Chuanliang Feng

Sonochemical synthesis of TiO2 nanoparticles on graphene for use as photocatalyst

Using ultrasonication we succeed in a controlled incorporation of TiO(2) nanoparticles on the graphene layers homogeneously in a few hours. The average size of the TiO(2) nanoparticles was controlled at around 4-5 nm on the sheets without using any surfactant, which is attributed to the pyrolysis and condensation of the dissolved TiCl(4) into TiO(2) by ultrasonic waves. The photocatalytic activity of the resultant graphene-TiO(2) composites containing 25 wt.% TiO(2) is better than that of commercial pure TiO(2). This is partly due to the extremely small size of the TiO(2) nanoparticles and partly due to the graphene-TiO(2) composite structure consisting of homogeneous dispersion of crystalline TiO(2) nanoparticles on the graphene sheets. As the graphene in the composites has a very good contact with the TiO(2) nanoparticles it enhances the photo-electron conversion of TiO(2) by reducing the recombination of photo-generated electron-hole pairs.

Carbon-coated SnO2@C with hierarchically porous structures and graphite layers inside for a high-performance lithium-ion battery

A high-performance anode material was prepared from a hierarchically structured activated carbon which contains in situgraphene and nano-graphite. The activated carbon was immersed in a solution of SnCl2·2H2O and subjected to ultrasound. As a result, nanoparticles of SnO2 were uniformly deposited on the surface of the activated carbon. The composite material was then coated with a thin layer of carbon by soaking it in a sucrose solution, followed by carbonization of the adsorbed sucrose at 500 °C. The resulting composite showed an outstanding high-rate cycling performance that can deliver an initial discharge capacity of 1417 mAh g−1 and maintain a discharge capacity of more than 400 mAh g−1 after 100 cycles at a high current density of 1000 mA g−1. This outstanding electrochemical performance is likely to be related to a unique combination of the excellent electrical conductivity of the activated carbon with graphite layers formed inside, its hierarchical pore structure which enhances lithium-ion transportation, and the carbon coating which alleviates the effects of volume changes, shortens the distance for Li+ diffusion, facilitates the transmission of electrons, and keeps the structure stable.

Bioinspired fabrication of hierarchically structured, pH-tunable photonic crystals with unique transition.

We herein report a new class of photonic crystals with hierarchical structures, which are of color tunability over pH. The materials were fabricated through the deposition of polymethylacrylic acid (PMAA) onto a Morpho butterfly wing template by using a surface bonding and polymerization route. The amine groups of chitosan in Morpho butterfly wings provide reaction sites for the MAA monomer, resulting in hydrogen bonding between the template and MAA. Subsequent polymerization results in PMAA layers coating homogenously on the hierarchical photonic structures of the biotemplate. The pH-induced color change was detected by reflectance spectra as well as optical observation. A distinct U transition with pH was observed, demonstrating PMAA content-dependent properties. The appearance of the unique U transition results from electrostatic interaction between the -NH3(+) of chitosan and the -COO(-) groups of PMAA formed, leading to a special blue-shifted point at the pH value of the U transition, and the ionization of the two functional groups in the alkali and acid environment separately, resulting in a red shift. This work sets up a strategy for the design and fabrication of tunable photonic crystals with hierarchical structures, which provides a route for combining functional polymers with biotemplates for wide potential use in many fields.

Synthesis of Cu-doped WO3 materials with photonic structures for high performance sensors

Cu-doped photonic crystal (PC) WO3 replicas from Morpho butterfly wings have been prepared by using a combined sol–gel templating and calcination method. The exact replications in the Cu-doped PC WO3 replicas at the micro- and nanoscales were confirmed by scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). A combination of X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman and X-ray photoelectron spectra (XPS) measurements revealed that copper does not form clusters, but is randomly distributed inside the WO3 matrix lattice. The optical properties of the Cu-doped PC WO3 replica as well as the Morpho butterfly wing template were investigated by using reflectance spectroscopy, and it was found that the reflected light chromaticity of the Cu-doped PC WO3 replica was inherited from the PC Morpho butterfly wings. Cu-doped WO3 replicas without photonic crystal structures (Cu-W replica) were also fabricated in the same way as the Cu-doped PC WO3 replica but using Euploea mulciber butterfly wings as the template. Chemical sensors fabricated from the Cu-doped PC WO3 as well as the non-PC Cu-doped WO3 replicas were tested for a range of gases: (CH3)3N (TMA), NH3, C2H5OH, HCHO, CH3OH, acetone, H2, CO and NO2 and they showed a high selectivity for TMA. The sensitivity of the Cu-doped PC WO3 replica sensors can reach up to 2.0 for a trimethylamine concentration as low as 0.5 ppm at 290 °C. The high sensitivity of the Cu-doped WO3 replica sensors to TMA is attributed to the catalytic effect of Cu on the reaction between the testing gas and the oxide surface. Furthermore, the Cu-doped PC WO3 replica sensor is twice as sensitive as the Cu-doped non-PC WO3 replica to trimethylamine. This may be explained by the photonic crystal structure of the Cu-doped PC WO3.

