Daodao Hu

Preparation and properties of chitosan-poly(N-isopropylacrylamide) full-IPN hydrogels

A new kind of full-IPN chitosan/poly(N-isopropylacrylamide) (CS/PNIPAM) hydrogels was prepared by chemical combination of methylene bis-acrylamide (MBAM) cross-linked PNIPAM network with formaldehyde (HCHO) cross-linked CS network. It was demonstrated that the properties of the gels, including the extractability of PNIPAM within it, the phase transition behavior, the swelling dynamics in aqueous phase, the swelling behavior in ethanol/water mixtures and even the microstructure are quite different from those of the semi-IPN CS/PNIPAM hydrogels, in which PNIPAM was simply embedded. Like the semi-IPN CS/PNIPAM hydrogels, however, the new gel is also temperature sensitive, that is the gel is transparent below 30°C, whereas opaque above the temperature. It is expected that the finding of the new smart hydrogels may find some uses in separation science and in the design and preparation of new soft machines.

Preparation and properties of chitosan-poly(N-isopropylacrylamide) semi-IPN hydrogels

Chitosan (CS), CS-poly(N-isopropylacrylamide)(PNIPAM) and their dyed (pyrene) hydrogels were prepared using glutaraldehyde (Glu) as a crosslinker. The gelation rate, swelling behaviors in ethanol/water mixtures, electricity-induced contraction and thermoresponse of the gels were investigated using fluorescence probe technique. Results showed that CS/Glu, and PNIPAM-containing CS/Glu gels exhibited similar properties in all aspects examined, except that the transparence of the CS-PNIPAM/Glu gel is very dependent upon the temperature. The CS-PNIPAM/Glu gel is transparent below 30°C, whereas opaque above 32°C. It is expected that this observation may be useful for the design and preparation of new kinds of hydrogel devices.

Nano-magnetic particles as multifunctional microreactor for deep desulfurization.

Oxidation of dibenzothiophene with hydrogen peroxide using a recyclable amphiphilic catalyst has been studied. The catalyst was synthesized by surfacely covering magnetic silica nanospheres (MSN) with the complexes between 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (AEM) and phosphotungstic acid (PTA). The morphology and components of the composite material were characterized by TEM, EDX, XPS, FT-IR, and VSM, respectively. The effects of several factors on desulfurization reactivity were systematically investigated. The results showed that the composite nanospheres have core/shell structure with the properties of amphiphilicity and superparamagnetism. The composite nanospheres have high catalytic activity in the oxidation of dibenzothiophene to corresponding sulfones by hydrogen peroxide under mild reaction conditions. The sulfur level could be lowered from 487 ppm to less than 0.8 ppm under optimal conditions. Additionally, the amphiphilic catalyst and the oxidized product could be simultaneously separated from medium by external magnetism, and the recovered composite material could be recycled for three times with almost constant activity.

Composite microspheres with PAM microgel core and polymerisable surfactant/polyoxometalate complexes shell

The composite microspheres of poly(acrylamide) microgels (PAM) surfacely covered with [3-(acryloylamino)propyl]dodecyldimethyl ammonium-tungstophosphate complexes (APDDAB-PWA) were synthesized by using an ion-exchange reaction between APDDAB located within the porous PAM microgels and PWA in aqueous solution. The morphology and component of the composite microspheres were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis, respectively. The results indicated that PAM/APDDAB-PWA composite microsphere with different hierarchical surface structures could be obtained by controlling the weight ratio of APDDAB to PAM microgels, cross-linking degree of PAM microgels, the amount of PWA reacted with APDDAB in PAM/APDDAB, and solvent-washing process. Although the surface morphologies of the composite microspheres in detail were different, a general feature was of the core-shell structure and the wrinkly surface covered with APDDAB-PWA particles. The formation of the wrinkly surface is attributed to the difference in shrink between inside and outside of PAM microgel frameworks, and the formation of APDDAB-PWA small particles originates from the reaction between APDDAB aggregation and PWA. This composite microsphere with PAM hydrogel core is suitable to store water-soluble substances, and the shell composed of the surfactant/Keggin-type polyoxometalate complexes is not only amphiphilic but also catalytic. Additionally, PAM/APDDAB-PWA composite microspheres with big size and APDDAB-PWA particles with small size make the composite microspheres not only easy for separation but also beneficial for catalysis. These properties have been verified by the application of PAM/APDDAB-PWA composite microspheres to the deep desulfurization of fuel oil. This material provides an example to construct microreactors with new structure used in diphase catalytic reaction.

Preparation and nitromethane sensing properties of chitosan thin films containing pyrene and β-cyclodextrin units

Chitosan thin films, coated on a quartz plate surface, containing pyrene (Py) and β-cyclodextrin (β-CD) units on their surfaces have been designed and prepared as novel sensing materials for nitromethane. Fluorescence studies revealed that the immobilized Py was included in the cavity of its neighbor β-CD. This structure makes the fluorescence emission of the films could not be quenched by commonly used quenchers, including copper, cobalt and some other transition metal salts, KI and acrylamide. However, addition of nitromethane quenched the emission dramatically. Considering the high selectivity and sensitivity, great reversibility and stability, wide dynamic range and long storage time, it is proposed that these novel films could be applicable to the sensing of nitromethane in some energetic fuels.

