Latest ArticlesMetal-semiconductor diodes constructed from two-dimensional (2D) van der Waals heterostructures show excellent gate electrostatics and a large built-in electric field at the tunnel junction, which can be exploited to make highly sensitive photodetector. Here we demonstrate a metal-semiconductor photodiode constructed by the monolayer graphene (Gr) on a few-layer black phosphorus (BP). Due to the presence of a built-in potential barrier (~0.09 ± 0.03 eV) at the Gr-BP interface, the photoresponsivity of the Gr-BP device is enhanced by a factor of 672%, and the external quantum efficiency (EQE) increases to 648% from 84% of the bare BP. Electrostatic gating allows the BP channel to be switched between p-type and n-type conduction. We further demonstrate that excitation laser power can be used to control the current polarity of the Gr-BP device due to photon-induced doping. The versatility of the Gr-BP junctions in terms of electrostatic bias-induced or light-induced switching of current polarity is potentially useful for making dynamically reconfigurable digital circuits.
Surface oxygen vacancy defects of mesoporous CeO2 nanosheets assembled microspheres (D-CeO2) are engineered by polymer precipitation, hydrothermal and surface hydrogenation strategies. The resultant D-CeO2 with a main pore diameter of 9.3 nm has a large specific surface area (~102.3 m2/g) and high thermal stability. The mesoporous nanosheets assembled microsphere structure prevents the nanosheets from aggregation, which is beneficial to effective mass transfer and shortens the migration distance of charge carriers. After surface hydrogenation, the photoresponse extends to long wavelength region, combing with the band gap from 2.63 eV reduced to 2.39 eV. Under AM 1.5 G radiation, the photocatalytic degradation rate of tetracycline (TC) can be up to 99.99%, which is three times as high as that of pristine CeO2 microspheres. The excellent solar-driven photocatalytic performance can be attributed to the efficient surface oxygen vacancy engineering and the mesoporous nanosheets assembled microsphere structure, which narrows the band gap, shortens the migration distance of carriers, promotes the spatial separation of photogenerated electron-hole pairs and favors mass transfer. The strategy provides new insights for fabricating other high-efficient oxide photocatalysts.
Developing highly efficient and cost-effective catalysts for electrochemically oxidizing biomass-derived 5-hydroxymethylfurfural (HMF) into value-added 2,5-furandicarboxylic acid (FDCA) is of great importance. Herein, we report a controllable nitrogen doping strategy to significantly improve the catalytic activity of Co3O4 nanowires for highly selective electro-oxidation of HMF into FDCA. The nitrogen doping leads to the generation of defects including nitrogen dopants and oxygen vacancies in Co3O4 nanowires, which is conducive to the formation of catalytically active sites. As a result, the electro-oxidation potential for HMF is only 1.38 V (vs. RHE) when the current density reaches 50 mA/cm2. More importantly, the conversion rate of HMF is as high as 99.5%, and the yield of FDCA is up to 96.4%.
Conversion of methane into liquid alcohol such as ethanol at low temperature in a straight, selective and low energy consumption process remains a topic of intense scientific research but a great challenge. In this work, CuFe2O4/CNT composite is successfully synthesized via a facile co-reduction method and used as catalysts to selectively oxidize methane. At a low temperature of 150 ℃, methane is directly converted to ethanol in a single process on the as-prepared CuFe2O4/CNT composite with high selectivity. A mechanism is also proposed for the significant methane selective oxidation performance of the CuFe2O4/CNT composite catalysts.
Electrochemical synthesis of ammonia has the advantages of low energy consumption and promising environmental protection, as compared to the traditional Haber-Bosch process. However, the commercial utilization of this novel system is limited by the low Faradaic efficiency, poor ammonia yield and high overpotential due to the strong N≡N bond and the dominant competing reaction of hydrogen evolution reaction (HER). Herein, a BiOCl-modified two-dimensional (2D) titanium carbide MXenes nanocomposite (BiOCl@Ti3C2Tx) is proposed as a promising electrocatalyst for ambient nitrogen (N2) reduction reaction with excellent catalytic performance and superior long-term stability at low overpotential. In 0.1 mol/L HCl, this catalyst attains a high Faradic efficiency of 11.98% and a NH3 yield of 4.06 µg h−1 cm−2 at −0.10 V (vs. RHE), benefiting from its strong interaction of Bi 6p band with the N 2p orbitals, combined with its large specific surface area and the facile electron transfer.
