Photocatalytic Performance of Na- and K-Doped and Undoped TiO2 for Phenoxyacetic Acid Degradation in Wastewater: A Comparative Study

Introduction: The degradation of persistent organic contaminants by photocatalysis has become a viable and effective wastewater treatment technique. TiO2 is widely studied, but its efficiency is limited by its wide band gap and poor visible light response. This study aimed to enhance the photocatalytic performance of TiO2 by doping it with sodium (Na) and potassium (K) for the degradation of phenoxyacetic acid under different light sources. Methods: In this study, sodium (Na) and potassium (K) doped as well as undoped TiO2 nanoparticles were synthesized via a modified sol-gel technique. XRD, FTIR, UV-DRS, SEM-EDS, and TEM-SAED methods were used to investigate the photocatalysts' structural, morphological, and optical characteristics. Under ultraviolet (UV), visible, and solar light irradiation, the synthetic materials' photocatalytic ability was examined for the degradation of phenoxyacetic acid (PAA) at acidic pH conditions. Results: Photocatalytic experiments demonstrated that Na-doped TiO₂ exhibited the highest degradation percentage under UV (50.42%) and visible light (37.87%), while K-doped TiO2 showed superior activity under solar irradiation (45.52%) at pH 3.4 (initial). Discussion: The study reveals that alkali metal doping enhances TiO2's photocatalytic activity by facilitating charge carrier separation and expanding light absorption into the visible spectrum, compared to undoped TiO2. These differences were attributed to variations in crystallite size (Nadoped TiO2: 11-16 nm and K-doped TiO2: 5-15 nm), band gap narrowing (Na-doped TiO2: 3.13 eV and K-doped TiO2: 3.14 eV), and light absorption properties induced by alkali metal doping. Conclusion: Na- and K-doped TiO2 showed superior photocatalytic efficiency compared to undoped TiO2, with degradation of PAA following pseudo-first-order kinetics, demonstrating the effectiveness of alkali metal doping for enhancing photocatalytic processes in wastewater treatment.