Optimization and suppression of photocatalysis in Al-doped TiO2 particles using fractional factorial design to enhance optical performance in light-emitting diodes encapsulation

Abstract

This study tackles the challenge of high photocatalytic activity in TiO₂, a limiting factor for its use as a filler in LED encapsulants, by doping it with aluminum. We used the Fractional Factorial Design to investigate the impact of five parameters on the photocatalytic and adsorption performance of Al-doped TiO₂ particles. Characterization (XRD, SEM, EDX, FTIR, TGA, and nitrogen adsorption-desorption analysis) confirms the synthesis of mesoporous particles predominantly in the rutile phase, with traces of anatase. Successful Al incorporation yielded minimized agglomeration and enhanced thermal stability with a 0 %–0.9 % weight loss range. Our findings demonstrated that Al doping significantly reduced photocatalytic and adsorption performance, achieving a 97 % suppression of photocatalytic activity. Under optimized conditions, with an Al concentration of 0.51 g/L, calcination temperature of 900 °C, catalyst dosage of 1.5 g/L, MB solution temperature of 33.3 °C, and a pH of 4. The Al-doped TiO₂ exhibited a photodegradation efficiency of 3 % and a rate constant of 0.0004 min⁻¹, compared to 88 % PE and 0.02313 min⁻¹ RC for pure TiO₂. Calcination temperature significantly influences photocatalytic activity, while catalyst dosage and pH are key for adsorption. Epoxy films with Al-doped TiO₂ particles showed higher transparency (85 %), a refractive index of 1.52, and the ASTM E313 Yellowness Index showed lower yellowing (YI 5) after UV exposure compared to TiO₂ films (YI 7). The optical bandgap was found to be 3.45 eV for the pure epoxy film, slightly reduced to 3.39 eV with TiO₂ incorporation, and restored to 3.45 eV with Al-doped TiO₂, indicating that Al doping mitigates the bandgap reduction caused by TiO₂. These results make Al-doped TiO₂ particles promising for enhancing the application of TiO₂ materials in light-emitting diode devices.