Adsorptive Removal of Congo Red Dye From Aqueous Media Using Composite of Graphitic Carbon Nitride Nanosheet and the Biopolymer Alginate

Abstract

The removal of dyes from wastewater using stable adsorbents is well documented in numerous scientific reports. Therefore, this study aimed to evaluate a composite of graphitic carbon nitride nanosheet (g-C₃N₄NS) and the biopolymer alginate for the removal of Congo red (CR) dye from aqueous media. To address the challenges associated with the independent use of calcium alginate and g-C₃N₄NS in water, particularly regarding recovery issues, silica-coated magnetic nanoparticles (SMNPs) were incorporated into the composite. To achieve this objective, an alginate-based bioadsorbent was synthesized by crosslinking sodium alginate with calcium chloride in the presence of g-C₃N₄NS and SMNPs using an in situ method. Structural characterization was conducted using BET, TGA, TEM, FE-SEM, and EDX-Mapping analyses. Subsequently, the bioadsorbent was utilized to remove CR dye. The influence of various parameters, including initial concentration, contact time, adsorbent dosage, and pH, was subsequently investigated. According to the isotherm models, the linear Langmuir model exhibited a good fit to the experimental data for CR, indicating a maximum adsorption capacity of 68.03 mg g⁻¹ at pH 5 within 120 min. The synthesized composite has the potential to pave the way for novel applications in both organic and inorganic transformations, as well as in the physical or chemical remediation of diverse pollutants.