Highly efficient adsorbent for removal of Crystal Violet Dye from Aqueous Solution by CaAl/LDH supported on Biochar

Abstract

This work presents the development of a novel highly efficient adsorbent produced from CaAl/LDH supported on biochar chemically activated with phosphoric acid [CaAl/Biochar(H₃PO₄)] in order to maintain a great adsorbent capacity and prevent LDH disintegration. Its adsorptive efficiency was compared to an adsorbent formed from CaAl/LDH supported on untreated biochar (CaAl/Biochar). Biochar was produced from the pyrolysis of Eucalyptus saligna sawdust. The adsorbents were applied to remove crystal violet (CV) dye from aqueous solutions in a batch adsorption process. The adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and scanning electron microscopy (SEM). Adsorption kinetics, isotherms and thermodynamics were evaluated. The characterization results suggested that the CaAl/LDH was successfully synthesized and supported on biochar. The results indicate that pH 8 was more suitable for CV dye adsorption, with an adsorptive capacity over 101 mg g⁻¹ for CaAl/Biochar(H₃PO₄). Furthermore, adsorption experimental data fitted well with the pseudo-second order kinetics model and the Freundlich isotherm model. It was obtained a maximum adsorption capacity of 496.55 mg·g⁻¹ at 50 °C. For CaAl/Biochar(H₃PO₄), the thermodynamic results revealed a favorable, spontaneous and endothermic process. In addition, the results showed that the pre-treatment of the biochar with phosphoric acid maintained 71% of the initial adsorptive capacity even after four cycles of reuse. Therefore, CaAl/Biochar(H₃PO₄) is a sustainable adsorbent with high performance for CV contaminated wastewater treatment and groundwater remediation.