Photocatalytic hydrogen production using stable metal-organic frameworks (MOFs), especially the titanium-based MOFs (Ti-MOFs) as photocatalysts is one of the most promising solutions to solve the energy crisis. However, due to the high reactivity and harsh synthetic conditions, only a limited number of Ti-MOFs have been reported so far. Herein, we synthesized a new amino-functionalized Ti-MOFs, named NH2-ZSTU-2 (ZSTU stands for Zhejiang Sci-Tech University), for photocatalytic hydrogen production under visible light irradiation. The NH2-ZSTU-2 was synthesized by a facile solvothermal method, composed of 2,4,6-tri(4-carboxyphenylphenyl)-aniline (NH2-BTB) triangular linker and infinite Ti-oxo chains. The structure and photoelectrochemical properties of NH2-ZSTU-2 were fully studied by powder x-ray diffraction, scanning electron microscope, nitro sorption isotherms, solid-state diffuse reflectance absorption spectra, and Mott–Schottky measurements, etc., which conclude that NH2-ZSTU-2 was favorable for photocatalytic hydrogen production. Benefitting from those structural features, NH2-ZSTU-2 showed steady hydrogen production rate under visible light irradiation with average photocatalytic H2 yields of 431.45 μmol·g−1·h−1 with triethanolamine and Pt as sacrificial agent and cocatalyst, respectively, which is almost 2.5 times higher than that of its counterpart ZSTU-2. The stability and proposed photocatalysis mechanism were also discussed. This work paves the way to design Ti-MOFs for photocatalysis.
Charge trap memory devices with Zr x Si 1-x O 2 films as charge trapping layer consisting of nine [(ZrO 2 ) m (SiO 2 ) n (ZrO 2 ) m (SiO 2 ) n ] units have been fabricated and investigated. The composition distribution was modulated by controlling the m and n values in each unit. It is observed that the variation of composition distribution can induce the energy band bending and additional potential barrier, which significantly improve the program/erase speed and data retention characteristics as well as extending the temperature insensitive range. When the effective potential barrier including classic potential barrier and additional potential barrier is 1.52 eV, the memory device exhibits a lower charge loss of 4.5% at 200 °C over a period of 10 4 s, a wider temperature insensitive range of 20 °C-111 °C, and a faster program time of 4.0×10 −5 s achieving +6 V flat band voltage shift. The effective potential barrier values should be in the range of 1.52-1.36 eV, taking into consideration the trade-off between the retention and program/erase speed. The additional potential barrier can increase the electron tunneling distance in the directions of tunneling layer and blocking layer, giving rise to recapture process and temperature insensitive of retention characteristics. In addition, the additional potential barrier decreases the electron tunneling distance arriving trapping layer conduction band, improving the program speed. The results provide a reference to trapping layer composition distribution for future charge trap memory applications.
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