Guangqun Cao

A facile method to fabricate polystyrene/silver composite particles and their catalytic properties

Herein a facile method is developed for fabrication of polystyrene/silver (PS/Ag) composite particles based on colloid thermodynamics. In our system, once the silver nanoparticles are formed in the presence of PS microspheres, they will play the role of steric stabilizer and attach spontaneously onto the surface of PS microspheres to reduce the Gibbs free energy of the colloidal system. The resultant PS/Ag composite particles have been characterized extensively by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. The results indicate that the structure and morphology of the PS/Ag composite particles could be controlled easily by changing the molar ratio of sodium borohydride and silver nitrate. More significantly, the PS/Ag composite particles exhibit good catalytic activity and reusability at low catalyst concentration during the reduction of p-nitrophenol by sodium borohydride. Hence, it is expected that the as-prepared PS/Ag composite particles show promise and great potential for practical application in catalysis.

Determination of phthalates in food packing materials by electrokinetic chromatography with polymeric pseudostationary phase

Polymeric pseudostationary phase (PSP), formed by random copolymer poly (stearyl methacrylate-co-methacrylic acid) (P(SMA-co-MAA)), was used in electrokinetic chromatography (EKC) to separate 15 kinds of phthalates (PAEs). The organic solvent modifier is a key factor for the separation of PAEs. Without organic solvents, only four kinds of PAEs with smaller molecular weight could be separated in the running buffer containing 1% P(SMA-co-MAA). The other eleven kinds of PAEs with larger molecular weight could be separated within 25 min by adding 40% (v/v) methanol and 2% (v/v) 1-butanol in the running buffer. The linear ranges of 15 kinds of PAEs were between 2 and 200mg/L, and the limit of detection based on the ratio of signal to noise of 3 were between 1 and 3mg/L. The method was applied to determination of PAEs in 6 kinds of food packing materials. The recoveries were between 81% and 118% with the RSD less than 4%.

Facile and controllable synthesis of polystyrene/palladium nanoparticle@polypyrrole nanocomposite particles

Herein is reported a facile and controllable route for coating polystyrene (PS) particles with palladium nanoparticle@polypyrrole (PdNP@PPy) nanocomposites based on the “Swelling–Diffusion–Interfacial-Polymerization Method” (SDIPM). The formation of PdNP@PPy nanocomposites was achieved by using palladium chloride as the oxidant for pyrrole. The synthesized PS/PdNP@PPy nanocomposite particles were characterized extensively by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, and C, H, and N elemental microanalyses. Significantly, it is clearly found that highly dispersed PdNPs with small size are well embedded in the PPy shell. Moreover, the resultant PS/PdNP@PPy nanocomposite particles have a well-defined core/shell structure, and then the mass loading of PdNP@PPy nanocomposites on the surface of PS particles can be controlled simply by changing the weight ratio of pyrrole/PS. The synthesized PS/PdNP@PPy nanocomposite particles also show good catalytic activity and reusability in the reduction of p-nitrophenol by NaBH4.

Electrochemical sensor based on magnetic molecularly imprinted nanoparticles modified magnetic electrode for determination of Hb

A fast and selective electrochemical sensor for determination of hemoglobin (Hb) was developed based on magnetic molecularly imprinted nanoparticles modified on the magnetic glassy carbon electrode. The nanoparticles Fe3O4@SiO2 with a magnetic core and a molecularly imprinted shell had regular structures and good monodispersity. Hb could be determined directly by electrochemical oxidization with the modified electrode. A magnetic field increased electrochemical response to Hb by two times. Imprinting Hb on the surface of Fe3O4@SiO2 shortened the response time within 7min. Under optimum conditions, the imprinting factor toward the non-imprinted sensor was 2.8, and the separation factor of Hb to horseradish peroxidase was 2.6. The oxidation peak current had a linear relationship with Hb concentration ranged from 0.005mg/ml to 0.1mg/ml with a detection limit (S/N =3) of 0.0010mg/ml. The sensors were successfully applied to analysis of Hb in whole blood samples with recoveries between 95.7% and 105%.

