High adsorption capability and selectivity of ZnO nanoparticles for dye removal

In this study, the removal of both cationic dye (malachite green, called MG for short) and anionic dyes (acid fuchsin and Congo red, called AF and CR) by ZnO nanoparticles from aqueous solution was investigated. The adsorption process is dependent on pH and temperature. The adsorption for MG, AF, and CR is spontaneous and exothermic. The adsorption process can be well described by the pseudo-second-order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity is 2963, 3307, and 1554 mg/g for MG, AF, and CR in this work, respectively. Chemical precipitation, electrostatic attraction, and hydrogen bonding are mainly responsible for the binding mechanism. The used ZnO nanoparticles could be reused for five cycles without a significant loss of adsorption ability. Furthermore, the ZnO nanoparticles showed selective adsorption in the case of mixed dyes. Overall, we provide a highly effective and selective adsorbent with reusability in multi-dye adsorption system. (C) 2016 Elsevier B.V. All rights reserved.