Effects of Capping Agents on the Congo Red Adsorption of Ultrasonic-Assisted Synthesised Cobalt Aluminates

The spinel type of cobalt aluminate was achieved by an ultrasonic-assisted coprecipitation method. The morphologies of the cobalt aluminate nanoparticles were enhanced by the capping agent effect. The samples were characterised with the techniques of colour analyses, X-ray diffraction (XRD), UV-Vis spectroscopy, Brunauer-Emmett-Teller (BET), and scanning electron microscope (SEM). The characteristic blue colour of the powders was characterised by the b* values ranging from -42 to -51. The prepared compounds were identified as cubic forms of spinel (CoAl2O4). The BET analysis results indicated the highest surface area of 14.35 m2/g for the PVP-capped CoAl2O4. In comparison with the traditional methods, smaller particles were synthesised following the SEM analyses. The samples at different particle sizes and distributions were utilised in the removal of Congo red (CR) dye from wastewater by using a batch adsorption route. The sample prepared by the PVP capping agent was the most effective in CR adsorption. Among the applied isothermal and kinetic analyses, the adsorption mechanism could be explained by the Langmuir isothermal method (R2 = 0.9996 and RL = 0.7280) and the intraparticle diffusion kinetic model (R2 = 0.9650-0.9870).