Jiabin Zhou

Novel hollow microspheres of hierarchical zinc–aluminum layered double hydroxides and their enhanced adsorption capacity for phosphate in water

Hollow microspheres of hierarchical Zn-Al layered double hydroxides (LDHs) were synthesized by a simple hydrothermal method using urea as precipitating agent. The morphology and microstructure of the as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), nitrogen adsorption-desorption isotherms and fourier transform infrared (FTIR) spectroscopy. It was found that the morphology of hierarchical Zn-Al LDHs can be tuned from irregular platelets to hollow microspheres by simply varying concentrations of urea. The effects of initial phosphate concentration and contact time on phosphate adsorption using various Zn-Al LDHs and their calcined products (LDOs) were investigated from batch tests. Our results indicate that the equilibrium adsorption data were best fitted by Langmuir isothermal model, with the maximum adsorption capacity of 54.1-232 mg/g; adsorption kinetics follows the pseudo-second-order kinetic equation and intra-particle diffusion model. In addition, Zn-Al LDOs are shown to be effective adsorbents for removing phosphate from aqueous solutions due to their hierarchical porous structures and high specific surface areas.

Rattle-type Carbon−Alumina Core−Shell Spheres: Synthesis and Application for Adsorption of Organic Dyes

Porous micro- and nanostructured materials with desired morphologies and tunable pore sizes are of great interests because of their potential applications in environmental remediation. In this study, novel rattle-type carbon-alumina core-shell spheres were prepared by using glucose and metal salt as precursors via a simple one-pot hydrothermal synthesis followed by calcination. The microstructure, morphology, and chemical composition of the resulting materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N(2) adsorption-desorption techniques. These rattle-type spheres are composed of a porous Al(2)O(3) shell (thickness ≈ 80 nm) and a solid carbon core (diameter ≈ 200 nm) with variable space between the core and shell. Furthermore, adsorption experiments indicate that the resulting carbon-alumina particles are powerful adsorbents for the removal of Orange-II dye from water with maximum adsorption capacity of ~210 mg/g. It is envisioned that these rattle-type composite particles with high surface area and large cavities are of particular interest for adsorption of pollutants, separation, and water purification.

Hierarchically porous calcined lithium/aluminum layered double hydroxides: Facile synthesis and enhanced adsorption towards fluoride in water

Lithium/aluminum layered double hydroxides (Li/Al-LDHs) were synthesized via a facile hydrothermal route, using lithium and aluminum chloride mixed solutions with various molar ratios (Li+/Al3+ = 2, 3, 4, 5) as precursors and urea as a precipitating agent. The structure, morphology, and textural properties of the calcined Li/Al-LDHs (Li/Al-CLDHs) were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption-desorption. It was found that the three-dimensional petal-like Li/Al-CLDHs assemblies were constructed from hexagonal nanosheets with different sizes. The Li/Al-CLDHs contain three types of hierarchical porous organization such as small mesopores (ca. 4.5–10 nm), large mesopores (ca. 40–50 nm) and macropores (ca. 200–500 nm). The as-prepared Li/Al-CLDHs samples exhibit excellent adsorption capacity of 158.7 mg g−1 towards fluoride species in water. Thermodynamic and kinetic studies revealed that the adsorption process was spontaneous and endothermic in nature. Analyses by X-ray photoelectron spectroscopy confirmed that fluoride is distributed in the layer channel by ion exchange, physical adsorption as well as insertion into the host layer lattice during the rehydration process. The superior sorption capacity of Li/Al-CLDHs is attributed to the unique hierarchically porous structures and high specific surface areas.

Facile synthesis of alumina hollow microspheres via trisodium citrate-mediated hydrothermal process and their adsorption performances for p-nitrophenol from aqueous solutions

Alumina hollow microspheres with high adsorption affinity toward p-nitrophenol in water were prepared by using urea and trisodium citrate as precipitating and mediating agents, respectively, via a simple one-pot hydrothermal synthesis followed by calcination. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and nitrogen adsorption-desorption isotherms measurement. This study shows that the morphology, specific surface area, and the pore structure of the resulting materials can be controlled by varying the concentration of trisodium citrate. The result of adsorption of p-nitrophenol onto the as-prepared samples revealed that the pseudo-second-order kinetic equation can better describe the adsorption kinetics. Furthermore, adsorption isotherm studies indicated that the resulting alumina microspheres are powerful adsorbents for the removal of p-nitrophenol from water with maximum adsorption capacity of 217.4 mg/g.