Bioinspired Hierarchical Surface Structures with Tunable Wettability for Regulating Bacteria Adhesion

To circumvent the influence from varied topographies, the systematic study of wettability regulated Gram-positive bacteria adhesion is carried out on bioinspired hierarchical structures duplicated from rose petal structures. With the process of tuning the interfacial chemical composition of the self-assembled films from supramolecular gelators, the varied wettable surfaces from superhydrophilicity to superhydrophobicity can be obtained. The investigation of Gram-positive bacteria adhesion on the hierarchical surfaces reveals that Gram-positive bacteria adhesion is crucially mediated by peptidoglycan due to its different interaction mechanisms with wettable surfaces. The study makes it possible to systematically study the influence mechanism of wettability regulated bacteria adhesion and provides a sight to make the bioinspired topographies in order to investigate wettability regulated bioadhesion.

Multiresponsive Hydrogel Coassembled from Phenylalanine and Azobenzene Derivatives as 3D Scaffolds for Photoguiding Cell Adhesion and Release

A multiresponsive hydrogel system coassembled from phenylalanine derivative gelator (LPF2) and azobenzene (Azo) derivative (PPI) is constructed, which can respond to temperature, pH, host-guest interaction, and photoirradiation. A set of techniques including circular dichroism, Fourier transform infrared spectroscopy, (1)H NMR, and X-ray powder diffraction confirm that the hydrogel is formed through hydrogen bonds between amide moieties/pyridine and carbonyl groups, enduing the coassembled hydrogel with multiresponsive properties that make it possible to control cell encapsulation and release in three-dimensional environments under multistimulus, for example, UV irradiation. This study brings a novel approach to develop multistimuli-responsive hydrogels by coassembly of various responsive components for biomedical interest, for example, the controlled delivery of various therapeutic biological agents.

C2-symmetric benzene-based hydrogels with unique layered structures for controllable organic dye adsorption

With the development of industry, organic dyes used in printing, textile, plastic, foods, and cosmetics have brought health and environmental issues. A C2-symmetric benzene-based hydrogel with unique layered structure mimicking activated carbon was developed and found capable of the controllable adsorption of 97–99% of certain organic dyes (methylene blue and methyl violet 2B) within two minutes. The adsorption equilibrium of the dyes is in good agreement with the Langmuir adsorption isotherm model. The controllable adsorption of the dyes was confirmed by varying the pH of the medium. The hydrogels rapid, highly effective, reusable, and controllable adsorption of organic dyes makes it possible to not only adsorb toxic dyes from wastewater, but also be used as potential delivery vehicles for small drug molecules in the field of drug delivery.

Morphological Effects on Surface-Enhanced Raman Scattering from Silver Butterfly Wing Scales Synthesized via Photoreduction

Through a simple room-temperature photoreduction process, this letter conformally replicates 3D submicrometer structures of wing scales from two butterfly species into Ag to generate practical surface-enhanced Raman scattering (SERS) substrates. The Ag replicas of butterfly scales with higher structural periodicity are able to detect rhodamine 6G at a low concentration down to 10(-9) M, which is three orders of magnitude lower than the detectable concentration limit of using quasi-periodic Ag butterfly structures. This result presents a way to select suitable scale morphologies from 174,500 species of Lepidopterans to replicate, as consumable SERS substrates with low cost and high reproducibility.

The Detection of DNA Hybridization on Phosphorus Dendrimer Multilayer Films by Surface Plasmon Field Enhanced-Fluorescence Spectroscopy

Dendrimer multilayers on gold substrates prepared via layer-by-layer (LbL) assembly technique were characterized and used as substrates for DNA immobilization/hybridization. The multilayers, built using alternately polycationic and polyanionic phosphorus dendrimers of generation 4, were studied by surface plasmon resonance (SPR) spectroscopy. By varying the concentration of NaCl, the optimized optical thickness of a single dendrimer layer (about 4.5 nm) was achieved. Using the multilayers as the substrate, a high loading of DNA probes was obtained through covalent coupling of probe DNA on dendrimer multilayer film. The following hybridization of Cy5-dye labeled complementary target DNA with immobilized probe DNA was detected by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The limit of detection of target DNA upon hybridization reached 50 pM and 30 pM on 1 bilayer and 4 bilayers, respectively. The phosphorus dendrimer multilayer films display high stability during repeated regeneration and hybridization cycles. The sensitive platforms based on dendrimer multilayers deposited in the presence of NaCl make them attractive candidates for application in DNA sensing.

Mechanical reinforcement of C2-phenyl-derived hydrogels for controlled cell adhesion

Many low molecular weight (LMWG) hydrogels have been widely used as scaffolds and substrates due to their particular structures and properties. However, LMWG hydrogels generally show a weak mechanical performance which confines their applications in the field of tissue engineering. Here, we report a new kind of hydrogel derived from the combination of a C2-phenyl-derived gelator and a polysaccharide (alginate). Rheology testing showed that the elastic modulus of C2-phenyl-derived hydrogels could be increased by nearly one order of magnitude by interpenetrating them with an alginate–calcium network. Increasing the concentrations of the gelator and calcium ions or decreasing the concentration of alginate will lead to an increase of the elastic modulus of the hybrid hydrogels. Imaging and spectroscopic analysis confirmed that the surface roughness and morphology of the hybrid hydrogels were almost the same with that of a pure C2 hydrogel. Significant improvements in cell adhesion and spreading were observed on the reinforced hydrogels. The new hybrid hydrogels have great potential for tissue engineering applications in vivo.