Congo Red Photodegradation using Magnesium Borate under UV Irradiation and Modelling by the Box Behnken Method

This study investigates, the photocatalytic potential of hydrothermally synthesised magnesium borate hydrate (Admontite, MgO·3B 2 O 3 ·7H 2 O) for the removal of Congo Red (CR), a persistent azo dye, from aqueous solutions under UV irradiation. The photocatalyst was synthesised via a simplified hydrothermal route and comprehensively characterised by X-Ray Diffraction (XRD), Fourier Transmission Infrared Spectroscopy (FT-IR), and Scanning Electron Microscopy (SEM) analyses, confirming the formation of a single-phase admontite structure with submicron, multi-angular morphology. The effects of photocatalyst dosage, irradiation time, and initial dye concentration on CR removal efficiency were systematically evaluated using a Box–Behnken response surface methodology. Statistical analysis demonstrated that the reduced quadratic model described the experimental data (R 2 = 0.9985, p < 0.0001). The maximum CR removal efficiency of 58.74% was achieved under optimal conditions of 0.10 g photocatalyst dosage, 60 min irradiation time, and 50 ppm initial dye concentration. Radical scavenging experiments revealed that superoxide radicals (O 2 − ·) played a dominant role in the photodegradation mechanism. These findings highlight magnesium borate hydrate as a cost-effective, environmentally benign, and structurally stable photocatalyst, offering a promising alternative for dye-contaminated wastewater treatment.