We herein demonstrate self-doping of the CO 3 2− anionic group into a wide bandgap semiconductor Bi 2 O 2 CO 3 realized by a one-pot hydrothermal technique. The photoresponsive range of the self-doped Bi 2 O 2 CO 3 can be extended from UV to visible light and the band gap can be continuously tuned. Density functional theory (DFT) calculation results demonstrate that the foreign CO 3 2− ions are doped in the caves constructed by the four adjacent CO 3 2− ions and the CO 3 2− self-doping can effectively narrow the band gap of Bi 2 O 2 CO 3 by lowering the conduction band position and meanwhile generating impurity level. The photocatalytic performance is evaluated by monitoring NO removal from the gas phase, photodegradation of a colorless contaminant (bisphenol A, BPA) in an aqueous solution, and photocurrent generation. In comparison with the pristine Bi 2 O 2 CO 3 which is not sensitive to visible light, the self-doped Bi 2 O 2 CO 3 exhibits drastically enhanced visible-light photoreactivity, which is also superior to that of many other well-known photocatalysts such as P25, C 3 N 4 , and BiOBr. The highly enhanced photocatalytic performance is attributed to combination of both efficient visible light absorption and separation of photogenerated electron− hole pairs. The self-doped Bi 2 O 2 CO 3 also shows decent photochemical stability, which is of especial importance for its practical applications. This work demonstrates that self-doping with an anionic group enables the band gap engineering and the design of high-performance photocatalysts sensitive to visible light.
Semiconductor photocatalysis as a desirable technology shows great potential in environmental remediation and renewable energy generation, but its efficiency is severely restricted by the rapid recombination of charge carriers in the bulk phase and on the surface of photocatalysts. Polarization has emerged as one of the most effective strategies for addressing the above‐mentioned issues, thus effectively promoting photocatalysis. This review summarizes the recent advances on improvements of photocatalytic activity by polarization‐promoted bulk and surface charge separation. Highlighted is the recent progress in charge separation advanced by different types of polarization, such as macroscopic polarization, piezoelectric polarization, ferroelectric polarization, and surface polarization, and the related mechanisms. Finally, the strategies and challenges for polarization enhancement to further enhance charge separation and photocatalysis are discussed.
Efficient photo- and piezoelectric-induced molecular oxygen activation are both achieved by macroscopic polarization enhancement on a noncentrosymmetric piezoelectric semiconductor BiOIO . The replacement of V ions for I in IO polyhedra gives rise to strengthened macroscopic polarization of BiOIO , which facilitates the charge separation in the photocatalytic and piezoelectric catalytic process, and renders largely promoted photo- and piezoelectric induced reactive oxygen species (ROS) evolution, such as superoxide radicals ( O ) and hydroxyl radicals ( OH). This work advances piezoelectricity as a new route to efficient ROS generation, and also discloses macroscopic polarization engineering on improvement of multi-responsive catalysis.
The fabrication of multiple heterojunctions with tunable photocatalytic reactivity in full-range BiOBr-BiOI composites based on microstructure modulation and band structures is demonstrated. The multiple heterojunctions are constructed by precipitation at room temperature and characterized systematically. Photocatalytic experiments indicate that there are two types of heterostructures with distinct photocatalytic mechanisms, both of which can greatly enhance the visible-light photocatalytic performance for the decomposition of organic pollutants and generation of photocurrent. The large separation and inhibited recombination of electron-hole pairs rendered by the heterostructures are confirmed by electrochemical impedance spectra (EIS) and photoluminescence (PL). Reactive species trapping, nitroblue tetrazolium (NBT, detection agent of (•)O2(-)) transformation, and terephthalic acid photoluminescence (TA-PL) experiments verify the charge-transfer mechanism derived from the two types of heterostructures, as well as different enhancements of the photocatalytic activity. This article provides insights into heterostructure photocatalysis and describes a novel way to design and fabricate high-performance semiconductor composites.