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.

Carbon nanotube sponges as a solid-phase extraction adsorbent for the enrichment and determination of polychlorinated biphenyls at trace levels in environmental water samples

Carbon nanotube (CNT) sponges has recently attracted considerable attention in numerous fields because of its excellent properties, such as high porosity, light weight, and large surface area. The potential of CNT sponges for the solid-phase extraction (SPE) of organic pollutants at trace levels was investigated in this study for the first time. Seven polychlorinated biphenyls (PCBs) were selected as analytes, and gas chromatography-tandem mass spectrometry was employed for the detection. We optimized important parameters that may influence the efficiency of SPE, including the kind and volume of elution solvent, sample pH, and sample flow rate and volume. Under optimized conditions, low limits of detection (0.72-1.98ngL(-1)), wide range of linearity (10-1000ngL(-1)) and good repeatability (2.69-6.85%, n=5) were obtained. CNT sponges exhibited higher extraction performance than other adsorbent materials under the optimized conditions. Real environmental water samples were analyzed, and satisfactory recoveries (81.1-119.1%) were achieved. All these results demonstrated that CNT sponges are suitable SPE material for the enrichment and sensitive determination of PCBs at trace levels.

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.

Hydrothermal Synthesis of Modified Hydrophobic Zn–Al-Layered Double Hydroxides Using Structure-Directing Agents and Their Enhanced Adsorption Capacity for p-Nitrophenol

Hollow microspheres of hierarchical ZnAl-layered double hydroxides (LDHs) were synthesized by a simple hydrothermal method using hexamethylenetetramine as precipitating agent, sodium dodecyl benzene sulphonate (SDBS) as surfactant and sodium tartrate, sodium citrate and sodium salicylate (SS) as structure-directing agents, respectively. Characterization results of the microspheres synthesized indicate that the modified ZnAl–LDHs formed a variety of morphologies, surface areas and pore volumes. The hierarchical porous ZnAl/SDBS–LDH prepared using SS possesses the highest surface area (128.9 m2/g) and the greatest pore volume (0.37 cm3/g). A possible formation mechanism of the special three-dimensional nanostructures from the primary LDH nanosheet building units is proposed on the basis of the interaction between SS molecules and LDH crystals. The size of the channel height is approximately equal to the diameter of the intercalated anion SDBS, indicating that SDBS is in a vertical single-layer arrangement. using p-nitrophenol as model pollutant, the effects of initial concentration of p-nitrophenol and contact time on the adsorption of p-nitrophenol using various ZnAl–LDHs were investigated by performing a series of experiments. Results of these experiments indicate that the microsphere hydrophobic ZnAl/SDBS–LDH modified using SS has a maximum p-nitrophenol adsorption capacity of 101.6 mg/g.

Simultaneous determination of copper, cobalt, and mercury ions in water samples by solid-phase extraction using carbon nanotube sponges as adsorbent after chelating with sodium diethyldithiocarbamate prior to high performance liquid chromatography

Recently, a sponge-like material called carbon nanotube sponges (CNT sponges) has drawn considerable attention because it can remove large-area oil, nanoparticles, and organic dyes from water. In this paper, the feasibility of CNT sponges as a novel solid-phase extraction (SPE) adsorbent for the enrichment and determination of heavy metal ions (Co2+, Cu2+, and Hg2+) was investigated for the first time. Sodium diethyldithiocarbamate (DDTC) was used as the chelating agent and high performance liquid chromatography (HPLC) for the final analysis. Important factors which may influence extraction efficiency of SPE were optimized, such as the kind and volume of eluent, volume of DDTC, sample pH, flow rate, etc. Under the optimized conditions, wide range of linearity (0.5–400xa0μgxa0L−1), low limits of detection (0.089~0.690xa0μgxa0L−1; 0.018~0.138xa0μg), and good repeatability (1.27~3.60xa0%, nu2009=u20095) were obtained. The developed method was applied for the analysis of the three metal ions in real water samples, and satisfactory results were achieved. All of these findings demonstrated that CNT sponges will be a good choice for the enrichment and determination of target ions at trace levels in the future.