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Biopolymer of chitosan (CS) and titanium pillared clays (Ti-PILCs) have been combined in a hybrid as advanced supports for immobilization of PdOx=0,1 species to prepare novel PdOx=0,1@Ti-PILC/CS nano-composite catalysts. The Ti-PILC materials showed high specific surface areas and abundant meso-porous structure with many irregular pore channels caused by collapses of layered structure of clay during Ti pillaring process. Both CS chains and sub-nano sized PdOx particles were successfully incorporated into the pore channels of Ti-PILC, resulting in a decrease in both the specific surface areas and uniform distribution of pore size. Besides conventional methods characterizations, the strong interactions between PdOx species and Ti-PILC/CS support were further evidenced with positron annihilation lifetime spectroscopy studies. The resultant PdOx@Ti-PILC/CS catalyst was highly active for the coupling reactions of aryl halides with phenyl acetylenes. It was recyclable and gave excellent yield up to 13 runs with low leaching of Pd species.

Cobalt, nickel and iron are efficient catalysts for numerous chemical and biological reactions, but they are hardly immobilized on solid matrixes due to their relatively weak chelation with the surface molecules. We have employed a co-electrospraying coupling with glutaraldehyde cross-linking technique to prepare cobalt (Co2+), nickel (Ni2+) and iron (Fe2+) catalyst embedded chitosan microparticles (M@MicroCS) (M = Co, Ni and Fe). The Co@MicroCS beads exhibited excellent catalytic activity for the Heck cross-coupling reactions of aromatic iodides with alkenes. Moreover, the Co@MicroCS bead catalyst could be even reused at least for five times without significant loss of the catalytic activities. The average diameter of the free volume holes for the porous Co@MicroCS beads was determined to be much larger than the size of the reactant and product molecules, allowing them to freely migrate through the catalytic sites inside the chitosan beads. These results clearly indicate that the Heck reactions catalyzed by the Co@MicroCS beads primarily occurs inside the porous chitosan beads. Taken together, we have demonstrated a straightforward approach to prepare efficient and recyclable heterogeneous catalysts derived from the first-row transition metal catalysts by entrapping them inside the chitosan microparticles.

Uniform chitosan composite nanofiber mats (CS/PAAS) containing 4.0 wt% polyacrylic acid sodium loading have been prepared by electrospinning, followed by annealing at elevated temperature to improve solvent resistance and mechanical strength. The CS/PAAS nanofiber mats have been characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and tensile strength analysis. The prepared nanofiber mats have been shown to be much better than the pristine chitosan powder to adsorb the chromium (VI) ion. SEM-Energy dispersive X-ray spectroscopic (SEM-EDS) and positron annihilation lifetime spectroscopic (PALS) analysis show that Cr(VI) ion can freely permeate into the composite nanofiber and coordinate with the internal chitosan chain molecules. The adsorption abilities of these cross-linked CS/PAAS nanofiber mats are dependent on the chitosan contents as well as N-atom basicity of the chitosan chain. The adsorption capacity toward Cr(VI) ion was improved to 78.92 mg/g after modification of the chelating ligands for the cross-linked CS/PAAS composite nanofibers.

Biopolymer of chitosan (CS) and titanium pillared clays (Ti-PILCs) have been combined in a hybrid as advanced supports for immobilization of PdO

In this study, an efficient heterogeneous catalyst including palladium (Pd) and zinc (Zn) nanoparticles supported on chitosan/silica (CS/SiO2) composite membrane is synthesized using partially etching of SiO2 technique. N2 sorption isotherm results shows that the prepared Pd-Zn@CS/SiO2 (1/1) porous membrane had a BET surface area of 26.50m2/g. High-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS), characterization of the catalyst shows that the Pd0 nanoparticles (below 5nm), and Zn0 aggregates (about 10-15nm) dispersed well in the CS/SiO2 matrix. Zinc crystal was also detected by X-ray diffraction study and HR-TEM observation. The prepared Pd-Zn@CS/SiO2 membrane catalyst is highly active for Ullmann reductive homocoupling reactions of aryl iodides and aryl bromides, and can be recycled 5 times without significant loss of activities. This work supplies a successful approach to realize Pd catalysts and Zn reducing reagent co-immobilized in the same carrier material with excellent catalytic performances.

In this study, a biocompatible chitosan/montmorillonite (CS/MMT) composite microsphere was developed as a carrier for loading and sustained-release of the hydrophobic drug of tanshinone IIA. Though the compatibility between hydrophobic drugs and hydrophilic matrix was fairly poor, tanshinone IIA was successfully loaded on the microsphere by the solvent exchange process during chitosan matrix dehydration. The microstructure of the resulting microspheres was characterized with several techniques, such as X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). The results of drug loading and in vitro release study of the tanshinone IIA loaded CS/MMT composite microspheres showed that the incorporation of MMT into CS matrix would enhance the drug encapsulation and retard drug migration. The sample with mass ratio of CS: MMT (10:2) exhibited highest encapsulation efficiency (48.18% ± 2.54%) and slowest continuous cumulative release of drug in phosphate buffer solution (pH 7.4). It was found that the tanshinone IIA release kinetics fit the Higuchi model and the release mechanism was non-Fickian diffusion. Cell viability studies by CCK-8 assay showed that the microspheres showed no obvious cytotoxicity at the dosages below 80 μg/ml, and the MMT content had no significant effect on cell viability. This work provided a successful method of incorporating hydrophobic drugs into hydrophilic matrices, and has been successfully applied to the preparation of effective and biocompatible drug delivery for tanshinone IIA.

