Adsorption of Congo red from aqueous solution using ZnO-modified SiO2 nanospheres with rough surfaces

As one of the toxic dyes, Congo Red (CR) is considered as emerging pollutant in surface water, thus, the development of novel adsorbent for its efficient removal is necessary. Here, ZnO/SiO2 nanosphere composites with rough surfaces were synthesized by a facile wet impregnation method. The structure and morphology of as-prepared composites were characterized and their performances toward CR adsorption were evaluated. The ZnO/SiO2-1 composite exhibited high adsorption capacity of ~ 83 mg/g and fast adsorption kinetic for removal of CR from aqueous solution. The adsorption kinetic and isotherm data could be well interpreted by the Pseudo-second-order rate equation and Langmuir adsorption isotherm, respectively. Moreover, the ZnO/SiO2-1 could be easily regenerated by calcination and the adsorption capacity could be maintained at high level (up to 83%) for at least 4 adsorption-regeneration cycles.