Development of fly ash/melamine composites for crystal violate dye removal from aqueous media

Fly ash (FA) as a low-cost and easily obtainable by-product from thermal power plants is considered for the decontamination of inorganic and organic pollutants from wastewater. In this work, FA was grafted with melamine and the obtained composite was used for the adsorption of crystal violet (CV) from water. By modification of melamine, the surface of FA was enhanced with amide groups as effective binding groups for CV molecules and therefore achieved higher sorption capacity. The chemical and textural characteristics of the FA/Melamine composite were studied by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Factorial designing was used for evaluating optimum adsorption parameters. ANOVA analysis of the P-value of individuals and combined variables was significant due to a P-value of less than 0.05 and a higher F-value. Equilibrium results show a monolayer isotherm model by Langmuir isotherm model with a maximum CV uptake capacity of 487 mg g⁻¹ under optimized conditions (250 mg adsorbent dosage, 10 ppm concentration, 30 min contact time and pH 6.0). Kinetic studies revealed that CV removal was nominated by the pseudo-second-order (PSO) model. CV dye molecules were adsorbed onto FA/Melamine composite via electrostatic attractions dipole–dipole interactions and n-π stacking interactions. Furthermore, the obtained results exposed that the synthesized FA/Melamine composite can be assessed as a promising sorbent for CV dye removal with high adsorption capacity.