Competitive adsorption removal of indigo carmine and Congo red dyes from residual effluents by Zn2Al-LDH prepared by co-precipitation

ABSTRACT In this work, Zn 2 Al-LDH (layered double hydroxides) hydrotalcite was synthesized via co-precipitation method at pH = 9 and molar ratio Zn 2+ /Al 3+ of 2. The as-prepared LDH was characterized by X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, N2 adsorption–desorption isotherms, scanning electron microscopy, and pH (point of zero charge). The effective adsorption of Indigo carmine (IC) and Congo red (CR) from single and binary dye systems was assessed under various experimental keys parameters (adsorbent dosage, initial dye concentration, reaction time, pH solution, and temperature of the system). The First derivative spectrophotometric method was used to treat the adsorption data from the binary system. Results showed that the adsorption equilibrium of both dyes was reached within 60 min either in single or binary dye systems. The dynamical data of both dyes were well fitted with the pseudo-second- order kinetic model. All the explored temperatures showed that the adsorption process is endothermic and spontaneous. Besides, the equilibrium sorption data of dyes on both systems were well described with the modified Redlich–Peterson extended Freundlich and extended Sips. Zn 2 Al- LDH exhibited a greater affinity towards IC (162.87 mg/g) than that for the CR (25.11 mg/g) in a binary system. The adsorption mechanism was mainly monitored by electrostatic interactions between the positively charged LDH layer and negatively charged dyes molecules.