Fabrication of hierarchical porous ZnO/NiO hollow microspheres for adsorptive removal of Congo red

摘要

Graphical abstractDisplay OmittedHighlights•Hierarchical porous ZnO/NiO hollow microspheres prepared by a hydrothermal process.•Hierarchical porous ZnO/NiO hollow microspheres show high adsorption for Congo red.•The bimetallic oxide microspheres show enhanced CR adsorption than single oxide.AbstractHierarchical porous zinc oxide (ZnO)ickel(II) oxide (NiO) hollow microspheres were fabricated by a facile hydrothermal approach and subsequent calcination process. The synthesized samples were used as adsorbent for removing Congo red (CR), a commercial azo dye. The synthesized hierarchical porous ZnO/NiO composites exhibit a superior adsorption capacity for CR (518 mg/g), compared with pure NiO (397 mg/g) and ZnO (304 mg/g). The high CR adsorption capacity of ZnO/NiO composites was associated with its hierarchical porous hollow structures and large specific surface area (130 m2/g), which provide a large quantity of active sites for CR molecules. The adsorption kinetics data were perfectly fitted to a pseudo-second-order model. The isotherms were accurately described by the Langmuir model. The results suggest that the as-prepared hierarchical porous ZnO/NiO composites are a highly efficient adsorbent for treating organic dye-impacted wastewater.