Shenmin Zhu

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.

Grafting of thermo-responsive polymer inside mesoporous silica with large pore size using ATRP and investigation of its use in drug release

The design of a delivery system was reported based on stimuli-responsive poly(N-isopropylacrylamide) (PNIPA) inside a mesostructured cellular foam (MCF) via atom transfer radical polymerization (ATRP), and the control of drug release in response to the environmental temperature was investigated. The successful synthesis of PNIPA inside the MCF was confirmed by Fourier transform infrared (FT-IR), transmission electron microscopy (TEM) and nitrogen adsorption/desorption measurements. Control of drug release through the porous network was performed by measuring the uptake and release of ibuprofen (IBU). The delivery system of MCF-PNIPA demonstrated a high IBU storage capacity of 58 wt% (IBU/silica), which is much higher than that reported for functional SBA-15 (37 wt%). The multilayer polymers inside the pores of the MCF were considered to form an internal cavity for drug molecules in addition to responding to changes in external temperature.

Synthesis of WO3@Graphene composite for enhanced photocatalytic oxygen evolution from water

Nano tungsten oxide (WO3) particles were synthesized on the surface of graphene (GR) sheets by using a simple sonochemical method. The obtained composite, WO3@GR, was characterized by X-ray diffraction, N2adsorption/desorption analysis, thermo-gravimetric analysis, Raman spectroscopy and UV-vis diffuse reflectance spectra measurements. It was found that chemical bonds between the nano WO3 particles and the GR sheets were formed. The average particle size of the WO3 was evidenced to be around 12 nm on the GR sheets. When used as photocatalyst for water splitting, the amount of evolved O2 from water for the WO3@GR composite with 40 wt% GR inside was twice and 1.8 times as much as that for pure WO3 and mixed-WO3/GR, respectively. The excellent photocatalytic property of the WO3@GR composite is due to the synergistic effects of the combined nano WO3 particles and GR sheets. The sensitization of WO3 by GR enhances the visible light absorption property of WO3@GR. The chemical bonding between WO3 and GR minimizes the interface defects, reducing the recombination of the photo-generated electron–hole pairs. Furthermore, the GR sheets in the WO3@GR composite enhance electrons transport by providing low resistance conduction pathways, leading to improved photo-conversion efficiency. The methodology opens up a new way of obtaining photoactive GR-semiconductor composites for photodissociating water under visible light.

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.

N-doped porous carbon with magnetic particles formed in situ for enhanced Cr(VI) removal

A newly designed N-doped porous carbon with magnetic nanoparticles formed in situ (RHC-mag-CN) was fabricated through simple impregnation then polymerization and calcination. The doped nitrogen in RHC-mag-CN was in the form of graphite-type layers with the composition of CN. The resultant nanocomposite maintained a high surface area of 1136 m(2) g(-1) with 18.5 wt% magnetic nanoparticles (Fe3O4 and Fe) inside, which showed a saturation magnetization (Ms) of 22 emu/g. When used as an adsorbent, the RHC-mag-CN demonstrated a very quick adsorption property for the removal of Cr(VI), during which 92% of Cr(VI) could be removed within 10 min for dilute solutions at 2 g L(-1) adsorbent dose. The high adsorption capacity (16 mg g(-1)) is related to the synergetic effects of physical adsorption from the surface area and chemical adsorption from complexation reactions between Cr(VI) and Fe3O4. Importantly, the basic CNs in RHC-mag-CN increase its negative charge density and simultaneously increase the adsorption of metallic cations, such as Cr(3+) formed in the acid solution from the reduction of Cr(VI). The formation of magnetic nanoparticles inside not only supplies complexing sites for the adsorption of Cr(VI), but also shows perfect magnetic separation performance from aqueous solution.

