다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

Crystal facet engineering of photoelectrodes for photoelectrochemical water splitting

Bismuth-based semiconductors are a unique and promising group of recently developed advanced photocatalytic materials. They have been widely applied in several areas including the generation of H2 by splitting water, decomposition of organic and inorganic pollutants in both wastewater and polluted air, and organic synthesis through harvesting the energy of light. The electronic structure of bismuth-based semiconductors confers them with a suitable band gap for visible-light response and a well-dispersed valence band composed of hybrid orbitals of Bi6s and O2p, making them a promising candidate when compared to other metal oxide semiconductors. In addition, they are simple to operate and prepare with controlled morphologies, making them attractive as potential photocatalysts. The purposes of this review are (1) summarization of advanced bismuth-based compounds that have been applied to date, (2) statement of challenges facing this material and possible approaches to overcome them, and (3) suggestions for future work.

Bismuth-based photocatalytic semiconductors: Introduction, challenges and possible approaches

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Review on nanoscale Bi-based photocatalysts

Bismuth oxyhalide layered materials for energy and environmental applications

In order to develop low-cost photocatalyst, commercial Bi2O3 was utilized as raw material to prepare α-Bi2O3/BiOCl core-shell heterojunction via a facile in situ chemical transformation method. To clarify experimentally the band alignment relationships between the α-Bi2O3 and BiOCl (0 0 1), the α-Bi2O3/BiOCl (0 0 1) core–shell heterojunction band offsets were analyzed by X-ray photoelectron spectroscopy (XPS). Here based on energy gaps, valence band values of α-Bi2O3 and BiOCl (0 0 1), core levels difference of Bi 4f in α-Bi2O3/BiOCl (0 0 1) heterojunction, we demonstrate that band alignment of ∼0.28 eV exists between α-Bi2O3 and BiOCl with α-Bi2O3 possessing the higher valence band potential or electron affinity which is a driving force of valence band holes from α-Bi2O3 to BiOCl (0 0 1). While, the electrons in conduction band were driven to migrate through conduction band potential difference (0.49 eV) from BiOCl (0 0 1) to α-Bi2O3.

Band alignment and enhanced photocatalytic activation for α-Bi2O3/BiOCl (0 0 1) core–shell heterojunction

The assembling heterojunction, one of the key topics in photocatalysts and semiconductors (SCs), is generally accomplished in at least two steps, of which the first step is the synthesis of a matrix, and then the growth of the second phase on the matrix. Herein we present the preparation of α/β-Bi2O3 heterojunctions by an in situ phase transformation technique. Under normal pressure, a facile citrate method was used to synthesize β-Bi2O3 nanosheets and α/β-Bi2O3 heterojunctions. The novel features of the process are the mild operating conditions by an appropriate selection of heat treatment temperature and time. Using transmission electron microscopy (TEM), we found that a number of nano-sized α-Bi2O3 form on the β-Bi2O3 nanosheet via a controlled β→α phase transition, generating a large number of heterojunctions. The CM1 (calcining β-Bi2O3 precursor at 363 °C for 4 h) heterojunction achieves a strong visible light absorption and dye absorption capacity and produces a very high reaction rate for Rhodamine B (RhB) photodegradation. Electrochemical impedance spectroscopy (EIS) revealed excellent charge transfer characteristics of the heterojunction, which accounts for its high photoactivity. Using the X-ray electron valence band spectra, it is found that the valence band of α-Bi2O3 is more negative than that of β-Bi2O3. Thus, in heterojunctions, the photogenerated holes in β-Bi2O3 are transferred to α-Bi2O3 with good charge transport characteristics by the intrinsic driving force in the interface field. Furthermore, a separated hole can accomplish a transfer process from α-Bi2O3 to the aqueous solution within its lifetime due to the diameter of α-Bi2O3 being less than 17.6 nm.

Band alignment and enhanced photocatalytic activation of α/β-Bi2O3 heterojunctions via in situ phase transformation.

It is commonly considered that the upconversion (UC) photocatalytic material is prepared by at least two steps which the first step is the synthesis of up-conversion fluorescent material, and then growth of the corresponding semiconductor on the fluorescent material. Herein, we report on the design and synthesis of core (BiVO4)–shell (BiVO4: Er3+, Yb3+) composite UC photocatalyst by in situ process. The novel features of the process are the mild operating conditions by a doping selection of Er3+, Yb3+. Using transmission electron microscopy (TEM), we found the composite is characteristic of monoclinic scheelite structure. Through X-ray photoelectron spectroscopy (XPS), it suggests that the photocatalyst comprised of core (BiVO4)–shell (BiVO4: Er3+, Yb3+). The presence of dopant (Er3+ and Yb3+) in the shell could suppress the radiative recombination process, leading to higher photon efficiency. Furthermore, photoactivities for near infrared (NIR)-light-driven photoelectrochemical (PEC) water splitting demonstrate that the photocatalytic performance of the Er/Yb co-doped BiVO4 (U08, 3.22 μA cm−2, 0.7 V vs. RHE) is about 7 times that of undoped BiVO4 (U0, 0.48 μA cm−2, 0.7 V vs. RHE). This enhancement was also proven by the elimination efficiency of RhB under the NIR illuminations. The valence spectra reveal that the shell layer photocatalyst plays crucial roles in enhancing charge carrier mobilities.

Lianwei Shan

Papers

Band alignment and enhanced photocatalytic activation for α-Bi2O3/BiOCl (0 0 1) core–shell heterojunction

Band alignment and enhanced photocatalytic activation of α/β-Bi2O3 heterojunctions via in situ phase transformation.

Er3+, Yb3+ doping induced core–shell structured BiVO4 and near-infrared photocatalytic properties

Solar light driven pure water splitting of B-doped BiVO4 synthesized via a sol–gel method

Photoelectrochemical (PEC) water splitting of BiOI{001} nanosheets synthesized by a simple chemical transformation