Chestnut husk-like nickel cobaltite hollow microspheres for the adsorption of Congo red

Although many materials have been investigated for treating organic dye-containing wastewater, their practical applications are limited because of the high cost, secondary pollution or intricate synthesis method. Herein, magnetic nickel cobaltite (NiCo2O4) hollow microspheres were fabricated by a simple solvothermal method followed by calcination at relatively low temperature, and evaluated for adsorptive removal of Congo red (CR) from water. The electron microscopy images demonstrated that the as-synthesized NiCo2O4 sample had a morphology of chestnut husk-like hollow microspheres with diameters ranging from 4 to 5 mm, which were assembled with plentiful nanorods. Due to the hierarchical hollow structure and positive surface charge under neutral pH condition, the NiCo2O4 hollow microspheres displayed better adsorption capacity compared with single-metal oxides of nickel and cobalt. Intra-particle diffusion and the pseudo-second-order models could well interpret the sorption kinetics of NiCo2O4 hollow microspheres. Meanwhile, the Langmuir model could well explain the isotherm process, and the maximal adsorption quantity of NiCo2O4 was 366 mg g(-1). Moreover, the NiCo2O4 sample demonstrated fair recyclability, with a modest decline of the adsorption capacity after five cycle tests, even with a low regeneration temperature of 250 degrees C. These results imply the potential application of the as-synthesized NiCo2O4 hollow microspheres for the treatment of dye wastewater. (C) 2017 Elsevier B.V. All rights reserved.