Binyuan Zhao

The depolymerization mechanism of chitosan by hydrogen peroxide

Water-soluble chitosan with low molecular weight was prepared by the depolymerization of chitosan with aqueous H2O2 solution. The IR and 1H-NMR studies verify that depolymerization leads to the breakage of 1,4-β-D-glucoside bonds of chitosan. X-ray analysis shows the depolymerization takes place at the surface of the chitosan in crystal region by so called peeling-off process while the amorphous portion is depolymerized by penetrating pattern.

Tunable Photonic Polyelectrolyte Colorimetric Sensing for Anions, Cations and Zwitterions

www.MaterialsViews.com C O M M Tunable Photonic Polyelectrolyte Colorimetric Sensing for Anions, Cations and Zwitterions U N IC By Wei Hong , Xiaobin Hu , * Binyuan Zhao , Fan Zhang , * and Di Zhang * A IO N Reversible non-covalent interactions between hydrogels and ions mainly refer to hydrogen bonding, metal coordination, van der Waals forces, ion–ion interactions, and ion–dipole interactions. Among them, ion-ion interaction is one of the strongest due to its high bond energy which can compare with covalent bond. Hydrogels based on strong polyelectrolytes whose ionization degree is almost constant in aqueous solutions can hold counterions despite of pH variation. Many of their properties, including strong intraand interchain interactions, surface activity, and interaction with ions in solution, vary with different counterions in respect that different counterions have different degrees of solvation, charge densities, and chemical structures, which cause various degrees of swelling. [ 1 ] Moreover, strong polyelectrolyte copolymers can be modifi ed to change aggregation and conformation with different counterions and solvent, owing to their amphiphilic structures (hydrophobic non-ionic segment and hydrophilic ionic segment). [ 2–4 ] Since these effects could lead to volume changes of hydrogels, strong polyelectrolytes can be applied in hydrogel sensors for multiple anion, cation, and zwitterion detection. Therefore, strong polyelectrolytes have an enormous potential for developing sensitive and universal ion sensors. Three-dimensional photonic crystals are materials with a periodic refractive index, where the propagation of electromagnetic waves can be modulated. [ 5–7 ] Responsive photonic crystals, whose photonic bandgap (PBG) shifts as the external ambient changes, have attracted increasing attention because they can be used as self-reporting sensors to measure various environmental stimuli. Since a number of hydrogels can reversibly respond to pH and ionic strength, [ 8 ] temperature, [ 9 ] solvent, [ 10 ]

Full-color CO2 gas sensing by an inverse opal photonic hydrogel

CO2 gas sensing is of great importance because of the impact of CO2 on global climate change. Here, utilizing an inverse opal hydrogel, we describe a CO2 gas sensing method that allows highly sensitive and selective detection over a wide concentration range. The CO2 sensor is specific, quantitative, interference tolerant and without the need for special instruments.

Highly sensitive colorimetric sensing for heavy metal ions by strong polyelectrolyte photonic hydrogels

Taking Cu2+, Pb2+ and Ag+ as examples of target cations, we describe a general strategy for constructing photonic metal ion sensing hydrogels that allow highly sensitive and selective detection via visual color changes. The sensors consist of heavy metal ion sensitive hydrogels with inverse opal structure. The presence of target cations causes shrinkage of the hydrogels and blue shift of the refraction peak wavelength with a detection limit lower than 1 nM. The interconnected macropores and the preorganized ligands makes these sensors sensitive and selective to the target ions without significant interference from pH, while the response mechanism based on the release of water of hydration after coordination prevents interference from ionic strength and anions. With this sensory system, direct, sensitive, rapid and selective detection of heavy metal ions with a broad dynamic range is achieved without expensive instruments, providing general methods for designing colorimetric metal ion sensing materials.

