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

Abstract 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.