One step fabrication of C-doped BiVO4 with hierarchical structures for a high-performance photocatalyst under visible light irradiation

A novel sol–gel method was developed for the fabrication of a C-doped BiVO4 (BVOB@xC) photocatalyst with fine hierarchical structures templated from Papilio paris butterfly wings. The fine hierarchical butterfly wing structures of BVOB@xC were confirmed by the SEM and TEM observations. The doped carbon in BVOB@xC was formed in situ from the biotemplate during a calcination process and the amount of doping could be controlled from 0.6–2.4 wt% by adjusting the calcination temperature. It was found that the sample calcined at 400 °C with a carbon content of 1.5 wt% (BVOB@1.5C) demonstrated the best photocatalytic activity in both photocatalytic degradation and O2 evolution from water splitting (ca. 800 μmol L−1). Under visible light irradiation (λ > 420 nm), the photocatalytic O2 evolution from BVOB@1.5C (ca. 800 μmol L−1, after 5 h) is 16 times higher than that of pure BiVO4 powder (BVOP) (ca. 49 μmol L−1), and the photocatalytic decomposition efficiency of MB for BVOB@1.5C is 6.3 times higher than that of pure BVOP. The improved photocatalytic performance is attributed to the synergetic effect of the unique morphology and composition control. It is believed that the hierarchical butterfly wing structures of BVOB@1.5C contribute significantly to the absorption enhancement under visible light (480 to 700 nm), which was supported by UV-Vis diffuse reflectance measurements. The photocatalytic performance was further enhanced by the C-doping as it improves the efficient separation and transfer of the photogenerated electrons and holes, as evidenced by the electron paramagnetic resonance (EPR) measurements. This strategy provides a simple one-step method to fabricate a high-performance photocatalyst, which enables the simultaneous control of the crystal phase, morphology, and carbon element doping.

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.

Iridescent large-area ZrO2 photonic crystals using butterfly as templates

Intact ZrO2 (with refractive index of 2.12) replica, which is large in size (about 3×4 cm2), has been synthesized by using natural butterfly wings as templates. Microstructure characters of original butterfly wing scales are maintained faithfully in this biomorphic ZrO2. All replicas can reflect iridescent visible lights, which can even be observed by naked eyes. Optical microscope investigations indicate that colors reflected by one single scale are different from those done by the overlapped two or even more scales. Colors are not only determined by materials’ refractive index, observation angle, and the structure of every single scale, but also by its piled number and modes. With the increase in the number of piled scales, the color is not simply redshifted or blueshifted, which is the most direct and powerful evidence for structural colors.

Processable 3-nm thick graphene platelets of high electrical conductivity and their epoxy composites

Graphene platelets (GnPs) are a class of novel 2D nanomaterials owing to their very small thickness (∼3 nm), high mechanical strength and electric conductivity (1460 S cm(-1)), and good compatibility with most polymers as well as cost-effectiveness. In this paper we present a low-cost processing technique for producing modified GnPs and an investigation of the electrical and mechanical properties of the resulting composites. After dispersing GnPs in solvent N-methyl-2-pyrrolidone, a long-chain surfactant (Jeffamine D 2000, denoted J2000) was added to covalently modify GnPs, yielding J2000-GnPs. By adjusting the ratio of GnPs to the solvent, the modified GnPs show different average thickness and thus electrical conductivity ranging from 694 to 1200 S cm(-1). To promote the exfoliation and dispersion of J2000-GnPs in a polymeric matrix, they were dispersed in the solvent again and further modified using diglycidyl ether of bisphenol A (DGEBA) producing m-GnPs, which were then compounded with an epoxy resin for the development of epoxy/m-GnP composites. A percolation threshold of electrical volume resistivity for the resulting composites was observed at 0.31 vol%. It was found that epoxy/m-GnP composites demonstrated far better mechanical properties than those of unmodified GnPs of the same volume fraction. For example, m-GnPs at 0.25 vol% increased the fracture energy release rate G1c from 0.204 ± 0.03 to 1.422 ± 0.24 kJ m(-2), while the same fraction of unmodified GnPs increased G1c to 1.01 ± 0.24 kJ m(-2). The interface modification also enhanced the glass transition temperature of neat epoxy from 58.9 to 73.8 °C.