Adsorption of Sudan II dye onto fly ash/polyacrylic acid/melamine composite: Factorial design optimization, reusability performance and removal mechanism

This study aims to develop fly ash (FA) modified with melamine (M) and polyacrylic acid (PAA) for strong adsorption of Sudan II dye from aquatic media. Surface functionality and morphological characteristics of the prepared FA/PAA/M composite were characterized using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) techniques. A factorial design model was applied to estimate the influence of adsorption and interactions of adsorption parameters such as contact time, pH, adsorbent dose, and initial dye solution. The significant interactions among these factors were investigated by analysis of variance (ANOVA). The isotherm modeling data indicated the Langmuir adsorption capacity for raw FA and FA/PAA/M composite as 57.4 and 142.3 mg/ g, respectively. This means that the Sudan II dye adsorption capacity of FA was boosted more than one time after modification with PAA/M polymer due to increased affinity towards the dye molecules by amide and hydroxyl groups onto the surface of the composite adsorbent. The adsorption kinetic evaluation revealed that the Sudan II dye adsorption by the composite was well-defined by the pseudo-second-order model. The produced FA/PAA/M showed a reasonable regeneration performance of 72/66 % after the adsorption/desorption processes were repeated four times. The adsorption mechanism between dye molecules and surface functional groups of the composite was described by hydrogen bonding interactions, π- π interactions, metal-π interaction and electrostatic attractions. The results indicated that the composite could be a promising adsorbent for dye removal from industrial wastewater due to its strong adsorption capacity, easy preparation, and good reusability performance.