Baodong Mao

Visible-light-driven reversible and switchable hydrophobic to hydrophilic nitrogen -doped titania surfaces: correlation with photocatalysis

Visible-light-responsive nitrogen-doped titanium dioxide nanorods have been synthesized by a hydrothermal method at low temperature. X-Ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and contact angle measurements were used to obtain the crystal structures, morphologies, visible-light absorbance, and hydrophobicity, respectively, of the prepared nanorods. The surface wettability of the samples could be reversibly tuned from hydrophobic to hydrophilic upon visible-light illumination. This switchable surface wettability is crucial since the photocatalytic activity of this nanoscaled catalyst for the decomposition of organic molecules exhibits a strong dependence on the surface wettability.

One-step, size-controllable synthesis of stable Ag nanoparticles

A simple one-step process was developed for the preparation of stable Ag nanoparticles with high yield. Direct solvothermal treatment of an ethanol solution of AgNO3 and dodecanethiol (DT) resulted in the formation of Ag nanoparticles. X-ray powder diffraction (XRD) analysis indicated that the solid was composed of fcc-structured metal Ag. Infrared (IR) spectroscopy analysis demonstrated the presence of DT in the products. Transmission electron microscopy (TEM) showed that the particle size could be tuned from 5?nm to 100?nm by changing the synthesis parameters. The samples were stable (no irreversible precipitation) in the solid state for more than 8 months and could be redispersed into nonpolar organic solvent (cyclohexane) to form stable colloidal dispersions. A possible formation and size evolution mechanism is proposed.

Zinc alloyed iron pyrite ternary nanocrystals for band gap broadening

Iron pyrite (FeS2) is one of the most promising photovoltaic materials with high natural abundance and low cost but with a lower-than-optimum band gap of 0.95 eV. Here the feasibility of band gap broadening was explored by zinc alloying of FeS2 nanocrystals (NCs). A significant amount of zinc up to 6 at%, 30 times higher than previously reported, was incorporated into the FeS2 NCs. In contrast to band gap bowing predicted by first-principles calculations, a band gap enlargement of ∼0.1 eV was observed by zinc alloying. A more than five-times reduction of dark current in the zinc alloyed FeS2 photoconductor was observed and should ascribe to the increased band gap.

Interactive metal ion–silicon oxidation/reduction processes on fumed silica

Fumed silica is shown to represent an active oxidation/reduction site. Arresting results demonstrate that the average oxidation state of silicon, at least at the surface of fumed silica, is +1 in contrast to the assumed value of +4, thus allowing the preparation of silica with desired reduced silicon surface oxidation states without post-synthesis treatment. The nature of this silica interface is demonstrated by preparing Fe/silica and Cu/silica materials with unprecedented control of the transition metal oxidation state. Supported iron or copper catalysts were prepared by contacting anhydrous iron(III) chloride, iron(III) nitrate nonahydrate, or hydrated copper(II) chloride with fumed, amorphous silica (CAB-O-SIL®) in dry methanol at room temperature. Subsequently, the solids were vacuum-dried (∼10−3 Torr) at room temperature for two hours. These solids, and in particular the iron-silica interface, were examined by X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy, UV-vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), colour analysis, and water contact angle analysis. No discernible evidence was found that indicated the formation of large crystallites of the transition metals. The products of iron(III) interaction at the interface with amorphous silica were also investigated using phenanthroline complexation to confirm the presence of Fe(II) ions. This body of data showed compelling evidence that a portion of the transition metal ions in contact with the fumed silica were reduced to lower oxidation states while some of the silicon ions were observed to be “oxidized” to higher oxidation states. The ratio of Fe(II) over Fe(III) found by XPS deconvolution for the chloride spectra matches well with theoretical prediction based upon a simple surface reaction between the Fe(III) ions and the lower valent Si ions. The Fe doping was deduced to be more likely at the axial position of the Si–O bond rather than the equatorial. It is remarkable that these observed transitions in the metal ion oxidation states occurred at room temperature. The inherent simplicity of this technique is general to many reducible metal oxides, and thus, its use in preparations may provide a new way of controlling the ratio of various oxidation states of metal elements.

New Insight of Water-Splitting Photocatalyst: H2O2-Resistance Poisoning and Photothermal Deactivation in Sub-micrometer CoO Octahedrons

Hydrogen production by photocatalytic overall water-splitting represents an ideal pathway for clean energy harvesting, for which developing high-efficiency catalysts has been the central scientific topic. Nanosized CoO with high solar-to-hydrogen efficiency (5%) is one of the most promising catalyst candidates. However, poor understanding of this photocatalyst leaves the key issue of rapid deactivation unclear and severely hinders its wide application. Here, we report a sub-micrometer CoO octahedron photocatalyst with high overall-water-splitting activity and outstanding ability of H2O2-resistance poisoning. We show that the deactivation of CoO catalyst originates from the unintended thermoinduced oxidation of CoO during photocatalysis, with coexistence of oxygen and water. We then demonstrate that introduction of graphene, as a heat conductor, largely enhanced the photocatalytic activity and stability of the CoO. Our work not only provides a new insight of CoO for photocatalytic water splitting but also demonstrates a new concept for photocatalyst design.