Preparation of Pickering emulsions with short, medium and long chain triacylglycerols stabilized by starch nanocrystals and their in vitro digestion properties

Food-grade Pickering emulsions are receiving more attention in the development of new delivery systems in food and pharmaceutical areas. In this study, starch nanocrystals (SNCs) prepared via acid hydrolysis of waxy maize starches were used as food-grade particle emulsifiers, to stabilize three typical edible oils with different chain lengths of fatty acid: short, medium and long chain triacylglycerols (SCT, MCT and LCT, respectively). On increasing the SNC concentrations from 0.1 to 3.0 wt%, the droplet size of these three Pickering emulsions decreased until 1.0 wt%. At this concentration, these three emulsions showed high stability against Ostwald ripening (for SCT) and coalescence (for MCT and LCT) for 90 days at 25 °C. However, the in vitro digestion properties of these three emulsions were significantly different. The rate of lipid digestion increased in the order LCT MCT > SCT. The inverse relationship between lipid and SNC hydrolysis rates may be due to, with the higher rate of lipid hydrolysis, more SNCs being displaced from the interface which would decrease the surface areas to enzymes. At the same time, calcium in digesta may absorb to SNCs to reduce the digestibility. These results may provide information about the physical and digestive properties of food-grade Pickering emulsions of different chain length triacylglycerols.

Facile fabrication of a magnetically assembled colloidal photonic crystal film via radical polymerization

A facile, economical and practical technique to fabricate a magnetically assembled colloidal photonic crystal in a polyacrylamide hydrogel matrix was demonstrated by an instant radical polymerization. By taking advantage of the instantaneousness of magnetic assembly, magnetic colloids were successfully assembled into photonic crystal structures with tunable stop bands in aqueous solution. The Bragg diffraction color could be simply controlled by tuning the strength of the external magnetic field to achieve diffraction covering the entire visible spectrum. An appropriate amount of an ionic initiator, APS, was key in the radical polymerization of the photonic crystal hydrogel film. 0.3 mg mL−1 of APS was chosen, not only to allow a rapid formation of the polyacrylamide hydrogel, but also to avoid coagulation of these magnetic colloids in the hydrogel. Due to the significantly instantaneous properties of magnetic assembly and radical polymerization, coagulation of these magnetic assemblies owing to their long exposure time to an external magnetic field could be prevented. Therefore, a photonic crystal hydrogel film with a uniform diffraction color could be obtained. Notably, the flexible hydrogel film displayed obvious deformation responsiveness. The diffraction light got red-shifted as the level of deformation rose. The achievement in immobilization demonstrates the system to be a major stride toward practical applications in responsive photonic materials.

Electrokinetic chromatographic characterization of novel catanionic surfactants vesicle as pseudostationary phase.

A novel catanionic surfactants vesicle system composed of octyltriethylammonium bromide/ sodium dodecyl benzene sulfonate (C8NE3Br/SDBS) has been developed as pseudostationary phase (PSP) in EKC. The C8NE3Br/SDBS system possesses a large vesicle phase region and none of agglomeration phenomena appeared while mixing cationic and anionic surfactants at any molar ratio. Electrophoretic and chromatographic parameters including elution window, hydrophobic selectivity, polar group selectivity, and shape selectivity were characterized using the vesicle at molar ratio of C8NE3Br to SDBS of 3:7 as PSP. Compared with SDS micelles, the vesicle PSP possessed a wider elution window and a better selectivity. The retention behavior and selectivity differences between the novel vesicle and SDS micelles were evaluated through linear solvation energy relationship (LSER) analysis. Though the cohesiveness and the hydrogen bond acidity have greatest influences on the solutes retention and selectivity in both the vesicle and SDS micelle, the vesicle PSP demonstrated a higher hydrophobicity and a lower hydrogen bonding donating capability owing to compact bilayer structure of vesicle. Additionally, the vesicle system had a stronger hydrogen bond accepting capability than SDS micelle. Consequently, according to LSER analysis, the bigger coefficients for v, b, and a revealed the vesicle PSP had a better separation selectivity than conventional SDS micelle.

