Adsorption performance of Ba2Mg(BO3)2 for selective removal of anionic dye Acid Orange 7: Kinetics, isotherm, and thermodynamics investigations

Abstract

Crystalline Ba₂Mg(BO₃)₂ powders were synthesized via the solution combustion technique, and their potential as a novel and effective adsorbent for the removal of Acid Orange 7 (AO7) from aqueous solutions was systematically evaluated. Post-synthesis characterization of the material's morphology and structure was conducted using FTIR, XRD, and SEM-EDS analyses. A series of batch adsorption experiments was performed to assess the influence of operational parameters, including adsorbent dosage, contact time, pH, initial AO7 concentration, and temperature. The optimum adsorption performance was achieved at pH 5, with a contact time of 60 min, an adsorbent dosage of 1.5 g/L, and a temperature of 25 °C. The highest adsorption capacity of Ba₂Mg(BO₃)₂ for AO7 was determined as 263.157 mg/g. Among the tested models, the Freundlich isotherm and the pseudo-second-order kinetic model provided the best fit to the experimental data, indicating multilayer adsorption on a heterogeneous surface and chemisorption as a rate-controlling step. Kinetic analyses revealed that both film diffusion and intraparticle diffusion contributed to the overall adsorption process. The adsorption mechanism involved a combination of physical and chemical interactions between the dye molecules and the adsorbent surface. Thermodynamic analysis indicated that the adsorption process was exothermic, spontaneous, and thermodynamically favorable. Furthermore, reusability assessments demonstrated the stability and efficiency of Ba₂Mg(BO₃)₂, maintaining a removal efficiency of 61.05 % after six successive adsorption–desorption cycles. These findings highlight the considerable potential of Ba₂Mg(BO₃)₂ as an effective adsorbent for the elimination of anionic azo dyes from aqueous environments.