Defect engineering in photocatalytic materials

N2 fixation by the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to achieve NH3 production, which still heavily relies on the Haber-Bosch process at the cost of huge energy and massive production of CO2 . A noble-metal-free Bi4 V2 O11 /CeO2 hybrid with an amorphous phase (BVC-A) is used as the cathode for electrocatalytic NRR. The amorphous Bi4 V2 O11 contains significant defects, which play a role as active sites. The CeO2 not only serves as a trigger to induce the amorphous structure, but also establishes band alignment with Bi4 V2 O11 for rapid interfacial charge transfer. Remarkably, BVC-A shows outstanding electrocatalytic NRR performance with high average yield (NH3 : 23.21 μg h-1  mg-1cat. , Faradaic efficiency: 10.16 %) under ambient conditions, which is superior to the Bi4 V2 O11 /CeO2 hybrid with crystalline phase (BVC-C) counterpart.

An Amorphous Noble-Metal-Free Electrocatalyst that Enables Nitrogen Fixation under Ambient Conditions.

Constructing two-dimensional (2D) composites using layered materials is considered to be an effective approach to achieve high-efficiency photocatalysts. Herein, a 2D/2D g-C3N4/MnO2 heterostructured photocatalyst was synthesized via in situ growth of MnO2 nanosheets on the surface of g-C3N4 nanolayers using a wet-chemical method. The hybrid nanomaterial was characterized by a range of techniques to study its micromorphology, structure, chemical composition/states, and so on. The g-C3N4/MnO2 nanocomposite exhibited greatly improved photocatalytic activities for dye degradation and phenol removal in comparison to the single g-C3N4 or MnO2 component. On the basis of the electron paramagnetic resonance spectra, X-ray photoelectron spectra, and the Mott–Schottky measurements, we consider that a Z-scheme heterojunction was generated between the g-C3N4 nanosheets and MnO2 nanosheets, wherein the photoinduced electrons in MnO2 combined with the holes in g-C3N4, leading to enhanced charge carrier extraction and ut...

2D/2D g-C3N4/MnO2 Nanocomposite as a Direct Z-Scheme Photocatalyst for Enhanced Photocatalytic Activity

The high carrier recombination rate and serious photocorrosion of Ag3PO4 greatly restrict its photocatalytic application. Here, we fabricated an Ag3PO4/Ti3C2 Schottky catalyst and found that Ti3C2 can greatly enhanced the catalytic activity and stability of Ag3PO4. This arises from: (i) the abundant surface hydrophilic functional groups of Ti3C2 construct strong interfacial contact with Ag3PO4, which facilitate the separation of carriers; (ii) the strong redox reactivity of surface Ti sites promote multiple electron reduction reactions to induce more OH production; and (iii) a Schottky junction formed at Ag3PO4-Ti3C2 interface timely transfer electrons to Ti3C2 surface by built-in electric field, inhibiting the photocossion of Ag3PO4 caused by photogeneration electrons. Consequently, Ag3PO4/Ti3C2 exhibited excellent photocatalytic activity and stability for the degradation of organic pollutants. Especially, the apparent rate constant of 2,4-Dinitrophenol degradation with Ag3PO4/Ti3C2 was 2.5 times that of Ag3PO4/RGO and 10 times that of Ag3PO4. The photocatalytic performance of Ag3PO4/Ti3C2 toward tetracycline hydrochloride still maintained 68.4% after 8 cycles, while Ag3PO4/RGO and Ag3PO4 only maintained 36.2% and 7.8%, respectively. Furthermore, the efficient photoreduction of Cr6+ using AgI/Ti3C2 further illustrated an enormous potential in coupling Ti3C2 with other photosensitivity semiconductor to improve their catalytic activity and stability.