Studies on CoSalen immobilized onto N-(4-pyridylmethylidene)–chitosan

Abstract A chitosan (CS) derivative, N-(4-pyridylmethylidene)–CS (PMC) was synthesized and a cobalt(II) complex of bis(salicylideneethylene diamine) (CoSalen) was immobilized on it. The structure of the immobilized CoSalen was characterized by elemental analysis, IR, XPS, fluorescence and ESR spectrocopy. It was demonstrated that the immobilization of CoSalen was realized through the coordination of nitrogen atom of the pendant group, pyridyl in PMC to the Co(II) in CoSalen. The polymer supported complex is more efficient than the corresponding monomeric complex in catalysing the oxidation of DOPA using oxygen as an oxidizer. The results may be attributed to site isolation effect offered by the supporting polymer chain. A mechanism similar to that for an enzymatic catalysis was proposed.

Fluorescence properties of immobilized pyrene on quartz surface

Abstract A novel nitrite sensing film has been prepared by chemical immobilization of pyrene (Py) onto an aminiated quartz plate surface. Fluorescence excitation and emission measurements and fluorescence quenching studies demonstrated that the immobilized fluorophore, Py, exists mainly in isolated state, rather than aggregated state. The profile and intensity of the emission of the plate are hardly affected by the presence of common chemicals including fluorescence quenchers like TlNO 3 , Cu(NO 3 ) 2 , and CH 3 NO 2 . Changes in pH values from 2 to 8 has little effect upon the emission. Introduction of a small amount of nitrite, however, quenches the fluorescence emission significantly. The quenching is very pH dependent and is totally reversible. This makes it a potential sensing materials for nitrite. The analytical applications of the plate have been conducted in our laboratory.

A green synthesis of CTAB–PTP/PAM microhydrogel and its application in oxidation of DBT

Polyacrylamide (PAM) microgels covered with hexadecyltrimethylammonium (CTAB)-peroxotungstophosphate (PTP) complexes were synthesized and characterized by scanning electron microscopy and Fourier transform infrared. The results indicate the CTAB–PTP/PAM composite microsphere with surface-wrinkling morphology and PAM microgel core/CTAB–PTP shell structure. The surface-wrinkling structure changed with the amount of CTAB–PTP supported on the PAM microgels. The results based on CTAB–PTP/PAM composite microspheres used in oxidation of dibenzothiophene demonstrated that the resulting microspheres have high catalytic performance and could be reused three times with a small decrease in activity. The proposed method is commonly significant for construction of reusable catalyst used in diphase catalysis.

PMAA microgel surface-supported phase transfer catalyst as reusable microreactors for ultra-deep desulfurization

The reusable microreactors, poly(methacrylic acid) (PMAA) microgels surfacely covered with 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (AEM) and K2{W(=O)(O2)2(H2O)}2 (W2) complexes, have been synthesized by using an ion exchange reaction between AEM located on PMAA microgels and W2 in aqueous solution. The final composite microspheres and intermediate products are characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectrophotometer, and thermogravimetric analysis, respectively. The results indicated the PMAA/AEM/W2 composite microspheres with surface-wrinkling morphology and core-shell structure. The feasibility of the composite microspheres used as reusable microreactors in catalytic oxidation of dibenzothiophene (DBT) was investigated. Additionally, the effects of some factors, including the amount of the microreactors, temperature, H2O2/DBT molar ratio, the loaded amount of AEM, DBT concentration, and recycling times, on the catalytic oxidation were examined. The results demonstrated that the prepared composite microspheres possess high catalytic performance and reusability in the catalytic oxidation of DBT.

Synthesis of P(AM-co-MAA)/AEM composite microspheres with lichi–like surface structure using porous microgel as template

The P(AM-co-MAA)/AEM composite microspheres with lichi-like structure were synthesized by the hydrolysis and condensation of 3-(trimethoxysilyl)-propyldimethyloctadecyl-ammonium chloride (AEM) located within porous poly(acrylamide-co-methylacrylic acid) (P(AM-co-MAA)) microgels in an ammonia water atmosphere. The morphology and composition of the composite microspheres were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectrometer (FI-IR), and X-ray photoelectron spectroscopy (XPS), respectively. The results indicated that the composite microspheres with lichi-like surface structure could be obtained by controlling the loaded amount of AEM, the hydrolysis-condensation time of AEM, and the cross-linking degree of the porous P(AM-co-MAA) microgels. On the basis of the results, the mechanism on the formation of the microspheres with lichi-like surface structure was proposed. The multiple factors play a role in the formation of the specific surface morphology. The pores of the porous microgels make AEM behavior localized; the migration of AEM along with solvent evaporation leads to the structural change; the hydrolysis-condensation of AEM brings the temporarily structural solidification; the surface tension of hydrophobic AEM in hydrophilic atmosphere induces AEM liquid membrane constriction. Although the mechanism is complicated, the method is very simple. Based on the analogous principle, other composite materials with lichi-like structure could be constructed by altering precursor and porous template.