Strong Second-Harmonic Generation Induced by a Triphenylamine-Based Bismuth-Organic Framework for Photocatalytic Activity Enhancement

Taking advantage of the well-defined geometry of metal centers and highly directional metal-ligand coordination bonds, metal-organic frameworks (MOFs) have emerged as promising candidates for nonlinear optical (NLO) materials. In this work, taking a photoresponsive carboxylate triphenylamine derivative as an organic ligand, a bismuth-based MOF, Bi-NBC, NBC = 4',4‴,4‴″-nitrilotris(([1,1'-biphenyl]-4-carboxylic acid)) is obtained. Structure determination reveals that it is a potential NLO material derived from its noncentrosymmetric structure, which is finally confirmed by its rarely strong second harmonic generation (SHG) effect. Theoretical calculations reveal that the potential difference around Bi atoms is large; therefore, it leads to a strong local built-in electric field, which greatly facilitates the charge separation and transfer and finally improves the photocatalytic performance. Our results provide a reference for the exploration of MOFs with NLO properties.

Efficient NO removal and photocatalysis mechanism over Bi-metal@Bi2O2[BO2(OH)] with oxygen vacancies

Photocatalysis technology prevails as a feasible option for air pollution control, in which high-efficiency charge separation and effective pollutant activation are the crucial issues. Here, this work designed Bi-metal@ Bi₂O₂[BO₂(OH)] with oxygen vacancies (OVs) catalyst for photocatalytic oxidation of NO under visible light, to shed light on the above two processes. Experimental characterizations and density functional theory (DFT) calculations reveal that a unique electron transfer covalent loop（[Bi₂O₂]²⁺ → Bi-metal → O^2-）can be formed during the reaction to guide the directional transfer of carriers, significantly improving the charge separation efficiency and the yield of active oxygen species. Simultaneously, the defect levels served by OVs also play a part. During the NO purification process, in-situ DRIFTS assisted with DFT calculations reveal that Bi metals could be functioned as electron donors to activate NO molecules and form NO^-, a key intermediate. This induces a new reaction path of NO → NO^- → NO₃^- to achieve the harmless conversion of NO, effectively restraining the generation of noxious intermediates (NO₂, N₂O₄). It is expected that this study would inspire the design of more artful photocatalysts for effective charge transfer and safe pollutants purification.

Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2-x-OV surface

To understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO_2-x-OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti⁴⁺ to the lower oxidation state Ti^{(4- x)+}, and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution. Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO_2-x-OV, thereby boosting O₂ adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O₂ (O_ads) and lattice O (O_lat) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO_2-x-OV and TiO₂, respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO₂ and H₂O in TiO_2-x-OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO₂ in TiO₂, owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification.

Crystal facet and phase engineering for advanced water splitting

This review covers the principles and recent advances in facet and phase engineering of catalysts for photocatalytic, photoelectrochemical, and electrochemical water splitting. It suggests the basis of catalyst design for advanced water splitting.

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.

Rationalize the Significantly Enhanced Photocatalytic Efficiency of In3+-doped α'-Ga2S3 by Bond Theory and Local Structural Distortion

Mechanistic understanding on the electronic structure of α'-Ga₂S₃ unravel that the electrons in nonbonding 3p_z orbitals of two-coordinated S^2- anions are photoexcited to the adjacent σ-type antibonding orbitals (Ga-4s and S-3p) and migrate thereafter to the surface along the a-axis. By introduction of the In-S antibonding on the one hand and modifying the local dipole moment on the other hand, the light absorption ability and charge separation efficiency can be both enhanced by In³⁺-to-Ga³⁺ substitution, and the photocatalytic H₂ evolution rate can be significantly promoted. Local geometric distortion is common in solid solutions, but its effect on charge migration behavior has yet been considered in semiconducting photocatalysis. Our case study on In³⁺-doped Ga₂S₃ is a good reminder of such the importance.

Impact of Average, Local, and Electronic Structure on Visible Light Photocatalysis in Novel BiREWO6 (RE = Eu and Tb) Nanomaterials

Crystal structures of hydrothermally synthesized BiEuWO₆ and BiTbWO₆ nanomaterials are deduced for the first time by combined Rietveld refinement of neutron and synchrotron data using the ordered and disordered models available in literature. The ordered model is validated for the average structure of these nanomaterials, and it is further supported by the local structure analysis using neutron pair distribution function. Nanomaterials are characterized by field-emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller surface area, diffused reflectance spectroscopy, and Raman Spectroscopy. Rare-earth-substituted nanomaterials are found to be efficient photocatalysts over the parent Bi₂WO₆ under visible light irradiation for Congo-red dye degradation. Particularly, BiTbWO₆ shows an enhanced photocatalytic (PC) activity compared to BiEuWO₆, as evidenced from the photoelectrochemical and time-resolved fluorescence studies. The difference in the observed PC activity of these nanomaterials is also explored through a detailed comparison of crystal structure and electronic structure calculated through the density functional theory method.

