Biomedical subjects
Publications and source records attributed to Wuzong Zhou.
Mesostructured silicates containing metal nanoparticles have been synthesised via templating around a pre-formed, metal-containing mesophase using a non-ionic surfactant.
Using a one-pot approach employing true liquid crystal templating on neutral surfactants and simple metal salt precursors, mesostructured, mesoporous silicates have been prepared in which bimetallic nanoparticles are deposited; magnetic properties of PtCo systems so prepared are evaluated.
Point defects largely govern the electrochemical properties of oxides: at low defect concentrations, conductivity increases with concentration; however, at higher concentrations, defect-defect interactions start to dominate. Thus, in searching for electrochemically active materials for fuel cell anodes, high defect concentration is generally avoided. Here we describe an oxide anode formed from lanthanum-substituted strontium titanate (La-SrTiO3) in which we control the oxygen stoichiometry in order to break down the extended defect intergrowth regions and create phases with considerable disordered oxygen defects. We substitute Ti in these phases with Ga and Mn to induce redox activity and allow more flexible coordination. The material demonstrates impressive fuel cell performance using wet hydrogen at 950 degrees C. It is also important for fuel cell technology to achieve efficient electrode operation with different hydrocarbon fuels, although such fuels are more demanding than pure hydrogen. The best anode materials to date--Ni-YSZ (yttria-stabilized zirconia) cermets--suffer some disadvantages related to low tolerance to sulphur, carbon build-up when using hydrocarbon fuels (though device modifications and lower temperature operation can avoid this) and volume instability on redox cycling. Our anode material is very active for methane oxidation at high temperatures, with open circuit voltages in excess of 1.2 V. The materials design concept that we use here could lead to devices that enable more-efficient energy extraction from fossil fuels and carbon-neutral fuels.
Silicon nanowires with narrowly distributed diameters of 20-30 nm have been fabricated by chemical vapor deposition on an anodized aluminum oxide (AAO) substrate. The first-order and second-order Raman scatterings of the silicon nanowires have been studied in a temperature range from 123 to 633 K. Both of the first-order and second-order Raman peaks were found to shift and broaden with increasing temperature. The experimental results were analyzed by combining the phonon confinement effect, anharmonic phonon processes and lattice stress effect. It was found that the intensities of the first-order and second-order Raman bands have different dependences on temperature. The value of relative intensities I(2TA)int/I(2TO)int for silicon nanowires was found to be larger than that of bulk silicon, and increase with rising measurement temperature. We ascribe this phenomenon to the participation of phonons with a large wave vector value of Raman scattering caused by both the phonon confinement effect and the temperature effect.
The size- and composition-controlled synthesis of Ni-P nanospheres from nickel chloride and sodium hypophosphite has been systematically investigated by changing the conditions, such as the ratio of the starting materials, pH value, and reduction temperature. It was found that when the starting ratio of H2PO2(-)/Ni2+ was changed the size and chemical composition of the nanoparticles changed simultaneously. Within a suitable pH range, the phosphorus content was altered without affecting the particle size. Increasing the reduction temperature resulted in smaller Ni-P nanospheres but invariable phosphorus content. The Ni-P nanospheres were amorphous when the phosphorus content was higher than 10.0 mol %, while lower phosphorus content led to a composite of amorphous Ni-P and face-centered cubic (fcc) Ni. During postsynthesis calcinations, amorphous Ni-P nanospheres with a low phosphorus content directly crystallized to Ni3P and fcc Ni. However, the specimens with high phosphorus content crystallized via some intermediate phases such as Ni5P2 and Ni12P5. In the latter, an amorphous P-rich shell was developed simultaneously. A preliminary catalytic test of growth of carbon nanofibers on the Ni-P nanospheres has been carried out.
Single-crystal Cr2O3 with regular mesopores has been synthesized using mesoporous silica KIT-6 as a template and characterized by using XRD, HRTEM and nitrogen adsorption/desorption.
By employing a novel low-temperature synthetic pathway, highly ordered cubic mesoporous materials with hitherto the largest pores (up to 27 nm) and unit cells (up to 44 nm) have been successfully obtained.
The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+-loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non-dealuminated materials. Analysis of the 1H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd3+-loaded cavities did not change significantly, which suggests that the windows of the Gd3+-loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd3+-loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+-doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T1 MRI contrast agents at low field, and as T2 agents at higher fields.