The demand for deep-ultraviolet (deep-UV) coherent light sources (l < 200 nm) has become increasingly urgent because they have important applications in semiconductor photolithography, laser micromachining, modern scientific instruments (super-high-resolution and angle-resolved photoemission spectrometer, for example) and so forth. To date, the most effective method to generate deep-UV coherent light with solid-state lasers is through cascaded frequency conversion, in particular multiharmonics, using deep-UV nonlinear optical (NLO) crystals. Therefore, the discovery of suitable deep-UV NLO crystals is of great importance.In the past decades, the anionic group theory,  which reveals that the overall nonlinearity of a crystal is the geometrical superposition of the microscopic second-order susceptibility tensors of the NLO-active anionic groups, has been very successful in developing borate NLO crystals. Several important NLO crystals have been discovered, including b-BaB 2 O 4 (BBO),  LiB 3 O 5 (LBO),  CsB 3 O 5 (CBO),  CsLiB 6 O 10 (CLBO), [7,8] and YCa 4 O(BO 3 ) 3 (YCOB),  which have been widely used in NLO optics. However, they cannot be used to generate deep-UV coherent light (l < 200 nm) by multiharmonic generation owing to some inherent shortcomings. Thus, the search for new NLO materials, particularly for deep-UV applications, has attracted considerable attention.  A deep-UV NLO material must have a very short absorption edge, and in this respect, beryllium borates are attractive as they are supposed to possess very large energy gap. It is also well known that the incorporation of fluorine can effectively cause the UV absorption edge of a crystal to blue-shift, so our group has made great efforts to search for new deep-UV NLO fluorine beryllium borate crystals. After more than ten years of intensive research in our group, the  Unfortunately, the KBBF crystal is very difficult to grow in thickness because of its strong layering tendency, which severely limits the coherent output power. Therefore, there is great demand for new types of fluorine beryllium borates which have deep-UV transmission, moderate birefringence, and relatively large second harmonic generation (SHG) coefficients, and at the same time overcome the crystal-growth problems found in the KBBF crystal.Alkali-metal and alkaline-earth-metal cations are favorable for the transmission of UV light because there are no d-d electron or f-f electron transitions in this spectral region. As shown in numerous explorations, the size and charge of cations have great influence on the macroscopic packing of anions, which in turn determines the overall NLO properties in a crystal. [21,22] Herein, we utilize both alkali-metal and alkaline-earth-metal cations. Different charge/size combinations of mixed cations may have different influences on the packing of anions, so it is more likely to isolate new phases with interesting stoichiometries, structures, and properties. To date, no fluorine beryllium borates with...
The identification of structural damage is an important objective of health monitoring for civil infrastructures. System identification and damage detection based on measured vibration data have received intensive studies recently. Frequently, damage to a structure may be reflected by a change of some system parameters, such as a degradation of the stiffness. In this paper, we propose an adaptive tracking technique, based on the extended Kalman filter approach, to identify the structural parameters and their changes when vibration data involve damage events. The proposed technique is capable of tracking the changes of system parameters from which the event and severity of structural damage may be detected on‐line. Our adaptive filtering technique is based on the current measured data to determine the parametric variation so that the residual error of the estimated parameters is contributed only by noise. This technique is applicable to linear and nonlinear structures. Simulation results for tracking the parametric changes of nonlinear elastic, hysteretic and linear benchmark structures are presented to demonstrate the application and effectiveness of the proposed technique in detecting structural damage, using measured vibration data. Copyright © 2005 John Wiley & Sons, Ltd.
A facile and controllable in situ reduction strategy is used to create surface oxygen vacancies (OVs) on Aurivillius‐phase Sr2Bi2Nb2TiO12 nanosheets, which were prepared by a mineralizer‐assisted soft‐chemical method. Introduction of OVs on the surface of Sr2Bi2Nb2TiO12 extends photoresponse to cover the whole visible region and also tremendously promotes separation of photoinduced charge carriers. Adsorption and activation of CO2 molecules on the surface of the catalyst are greatly enhanced. In the gas‐solid reaction system without co‐catalysts or sacrificial agents, OVs‐abundant Sr2Bi2Nb2TiO12 nanosheets show outstanding CO2 photoreduction activity, producing CO with a rate of 17.11 μmol g−1 h−1, about 58 times higher than that of the bulk counterpart, surpassing most previously reported state‐of‐the‐art photocatalysts. Our study provides a three‐in‐one integrated solution to advance the performance of photocatalysts for solar‐energy conversion and generation of renewable energy.
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