Effect of water presence on choline chloride-2urea ionic liquid and coating platings from the hydrated ionic liquid

In the present study, hygroscopicity of the choline chloride-urea (ChCl-2Urea) ionic liquid (IL) was confirmed through Karl-Fisher titration examination, indicating that the water content in the hydrated ChCl-2Urea IL was exposure-time dependent and could be tailored by simple heating treatment. The impact of the absorbed water on the properties of ChCl-2Urea IL, including viscosity, electrical conductivity, electrochemical window and chemical structure was investigated. The results show that water was able to dramatically reduce the viscosity and improve the conductivity, however, a broad electrochemical window could be persisted when the water content was below ~6 wt.%. These characteristics were beneficial for producing dense and compact coatings. Nickel (Ni) coatings plating from hydrated ChCl-2Urea IL, which was selected as an example to show the effect of water on the electroplating, displayed that a compact and corrosion-resistant Ni coating was plated from ChCl-2Urea IL containing 6 wt.% water doped with 400 mg/L NA at a moderate temperature. As verified by FTIR analysis, the intrinsic reason could be ascribed that water was likely linked with urea through strong hydrogen bond so that the water decomposition was suppressed during plating. Present study may provide a reference to prepare some similar water-stable ILs for plating.

Tunable growth of nanodendritic silver by galvanic-cell mechanism on formed activated carbon

Well-defined silver dendritic nanostructures have been prepared in large quantities in an ambient environment using formed activated carbon (FAC) only. A reasonable mechanism (step 1: reduction by surface reductive groups; step 2: growing in the form of a galvanic cell) is suggested.

Green “planting” nanostructured single crystal silver

Design and fabrication of noble metal nanocrystals have attracted much attention due to their wide applications in catalysis, optical detection and biomedicine. However, it still remains a challenge to scale-up the production in a high-quality, low-cost and eco-friendly way. Here we show that single crystalline silver nanobelts grow abundantly on the surface of biomass-derived monolithic activated carbon (MAC), using [Ag(NH3)2]NO3 aqueous solution only. By varying the [Ag(NH3)2]NO3 concentration, silver nanoplates or nanoflowers can also be selectively obtained. The silver growth was illustrated using a galvanic-cell mechanism. The lowering of cell potential via using [Ag(NH3)2]+ precursor, together with the AgCl crystalline seed initiation, and the releasing of OH− in the reaction process, create a stable environment for the self-compensatory growth of silver nanocrystals. Our work revealed the great versatility of a new type of template-directed galvanic-cell reaction for the controlled growth of noble metal nanocrystals.

Independent multifunctional detection by wettability controlled inverse opal hydrogels

Utilizing the wettability of inverse opal hydrogels, we report a new strategy to construct photonic hydrogels with multiple types of reliable signals, such as non-wetting (transparent), image contrast (weak color) with shifts of diffraction maximum (bright color), developing optical sensors for multifunctional detection.

Woodceramics Prepared from Wood Powder/Phenolated Wood Composite

In this paper, composites were made from wood powder and its phenolated product, and then were carbonized into woodceramics. The effects of the content of the phenolated wood in the composites on the forming ability, size, density, compressive strength, volume electrical resistivity, and specific surface area of the woodceramics were investigated. It is suggested that in the preparation of woodceramics, phenolic resin can possibly be substituted totally by phenolated wood that is the main constituent of liquefied wood.

Au@SiO2 nanoparticles coupling co-sensitizers for synergic efficiency enhancement of dye sensitized solar cells

A new configuration of a co-sensitized DSSC was proposed, in which different dye molecules are deposited onto the electrodes layer-by-layer, with Au@SiO2 nanoparticles uniformly distributed in the electrodes. Au@SiO2 nanoparticles coupled with dye pairs were proven to have a synergic effect: not only to enhance the light absorption but also accelerate energy transfer from one dye to another, therefore offsetting the inefficiency of bare co-sensitized DSSC which is apt to lose excited photoelectrons because of recombination at the interface between electrode and electrolyte. According to our analysis, the absorption spectra of the dye pair should match with each other to have a positive effect. With a proper pair of dyes (N3 and N719 as an example), we achieved the upmost conversion efficiency with the fabricated co-sensitized solar cell with Au@SiO2 nanoparticles, which is an exception to the current general idea that mono-layered dye molecule-sensitized cells exhibit the greatest efficiency.