Guiping Ma

Cobalt sulfide/N,S codoped porous carbon core-shell nanocomposites as superior bifunctional electrocatalysts for oxygen reduction and evolution reactions.

Exploring highly-efficient and low-cost bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) in the renewable energy area has gained momentum but still remains a significant challenge. Here we present a simple but efficient method that utilizes ZIF-67 as the precursor and template for the one-step generation of homogeneous dispersed cobalt sulfide/N,S-codoped porous carbon nanocomposites as high-performance electrocatalysts. Due to the favourable molecular-like structural features and uniform dispersed active sites in the precursor, the resulting nanocomposites, possessing a unique core-shell structure, high porosity, homogeneous dispersion of active components together with N and S-doping effects, not only show excellent electrocatalytic activity towards ORR with the high onset potential (around -0.04 V vs.-0.02 V for the benchmark Pt/C catalyst) and four-electron pathway and OER with a small overpotential of 0.47 V for 10 mA cm(-2) current density, but also exhibit superior stability (92%) to the commercial Pt/C catalyst (74%) in ORR and promising OER stability (80%) with good methanol tolerance. Our findings suggest that the transition metal sulfide-porous carbon nanocomposites derived from the one-step simultaneous sulfurization and carbonization of zeolitic imidazolate frameworks are excellent alternative bifunctional electrocatalysts towards ORR and OER in the next generation of energy storage and conversion technologies.

Synthesis and characterization of chitosan-based hydrogels.

Biocompatible hydrogels based on water-soluble chitosan-ethylene glycol acrylate methacrylate (CS-EGAMA) and polyethylene glycol diamethacrylate (PEGDMA) were synthesized by photopolymerization. Characterization of morphology, weight loss, water state of hydrogel, pH-sensitivity and cytotoxicity were investigated by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), swelling test and methylthiazolydiphenyl-tetrazolium bromide (MTT) assay. The results indicated that the hydrogels were sensitive to pH of the medium, no cytotoxicity for L929 and SW1353, satisfactory for the composite to be used in bioapplications.

Electrodeposition of alginate/chitosan layer-by-layer composite coatings on titanium substrates

In this study, alginate/chitosan layer-by-layer composite coatings were prepared on titanium substrates via electrodeposition. The mechanism of anodic deposition of anionic alginate based on the pH decrease at the anode surface, while the pH increase at the cathode surface enabled the deposition of cationic chitosan coatings. The surface of coatings was characterized by using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The properties of coatings were characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). Indirect in vitro cytotoxicity test showed that the extracts of coating had no significant effects on cell viability. Moreover, in vitro cytocompatibility test exhibited cell population and spreading tendency, suggesting that the coatings were non-toxic to L929 cells. However, the results revealed that alginate coating was more benefit for cells growing than chitosan coating. The results indicated that the proposed method could be used to fabricate alginate/chitosan layer-by-layer composite coatings on the titanium surface at room temperature and such composite coatings might have potential applications in tissue engineering scaffolds field.

Photopolymerized water-soluble chitosan-based hydrogel as potential use in tissue engineering

Novel biodegradable hydrogels by photocrosslinking macromers based on chitosan derivative are reported. Photocrosslinkable macromers, a water-soluble (methacryloyloxy) ethyl carboxyethyl chitosan were prepared by Michael-addition reaction between chitosan and ethylene glycol acrylate methacrylate. The macromers were characterized by Fourier transform infrared spectroscopy, (1)H NMR and (13)C NMR. Hydrogels were fabricated by exposing aqueous solutions of macromers with 0.1% (w/v) photoinitiator to UV light irradiation, and their swelling kinetics as well as degradation behaviors was evaluated. The results demonstrated that the degradation rates were affected strongly by crosslinking density. The hydrogel was compatible to Vero cells, not exhibiting significant cytotoxicity. Cell culture assay also demonstrated that the hydrogels were good in promoting the cell attachment and proliferation, showing their potential as tissue engineering scaffolds.

Design and characterization of antitumor drug paclitaxel-loaded chitosan nanoparticles by W/O emulsions.

Chitosan nanoparticles and paclitaxel loaded chitosan nanoparticles were prepared by emulsification-crosslinking method in a W/O emulsion system, using glutaraldehyde as crosslinking agent. The mean diameter of chitosan nanoparticles decreased with increase of pH value of the reaction system from 4.5 to 6.5, and increased when the pH exceeded 6.5. Ultraviolet spectrum analysis showed that the largest loading efficiency and encapsulation efficiency could be 8.55% and 94.01%, respectively. In vitro drug release profile was also determined by ultraviolet spectrometry. MTT assays revealed that the blank chitosan nanoparticles had almost none toxicity, and cell culture was carried out accordingly.

