Controlled Laser-Induced Defect Engineering in TiO ₂ Enhances Charge Separation and Solar Driven Activity

Photoelectrochemical (PEC) water splitting is a clean method to produce hydrogen from visible light, but titanium dioxide (TiO2), a common semiconductor, faces challenges due to limited absorption of visible light and rapid recombination of charge carriers. Creating defects in TiO2 using laser irradiation has shown promise for improving its performance. However, the exact role of laser pulse duration on defect formation and resulting improvements in PEC and photocatalytic activity is not fully clear. This study investigates how femtosecond and nanosecond laser pulses affect TiO2 nanoparticles differently. The nanosecond laser causes bulk defects by heating, leading to a phase change from anatase to rutile, increased lattice disorder, and a significant reduction in bandgap (from 3.2 to 2.13 eV). In contrast, the femtosecond laser creates defects mainly on the surface without causing phase changes, keeping the anatase structure intact and slightly reducing the bandgap (to 2.9 eV). Despite having a higher bandgap, femtosecond-treated TiO2 nanoparticles showed better photocatalytic dye breakdown (51% degradation efficiency) and significantly improved PEC water splitting (66% higher photocurrent density compared to untreated TiO2). These improvements come from better separation of charges due to surface defects. The study highlights the importance of defect location and type, rather than just lowering the bandgap, to enhance TiO2 performance. This laser method provides a simple, accurate, and environmentally friendly way to control defects, helping improve solar hydrogen generation and pollution control applications.