Strategic nitrogen doping of Ca-TiO2 photocatalyst for improved dye degradation under UV–Vis irradiation

Calcium and nitrogen co-doped titanium dioxide (Ca-TiO 2 @N) photocatalyst was successfully synthesized via a two-step wet impregnation–hydrothermal method to enhance photocatalytic degradation of methylene blue (MB) under UV–Vis irradiation. Structural, morphological, and optical characterizations using XRD, SEM, EDX, FTIR, and diffuse reflectance spectroscopy confirmed successful incorporation of Ca and N into the TiO 2 lattice without altering the anatase phase, while promoting reduced particle size, increased surface porosity, and bandgap narrowing. The synergistic effect of Ca and N co-doping improved visible-light absorption, enhanced charge separation, and suppressed electron–hole recombination, leading to greater reactive oxygen species generation. Under optimal conditions, Ca-TiO 2 @N achieved 87.48% MB degradation and 67.92% total organic carbon removal within 180 min, following pseudo-first-order kinetics with a rate constant of 0.0114 min −1 , significantly outperforming pure and Ca-doped TiO 2 . The improved performance is attributed to bandgap reduction, defect-state formation, enhanced surface activity, and efficient charge transfer. These findings demonstrate that post-calcination nitrogen incorporation into Ca-doped TiO 2 is an effective strategy for developing stable, visible-light-responsive photocatalysts for sustainable textile wastewater treatment. • Two steps were used to synthesize the Ca-TiO 2 @N photocatalyst. • Nitrogen was doped into the Ca-TiO 2 photocatalyst through hydrothermal treatment. • Characterization results indicated that Ca and N were successfully incorporated into TiO 2 lattice. • Synthesis resulted in reduced bandgap energy and enhanced light absorption capacity. • Ca-TiO 2 @N photocatalyst achieved a maximum of 87.48% methylene blue degradation. • Both pure TiO 2 , N-TiO 2 and Ca-TiO 2 demonstrated lower activity than Ca-TiO 2 @N under similar conditions.