Yao Le

Synthesis of hierarchical Ni(OH)2 and NiO nanosheets and their adsorption kinetics and isotherms to Congo red in water

Ni(OH)(2) and NiO nanosheets with hierarchical porous structures were synthesized by a simple chemical precipitation method using nickel chloride as precursors and urea as precipitating agent. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy and nitrogen adsorption-desorption isotherms. Adsorption of Congo red (CR) onto the as-prepared samples from aqueous solutions was investigated and discussed. The pore structure analyses indicate that Ni(OH)(2) and NiO nanosheets are composed of at least three levels of hierarchical porous organization: small mesopores (ca. 3-5 nm), large mesopores (ca. 10-50 nm) and macropores (100-500 nm). The equilibrium adsorption data of CR on the as-prepared samples were analyzed by Langmuir and Freundlich models, suggesting that the Langmuir model provides the better correlation of the experimental data. The adsorption capacities for removal of CR was determined using the Langmuir equation and found to be 82.9, 151.7 and 39.7 mg/g for Ni(OH)(2) nanosheets, NiO nanosheets and NiO nanoparticles, respectively. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The results indicate that pseudo-second-order kinetic equation and intra-particle diffusion model can better describe the adsorption kinetics. The as-prepared Ni(OH)(2) and NiO nanosheets are found to be effective adsorbents for the removal of Congo red pollutant from wastewater as a result of their unique hierarchical porous structures and high specific surface areas.

Preparation and enhanced photocatalytic activity of Ag@TiO2 core–shell nanocomposite nanowires

Ag@TiO(2) core-shell nanocomposite nanowires were synthesized via a vapor-thermal method using Ag nanowires as templates and tetrabutyl titanate (TBOT) as precursors at 150 degrees C for 10h. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption isotherms. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature under UV-light irradiation. The results show that the Ag@TiO(2) core-shell nanowires exhibit highly efficient and recyclable photocatalytic activity for the degradation of RhB aqueous solution. Moreover, in contrast to the discrete nanoparticles, the Ag@TiO(2) nanowires can be readily separated from the treated solution by natural settlement after photocatalytic reaction.

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.

Fabrication and CO2 adsorption performance of bimodal porous silica hollow spheres with amine-modified surfaces

Carbon dioxide capture and storage (CCS) solutions have received enormous attention because CO2 is a primary greenhouse gas and plays a key role in global warming and climate change. In this work, bimodal meso-/macroporous SiO2 hollow sphere (BMSHS) samples with high specific surface areas were prepared by a hydrothermal method. Cetyltrimethylammonium bromide (CTAB) and perfluorododecanoic acid (PFDOA) were used as cotemplates and the CTAB/PFDOA weight ratio (R) was varied. The prepared samples were further modified with tetraethylenepentamine (TEPA), and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and N2 physisorption techniques. This was followed by CO2 capture tests using a pure CO2 stream in the temperature range of 35–130 °C. The results showed that all of the prepared samples contained small mesopores with a peak pore size of ca. 3–4 nm and larger mesopores or macropores with a peak pore diameter of ca. 103 to 117 nm. The mesopores and macropores are from the shell and the cavity of hollow spheres, respectively. The R exhibited a significant influence on the specific surface area, as the specific surface areas increased with increasing R. All of the TEPA-modified samples exhibited good CO2 adsorption abilities, which were related to the amount of loaded TEPA, adsorption temperature, and the specific surface areas of the samples. A optimal amount of TEPA loading (about 50 wt%) and adsorption temperature (about 110 °C) were determined. The CO2 adsorption amount increased proportionally with the specific surface area. The maximum CO2 adsorption amount (4.41 mmol g−1 adsorbent) was achieved on the BMSHS sample prepared at R = 40 and TEPA loading of 50 wt%. The present study provides new insight into the design and synthesis of novel porous materials for CO2 capture.

Amine-functionalized monodispersed porous silica microspheres with enhanced CO2 adsorption performance and good cyclic stability.

Carbon dioxide capture using solid adsorbent has caused more and more attention in the world. Herein, amine-functionalized monodispersed porous silica microspheres (MPSM) were prepared by the hydrolysis and condensation of tetraethoxysilane (TEOS) in a water-ethanol-dodecylamine mixed solution, then calcined at 600°C, and finally functionalized with tetraethylenepentamine (TEA). The CO2 adsorption performance of the prepared samples was measured using a Chemisorb 2720 pulse chemisorption system (Micromeritics, USA). The results showed that the specific surface area and pore volume of the 600°C-calcined SiO2 microspheres reached 921m(2)/g and 0.48cm(3)/g, respectively. All the TEA-functionalized samples exhibited good CO2 adsorption performance, which were related to the amount of loaded TEA, adsorption temperatures, and the specific surface areas of the prepared samples. An optimal TEA loading amount (34wt%) and adsorption temperature (75°C) were determined. The maximum CO2 adsorption amount (4.27mmolg(-1) adsorbent) was achieved on the 600°C-calcined SiO2 microsphere sample with TEA loading of 34wt%. Repeated adsorption/desorption cycle experiments revealed that the TEA-functionalized SiO2 microspheres were good CO2 adsorbents exhibiting excellent cyclic stability.

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.