Colorimetric sensing of melamine using colloidal magnetically assembled molecularly imprinted photonic crystals

A visually perceptible, highly selective and structurally simple colorimetric sensor for melamine (MEL) based on colloidal magnetically assembled molecularly imprinted photonic crystals (MIPCs) has been constructed. The color of the MIPCs red-shifted significantly as the MEL concentration increased. The largest redshift could reach 200 nm, and the detection limit for MEL was 10−5 mg mL−1.

The effects of organic modifier on physicochemical and chromatographic characteristics of self-assembled micelle from poly (stearyl methacrylate-co-methacrylic acid) in electrokinetic chromatography.

In our previous work, organic solvents, especially 1‐butanol, play a key role to separate highly hydrophobic analytes in EKC using the polymeric micelle self‐assembled from amphiphilic random copolymer poly (stearyl methacrylate‐co‐methyl acrylic acid) (P(SMA‐co‐MAA)) as a novel pseudostationary phase. Herein, the influences of organic solvents on polymeric micelle physicochemical properties including environmental micropolarity and dimension, as well as chromatographic characteristics containing elution window, hydrophobic selectivity and polar group selectivity were investigated in detail. P(SMA‐co‐MAA) has extremely low CMC of 1.26 × 10−6 g/mL, and the self‐assembled micelles with selective solvent method had regular spherical structure with diameter about 50 nm. The experimental results showed that methanol, isopropanol or acetonitrile molecules could not penetrate into the interior of the polymeric micelles, and mainly affected the properties of surrounding running buffer. Too much these organic solvents led to elution window narrowed down, methylene selectivity and group selectivity weaken, even the micelles collasped. Whereas, addition of 2% 1‐butanol did not influence the elution window, instead, improved the hydrophobic selectivity. Furthermore, both better group selectivity and faster migration for relatively hydrophobic analytes could be achieved simultaneously. It indicated that 1‐butanol could insert into the polymeric micelle and 2% 1‐butanol was enough to modify the structure of the micelles.

Viscoelastic system from mixing cetyltrimethylammonium bromide and poly(styrene-co-methacrylic acid) in aqueous solution

A viscoelastic system was developed by forming hybrid wormlike micelles with poly(styrene-co-methacrylic acid) (P(St-co-MAA)) and cetyltrimethylammonium bromide (CTAB) in aqueous solution. The molar monomer ratio of St to MAA in the copolymer and the mixing ratio (r) of P(St-co-MAA) to CTAB were the two key factors to obtain the viscoelastic system. Phase behaviors of P(St-co-MAA)/CTAB aqueous solutions as the functions of the monomer ratio in the copolymer, as well as the mixing ratio were investigated. It was found that there was no phase separation in any mixing ratios as monomer ratio of 6 : 4 and 7 : 3. On the other hand, the biggest viscosity was observed as the molar ratio of phenyl group in copolymer to CTAB was close to 1, rather than at charge stoichiometry between MAA and CTA+. It is found that as r between 1.0 and 1.24 and the monomer ratio of St to MAA at 7 : 3, the mixing system had the largest viscosity. The effects of the total concentration of the mixture system, the salt concentration, the temperature, and the shear rate on the viscosity were studied in detail. The experimental results showed that the complex system had excellent thickening property even the copolymer concentration as low as 0.90% (w/v), good electrolyte tolerance as inorganic salt concentration lower than 1.8 M, and acceptable heat-resistance at room temperature. The complex system had a potential application as the thickeners in various fields.