General Strategy for Preparing Uniform Polyoxometalate Microcrystals with Selectively Exposed Low-Index Facets

Polyoxometalate (POM) microcrystals have unique molecular structures and abundant acid–base sites, making them good candidates as crystalline catalysts. The facets of POM materials can greatly affect their catalytic activity due to the different atomic arrangements in various facets. Many factors affect the nucleation and growth processes of crystalline materials; therefore, preparing uniform POM microcrystals with selectively exposed facets is a challenge. In this work, we report a general strategy for preparing polyoxometalate microcrystals of ammonium salts with selective exposure of low-index facets by the hydrothermal decomposition of urea. The obtained NH4–PMo ([PMo12O40]3–) microcrystals show uniform dodecahedral cubes with selective exposure of (110) facets. A series of controlled experiments demonstrates that the rate and amount of NH4+ production play key roles in the growth of POM microcrystals. NH4–PMo microcrystals exhibit excellent activity in the Knoevenagel condensation reaction, and their catalytic activities have a positive correlation with the exposed (110) facets of NH4–PMo. NH4–PMo microcrystals can provide more Lewis acid–base sites due to their high specific surface area and selectively exposed (110) facets. Moreover, NH4–PW ([PW12O40]3–) microcrystals with selectively exposed (110) facets were also successfully prepared by the same method, indicating that this preparation strategy has great potential to be applied to the synthesis of other valuable POM microcrystals

Preparation of Mesoporous TiO₂/Co₃O₄ Nanosheets for Efficient Photocatalytic Oxygen and Hydrogen Evolution

TiO2-based two-dimensional nanosheet composite materials are promising photocatalysts for water splitting. The mesoporous structure possesses a high surface-to-volume ratio with more active sites. It is fantastic for photocatalysts to integrate the advantages of a porous structure into two-dimensional materials. The calcined ultrathin layered double hydroxides (LDHs) are porous metal oxide nanosheets, which are considered ideal templates to construct photocatalysts. In this work, we report the design and fabrication of amorphous aluminum oxide-supported anatase TiO2/spinel Co3O4 (TiO2/Co3O4) mesoporous nanosheets by calcinating ultrathin TiO2/CoAl-LDH precursors. The built-in electric field in the TiO2/Co3O4 interface facilitates the charge transfer, and Co3O4 acts as a cocatalyst to further enhance the oxygen evolution reaction activity. Consequently, the TiO2/Co3O4 photocatalyst exhibits excellent photocatalytic performances for the evolution of O2 and H2. This strategy for preparing mesoporous nanosheet photocatalysts is expected to extend to the other metal oxide semiconductor systems

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A simple imaging protocol for autofluorescence elimination and optical sectioning in fluorescence endomicroscopy: supplementary materia

Regrowth-free AlGaInAs MQW polarization controller integrated with sidewall grating DFB laser

We report an AlGaInAs multiple quantum well integrated source of polarization controlled light consisting of a polarization mode converter PMC, differential phase shifter(DPS), and a side wall grating distributed-feedback DFB laser. We demonstrate an asymmetrical stepped-height ridge waveguide PMC to realize TE to TM polarization conversion and a symmetrical straight waveguide DPS to enable polarization rotation from approximately counterclockwise circular polarization to linear polarization. Based on the identical epitaxial layer scheme, all of the PMC, DPS, and DFB laser can be integrated monolithically using only a single step of metalorganic vapor phase epitaxy and two steps of III V material dry etching. For the DFB-PMC device, a high TE to TM polarization conversion efficiency 98% over a wide range of DFB injection currents is reported at 1555 nm wavelength. For the DFB-PMC-DPS device, a 60 degree rotation of the Stokes vector was obtained on the Poincar\'e sphere with a range of bias voltage from 0 V to -4.0 V at IDFB is 170 mA

Stepped-height ridge waveguide MQW polarization mode converter monolithically integrated with sidewall grating DFB laser

We report the first demonstration of a 1555 nm stepped-height ridge waveguide polarization mode converter monolithically integrated with a side wall grating distributed-feedback (DFB) laser using the identical epitaxial layer scheme. The device shows stable single longitudinal mode (SLM) operation with the output light converted from TE to TM polarization with an efficiency of >94% over a wide range of DFB injection currents (IDFB) from 140 mA to 190 mA. The highest TM mode purity of 98.2% was obtained at IDFB=180 mA. A particular advantage of this device is that only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching are required for the whole integrated device fabrication, significantly reducing complexity and cost