Efficient removal of congo red dye using activated lychee peel biochar supported Ca-Cr layered double hydroxide

Abstract

Congo red is a known carcinogenic and mutagenic dye, so its presence in bodies of water is dangerous. The present work aims to synthesize and characterize a layered double hydroxide (LDH)-biochar composite and evaluate its application in the adsorption of Congo red dye (CR). CaCr/LDH was anchored over lychee activated biochar through coprecipitation. The composite was characterized using scanning electronic mapping (SEM), energy-dispersive spectrometer SEM (EDS-SEM), Fourier transform infrared (FT-IR), X-ray powder diffractometry (XRD) and Brunauer-Emmet-Teller (BET). The effect of pH, adsorption kinetics, isotherms, ionic strength, and thermodynamic parameters were evaluated. The pH results show a stable adsorption capacity in a useful range of pH (pH 4–9). Adsorption kinetics fitted the Elovich model, suggesting a heterogeneous system. The maximum adsorption capacity value (qe) calculated was achieved by applying the Sips model, with 631.1 mg g−1 at 50 °C. Ionic strength experiments show that the capacity increased with increasing NaCl concentration, which is desirable for real use as other ions are commonly present in dye wastewater. π-π interactions and hydrogen bonding seems to be involved in the adsorption mechanisms. CaCr-LDH/lychee biochar has better structure stability over several adsorption–desorption cycles with anionic exchange regeneration (in comparison with thermal regeneration), wide operational pH and high adsorption capacity. Therefore, this new composite presents a very good potential for the adsorption of dye from waste- or ground- water.