Synthesis of carboxylic graphene oxide‐carboxymethyl chitosan composite and its applications toward the remediation of U6+, Pb2+, Cr6+, and Cd2+ ions from aqueous solutions.

The current research work deals with the synthesis of a novel composite material of carboxylic graphene oxide‐carboxymethyl chitosan (COOH‐GO‐CMC) composite by ultrasound and microwave‐assisted processes. The composite was characterized by Fourier Transform Infra‐red spectroscopy, X‐ray Powder Diffraction, Raman Spectroscopy, Scanning Electron Microscopy, and X‐ray Photoelectron Spectroscopy. The synthesized composite was used to remove heavy toxic metal ions (HTMIs) such as uranium (U6+), lead (Pb2+), chromium (Cr6+), and cadmium (Cd2+) ions from aqueous solutions. The HTMIs removal study was carried out to verify the effects of pH, contact time, amount of adsorbent dose, initial concentration, and temperature. The linear and nonlinear Langmuir and Freundlich adsorption isotherms were fitted to the data of removal studies, and it was observed that the linear Langmuir adsorption isotherm (R2 > 0.99) was the best‐fitted model. The maximum adsorption capacities of COOH‐GO‐CMC were found to be 74.62, 416.66, 76.92, and 53.47 mg g−1 for U6+, Pb2+, Cr6+, and Cd2+ ions, respectively. The kinetics studies, including four types of models (linear and nonlinear pseudo‐first‐order, linear and nonlinear pseudo‐second‐order, Intraparticle diffusion, and Elovich kinetic models), were tested, and the results showed that the linear pseudo‐second‐order kinetics model (R2 > 0.99) was the best‐fitted model. The thermodynamic studies reveal that the adsorption of HTMIs is a spontaneous (ΔG < 0) and exothermic (ΔH < 0 and ΔS > 0) process in nature. [ABSTRACT FROM AUTHOR]