Selective Photodegradation of Alizarin Using Molecularly Imprinted Cu-Doped TiO₂ Photocatalysts

Abstract

The selective removal of dye contaminants from industrial wastewater remains a major challenge in environmental remediation. In this work, molecularly imprinted Cu-doped TiO₂ photocatalysts were synthesized via a sol–gel method using alizarin as a template molecule. The prepared photocatalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV–Vis diffuse reflectance spectroscopy (DRS). XRD analysis confirmed the formation of crystalline anatase TiO₂ with an average crystallite size of approximately 30–35 nm. FTIR spectra revealed characteristic Ti–O–Ti vibrations, indicating the formation of the oxide framework. DRS analysis demonstrated a red shift in the absorption edge after Cu doping, resulting in a reduction of band gap energy from 3.2 eV for pristine TiO₂ to 2.9, 2.7 and 2.5 eV for 0.1%, 0.5% and 1% Cu-doped TiO₂, respectively. Photocatalytic degradation experiments under visible light irradiation revealed that Cu-doped MIP-TiO₂ achieved 83.4% degradation of alizarin within 30 min. The degradation followed pseudo-first-order kinetics with an apparent rate constant of 0.061 min⁻¹, which was significantly higher than that of undoped TiO₂ (0.023 min⁻¹). The improved photocatalytic performance is attributed to the synergistic effects of Cu doping and molecular imprinting, which enhance selective adsorption of the target dye. These results demonstrate that molecularly imprinted Cu-doped TiO₂ photocatalysts are promising materials for selective dye degradation in wastewater treatment.