Synthesis, characterization, and adsorption study of Congo Red on melamine-formaldehyde nanocomposite microspheres

Considering the carcinogenic and mutagenic properties of azo anionic dyes on the environment and human health, the development of efficient adsorbents for the removal of these water pollutants is very important. Therefore, the main aim of this research is to develop cost-effective and efficient melamine-formaldehyde (MF) microspheres for the removal of anionic dyes from wastewater. MF nanocomposite (MF-NGQD) microspheres were prepared using varying amounts of N-doped graphene quantum dots (NGQDs) through a simple polycondensation method. According to the SEM images, the MF-NGQD microspheres contain up to 10 wt% monodisperse, with an average diameter of 427 nm, which is smaller than the MF microspheres with a diameter of ⁓2.1 μm. The measurement of zeta potential (ZP) as a function of solution pH showed that the amount of ZP is significantly affected not only by the pH of the solution but also by the content of NGQDs in the microspheres. BET results revealed higher surface area and larger pore volume of nanocomposite microspheres (11.40 m² g⁻¹ and 0.030 cm³ g⁻¹) compared to MF microspheres (5.40 cm³ g⁻¹ and 0.017 cm³ g⁻¹). Batch adsorption experiments were carried out to investigate the adsorption properties of microspheres on Congo Red (CR). The results indicated that MF-NGQD microspheres with an amount of 0.05 g/25 mL were able to remove CR up to 97% at pH 6.0 with C₀ of 50 mg L⁻¹ in 45 min with an adsorption capacity of 91.74 mg g⁻¹. Adsorption processes were further analyzed through isotherm and kinetic studies, which showed a better fit with the Freundlich model and pseudo-second-order model, respectively. In conclusion, our finding demonstrates that MF-NGQD-10 microspheres are highly effective adsorbents for the removal of anionic dyes such as Congo Red from textile effluents, offering a promising solution for wastewater treatment. Future studies should explore the scalability and real-world application of these microspheres.

Graphical abstract