Ag3PO4/Ti3C2 MXene interface materials as a Schottky catalyst with enhanced photocatalytic activities and anti-photocorrosion performance

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

Ionic group doping into the semiconductor photocatalyst is a new concept to improve photocatalytic performance, which always is a difficult challenge. In this paper, PO 4 -doped Bi 2 WO 6 photocatalyst is prepared by the urea-precipitation way in the hydrothermal process for the first time. The as-prepared sample presents the universal enhanced photocatalytic activity for removing various contaminants in water compared with the pristine Bi 2 WO 6 under visible-light irradiation, such as heavy metal Cr (VI), colored dye RhB, colorless phenol and different kind antibiotics. It attributes to the doping effect of PO 4 group in Bi 2 WO 6 influencing on energy band structure, light absorption property and separation efficiency of the charge carriers. This work provides a new insight into anionic group doping effects and takes an important step toward the development of improving Bi-based photocatalyst activity.

Doping effect of phosphate in Bi2WO6 and universal improved photocatalytic activity for removing various pollutants in water

Oxide defect engineering in semiconductors is of growing interest and considered as an important strategy for promoting photocatalytic performance, as it enables to couple solar energy into oxygen activation. Herein, the surface oxygen vacancies are introduced into bismuth-rich Bi4O5I2 nanosheets (Bi4O5I2-OV) via a facile solvothermal route. By introducing oxygen vacancies into Bi4O5I2, the molecule oxygen adsorption is significantly improved. More importantly, attributed to the molecular oxygen adsorption, an instantaneous surface-bulk homojunction is constructed, which facilitates the separation and transport of photogenerated charge carriers. Therefore, noticeable molecular oxygen activation and N2 fixation are achieved in Bi4O5I2-OV. These findings may shed light on designing highly efficient photocatalysts and provide fresh insights into understanding the charge migration mechanism in oxygen vacancies-related photocatalytic system.

Molecular adsorption promotes carrier migration: Key step for molecular oxygen activation of defective Bi4O5I2

Heterojunction with nanosized interfacial contact stands out in promoting the transfer photoinduced interfacial carriers. Herein, a heterojunction with nanosized interfacial contact was designed by constructing BiVO 4 /Bi 4 V 2 O 11 element-copied heterojunction nanofibres. The heterojunction was formed by combining BiVO 4 nanofibres and embedded Bi 4 V 2 O 11 nanocrystals. They offered favourable interfacial contact on nanosized level. The photocatalytic performance of heterojunction nanofibres with nanosized interfacial contact were indicated to be markedly enhanced compared with that of pure BiVO 4 nanofibres. Furthermore, we also observed a 10-fold enhancement in the photocurrent intensity for the heterojunction nanofibres with nanosized interfacial contact, indicating the enhancement of photocatalytic properties was attributed to the nanosized interfacial contact with wonderful interfacial photoinduced carriers transfer behavior.

Realizing nanosized interfacial contact via constructing BiVO4/Bi4V2O11 element-copied heterojunction nanofibres for superior photocatalytic properties

Bi5+-self-doped Bi4V2O11 (Bi5+-BVO) nanotubes with p–n homojunctions are fabricated via an oxygen-induced strategy. Calcinating the as-spun fibers with abundant oxygen plays a pivotal role in achieving Bi5+ self-doping. Density functional theory calculations and experimental results indicate that Bi5+ self-doping can narrow the band gap of Bi4V2O11, which contributes to enhancing light harvesting. Moreover, Bi5+ self-doping endows Bi4V2O11 with n- and p-type semiconductor characteristics simultaneously, resulting in the construction of p–n homojunctions for retarding rapid electron–hole recombination. Benefiting from these favorable properties, Bi5+-BVO exhibits a superior photocatalytic performance in contrast to that of pristine Bi4V2O11. Furthermore, this is the first report describing the achievement of p–n homojunctions through self-doping, which gives full play to the advantages of self-doping.

Congmin Zhang

Papers

Doping effect of phosphate in Bi2WO6 and universal improved photocatalytic activity for removing various pollutants in water

Molecular adsorption promotes carrier migration: Key step for molecular oxygen activation of defective Bi4O5I2

Realizing nanosized interfacial contact via constructing BiVO4/Bi4V2O11 element-copied heterojunction nanofibres for superior photocatalytic properties

Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a p–n Homojunction Toward Promoting the Photocatalytic Performance

Cyano group modified g-C3N4: Molten salt method achievement and promoted photocatalytic nitrogen fixation activity