Efficient preparation and characterization of LDH/GCN based 3D foam for sustainable continuous column removal of U6+ and Cd2+ from water: mechanistic insights and application feasibility

Abstract

Industrial effluents discharge uranium (U⁶⁺) and cadmium (Cd²⁺) into water bodies, posing serious environmental risks. We investigated using a magnesium iron layered double hydroxide intercalated with carbon nitride (LDH/g-C₃N₄) foam for removing U⁶⁺ and Cd²⁺ from aqueous solutions. The adsorbent was characterized using advanced spectroscopic techniques, revealing carbonyl, metal–oxygen, C–NC, and N–O groups, with a BET surface area of 48.21 m² g⁻¹ and pore volume of 0.108 cm³ g⁻¹. Maximum adsorption capacities were 238.43 mg g⁻¹ for U⁶⁺ at pH 4 and 184.39 mg g⁻¹ for Cd²⁺ at pH 6 and 293 K. Adsorption followed pseudo-second order kinetics and Langmuir isotherms, with favorable thermodynamic parameters indicating spontaneous adsorption. The metal ions adsorption process involves co-ordination covalent and electrostatic (non-covalent) interactions between metal ions and LDH/g-C₃N₄ surfaces, enhanced by functional groups. Importantly, the foam retained substantial removal efficiency (>75%) even after three regeneration cycles using EDTA, showcasing excellent stability and reusability. Continuous fixed-bed column experiments further validated the material's practical feasibility, achieving prolonged breakthrough times (up to 32 days for U⁶⁺ and 28 days for Cd²⁺ at 10 cm bed height). Continuous fixed-bed column tests showed increased adsorption with bed height, highlighting the potential of LDH/g-C₃N₄ foam as an eco-friendly U⁶⁺ and Cd²⁺ removal adsorbent for industrial use. Moreover, the adsorbent maintained high removal efficiency in real groundwater spiked with contaminants, despite the presence of competing ions. These findings affirm the LDH/g-C₃N₃ foam as a scalable, recyclable, and eco-friendly adsorbent for sustainable remediation of metal-contaminated waters.