One-pot synthesis of MgAl layered double hydroxide/graphene oxide composite: application and process optimisation for lead removal

Abstract

The pervasive contamination of water resources by lead (Pb²⁺) poses serious environmental and health risks due to its toxicity, persistence, and bioaccumulation potential. In this work, we report a facile one-pot synthesis of a MgAl layered double hydroxide/graphene oxide composite (GOLDH) via co-precipitation and hydrothermal treatment, yielding a hierarchical hybrid material with enhanced surface area and abundant active sites for Pb²⁺ adsorption. The composite was systematically characterised by SEM, TEM, XRD, FTIR, Raman spectroscopy, BET surface area analysis, TG-DTA, and XPS, confirming the successful integration of LDH nanoplates onto GO sheets, increased interlayer spacing, and strong interfacial interactions. Response surface methodology (Box–Behnken design) was applied to optimise key process parameters—contact time, pH, adsorbent dosage, temperature, and initial Pb²⁺ concentration—revealing that pH and initial metal content significantly influence removal efficiency. Adsorption isotherms fit the Langmuir model best, with a maximum monolayer capacity (q_m) of 913.85 mg g⁻¹ at 323 K, while kinetic data follow a pseudo-second order mechanism (R² = 0.99), indicating chemisorption control. Thermodynamic Analysis showed spontaneous (ΔG⁰ < 0) and exothermic (ΔH⁰ = −19.3 kJ mol⁻¹) adsorption, alongside increased randomness at the interface (ΔS⁰ = +14.9 J mol⁻¹ K⁻¹). Post-adsorption XRD, FTIR, and XPS studies reveal a dual ion exchange mechanism within LDH layers and surface complexation with GO's oxygenated functional groups. These findings demonstrate that GOLDH is a highly effective, robust, and reusable adsorbent for lead removal in wastewater treatment applications.