A facile approach to synthesize 3D flower-like hierarchical NiCo layered double hydroxide microspheres and their enhanced adsorption capability

Uniform flower-like hierarchical NiCo-layered double hydroxide (NiCo-LDH) microspheres were fabricated by a facile hydrothermal method via the hydrolysis of hexamethylenetetramine (HMT). The diameter of the microspheres and thickness of the NiCo-LDH nanosheets are about 5-6 mu m and 25 nm, respectively. The adsorption performance was estimated by the removal of methyl orange (MO) dye. The effects of Ni/Co mole ratios, adsorption time, initial dye concentration, pH and temperature on MO adsorption property were investigated. The results reveal that LDH with Ni/Co feeding ratio of 1:1 (Ni1Co1-LDH) possesses the best adsorptive ability, exhibiting a short equilibrium time (5-50 min) and an ultrahigh MO adsorption capability (497 mg/g). The faster removal process and the higher adsorption capacity of the flower-like Ni1Co1-LDH than that of the stonelike LDH is ascribed to the speedy transport and porous structure of the 3D microspheres. Besides, the MO uptake behavior of Ni1Co1-LDH can be well described by the Langmuir isotherm and pseudo-second-order model, indicative of a monolayer and chemical adsorption that jointly derives from surface adsorption and anion exchange. Overall, the flower-like NiCo-LDH is potential cost-effective adsorbents to remove dye in wastewater.