Adsorption of crystal violet and malachite green onto dibarium magnesium orthoborate (Ba2Mg(BO3)2): equilibrium, kinetics and thermodynamics.

Dibarium magnesium orthoborate (Ba2Mg(BO3)2) is a borate based ceramic compound containing two different cations within its crystal structure. In this study, the synthesized Ba2Mg(BO3)2 was evaluated as an adsorbent for the removal of the cationic dyes malachite green (MG) and crystal violet (CRV) from aqueous solutions. The structural, morphological, surface and thermal properties of Ba2Mg(BO3)2 were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) surface area analysis, zeta-potential measurements and particle size analysis. Batch adsorption experiments were conducted to examine the effects of pH, initial dye concentration, adsorbent dosage, contact time and temperature on removal efficiency. The kinetic data were fitted to the pseudo-first-order (PFO), pseudo-second-order (PSO), and intra-particle diffusion models, with the PSO model providing the best fit for both dyes. Equilibrium data were evaluated using the nonlinear Langmuir, Langmuir Type II, Freundlich, Scatchard (Langmuir Type IV), and Temkin models. The nonlinear Langmuir model predicted q max values of 2283.835 and 2327.393 mg g-1 for MG and CRV, respectively. Under the investigated conditions, Ba2Mg(BO3)2 showed high removal performance for both MG and CRV. However, adsorbent induced aggregation can also contribute to dye removal.