Weiquan Cai

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.

Template-free synthesis of hierarchical spindle-like γ-Al2O3 materials and their adsorption affinity towards organic and inorganic pollutants in water

Hierarchical spindle-like γ-Al2O3 materials were prepared in the form of fray ended bundles of twisted nanoflakes by a non-template hydrothermal synthesis and sequential calcination route using aluminium nitrate or aluminium chloride as precursors and urea as precipitating agent. The microstructures, morphologies and textural properties of the resulting materials were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption techniques. It was found that the spindle-like γ-Al2O3 particles are composed of at least three levels of hierarchical organization: polycrystalline γ-Al2O3 at the nanoscale, oriented nanoflakes and uniform spindle-like assemblies. The hierarchical γ-Al2O3 particles prepared from aluminium nitrate show a slightly smaller size, fewer self-organized nanoplatelets and better textural properties than γ-Al2O3 prepared from aluminium chloride, due to the larger aqueous ionic radius of NO3− than that of Cl−. The reported experiments allowed us to propose the mechanism of formation of the spindle-like assemblies, which involves self-transformation of metastable amorphous aluminium hydroxide particles and their sequential cooperative assembly. The as-prepared γ-Al2O3 was found to be effective adsorbent for the removal of selective pollutants from wastewater as a result of its unique hierarchical structure and high specific surface area, indicating a promising potential of this material for environmental remediation.

Adsorption of N719 Dye on Anatase TiO2 Nanoparticles and Nanosheets with Exposed (001) Facets: Equilibrium, Kinetic, and Thermodynamic Studies

Anatase TiO(2) nanosheets (TiO(2) NS) with dominant (001) facets and TiO(2) nanoparticles (TiO(2) NP) with dominant (101) facets are fabricated by hydrothermal hydrolysis of Ti(OC(4)H(9))(4) in the presence and absence of hydrogen fluoride (HF), respectively. Adsorption of N719 onto the as-prepared samples from ethanol solutions is investigated and discussed. The adsorption kinetic data are modeled using the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations, and indicate that the pseudo-second-order kinetic equation and intraparticle diffusion model can better describe the adsorption kinetics. Furthermore, adsorption equilibrium data of N719 on the as-prepared samples are analyzed by Langmuir and Freundlich models; this suggests that the Langmuir model provides a better correlation of the experimental data. The adsorption capacities (q(max)) of N719 on TiO(2) NS at various temperatures, determined using the Langmuir equation, are 65.2 (30 °C), 68.2 (40 °C), and 76.6 (50 °C) mg g(-1), which are smaller than those on TiO(2) NP, 92.4 (30 °C), 100.0 (40 °C), and 108.2 (50 °C) mg g(-1), respectively. The larger adsorption capacities of N719 for TiO(2) NP versus NS are attributed to its higher specific surface areas. However, the specific adsorption capacities (q(max)/S(BET)) at various temperatures are 1.5 (30 °C), 1.6 (40 °C), and 1.7 (50 °C) mg m(-2) for TiO(2) NS, which are otherwise higher than those for NP, 0.9 (30 °C), 1.0 (40 °C), and 1.1 (50 °C) mg m(-2), respectively. The larger specific adsorption capacities of N719 for TiO(2) NS versus NP are because the (001) surface is more reactive for dissociative adsorption of reactant molecules compared with (101) facets. Notably, the q(max) and q(max)/S(BET) for both TiO(2) samples increase with increasing temperature, suggesting that adsorption of N719 on the TiO(2) surface is an endothermic process, which is further confirmed by the calculated thermodynamic parameters including free energy, enthalpy, and entropy of adsorption process. The present work will provide a new understanding on the adsorption process and mechanism of N719 molecules onto TiO(2) NS and NP, and this should be of great importance for enhancing the performance of dye-sensitized solar cells.

Effect of nonionic structure-directing agents on adsorption and structural properties of mesoporous alumina

