Internal Polarization Modulation in Bi2 MoO6 for Photocatalytic Performance Enhancement under Visible-Light Illumination

Constructing a interfacial electric field for efficient reduction of nitrogen to ammonia

Electrochemical nitrogen reduction (eNRR) is a cost-effective and environmentally sustainable approach for ammonia production. MoS2, as a typical layered transition metal compound, holds significant potential as an electrocatalyst for the eNRR. Nevertheless, it suffers from a limited number of active sites and low electron transfer efficiency. In this study, we constructed a heterostructure by depositing SnO2 (an n-type semiconductor) nanoparticles on MoS2 (a p-type semiconductor). This unique interfacial structure not only generates abundant interfacial contacts but also facilitates the transfer of electrons from SnO2 to MoS2, leading to the formation of an interfacial electric field. Theoretical calculations demonstrate that this electric field increases the number of active electrons, facilitating N2 adsorption and NN bond activation. Moreover, it increases the degree of orbital overlap between N2 and SnO2/MoS2, effectively reducing the energy barrier of the rate-determining step. Benefiting from the interfacial electric field effect, the SnO2/MoS2 catalyst exhibits significant catalytic activity and selectivity towards eNRR, with an ammonia yield of 47.1 µg h-1 mg-1 and a Faraday efficiency of 19.3 %, surpassing those reported for the majority of MoS2- and SnO2-based catalysts.

Chloride Adsorbates Enhance the Photocarrier Separation and Promote the Bio-Syngas Evolution

Photocarrier separation and migration to the surface are vital for photocatalysis. However, the mobility of the surface holes and electrons makes them easily recombine before participating in the surface reaction, which constrains the photocatalytic efficiency. Targeting this problem, herein, it is reported that chloride adsorbates enhance the photocarrier separation and promote the bio-syngas evolution. Chloride, adsorbed on the surface of CdS (CdS-Cl), can increase the internal electric field and enhance the charge separation and migration to the surface. Moreover, compared with pristine CdS where holes are mobile and distributed on all the surface atoms, CdSCl can reduce the hole mobility via delocalization on specific sites and thus prolong the photocarrier lifetime. This contributes to an 11-fold enhanced photocatalytic syngas evolution from glycerol. This study reports the pivotal effect of surface adsorbates on photocarrier separation and offers a convenient strategy to prohibit surface holes and electrons recombination for solar energy utilization.Chloride absorbates on CdS contribute to enhanced photocatalytic syngas evolution from glycerol by increasing the internal electric field.

A novel γ‒BMO@BMWO Z‒Scheme heterojunction for promotion photocatalytic performance: Nanofibers thin film by Co‒axial‒electrospun

Bismuth molybdate has three phases α-Bi₂MoO₆, β-Bi₂Mo₂O₉, and γ- Bi₂Mo₃O₁₂, each of which has unique properties that distinguish them from each other. Among them, Bi₂MoO₆ and Bi₂Mo₃O₁₂ have the most stability. In this research, γ-Bi₂MoO₆@Bi₂Mo_2.66W_0.34O₁₂ core‒shell nanofibers were deposited on the stainless steel mesh as effective and low‒cost substrate. The co‒axial electrospinning as a simple method was applied to form nanofibers on the substrate. Both of the abovementioned bismuth molybdates contents include different crystal facets, controlling the Red‒Ox properties. α-Bi₂MoO₆ possesses the vast numbers of oxygen vacancies in Mo-O bonding makes the oxidant {100} crystal facet. Likewise, γ‒Bi₂Mo_2.66W_0.34O₁₂ contains brittle facet of {010} with high concentration of Oxygen vacancies resulted in oxidative capability of the core‒shell composite. The obtained data indicated the key role of OH radical through photocatalytic reactions and a new heterojunction having direct Z‒scheme standing.