High-yield H-form trititanate nanotubes have been synthesized, and their structures have been characterized by using X-ray diffraction and high-resolution transmission electron microscopy. According to combined TGA/XRD studies, the nanotubes are not stable at high temperature. Thermal analysis suggests that the stoichiometry of the material is H(2)Ti(3)O(7).0.8H(2)O(abs). Conductivity measurements indicate that mainly protonic transport occurs at temperatures below 150 degrees C and that with increasing temperature and progressive breakdown of nanotubes and formation of crystalline TiO(2) phases protonic conductivity is lost, leaving only residual defect electronic conduction. The proton conductivity is ca. 5.5 x 10(-6) S cm(-1) at 300 K. The structural protons and trapped water were confirmed by solid-state NMR.
Nanoparticles of Co and NiPd, derived from colloidal precursors and supported on commercially available non-ordered mesoporous silica, are highly effective, cheap, recyclable and industrially viable catalysts for the hydrogenation of a range of nitro-substituted aromatics under mild conditions.
Mesoporous silicates are prepared by templating on the hexagonal (H1) mesophase of surfactant bipyridine complexes of ruthenium(II) using a true liquid-crystal templating approach. On calcination, the surfactant template is removed except for the central metal ion that is oxidised, forming nanoparticles of RuO2 that deposit within the pores. RuO2 is a known oxidation catalyst and, despite its anhydrous nature in these silicates, is found to be very active in catalyzing the oxidation of water by acidic CeIV.
High-resolution transmission electron microscopy reveals linear, "double pore" defects in the important zeolite beta. Structural interpretation of these defects gives evidence for the mechanism by which the zeolite crystallizes.
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A hierarchically structured composite material with interconnecting meso- and micropores has been developed with the aim to optimize zeolite performance. A general synthetic method has been developed that, in a controlled manner, allows for various types of nanosized zeolite to be incorporated into a three-dimensional mesoporous matrix. Nanosized zeolite Beta was used to exemplify this new approach, resulting in a system in which zeolite Beta shows a higher cracking activity per gram of zeolite than pure nanosized zeolite Beta for the model feed n-hexane. Additionally, FTIR studies of CO and NH3 adsorption revealed that the nature of the acid sites in the nanozeolite has been partially modified due to the interactions with the mesoporous matrix, TUD-1.
A high-silica zeolite (Si/Al = 7.1) with the STI framework topology, denoted TNU-10, has been synthesized in the presence of 1,4-bis(N-methylpyrrolidinium)butane and Na(+) cations as structure-directing agents, and its structure in the proton form has been refined against laboratory powder X-ray data in space group Fmmm (a = 13.533(1) A, b = 17.925(2) A, c = 17.651(2) A). The space group symmetry is supported by electron diffraction and energy minimization studies. The as-made and proton form of TNU-10 are extensively characterized by elemental and thermal analyses, scanning electron microscopy, N(2) adsorption, multinuclear solid-state NMR, IR, and temperature-programmed desorption of ammonia, and the location of the organic structure-directing agent in the channel system is determined by molecular modeling. The catalytic properties of H-TNU-10 and Co-TNU-10 are evaluated for the skeletal isomerization of 1-butene to isobutene and the selective reduction of NO with methane, respectively. When compared to H-ferrierite, a low selectivity to isobutene is observed for H-TNU-10. However, it is found that Co-TNU-10 exhibits a maximum NO conversion of 93% at 823 K under conditions of high concentrations of methane (16,000 ppm) and water vapor (10%) and in the presence of 2.6% O(2), which is considerable higher than even the value (74%) obtained from Co-ferrierite, known as the best catalyst for this reaction, under the identical conditions.
We report the assembly of a cubic array of cationic cadmium clusters encapsulated in zeolite A, and its characterization through Rietveld analysis of powder synchrotron X-ray diffraction data and high resolution transmission electron microscopy.
[reaction: see text] Pd nanoparticles (approximately 2 nm in size) microencapsulated in polyurea is an efficient and recyclable catalyst for reductive ring-opening hydrogenolysis of epoxides, using either HCOOH/Et(3)N or H(2) as a hydrogen donor.
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