Solid Solution Photocatalyst with Spontaneous Polarization Exhibiting Low Recombination Toward Efficient CO2 Photoreduction

Decreasing the recombination of photogenerated carriers is a major challenge for efficiently converting solar energy into chemical energy by photocatalysis. Here, we have demonstrated that growth of a polar GaN:ZnO solid solution single crystal along its polarization axis is beneficial to efficient separation of photogenerated carriers, owing to the periodic potential barriers and wells generated from the periodically positive and negative atom arrangements in crystal structure. Local charge imbalance caused by replacing Ga(3+) with Zn(2+) leads to a polarization vector in the {0 0 0 1} planes of GaN:ZnO solid solution, thus forming a 1 D electron transport path along [2 1‾  1‾  0] in the {0 0 0 1} planes of GaN:ZnO solid solution to decrease recombination. Shorting the hole-transport distance by synthesizing porous nanoplates can further decrease recombination under the polarization field and improve the performance of polar photocatalyst in photoreduction of CO2 into CH4 .

Giant Enhancement of Internal Electric Field Boosting Bulk Charge Separation for Photocatalysis

Incorporating carbon into Bi3 O4 Cl enhances its internal electric field by 126 times, which induces a bulk charge separation efficiency (ηbulk ) of 80%. This ultrahigh ηbulk value presents a state-of-the-art result in tuning the bulk charge separation. The generated C-doped Bi3 O4 Cl has a noble-metal- and electron-scavenger-free water-oxidation ability under visible light, which is difficult to achieve with most existing photocatalysts.

One-Pot Solvothermal Synthesis of Bi4V2O11 as A New Solar Water Oxidation Photocatalyst

Bi4V2O11 was prepared via a one-pot solvothermal method and characterized via XRD, Raman, XPS, Electrochemical impedance spectroscopy. The as-prepared Bi4V2O11 sample displays excellent photocatalytic activity towards oxygen evolution under light irradiation. The hierarchical structure is in favour of the spatial separation of photogenerated electrons and holes. Furthermore, the internal polar field also plays a role in improving the charge separation. Both of the two results are responsible for excellent activity of O2 evolution. The resulting hierarchical Bi4V2O11 sample should be very promising photocatalyst for the application of photocatalytic O2 evolution in the future.

Energy transfer in plasmonic photocatalytic composites

Among the many novel photocatalytic systems developed in very recent years, plasmonic photocatalytic composites possess great potential for use in applications and are one of the most intensively investigated photocatalytic systems owing to their high solar energy utilization efficiency. In these composites, the plasmonic nanoparticles (PNPs) efficiently absorb solar light through localized surface plasmon resonance and convert it into energetic electrons and holes in the nearby semiconductor. This energy transfer from PNPs to semiconductors plays a decisive role in the overall photocatalytic performance. Thus, the underlying physical mechanism is of great scientific and technological importance and is one of the hottest topics in the area of plasmonic photocatalysts. In this review, we examine the very recent advances in understanding the energy transfer process in plasmonic photocatalytic composites, describing both the theoretical basis of this process and experimental demonstrations. The factors that affect the energy transfer efficiencies and how to improve the efficiencies to yield better photocatalytic performance are also discussed. Furthermore, comparisons are made between the various energy transfer processes, emphasizing their limitations/benefits for efficient operation of plasmonic photocatalysts.

Multifunctional Single-Phase Photocatalysts: Extended Near Infrared Photoactivity and Reliable Magnetic Recyclability

A practical photocatalyst should be able to integrate together various functions including the extended solar conversion, a feasible and economic recyclability, and above the room temperature operation potential, et al., in order to fulfill the spreading application needs in nowadays. In this report, a multifunctional single-phase photocatalyst which possesses a high photoactivity extended into the near infrared region, an easy magnetic recyclability and the high temperature stability was developed by doping Co into a new layer-structured Bi₇Fe₃Ti₃O₂₁ material. Light absorption and photocatalytic activity of the resulted Bi₇Fe_3-xCo_xTi₃O₂₁ photocatalyst were extended to the long wavelength as far as 800 nm. Its strong ferromagnetism above the room temperature enables the nanopowders fully recyclable in viscous solutions simply with a magnet bar in an experimental demonstration. Furthermore, such photoactivity and magnetic recyclability were heavily tested under high-temperature and high-viscosity conditions, which was intended to simulate the actual industrial environments. This work brings the bright light to a full availability of a new multifunctional photocatalyst, via integrating the much enhanced ferromagnetic, ferroelectric, optoelectronic properties, most importantly, into a single-phase structure.

Enhancement of photocatalytic activity of a two-dimensional GeH/graphene heterobilayer under visible light

The structural, electronic, and optical properties of GeH as well as a GeH/graphene heterointerface are studied based on hybrid DFT calculations including the nonlocal vdW correction.

The synergistic effect between effective mass and built-in electric field for the transfer of carriers in nonlinear optical materials

The transfer of carriers is promoted by the synergistic effect between effective masses and built-in electric field in K₃B₆O₁₀X (X = Br, Cl).

Shape-dependent photocatalytic activity of Bi5O7I caused by facets synergetic and internal electric field effects

The shape-dependent photocatalytic activity of Bi₅O₇I is caused by facets synergetic and internal electric field effects.