Ammonia (NH3) is one of the most important building blocks of the chemical industry and a promising sustainable energy carrier. Conventional production of NH3 via the Haber-Bosch process requires high temperature and high pressure, which is energy demanding and suffers safety issues. Photocatalytic nitrogen reduction reaction (NRR) is a green and sustainable route for NH3 production, and has been expected to be an alternative for NH3 production under mild conditions. However, solar-driven N2 activated has appeared as the bottleneck for photocatalytic NRR. In this work, we propose that single Ru atom supported by BeO monolayer is a promising photocatalytic single atom catalyst (SAC) for efficient N2 activation with visible illumination. The high efficiency originates from the enhanced absorption in the visible range, as well as the back-donation mechanism when N2 were adsorbed on the SAC. Our results show that N2 can be efficiently activated by the Ru/BeO SAC and be reduced to NH3 with extremely low limiting potential of −0.41 V. The NRR process also exhibits dominate selectivity respect to hydrogen evolution.
Designing and developing the highly efficient photocatalysts is full of significance to achieve spontaneous photolysis water. In this work, using the first-principles calculations, we have performed a systematic theoretical study of water splitting photocatalytic activity of the InSe/g-CN heterojunction. It is concluded that the InSe/g-CN heterojunction is a typical type-Ⅱ semiconductor, whose electrons and holes can be effectively separated. And the potential of the conduction band minimum (CBM) and valence band maximum (VBM) satisfy the requirements for photolysis water. Moreover, the changes of Gibbs free energy (ΔG) of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) are calculated to investigate thermodynamic sustainability of photolysis water. The results show that when pH = 7, the potential driving force provided by the InSe/g-CN heterojunction can ensure the spontaneous progress of HER and OER. In addition, it is found that the solar conversion efficiency (ηS) of the InSe/g-CN heterojunction is up to 13.7%, which indicates it has broad commercial application prospects. Hence, the InSe/g-CN heterojunction is expected to be an excellent candidate for photolysis water.
Explore the photo-piezoelectric synergistic micro-mechanism by density functional theory (DFT) calculations at the electronic and atomic level is important. In this work, to understand the synergistic mechanism, atomic and electronic properties of typical piezoelectric and photocatalytic material BaTiO3 were initially investigated with different strains. Subsequently, the adsorption of volatile organic compounds (VOCs) on the BaTiO3 (001) surface was determined during the piezoelectric process. In addition, the relationship between deformation ratio, the electronic structure and adsorption energy was understood in the deformation ratio range of 7%-12% for the optimal catalytic effect. The results of charge density differences and Born effective charge reveal the synergistic mechanism of piezoelectric photocatalysis. The built-in electric field formed by polarization results in the enhanced separation of charges, which makes the surface charges aggregation, enhancing the adsorption of VOCs, and benefiting the subsequent photocatalytic degradation. This work can provide significant theoretical guidance for the piezoelectric photocatalytic degradation of pollutants with the optimal strain range.
How to utilize inexhaustible solar light as a means of disinfection technology for its cheap and green remains a challenge. In this work, core-shell ZnO@ZIF-8 was synthesized and used for bacterial inactivation synergizing with peroxymonosulfate (PMS) under visible light irradiation. It took 50 min to achieve thorough sterilization for 7.5-log Escherichia coli (E. coli) cells in vis/PMS/ZnO@ZIF-8 system, compared with that 4.5-log reduction completed in vis/PMS/ZnO system under the same conditions. The enhanced photocatalytic disinfection mechanisms of fabricated ZnO@ZIF-8 were investigated by UV–vis diffuse reflectance spectra, electrochemical impedance spectra and Mott-Schottky plots. The promoted bactericidal efficiency was attributed to higher charge-separation efficiency and stronger oxidation ability of photo-generated holes. Moreover, it was found that 1O2 and •OH induced bacterial cell lesion process, and the former was the main active species. The external reactive oxygen species (ROS) caused a series of cell wall damage, intercellular ROS up-regulation and genome DNA unwinding, finally resulted in irreversible bacterial death. A two-route mechanism in vis/PMS/ZnO@ZIF-8 system was proposed, in which the generation of 1O2 was supposed as the product of the oxygen oxidation of photo-generated holes and PMS dissociation. Our work is expected to provide advanced information about a low-cost water disinfection technology of visible light photocatalysis.
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