Synthesis, characterization, and application of riboflavin covalently functionalized graphene oxide (RF-GO composite) for selective removal of Cd2+

Abstract

Cadmium (Cd) pollution in water poses a serious environmental and health threat. GO composites exhibit significant potential as adsorbents for the removal of Cd²⁺ owing to their large surface area. However, their adsorption performances such as capacity, reusability, and selectivity can be further improved through rational functionalization. A novel RF-GO composite was fabricated through a facile covalent coupling method. The Cd²⁺ ion adsorption performance of the RF-GO composite was studied through batch adsorption experiments, and process parameter optimization including initial pH, temperature and contact time. The composite's structural morphology, surface functional groups, pore features, and thermal stability were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), specific surface area analysis (SSA), and thermogravimetric analysis (TGA). The RF-GO composite exhibited a higher adsorption capacity of 39.58 mg g⁻¹ for Cd²⁺ at pH = 8. The adsorption kinetics followed the pseudo-second-order kinetic model (R² = 0.995), demonstrating a chemisorption-dominated process. Equilibrium data were best fitted with the Langmuir isotherm model (R² > 0.97), suggesting the monolayer adsorption onto uniform active sites. Thermodynamic studies confirmed the endothermic and non-spontaneous nature of adsorption. Notably, the composite exhibited excellent reusability and structural stability, highlighting its potential as a sustainable and selective solution for Cd²⁺ removal from wastewater.