Mesoporous aluminas (MAs) with tailored adsorption, framework, and surface basic–acidic properties were prepared using different structure-directing agents (SDAs) such as Brij®78, Pluronic F108, poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) B50-6600 and Vorasurf™ 504 block copolymers, which so far were not explored for the synthesis of this important material viasolvent evaporation-induced self-assembly (EISA) strategy. Thermogravimetry, Fourier transform infrared spectroscopy, small-angle X-ray diffraction, nitrogen adsorption, transmission electron microscopy, and CO2 and NH3 temperature programmed desorption techniques were used to characterize the samples studied. Depending on the SDAs and aluminium precursors used in the EISA process, the BET surface area, pore volume and the average pore size of the MA samples were tailored in the range of 300–433 m2 g−1, 0.33–1.07 cm3 g−1, and 2.7–11.5 nm, respectively. Importantly, the use of F108 as a SDA and aluminium isopropoxide as an aluminium precursor gave a highly ordered MA with a large pore volume of 1.07 cm3 g−1 and enlarged mesopores centering at 11.5 nm, which are larger than those reported for the P123 and F127 Pluronic block copolymer-templated MA samples. However, the use of F108 as the SDA and AlCl3 as the aluminium precursor resulted in disordered MA with much smaller mesopores centering at 2.7 nm, enhancing the adsorption affinity towards CO2 (1261 μmol g−1) and NH3 (350 μmol g−1). This study shows that the EISA strategy does not require a stringent selection of SDA, and that the F108 block copolymer is an excellent SDA for the preparation of MA with a large pore volume and high adsorption capacity towards CO2, which exceeds substantially the value obtained for conventional alumina samples and for the previously reported ordered MA prepared in the presence of P123 and F127, which are commonly used as SDAs.

Effect of structure-directing agents on facile hydrothermal preparation of hierarchical γ-Al2O3 and their adsorption performance toward Cr(VI) and CO2.

Hierarchical flower-like and sphere-like mesoporous γ-Al2O3 microparticles were successfully prepared by a facile hydrothermal method followed by a calcination process using sodium aluminate as aluminum source, urea as precipitating agent, and Pluronic F127 (EO106PO70EO106), polyacrylic acid sodium (PAAS), and mixed F127-PAAS as structure-directing agents (SDAs), respectively. Effects of the SDAs on the phase structure, morphology, textural properties, surface alkaline, and the adsorption performance toward Cr(VI) and CO2 of the as-prepared samples were comparatively studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N2 adsorption-desorption, CO2 temperature programmed desorption (CO2-TPD), and UV-Vis spectrophotometric method. The results indicate that the sphere-like γ-Al2O3 obtained by using F127 as the SDA shows the best adsorption performance toward Cr(VI) with a high adsorption rate of 95% and adsorption capacity of 5.7 mg/g when the adsorption reaches equilibrium for 4h at room temperature. However, the flower-like γ-Al2O3 obtained by using PAAS as the SDA has the biggest CO2 adsorption capacity of 1.04 mmol/g at room temperature. This work provides a simple and practical way to prepare potentially bifunctional γ-Al2O3 adsorbent for the removal of pollutants in water and air treatment from cheap sodium aluminate by using different SDAs.

Force field for ZIF-8 flexible frameworks: atomistic simulation of adsorption, diffusion of pure gases as CH4, H2, CO2 and N2

A full set of flexible force field parameters for ZIF-8 is presented, based on the AMBER, UFF parameters and the partial charges computed by the density-derived electrostatic and chemical charge method (DDEC). The parameters for the 2-methyl imidazole (MeIM) ring are adopted from the AMBER force field, while the van der Waals (VDW) parameters for organic linkers and metal centers were determined by rescaling the UFF parameters as e = 0.635eUFF and σ = 1.0σUFF to fit the CH4 adsorption isotherms obtained by Grand Canonical Monte Carlo (GCMC) simulations with the force field parameters to the experimental ones. The CH4 adsorption isotherms on four different structures of ZIF-8 at 298 K obtained by GCMC simulations are compared with the experimental data. The results show that the simulated CH4 adsorption isotherms on the ZIF-8 structure reported from the Cambridge Crystallographic Data Centre (CCDC) are closest to the ones on the ZIF-8 structure from the report of Moggach et al. To test our model, adsorption isotherms of CH4, H2, CO2 and N2 at different temperatures were computed using GCMC simulations, and the results were found to be in a good agreement with the experimental data. In the case of H2, the equilibrium configurations obtained by GCMC simulations were statistically analyzed with ad hoc code to get probability density distribution profiles. These profiles were transformed to visual slice images, which indicate that the preferential adsorption sites of H2 molecules in ZIF-8 are located close to the MeIM rings, where the host–guest VDW or electrostatic interactions are maximal, as revealed by the potential energy surfaces (PES). In addition, these force field parameters were confirmed to well reproduce the ZIF-8 structural properties including lattice constants, bond lengths and angles over a wide range of temperatures. The self-diffusivities at the specific loadings of adsorbed gases (CH4, H2 and CO2) in ZIF-8 were calculated by the mean squared displacement (MSD) method. It was found that our self-diffusivities of H2 are slightly higher than the ones in the literature, and our self-diffusivity of CO2 is as about three times as the one in the literature, due to the different partial charges and the effect of different force field parameters on framework shape and flexibility in our simulations.

