Facile synthesis of cobalt-iron layered double hydroxide and its derived mixed metal oxide for Congo red and Pb(II) remediation

Abstract

This study reports the synthesis of CoFe-LDH and its derived mixed metal oxide using the facile co-precipitation and calcination methods, respectively. Morphological and physicochemical characteristics were investigated with advanced characterization techniques. The influence of various parameters on Congo red (CR) retention by the prepared adsorbents was systematically evaluated in batch mode to achieve the best removal efficiency. Experimental findings showed significantly enhanced CR adsorption and kinetic performance of CoFe-LDH, consistent with its higher BET surface area (96.02 m2/g) compared to its calcined counterpart, CoFe2O4 (42.56 m2/g). The Langmuir isotherm and pseudo-second-order model were best in explaining the CR adsorption and kinetics of CoFe-LDH, with a maximum adsorption capacity of 204.50 mg/g at an optimal pH of 3 and a contact time of 60 min. Thermodynamic studies indicated the spontaneous, feasible, and exothermic nature of the adsorption process. Reusability testing revealed the retention of significant CR removal performance (>70%) across four consecutive cycles. The efficacy of prepared adsorbents was also explored for Pb(II) ions mitigation. Under studied conditions, the maximum adsorption capacity of CoFe-LDH for Pb(II) was found to be 86.57 mg/g compared to 22.25 mg/g in the case of CoFe2O4. These findings not only suggest the excellent potential of CoFe-LDH as an economic adsorbent for wastewater treatment but also provide novel mechanistic understanding of how structural transformation after calcination affects the adsorption performance of the adsorbent.