Rapid synthesis of graphitic carbon nitride nanosheets as an efficient adsorbent for removal of Methylene Blue and Rhodamine B from Aqueous Solutions

Toxic dyes present in wastewater pose a severe threat to aquatic ecosystems, emphasizing the urgent need for eco-friendly and efficient remediation strategies. In this study, we report a novel rapid synthesis protocol for graphitic carbon nitride (g-C₃N₄) nanosheets via thermal polymerization of thiourea, followed by annealing in ambient air at 550 °C for two hours. The resulting g-C₃N₄ nanosheets were employed as adsorbents for the removal of methylene blue (MB) and rhodamine B (RhB) from aqueous solution. Comprehensive characterization using XRD confirmed the formation of a hexagonal crystalline phase, while FT-IR indicated the presence of nitrogen-rich heterocyclic structures. SEM and TEM images revealed the successful fabrication of few-layer nanosheets with edge thicknesses ranging from 6.9 to 20.88 nm. BET analysis demonstrated a Type IV porous structure with a surface area of 101.2 m²/g and an average pore diameter of 7.01 nm. Adsorption experiments utilizing 20 mg of g-C₃N₄ nanosheets at an initial dye concentration of 25 mg/L and a pH of 7.5 demonstrated a preferential affinity for RhB, achieving removal efficiencies of 99.80%, in contrast to 94.56% for MB. Kinetic and isotherm analyses revealed that dye adsorption conformed to the Freundlich and pseudo-second-order (PSO) models, indicating a spontaneous, endothermic process characterized by multilayer adsorption and increased interfacial disorder. Notably, the Freundlich isotherm predicted maximum adsorption capacities of 9.226 × 107 mg/g for RhB and 2.251 × 107 mg/g for MB, surpassing the estimations provided by alternative models. Reusability assessments demonstrated the g-C₃N₄ nanosheets maintained over 85% removal efficiency after five cycles, highlighting their potential as a sustainable, cost-effective solution for dye remediation in wastewater treatment.