Kinetic modeling: dependence of structural and sorption properties of ZnO—crucial role of synthesis

Zinc oxide nanoparticles were synthesized by two different routes namely pyrolytic and gel combustion methods and characterized using different techniques like XRD, TGA/DSC, diffuse reflectance spectrophotometry, zeta potential, NMR and IR. The efficiency of the nanoparticles with respect to sorption of different toxic species like chromate and rhodamine 6G was evaluated. The studies showed that the synthesis route adopted affects the characteristics of the nanoparticles, thus leading to the difference in sorption efficiency. The mechanism of sorption proposed was based on the different characterization studies and it was found that the sorption was not only an electrostatic interaction but can occur due to the presence of pores or some binding groups. The highly pH-dependent sorption efficiency of the nanoparticles is evident from the results, whereas their kinetics was described by a pseudo-second-order kinetic model and further explained by using Weber–Morris and Boyd models. The overall rate process appeared to be influenced by both external mass transfer and intraparticle diffusion. Considering the simplicity of the synthetic procedure and the possibility of a cost effective catalyst, the developed nanomaterials have great potential for applications in water treatment technologies.