In this study, an efficient heterogeneous catalytic material including Pd0 nanoparticles and Cu2+ cations supported on montmorillonite/chitosan (MMT/CS) composite was prepared by solution intercalation and complexion methods. The valence states of Pd (both Pd(0) and Pd(II) coexisting) and Cu (mainly Cu(II)) of the Pd0/Cu2+@MMT/CS catalyst were confirmed by the X-ray photoelectron spectroscopy (XPS) characterization. The d001 spacing was enlarged from 1.25nm (MMT) to 1.94nm (Pd0/Cu2+@MMT/CS). Pd0/Cu2+@MMT/CS catalyst had obviously bigger specific surface area (SBET) and total pore volume (Vp) than pure MMT. High resolution transmission electron microscopy (HR-TEM) observation of the Pd0/Cu2+@MMT/CS catalyst showed that separated Pd0 nanoparticles sized below 3nm dispersed well both in the interlayer space and surface of MMT layers. The positron annihilation lifetime spectroscopy (PALS) was very sensitive to the microstructure changes caused by the formation of nano particles Pd0 after reduction of Pd2+/Cu2+@MMT/CS to Pd0/Cu2+@MMT/CS. The prepared Pd0/Cu2+@MMT/CS catalysts are highly active for the Sonogashira reactions of aromatic halides and alkynes in H2O/ether solution, and can be recycled 6 times. The leaching of Cu species is much quicker than Pd species during recycling, which should be the main reason for the decrease in efficiency of the recycled Pd0/Cu2+@MMT/CS catalysts.

A novel palladium supported on chitosan porous membrane heterogeneous catalyst has been prepared by freeze-drying of Pd(2+)-crosslinked chitosan gel solution. The prepared membrane catalyst has three-dimensional porous structure (porosity: >70%). The crosslinking effects of Pd(2+) to chitosan were good for the improvement of the mechanical properties and thermal stabilities. Pd(2+) cations have been shown not only as the crosslinker, but also as the catalytic active sites. The reductive palladium species of the recycled membrane catalysts was found in the nanometer scale (20-40nm). Excellent cross-coupling yields were achieved using as low as 0.12mol% palladium catalyst loading for the Heck-type reaction of aromatic halides with acrylates. The catalyst could be recycled six times without obvious decreased conversion.

In this study, polyethylene glycol (PEG) with different molecular weight, polyvinyl pyrrolidone (PVP), and polyvinyl alcohol (PVA), are chosen as porogens for preparing chitosan base porous microsphere supported palladium catalyst for coupling reactions. The pore structure of the microspheres was controlled by the compatibility of chitosan and counterpart polymers. The prepared porous chitosan microspheres supported palladium heterogeneous catalysts have been evaluated using the well-established Ullmann reductive homocoupling and the Heck cross-coupling reactions. The activities, stabilities and recyclability of the porous chitosan microspheres supported palladium catalysts are not only highly dependent upon the surface areas of the solid supports, but also upon the chemical properties of the water-soluble polymers. The degradation of the prepared heterogeneous palladium catalysts is mainly caused by a combination of the palladium leaching and the morphological transformation of the palladium species from the amorphous into the crystals.

In this study, a heterogeneous catalyst including palladium nanoparticles supported on nitrogen-doped mesoporous carbon (Pd@N-C) is synthesized from palladium salts as palladium precursor, colloidal silica as template, and chitosan as carbon source. N2 sorption isotherm results show that the prepared Pd@N-C had a high BET surface area (640m(2)g(-1)) with large porosity. The prepared Pd@N-C is high nitrogen-rich as characterized with element analysis. X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy characterization of the catalyst shows that the palladium species with different chemical states are well dispersed on the nitrogen-containing mesoporous carbon. The Pd@N-C is high active and shows excellent stability as applied in Heck coupling reactions. This work supplies a successful method to prepare Pd heterogeneous catalysts with high performance from bulk biopolymer/Pd to high porous nitrogen-doped carbon supported palladium catalytic materials.

Significant enhancement of the catalytic stability and activity was obtained for the heterogeneous palladium catalyst supported on the shell powders-reinforced chitosan microspheres. For example, over 90% cross-coupling yields were achieved using as low as 0.05 mol% palladium catalyst loading for the Heck-type reaction of iodobenzene with n -butyl acrylate. Such significant enhancement of the catalytic stability and activity can be attributed to the intermolecular interactions of the surface polar molecules of the incorporated shell powders with the surrounding chitosan molecules as well as the deposited palladium species.