Changfeng Zeng

Investigation on efficient adsorption of cationic dyes on porous magnetic polyacrylamide microspheres.

We report here the preparation of porous magnetic polyacrylamide microspheres for efficient removal of cationic dyes by a simple polymerization-induced phase separation method. Characterizations by various techniques indicate that the microspheres show porous structures and magnetic properties. They can adsorb methylene blue with high efficiency, with adsorption capacity increasing from 263 to 1977 mg/g as the initial concentration increases from 5 to 300 mg/L. Complete removal of methylene blue can be obtained even at very low concentrations. The equilibrium data is well described by the Langmuir isotherm models, exhibiting a maximum adsorption capacity of 1990 mg/g. The adsorption capacity increases with increasing initial pH and reaches a maximum at pH 8, revealing an electrostatic interaction between the microspheres and the methylene blue molecules. The microspheres also show high adsorption capacities for neutral red and gentian violet of 1937 and 1850 mg/g, respectively, as well as high efficiency in adsorption of mixed-dye solutions. The dye-adsorbed magnetic polyacrylamide microspheres can be easily desorbed, and can be repeatedly used for at least 6 cycles without losing the adsorption capacity. The adsorption capacity and efficiency of the microspheres are much higher than those of reported adsorbents, which exhibits potential practical application in removing cationic dyes.

Versatile Preparation of Nonspherical Multiple Hydrogel Core PAM/PEG Emulsions and Hierarchical Hydrogel Microarchitectures†

The preparation of nonspherical materials composed of separated multicomponents by droplet-based microfluidics remains a challenge. Based on polymerization-induced phase separation and droplet coalescence in microfluidics, we prepared emulsions of variously shaped PAM/PEG core/shell droplets and hydrogels composed of two separated components, which show flexible and transformable hierarchical structures and microarchitectures. We find that AM/PEG aqueous droplets form a core/shell structure after polymerization resulting from phase separation. Thus multicore/shell droplets are easily produced by coalescence of core/shell structures. By changing the polymerization temperature and the flow rate, the morphology of the multicore droplets and the hydrogel can be easily adjusted. The hydrogels exhibit apparent anisotropy and different protein release rates depending on their structures. The preparation technique is simple and versatile and the resulting hydrogels have potential applications in many fields.

Continuous generation of alginate microfibers with spindle-knots by using a simple microfluidic device

We developed a simple microfluidic-based method to fabricate calcium alginate microfibers with spindle-knots. A co-axial type microfluidic device installed with a micropipette at its outlet was used with a sodium alginate solution as the continuous phase and liquid paraffin as the dispersed phase. We examined the effect of the micropipette, its diameter, the dispersed phase to the continuous phase flow rate ratio and the physical properties of the oil used as the dispersed phase on the formation of the knots, the width and height of the knot, the interval between two adjacent knots, and the diameter of the fiber. Use of the micropipette is crucial to successful formation of the knots, as the oil phase microdroplets are deformed when flowing through it and retract after flowing out of it. The height and width of the knot increase and the interval decreases with increasing the flow rate ratio and the microdroplet diameter. The viscosity of the oil phase plays an important role in the successful formation of the knots. The alginate fibers with spindle-knots exhibit water collection capability. This method is expected to be used for the fabrication of other types of fibers with spindle-knots.

Hydrothermal synthesis of SAPO-5 with novel morphologies from hydrogels containing acetic acid and high concentration of triethylamine under neutral or alkaline conditions

SAPO-5 with novel morphologies was hydrothermally synthesized from neutral or alkaline hydrogels containing acetic acid and high concentration of triethylamine (TEA) at 180 °C for 48 h. Bullet-like, pine cone-like and disk-shaped crystals were prepared at the TEA/Al2O3 molar ratio of 14 and the HAc/Al2O3 molar ratios of 5–17. All the samples are constructed from flakes with thicknesses ranging from 100 to 300 nm stacked together to form various geometries. Their aspect ratio decreases with increase in the HAc/Al2O3 molar ratio. Substitution of HCl for HAc results in the formation of SAPO-5 with hexagonal disk flower-like morphology at a TEA/Al2O3 molar ratio of 14 and HCl/Al2O3 molar ratio of 4.3. The above SAPO-5 with novel morphologies contains mesopores and exhibits higher ratios of the amounts of the weak acid site to intermediate acid site than those of the conventionally synthesized SAPO-5. The effect of interaction between acetic acid and TEA on formation of the novel morphology is discussed.