Ferroelectric-assisted charge carrier separation over Bi2MoO6 nanosheets for photocatalytic dye degradation

Low energy conversion efficiency from the absorbed photon to the catalytic species remains a major obstacle for the real application of photocatalysis. In recent years, the introduction of a built-in electric field has proved to be impactful in facilitating the photoinduced charge separation, among which, ferroelectric polarization is highly recommended by getting rid of mechanical stresses. Developing ferroelectrics directly as photoactive semiconductors is promising in view of the synergistic catalytic enhancement. Therefore, Bi₂MoO₆ nanosheets with ultrathin layered structure (<10 nm) and abundant oxygen vacancies were synthesized through the hydrothermal method. The two-dimensional nanostructure created more active sites and a convenient polarization condition. Subsequently, corona poling was applied on the Bi₂MoO₆ nanosheets, which can significantly accelerate the 100% degradation rate of RhB from 50 to 20 min, surpassing that of metal-free photocatalysts. The combined effect of semiconductor, ferroelectric polarization, oxygen vacancies, and nano-layered structure offers new strategies for designing multifield coupling catalysts, providing insights into the regulation of charge carrier dynamics.

Enhanced Sunlight-Driven Reactive Species Generation via Polarization Field in Nanopiezoelectric Heterostructures

Although it is established that the force-induced electric polarization field of piezoelectric semiconductors can be used to tune the transfer rate of photoexcited charge carriers, there is still a lack of successful strategies to effectively improve the photocatalytic reactivity and solar-to-chemical conversion efficiency (SCC) of piezoelectric materials. Here, we are the first to prepare and study a kind of catalyst based on nanopiezoelectric heterostructures of LiNbO₃-type ZnTiO₃·TiO₂ and tetragonal BaTiO₃ with Pt or FeO_x nanoparticle modification (i.e., ZBTO-Pt or ZBTO-FeO_x) for reactive species generation. With respect to the production of ^•OH and ^•O₂^- radicals, higher amounts were observed in piezophotocatalysis relative to those for individual piezo- and photocatalysis. Benefiting from the charge transfer resistance decreases by the deposition of Pt and FeO_x, the amounts of ^•OH radicals formed on ZBTO-Pt and ZBTO-FeO_x were approximately 48 and 21% higher than that on isolated ZBTO during piezophotocatalysis, and for the amounts of ^•O₂^- radicals the enhancements were approximately 11 and 6%, respectively. Furthermore, the concentrations of H₂O₂ formed on ZBTO-Pt and ZBTO-FeO_x under piezophotocatalysis reached approximately 315 and 206 μM after 100 min of reaction (and was still increasing) corresponding to 0.10 and 0.06% SCCs, respectively, which were also much higher than the concentrations and SCCs observed for piezo- and photocatalysis. The enhancements of piezophotocatalytic activities with these piezoelectric materials were related to the mechanical strain exerted on ZBTO, which generated a larger electric polarization field than those on ZnTiO₃·TiO₂ and BaTiO₃ as analyzed by a finite element method. This high-intensity electric polarization field accelerated the separation and transportation of photoexcited charge carriers in the highly sunlight responsive nanopiezoelectric heterostructures based on ZBTO-Pt and ZBTO-FeO_x.

Role of the Polar Electric Field in Bismuth Oxyhalides for Photocatalytic Water Splitting

The built-in electric field generated by polar materials is one of the most effective strategies to promote the separation of photogenerated electron-hole pairs in the field of photocatalysis. However, because of the complexity and diversity of the built-in electric field in polar materials, it is not clear how to enhance the photocatalytic performance and how to control the polar electric field effectively. To this end, four-layered bismuth oxyhalides, BiOX, and BiOXO₃ (X = Br, I) were synthesized by a simple hydrothermal method. X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis confirmed that they all have the structure characteristics of a sillenite phase. Scanning electron microscopy images show that they all have the morphology of nanosheets. Among them, BiOBrO₃ was successfully synthesized and characterized for the first time in the present work. The order of photocatalytic performance (including carrier's lifetime, photocurrent density, and H₂ evolution rate) of the four compounds is listed as follows: BiOBrO₃ > BiOI > BiOIO₃ > BiOBr. In the bulk of the BiOXO₃ photocatalyst, the spontaneous polar built-in electric field along the [001] direction is the crucial factor to inhibit the recombination of photogenerated electron-hole pairs, while the surface polar electric field in BiOI can outstandingly inhibit the recombination of photogenerated electron-hole pairs due to the breaking of the mirror symmetry. Therefore, regulating the microstructure and composition of the structure unit, which generates the built-in electric field, can indeed control the magnitude, direction, and effects of built-in electric fields. In practice, we should carefully adjust the strategy according to the actual situation so as to reasonably design and use the polar electric field, giving full play to its role and enhancing the photocatalytic performance.