DNA-mediated morphosynthesis of calcium carbonate particles

Calcium carbonate microspheres with different surface structures were successfully prepared by the reaction of sodium carbonate with calcium chloride in the presence of deoxyribonucleic acid (DNA) at room temperature. The as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) and fourier-transform infrared spectrometry (FTIR). The effects of concentration of DNA on the morphologies of the prepared CaCO(3) were investigated and discussed. The results show that the surface morphology or texture of CaCO(3) microspheres can easily be adjusted by varying the concentration of DNA. A critical implication was that DNA molecules could mediate the nucleation and growth of the inorganic phase and probably induce biomineralization in the biological system. This research may provide new insight into the control of morphologies of calcium carbonate and the biomimetic synthesis of novel inorganic materials.

Ultrahigh hydrogen storage capacity of novel porous aromatic frameworks

We proposed four novel porous aromatic frameworks (termed as PAF-322, PAF-324, PAF-332 and PAF-334) with low density and high free volume ratio, which were constructed by inserting a long and slim organic linker such as diphenylacetylene (DPA), 1,4-diphenyl-butadiyne (DPB), 1,4-bis (phenylethynyl) benzene (BPEB) or 1,4-bis (phenylbutadiynyl) benzene (BPBB) into each C–C bond of diamond. Then the hydrogen uptakes in these porous materials were predicted using grand canonical Monte Carlo (GCMC) simulations based on the force field derived from the first-principles calculations. The results show that these materials are the most promising candidates for hydrogen storage. Among the four novel PAFs, PAF-334 possesses the highest gravimetric hydrogen storage properties, which are a total gravimetric hydrogen uptake of 63.96 wt% at 77 K and 100 bar, and a excess gravimetric hydrogen uptake of 10.69 wt% at 77 K and 20 bar. In addition, the total gravimetric hydrogen uptake of these PAFs even at 243 K and 120 bar entirely exceeds the U.S. Department of Energys (DOE) 2015 gravimetric hydrogen storage target. In particular, the total gravimetric hydrogen uptake of PAF-334 at 298 K and 100 bar reaches 16.03 wt%, about three times the DOE target value.

Facile synthesis of boehmite/PVA composite membrane with enhanced adsorption performance towards Cr(VI).

A novel boehmite/PVA composite membrane (BPCM) with remarkably enhanced adsorption performance towards Cr(VI) was successfully synthesized from Al(NO3)3·9H2O using HAc as the peptizing agent via a facile sol-gel method. The physicochemical properties of the BPCM, the boehmite powder (BP) without PVA and a commercial boehmite powder (CBP) were comparatively characterized by XRD, TGA-DSC, FT-IR and XPS. Batch adsorption experiments showed that the adsorption performance of the BPCM is much better than those of BP and CBP. Its adsorption process was well described by the pseudo-second-order kinetic model, and its equilibrium data fit the Langmuir isotherm well with a maximum adsorption capacity of 36.41mgg(-1). Its interference adsorption experiment in presence of coexisting anions showed that SO4(2-) and HPO4(2-) have greater effect than those of the Cl(-), F(-), C2O4(2-) and HCO3(-). A three step action mechanism including adsorption of Cr(VI) anions, complexation between Cr(VI) anions and the functional groups on the surface of BPCM, and the reduction of Cr(VI) to Cr(III) was proposed to illustrate the adsorption process. This efficient film could be easily separated after adsorption, exhibiting great potential for the removal of Cr(VI) from aqueous solution, and other fields of environmental remediation.

Template-free synthesis of hierarchical γ-Al2O3 nanostructures and their adsorption affinity toward phenol and CO2

Hierarchical γ-Al2O3 nanostructures with tuneable morphologies including irregular nanoflake assemblies, melon-like nanoflake assemblies, flower-like ellipsoids, hollow core/shell and hollow microspheres were successfully synthesized for the first time via a facile template-free hydrothermal method using aluminium sulfate, aluminium chloride and aluminium nitrate as aluminium sources, respectively, and thiourea as precipitating agent. Their phase structures, morphologies, textural and basic properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), N2 adsorption–desorption and CO2 temperature programmed desorption (CO2-TPD). The results indicate that the thiourea, type of anion in the aluminium source and the molar ratio of thiourea to Al3+ play an essential role in the formation of the aforementioned hierarchical γ-Al2O3. A growth mechanism of chemically induced self-transformation followed by cooperative self-assembly to form hierarchical nanostructures was proposed. In contrast, the γ-Al2O3 hollow core/shell microspheres with average pore size of 14.3 nm obtained from aluminium sulfate show the highest adsorption capacity of 28 mg g−1 towards phenol at 25 °C. However, the hierarchical γ-Al2O3 obtained from aluminium chloride and aluminium nitrate with smaller average pore size of 5.2 nm and 5.4 nm, respectively, is more effective for CO2 capture. This study provides new insights into the design and synthesis of hierarchical nanostructures for environmentally relevant applications.