Macro-kinetics of styrene oxidation catalyzed by Co2+-exchanged X

The macro-kinetics and pathway of styrene oxidation catalyzed by Co2+-exchanged X, using O2 as oxidant, were investigated. The effects of external diffusion, internal diffusion, the styrene concentration, O2 pressure, the catalyst concentration and the reaction temperature on the styrene oxidation reaction rate were examined. The results showed that the reaction rate of styrene oxidation was 0.19 order with respect to the styrene concentration, 0.64 order with respect to O2 pressure, and zero to first order with respect to the different catalyst concentration. The calculated activation energy for this reaction was 13.79 kJ/mol. On the other hand, the three products in the styrene oxidation reaction were, respectively, used as the reactant to examine the reaction pathway of styrene oxidation. The results revealed that styrene oxidation reaction occurred as two parallel reactions. One was the production of styrene oxide and the other was the production of benzaldehyde and formaldehyde with former partially oxidized to benzoic acid and the latter mostly oxidized to O2 and H2O.

Combinatorial synthesis of SAPO-34 via vapor-phase transport

By applying a combinatorial method, SAPO-34 was successfully synthesized via vapor-phase transport technique, and the synthesis factors were systematically examined.

Hydrothermal Synthesis of Pencil‐like SAPO‐5 and Observation of Its Reversed Crystal‐Growth Process

SAPO-5 with a novel hexagonal pencil-like morphology was hydrothermally synthesized from hydrogels that contain triethylamine and high concentrations of acetic acid at 180 °C for 48 h. The effect of the acetic acid concentration was examined and indicated that usage of a high concentration of acetic acid is crucial to the synthesis of SAPO-5 with a pencil-like morphology. The time-dependent growth process of novel SAPO-5 was observed by scanning electron microscopy with the aid of acid treatment to remove the amorphous materials for clearer observation. The samples were also characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. The results show that the crystal growth at the early stage follows the reversed crystal-growth route. First, the crystallization occurs on the surface of the aggregated amorphous ellipsoidal particles to form a hexagonal prism crystal shell with the encapsulation of amorphous materials. Then, the amorphous materials wrapped inside start to grow to a hexagonal prism inside the hollow larger hexagonal prism shell. Finally, the interior hexagonal prism continues to grow to the two ends with its length beyond that of the larger one by means of the Ostwald ripening process, thus forming the pencil-like crystal.

Investigation of the crystallization of zeolite A from hydrogels aged under high pressure

This paper investigates the influence of the aging of zeolite A hydrogel under high pressure on the synthesis of zeolite A. The effects of the aging pressure, aging time and type of gas are examined. The products are characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The results indicate that high-pressure aging leads to an increase in the nucleation rate, facilitating the formation of zeolite A with high crystallinity, small particle sizes and narrow particle size distribution. The type of gas also exerts an influence on the synthesis of zeolite A, as hydrogels aged under high pressure in a gas with a higher solubility in water can produce zeolite A with smaller particle sizes. Thus, by adjusting the aging pressure and the type of gas used, the size of the resulting zeolite A can be controlled. The mechanism of the high-pressure aging is related to the interaction of the gel with the dissolved gas. An influence of the aging of hydrogels on the syntheses of zeolite Y, silicalite-1 and SAPO-34 is also observed.

Controllable hydrothermal synthesis of 2D and 3D dendritic aluminum phosphate crystals

In this work, a controllable hydrothermal synthesis of two-dimensional (2D) and three-dimensional (3D) dendritic aluminum phosphate crystals was implemented from a recipe containing alumina, phosphate, nitric acid and triethylamine (TEA) with or without the addition of cetyltrimethylammonium bromide (CTAB). The 2D dendrite has a three-fold symmetrical structure with angles of 60° between the trunk and branches and the branch and leaves, while the 3D dendrite is assembled by trunks growing from the same central point and reaching in different directions with branches growing perpendicular to them. Interestingly, CTAB functioning as a crystal morphology modifier can change the dendritic structure from 2D into 3D. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and thermogravimetric analysis. Their morphologies and phase compositions are dependent on the concentration of the hydrogels and the crystallization temperature. Through a series of time-dependent morphological evolution studies, the growth process of the dendritic aluminum phosphates has been systematically investigated and the corresponding growth mechanism is proposed.