Atomic-Level Charge Separation Strategies in Semiconductor-Based Photocatalysts

Semiconductor-based photocatalysis as a productive technology furnishes a prospective solution to environmental and renewable energy issues, but its efficiency greatly relies on the effective bulk and surface separation of photoexcited charge carriers. Exploitation of atomic-level strategies allows in-depth understanding on the related mechanisms and enables bottom-up precise design of photocatalysts, significantly enhancing photocatalytic activity. Herein, the advances on atomic-level charge separation strategies toward developing robust photocatalysts are highlighted, elucidating the fundamentals of charge separation and transfer processes and advanced probing techniques. The atomic-level bulk charge separation strategies, embodied by regulation of charge movement pathway and migration dynamic, boil down to shortening the charge diffusion distance to the atomic-scale, establishing atomic-level charge transfer channels, and enhancing the charge separation driving force. Meanwhile, regulating the in-plane surface structure and spatial surface structure are summarized as atomic-level surface charge separation strategies. Moreover, collaborative strategies for simultaneous manipulation of bulk and surface photocharges are also introduced. Finally, the existing challenges and future prospects for fabrication of state-of-the-art photocatalysts are discussed on the basis of a thorough comprehension of atomic-level charge separation strategies.

Oxygen-defective ZnO films with various nanostructures prepared via a rapid one-step process and corresponding photocatalytic degradation applications

The deposition of oxygen-defective ZnO films exhibiting varied nanostructures via Solution Precursor Plasma Spray (SPPS) route, a one-step, minute-scaled duration and large scale method, is reported. The in situ formation of oxygen vacancies in ZnO films was confirmed by UV-Visible, Raman and photoluminescence (PL) spectroscopy and the as-prepared samples exhibit a bandgap as low as 3.02 eV. Density functional theory (DFT) simulation demonstrates that the polarization of ZnO is enhanced by the created oxygen vacancies, leading to substantially improved photocatalytic activity. The comparative experiments also revealed that forming and preserving appropriate ZnO precursor clusters inside the plasma plume is requisite for obtaining propitious ZnO nanostructures, which was followed by the in situ transfer and growth of the clusters on the preheated substrate. The ZnO-NRs films fully degrade the aqueous Orange II dye solutions within 120 min and maintain a quasi-intact activity (95.8% retention) after five test runs, which highlight their good stability. The oxygen vacancies and the narrowing of the bandgap also enable a visible light-driven photodegradation activity with conversions as high as 54.1%. In summary, this work not only reveals that the photocatalytic activity of SPPS-deposited ZnO films benefit from oxygen vacancies and well nanostructures, but also suggests that the SPPS route is of high potential for preparing metal oxides films destined to functional applications.

Design and fabrication of polyaniline/Bi2MoO6 nanocomposites for enhanced visible-light-driven photocatalysis

PANI/Bi₂MoO₆ composites with improved photoelectrochemical performance and accessible interfacial active sites were fabricated for enhanced visible-light-driven photocatalytic degradation of RhB.

Facile Synthesis of Bi2MoO6 Microspheres Decorated by CdS Nanoparticles with Efficient Photocatalytic Removal of Levfloxacin Antibiotic

Developing high-efficiency and stable visible-light-driven (VLD) photocatalysts for removal of toxic antibiotics is still a huge challenge at present. Herein, a novel CdS/Bi2MoO6 heterojunction with CdS nanoparticles decorated Bi2MoO6 microspheres has been obtained by a simple solvothermal-precipitation-calcination method. 1.0CdS/Bi2MoO6 has stronger light absorption ability and highest photocatalytic activity with levofloxacin (LEV) degradation efficiency improving 6.2 or 12.6 times compared to pristine CdS or Bi2MoO6. CdS/Bi2MoO6 is very stable during cycling tests, and no appreciable activity decline and microstructural changes are observed. Results signify that the introduction of CdS could enhance the light absorption ability and dramatically boost the separation of charge carriers, leading to the excellent photocatalytic performance of the heterojunction. This work demonstrates that flower-like CdS/ Bi2MoO6 is an excellent photocatalyst for the efficient removal of the LEV antibiotic.

Rapid water disinfection over a Ag/AgBr/covalent triazine-based framework composite under visible light

An Ag/AgBr/covalent triazine-based framework composite was successfully utilized for the rapid photocatalytic inactivation of bacteria under visible light.