Chunsheng Lei

Superb adsorption capacity of hierarchical calcined Ni/Mg/Al layered double hydroxides for Congo red and Cr(VI) ions

The preparation of hierarchical porous materials as catalysts and sorbents has attracted much attention in the field of environmental pollution control. Herein, Ni/Mg/Al layered double hydroxides (NMA-LDHs) hierarchical flower-like hollow microspheres were synthesized by a hydrothermal method. After the NMA-LDHs was calcined at 600°C, NMA-LDHs transformed into Ni/Mg/Al layered double oxides (NMA-LDOs), which maintained the hierarchical flower-like hollow structure. The crystal phase, morphology, and microstructure of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy elemental mapping, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption methods. Both the calcined and non-calcined NMA-LDHs were examined for their performance to remove Congo red (CR) and hexavalent chromium (Cr(VI)) ions in aqueous solution. The maximum monolayer adsorption capacities of CR and Cr(VI) ions over the NMA-LDOs sample were 1250 and 103.4mg/g at 30°C, respectively. Thermodynamic studies indicated that the adsorption process was endothermic in nature. In addition, the addition of coexisting anions negatively influenced the adsorption capacity of Cr(VI) ions, in the following order: CO32->SO42->H2PO4->Cl-. This work will provide new insight into the design and fabrication of advanced adsorption materials for water pollutant removal.

Synthesis of hierarchical porous zinc oxide (ZnO) microspheres with highly efficient adsorption of Congo red

Hierarchical porous zinc oxide (ZnO) was successfully synthesized via a facile hydrothermal method followed by calcination, and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption, and Fourier transform infrared spectroscopy analyses. The as-prepared porous ZnO exhibits microsphere morphologies with diameters of 6-8μm, which are assembled from two-dimensional nanosheets. The as-prepared hierarchical porous ZnO microspheres possessed high specific surface areas (57m2/g), and were evaluated for adsorption of Congo red (CR) in aqueous solution. The adsorption kinetics data were described by the pseudo-second-order kinetics and intraparticle diffusion models, while the equilibrium adsorption data were well fitted to the Langmuir model, with a maximum adsorption amount of 334mg/g. The as-prepared hierarchical porous ZnO exhibited higher CR adsorption capacity than commercial ZnO and various other materials, and thus could be an effective adsorbent for removal of anionic organic dyes from wastewater.

Hierarchical NiO–SiO2 composite hollow microspheres with enhanced adsorption affinity towards Congo red in water

Hollow microspheres and hierarchical porous nanostructured materials with desired morphologies have gained remarkable attention for their potential applications in environmental technology. In this study, NiO-SiO2 hollow microspheres were prepared by co-precipitation with SiO2 and nickel salt as precursors, followed by dipping in alkaline solution and calcination. The samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption, and X-ray photoelectron spectroscopy. The synthesized hollow spheres were composed of a SiO2 shell and hierarchical porous NiO nanosheets on the surface. Adsorption experiments suggested that NiO-SiO2 composite particles were powerful adsorbents for removal of Congo red from water, with a maximum adsorption capacity of 204.1 mg/g. The high specific surface areas, hollow structures, and hierarchical porous surfaces of the hollow composite particles are suitable for various applications, including adsorption of pollutants, chemical separation, and water purification.

Hierarchically porous NiO–Al2O3 nanocomposite with enhanced Congo red adsorption in water

Congo red (CR) has been widely used in the textile industry. However, the discharge of wastewater containing CR is a subject of great concern with regard to environmental protection. Herein, NiO, Al2O3, and NiO–Al2O3 nanocomposite adsorbents with hierarchical porous structures were prepared by a simple solvothermal method. Adsorption removal of CR dye from aqueous solutions was investigated using the prepared samples as adsorbent, which had hierarchical porous structures composed of mesopores (2–50 nm) and macropores (>50 nm). The equilibrium adsorption data of CR on the NiO–Al2O3 samples were well fitted by the Langmuir model and yielded a maximum adsorption amount of 357 mg g−1, which was higher than that of NiO and Al2O3 samples. The high adsorption of the NiO–Al2O3 nanocomposite sample was caused by the synergic effect of its hierarchical porous structures, high specific surface area, and positive surface charge at pH 7. Adsorption kinetic data could be well fitted by the pseudo-second-order kinetic equation, suggesting that pseudo-second-order kinetics could well represent the adsorption kinetics of the NiO–Al2O3 samples. The calculated activation energy needed by NiO–Al2O3 samples to adsorb CR indicated that the adsorption of CR molecules on NiO–Al2O3 sample was facilitated by physical adsorption process.

Organic dye removal from aqueous solutions by hierarchical calcined Ni-Fe layered double hydroxide: Isotherm, kinetic and mechanism studies

Hierarchically porous nickel-iron-layered double hydroxide (NiFe-LDH) with a Ni2+/Fe3+ molar ratio of 3 was successfully synthesised through a simple hydrothermal route. After calcination at 400°C, NiFe-LDH transformed into nickel-iron-layered double oxides (NiFe-LDO). The as-prepared samples were characterised through X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption. The calcined and uncalcined NiFe-LDH was used as adsorbents to remove Congo red (CR) dye in an aqueous solution. The equilibrium adsorption data of NiFe-LDH and NiFe-LDO samples were well fitted to Langmuir model and were characterised by excellent adsorption capacities of 205 and 330mg/g, respectively. Pseudo-second-order kinetic and intra-particle diffusion models indicated that CR was well adsorbed on the adsorbent. The underlying adsorption mechanism was investigated and observed as anion exchange and reconstruction.