Biomimetic composite scaffolds based mineralization of hydroxyapatite on electrospun calcium-containing poly(vinyl alcohol) nanofibers

Nanocomposite materials consisting of polymer matrix and inorganic salts in the form of nanocrystals of hydroxyapatite (HA) are regarded as superior candidates for bone treatment. A biomimetic nanocomposite scaffold with HA formation on the electrospun poly(vinyl alcohol) (PVA) nanofibrous structure by employing a Ca-P alternate soaking method was developed in this work. The calcium-containing PVA nanofibers were prepared by adding calcium nitrate to the starting solution prior to electrospinning, and then mineralized by Ca-P treatment in incubation solution. With this rapid and effective procedure, a continuous biomimetic crystalline HA layer could be formed successfully without the need of a prior chemical modification of the substrate surface under very mild reaction conditions. Moreover, the HA formed with a relatively accelerated growth had a carbonated and poor crystalline structure, resembling biological apatite in the bone mineral. The introduction of calcium ions in nanofibers by electrospinning was a favorable approach to induce the deposition of calcium phosphate and improve the distribution, nucleation, and growth of crystalline HA layer on nanofibrous scaffolds. Bioactivity tests revealed that these mineralized PVA/HA composite scaffolds improved the biocompatibility. The porous polymer/HA composite scaffolds produced in the present study might have potential applications in bone tissue engineering.

Synthesis and properties of photosensitive chitosan derivatives(1)

A novel chitosan derivative carrying the benzene group was synthesized by Michael reaction. The chemical structures of the compounds were characterized by FT-IR, UV-vis spectrometry, XRD, elemental analysis, and 1H NMR spectroscopy in detail. The degree of substitution (DS) of chitosan derivative was calculated by elemental analysis. The UV-vis results indicated that the derivatives had ultraviolet absorption at 265 and 273 nm. XRD analysis showed that the derivatives were amorphous. The derivatives could dissolve in water. Taking advantage of the known capacity of solubility and ultraviolet absorption, the chitosan derivatives opened new possibilities for use as a sunscreen.

Preparation and characterization of water-soluble chitosan derivative by Michael addition reaction.

The efficient procedure to prepare novel water-soluble chitosan derivative was established by Michael addition reaction to introduce sodium allylsulfonate into the chitosan at mild condition. The chemical structure of the chitosan derivative was characterized by FT-IR, (1)H NMR and Elemental analysis. The degree of substitution (DS) was calculated by Elemental analysis. The chitosan derivative exhibited an excellent solubility in the distilled water. The physical properties were analyzed by XRD and TG. The XRD study indicated that the crystallinity of chitosan derivative decreased. The thermal analysis showed that chitosan derivative had lower thermal stability than chitosan.

Photo-polymeriable chitosan derivative prepared by Michael reaction of chitosan and polyethylene glycol diacrylate (PEGDA)

N-Alkyled photo-polymeriable chitosan derivative (PEGDA-CS) was synthesized by Michael reaction of chitosan and polyethylene glycol diacrylate (PEGDA) under mild reaction conditions. The chemical structure and physical properties of PEGDA-CS were characterized by FT-IR, (1)H NMR, XRD and TG techniques. The degree of substitution (DS) of PEGDA-CS could be calculated from (1)H NMR. PEGDA-CS exhibited good solubility in distilled water. XRD analysis showed that PEGDA-CS was amorphous. TG results demonstrated that thermal stability of the derivate was lower than that of chitosan. Antimicrobial test showed that PEGDA-CS had the antimicrobial activity on Escherichia coli. It could photopolymerize under ultraviolet light with 2959 as initiator.

A polymer/metal core–shell nanofiber membrane by electrospinning with an electric field, and its application for catalyst support

In the present study, PVP/Ag nanofibers with a core–shell structure have been successfully prepared by using the electrospinning technique under the action of electric field induction. PVP (polyvinyl pyrrolidone), as the functional template during electrospinning, plays an important role both as the reducing agent and as the capping agent. The structure and properties of the thus-obtained nanofibers have been investigated thoroughly through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have also been employed to analyze the coordination interactions and chemical states of the core–shell nanofiber surface. Moreover, a static simulation of an electric-field-induced experiment has been carried out and energy-dispersive X-ray analysis (EDS) has been performed to demonstrate the field-induced mechanism. The results prove the fact that the electric field plays an important role on the induction of silver migration and formation of core–shell nanofibers. On the other hand, UV-Vis spectrophotometry has been used to test the catalytic properties of the samples for the reduction of methylene blue (MB) by NaBH4, it shows that PVP/Ag core–shell nanofibers hold great potential in the field of catalysis.