Application of Ba₃(PO₄)₂/Fe₃O₄ as a novel magnetic adsorbent to remove methyl blue from aqueous solution

A novel magnetic composite adsorbent composed of Ba₃(PO₄)₂ nanoflakes and Fe₃O₄ microsphere (BPF) was prepared. The morphology, chemical structure, and magnetic property of BPF were characterized. Adsorption of methyl blue (MB) onto BPF was investigated with respect to pH, temperature, dosage, adsorption time, and initial MB concentration. Kinetics data and adsorption isotherm were better fitted by pseudo-second-order model and Langmuir equation, respectively. The high adsorption capacity of MB by BPF composite was 334.5 ± 12.5 mg g⁻¹. The values of activation parameters such as free energy (ΔG, −4.25 ± 0.16 mol⁻¹ to −6.06 ± 0.12 kJ mol⁻¹), enthalpy (ΔH, −24.93 ± 1.50 kJ mol⁻¹), and entropy (ΔS, −60.29 ± 3.20 J mol⁻¹ K⁻¹) were determined, indicating that the adsorption was spontaneous, favorable, and exothermic in nature. The removal of MB was attributed to the hydrogen bond and ionic interactions. Moreover, BPF was easily recovered, and the adsorption capacity was approximately 92 % of the initial saturation adsorption capacity after being used five times.