Adsorption behavior and mechanism of methyl blue on zinc oxide nanoparticles

The adsorption behavior and mechanism of methyl blue (MB) on zinc oxide (ZnO) nanoparticles were investigated in this work. The adsorption capacity of MB on the ZnO nanoparticles reached 10.70 ± 0.80 mmol/g, which was the highest among today’s adsorbents for removing MB. The adsorption process was independent of pH and temperature in the experimental range. The adsorption kinetics was elucidated by the pseudo-second-order model and exhibited 2-stage intra-particle diffusion model. The adsorption isotherm fitted well with the Temkin model. The calculated parameter from Temkin model indicated the adsorption process was spontaneous with a uniform distribution of binding energies. The mechanism studies by XPS analysis confirmed that ionic bonding between Zn2+ in Zn(OH)+ and sulfonic groups of MB was the major interaction between MB and ZnO nanoparticles. The adsorption for MB by ZnO nanoparticles was selective. This work indicates that ZnO nanoparticles are promising adsorbents for removal of MB from waste water.