Zhiguo Yi

Photocatalytic oxidation of methane over silver decorated zinc oxide nanocatalysts

The search for active catalysts that efficiently oxidize methane under ambient conditions remains a challenging task for both C1 utilization and atmospheric cleansing. Here, we show that when the particle size of zinc oxide is reduced down to the nanoscale, it exhibits high activity for methane oxidation under simulated sunlight illumination, and nano silver decoration further enhances the photo-activity via the surface plasmon resonance. The high quantum yield of 8% at wavelengths <400u2009nm and over 0.1% at wavelengths ∼470u2009nm achieved on the silver decorated zinc oxide nanostructures shows great promise for atmospheric methane oxidation. Moreover, the nano-particulate composites can efficiently photo-oxidize other small molecular hydrocarbons such as ethane, propane and ethylene, and in particular, can dehydrogenize methane to generate ethane, ethylene and so on. On the basis of the experimental results, a two-step photocatalytic reaction process is suggested to account for the methane photo-oxidation.

Potassium niobate nanostructures: controllable morphology, growth mechanism, and photocatalytic activity

Various potassium niobate (KNbO3) nanostructures, including nanowires, nanotowers, nanocubes and nanorods, were successfully fabricated through rather facile hydrothermal processes. By adjusting the concentration of potassium hydroxide, reaction temperature and reaction time, the product morphologies can be easily controlled. High crystallinity as well as the active (001) crystal plane exposed on KNbO3 nanocrystals offer enhanced photocatalytic activity for rhodamine B decomposition in aqueous solutions under UV-visible light irradiation. The level of photocatalytic activity depends strongly on the microstructure of KNbO3 and the photoreactivity towards RhB degradation follows the order of KNbO3 nanocubes > nanowires > nanorods > nanotowers. The KNbO3 nanocubes prepared at 200 °C for 7 days in the presence of 6.5 M KOH exhibited the enhanced photocatalytic performance for the degradation of RhB to 89% after 240 min of irradiation under a sunlight simulator.

Porous FeNi oxide nanosheets as advanced electrochemical catalysts for sustained water oxidation

Iron-nickel oxide porous nanosheets were synthesized via a controlled transformation from LDH precursors, which exhibit advanced OER performance with a low overpotential of 213 mV at 10 mA cm−2, small Tafel slope (32 mV dec−1) and long-term stability, due to their high specific surface area, abundant active sites, small charge transfer resistance, and suitable adsorption energy for intermediates.

Improved photocatalytic activity by utilizing the internal electric field of polar semiconductors: a case study of self-assembled NaNbO3 oriented nanostructures

How to promote separation of photo-generated carriers is one of the key issues determining the photocatalytic activity of a semiconductor. In this paper, we report a new strategy that utilizing an internal electric field of polar semiconductors to improve photocatalytic activity and, proving it by liquid-phase photodegradation (photocatalytic RhB degradation) as well as gas-phase photodegradation (photocatalytic oxidation of CH4) experiments upon the self-assembled NaNbO3 oriented nanocuboids that were fabricated by a facial hydrothermal route. The formation conditions and mechanisms of the ordered nanostructures were also discussed.

Improved propane photooxidation activities upon nano Cu2O/TiO2 heterojunction semiconductors at room temperature

Nano Cu2O/TiO2 heterojunctions with different weight percentage of Cu2O were fabricated by a facile impregnating method for propane oxidation at room temperature. The results indicate that the as-formed Cu2O/TiO2 heterojunctions can remarkably improve the propane photooxidation activity. Especially, for the 0.1 wt% Cu2O decorated TiO2 junctions, the activity was triple of that of the commercial P25. Moreover, the stability of Cu2O was significantly improved during the HC photooxidation. A direct Z scheme electrons and holes transfer mode was suggested to account for the improved activity as well as stability of the junctions. This study may provide a new way to improve photocatalytic activities by utilizing cheap and less stable materials.

Photocatalytic oxidation of methane over SrCO3 decorated SrTiO3 nanocatalysts via a synergistic effect

Because of the high C-H bond energy as well as the non-polar feature of CH4 molecules, oxidation of methane under mild conditions remains a challenging task for both C1 utilization and atmospheric environmental cleansing. Here we report that by using a sol-gel method SrCO3 decorated SrTiO3 nanocatalysts (SrTiO3-S) with an average particle size of ∼25 nm can be readily prepared, which surprisingly show efficient performance for photocatalytic oxidation of methane with the activity close to fourfold of P25, a benchmark photocatalyst. Further investigation revealed a synergistic effect between SrCO3 and SrTiO3 when combined together into a composite material as both of which are totally inactive for methane oxidation if used alone. Gas adsorption characterization disclosed that the SrCO3 can adsorb methane and cannot adsorb carbon dioxide, whereas the SrTiO3 will preferentially adsorb CO2 instead of CH4. Photocurrent and photoluminescence measurements indicate that SrCO3 exhibits a negligible photocurrent response relative to the SrTiO3 semiconductor under simulated solar light illumination but the formation of the SrCO3/SrTiO3 junction structure (SrTiO3-S) helps reduce surface recombination of the photogenerated electrons and holes. All these results refer to the synergistic mechanism in which the SrCO3 acts as a trapping agent to adsorb methane and weaken its C-H bond while the SrTiO3 acts as a photocatalyst to activate and oxidize methane under light illumination. The underlying photooxidation mechanism is further investigated with the aid of in situ electron paramagnetic resonance and infrared spectroscopy.

Ferroelectric, piezoelectric properties and thermal expansion of new Bi(Ni3/4W1/4)O3–PbTiO3 solid solutions

Ceramics of the Bi(Ni3/4W1/4)O3–PbTiO3 (BNW–PT) ferroelectric system were synthesized using a conventional solid-state sintering process. A morphotropic phase boundary (MPB) region separating tetragonal and rhombohedral phases has been determined based on X-ray diffraction (XRD) analysis. The composition-dependent phase transition behavior, thermal expansion, di/ferro/piezoelectric properties have been systemically investigated. The volume TECs (thermal expansion coefficients) for 0.1BNW–0.9PT and 0.2BNW–0.8PT are −1.01 × 10−5 per °C and −0.94 × 10−5 per °C, respectively, indicating the negative thermal expansion of some compositions for the binary system. The BNW–PT ceramics have Curie temperatures, TC, ranging from 460 °C to ∼152 °C with the variation of BNW constituent. The tetragonal-rich composition 0.20BNW–0.80PT is found to have the largest remnant polarization, Pr ∼ 23.4 μC cm−2. The highest piezoelectric coefficient d33 ∼ 145 pC N−1 is achieved at MPB composition 0.32BNW–0.68PT. The maximum strain value ∼0.194% is also obtained in the 0.32BNW–0.68PT ceramic.

Photocatalytic oxidation of small molecule hydrocarbons over Pt/TiO2 nanocatalysts

Highly active Pt/TiO2 catalysts were prepared by a simple photo-reduction method and used for catalytic oxidation of alkanes (C2H6 and C3H8) and alkenes (C2H4 and C3H6). It was found that significantly improved photo-activity can be reached even by loading a very small amount of Pt (0.2–0.5 wt%). Moreover, the Pt loading resulted in unexpected visible light activity for the oxidation of small molecule hydrocarbons. Further investigation using photoluminescence spectra indicate that the Pt loading helps reduce the charge carrier recombination within the TiO2 nanoparticles. Electron Paramagnetic Resonance (EPR) spectra reveal both oxygen molecules and lattice oxygen participate in the hydrocarbons photooxidation. The transfer and reaction mechanisms of charge carriers during the photo-oxidation process are discussed in detail.