Ultrasound assisted adsorptive removal of hazardous dye Safranin O from aqueous solution using crosslinked graphene oxide-chitosan (GOCH) composite and optimization by response surface methodology (RSM) approach

Chitosan (CH) was crosslinked with graphene oxide (GO) by combining solutions of CH and GO. Characterisations by ATR-FTIR, FE-SEM and XRD confirmed the formation of the GOCH composite. Removal of the dye Safranin Orange (SO) by ultrasonic adsorption from aqueous solution was tested by the composite. The removal of the cationic dye was more favourable at pH values greater than 5.2 and the optimum pH was found to be 6.5. The adsorption kinetics followed a pseudo-first order model and the rate-limiting step was identified as boundary layer diffusion from the Intraparticle diffusion model. The sonication assisted adsorption kinetic data were compared with the non-sonicated one and it was found that sonication has a marked effect on the adsorption kinetics. The Redlich Peterson adsorption isotherm described the adsorption with more resemblance to the Langmuir Model than the Freundlich Model suggesting that monolayer adsorption predominated. From Response Surface Methodology it was noted that the combined effect of pH and initial concentration was antagonistic while that of sonication time was synergistic. The optimum parameters from the RSM model were found to be pH 6.82, initial SO concentration 425 mg L−1 and sonication time 25 min. This was in good agreement with the experimental results.