1.21 × 10² to 2.63 × 10² nm when the amount of PEG increased. The wettability analysis results show that the water contact angle of the thin film decreased to 27.52° with the increase of PEG to 80 mg which indicated that the thin film has hydrophilic properties. The optical properties also improved significantly, where the light absorbance wavelength became wider and the band gap was reduced from 3.31 to 2.82 eV with the presence of PEG.

Polyaniline (PANI) and P-25 Titanium dioxide (TiO₂) was fabricated as immobilized P-25TiO₂/PANI/ENR/PVC film and reported on the photocatalytic study. PANI and TiO₂was immersed into the organic solvent and being coated onto glass plates under influenced of ENR/PVC polymeric binder by using a dip-coating method. It was found that, the removal of RR2 dye nearly good as suspension system after the pre-irradiation process. Based on COD and BET results, it showed that the optimum time of etching process was 7 hours irradiation time. This pre-irradiation process enhanced the removal of dye due to leached out of excessive binder and also exhibit visible light active after insertion of PANI into the immobilized system.

N doped titanium dioxide (TiO₂) was prepared under low temperature calcination of TiO₂ Degussa P25 powder and urea at various mixing ratios. Muffle furnace was used as heating media with the temperature used in the range of 300 to 500 °C. The prepared N doped TiO₂ was characterized by using UV-Vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). It was observed that N doped TiO₂ prepared at 0.5 g urea under the 400 °C calcination process (named as U2-400) is the optimum photocatalyst sample with the highest rate removal of Janus green B (JG) dye. The U2-400 had goes the photodegradation rate removal at 0.1071 min⁻¹ where it is 3.5 times faster compared to unmodified TiO₂ sample. The high photodegradation rate removal for U2-400 was due to the N incorporated with TiO₂ in U2-400 photocatalyst which narrowed the bandgap energy from 3.2 to 3.0 eV as observed by UV-Vis DRS spectra. This shows the U2-400 sample has increased its photocatalytic activity since it has become more active under wider an optical response compared to the unmodified TiO₂

The dye wastewater which directly discharges without treatment process will affect the environment. The semiconductor like titanium dioxide (TiO₂) has gained attention as most potential material for photocatalysis process to treat the dye wastewater with act as photocatalyst. However, this semiconductor has their limitation toward the photodegradation under visible light irradiation. In this study, TiO₂ has been modified by doping with nitrogen (N) to improve the effectiveness under visible light irradiation. This simple prepared N-doped TiO₂ was prepared by mixing of TiO₂ powder with urea as N precursor under microwave irradiation instead of using muffle furnace as heating media. The nitogen was chemically bonded with TiO₂ as proven by XPS analysis. N-doped TiO₂ sample show active under visible light irradiation due to lower band gaps energy of sample observed by UV/Vis-DRS. An active photo response under visible light was observed from N-doped TiO₂ with 80 minutes time irradiation to complete the reactive red 4 (RR4) color removal, while no photocatalytic degradation was observed from unmodified TiO₂ under the same irradiation.