Internal energy recycling in FAPbI3/MXene for enhanced photocatalytic H2 evolution

Carrier recombination is a significant impediment to efficient charge separation, thereby severely limiting the performance of photocatalytic systems. In this study, we feature an innovative internal energy cycling mechanism through the non-radiative fluorescence resonance energy transfer (FRET) between perovskite and MXene, to exploit the energy released by carrier recombination for enhancing H2 evolution rate. Consequently, a rapid H2 evolution rate of 2394 µmol g-1 h-1 under 1.5 AM simulated sunlight, from the composite of FAPbI3/MXene/Pt, was acquired, which is more than one order of magnitude higher than that of FAPbI3/Pt (64 µmol g-1 h-1). The innovative approach of FRET induced internal energy cycling will open up opportunities to design other novel heterogeneous catalytic materials and promote their application potential in various catalytic fields.

Phase-Migrating Z-Scheme Charge Transportation Enables Photoredox Catalysis Harnessing Water as an Electron Source

Z-schematic photocatalytic reactions are of considerable interest because of their potential for application to reductive molecular conversions to value-added chemicals using water as an electron source. However, most demonstrations of Z-scheme photocatalysis have been limited to overall water splitting. In particular, it has been basically impossible to couple the reduction of "water-insoluble compounds" with water oxidation by conventional Z-scheme systems in aqueous solution. In this work, an unconventional Z-scheme electron transportation system with a "phase-migrating" redox mediator is constructed that enables photocatalytic conversion of water-insoluble compounds by using water as an electron/proton source. In a dichloroethane (DCE)/water biphasic solution, a molecular Ir(III) complex acts as a photoredox catalyst for the reductive coupling of benzyl bromide by using ferrocene (Fc) as an electron donor in the DCE phase. On the other side, an aqueous dispersion of a Bi4TaO8Cl semiconductor loaded with a (Fe,Ru)Ox cocatalyst photocatalyzed water oxidation using ferrocenium (Fc+) as an electron acceptor. Because the partition coefficients of Fc+/Fc are significantly different, the Fc+ and Fc generated by photoinduced electron transfer in each reaction could be selectively extracted to the opposite liquid phase. Spontaneous phase migration enables direction-selective electron transport across the organic/water interface that connects the reduction and oxidation reactions in the separated reaction phase. Eventually, photocatalytic reductive conversion of "water-insoluble" organic compounds using "water as the electron/proton source" was demonstrated through the step-by-step Z-scheme photocatalysis with the phase-migrating Fc+/Fc electron transportation.

Filming evolution dynamics of Hg nanodroplets mediated at solid-gas and solid-liquid interfaces by in-situ TEM

Nanodroplets at multiphase interfaces are ubiquitous in nature with implications ranging from fundamental interfacial science to industrial applications including catalytic, environmental, biological and medical processes. Direct observation of full dynamic evolutions of liquid metal nanodroplets at nanoscale multiphase interfaces offers indispensable insights, however, remains challenging and unclear. Here, we fabricate gas and liquid cells containing HgS nanocrystals through electrospinning and achieve the statistical investigations of full picture of Hg nanodroplets evolving at solid-gas and solid-liquid interfaces by in-situ transmission electron microscopy. In the gas cells, the voids nucleate, grow and coalesce into the crack-like feature along the <001> direction, while Hg nanodroplets form, move rapidly on the ratchet surface and are evolved into bigger ones through the nanobridges. Distinctly, mediated by the solid-liquid interface, the liquid Hg with the ink-like feature jets in the liquid cells. Such ink-jetting behavior occurs multiple times with the intervals from several to several tens of seconds, which is modulated through the competition between reductive electrons and oxidative species derived from the radiolysis of liquids. In-depth understanding of distinct nanodroplets dynamics at nanoscale solid-gas and solid-liquid interfaces offers a feasible approach for designing liquid metal-based nanocomplexes with regulatory interfacial, morphological and rheological functionalities.

Atomic-Level Engineering of Transition Metal Dichalcogenides for Enhanced Hydrogen Evolution Reaction

2D transition metal dichalcogenides (2D-TMDs) have attracted considerable attention due to their characteristic layered structures, which provide abundant accessible surface sites. Significant research efforts are dedicated to designing nanostructures and regulating electron properties to enhance the catalytic performance of the hydrogen evolution reaction (HER) of TMDs. However, elucidating the HER mechanism, particularly the role of active sites, remains challenging owing to the complex surface and electronic structures introduced by nanoscale modification. Recent advances have focused on achieving efficient HER catalysis through atomic-level control of TMD surface structures and precise identification of the coordination environment of active sites. Atomic-level engineering of TMDs, including incorporating or removing specific atoms onto the basal surfaces or within the interlayer via advanced synthetic approaches, has emerged as a promising strategy. These modifications optimize the adsorption/desorption energy of H, increase the density of active sites, and create synergetic active sites by arranging atoms in controlled configuration, in single-atomic modified TMDs (SA-TMDs) catalysts. Further, the insights of a notable increase of HER performance in SA-TMDs are discussed in detail when compared to both their pure and conventionally doped counterparts. This review aims to advance the understanding of atomic-level catalysis and provides a basis for developing next-generation materials for energy applications.

Critical impacts of metal cocatalysts on oxidation kinetics and optimal reaction conditions of photocatalytic methane reforming

Metal cocatalysts in photocatalysis are typically regarded as promoting only the reduction reactions. Here, we demonstrate that photocatalytic oxidation kinetics and optimal pressure of methane vary significantly with the loading amount of metal cocatalysts. These variations are well described by kinetic analyses treating molecular-level congestion of oxidation intermediates.

High solar-to-hydrogen efficiency in Z-scheme AlN/GaO heterojunctions for visible light water splitting

Hydrogen production from solar energy is an important means to solve the problems of fossil fuel consumption and environmental pollution, and the efficiency of hydrogen production from solar energy is an important indicator. Photocatalytic water decomposition technology driven by solar energy is an ideal way to create clean energy. In this paper, a new Z-scheme AlN/GaO van der Waals heterojunction is proposed. Through first-principles calculations, we have systematically studied the electronic properties and photocatalytic hydrogen production performance of the AlN/GaO heterostructure. The calculation results show that the lattice mismatch rate of the AlN/GaO heterojunction is only 0.48%. At the same time, it not only performs well in terms of thermodynamics, kinetics and mechanical stability, but also has an appropriate band gap of 1.45 eV with an electron mobility of up to 2753.48 cm2 V-1 s-1. Under light irradiation, the transfer of internal photogenerated carriers forms a built-in electric field from AlN to GaO, which forms a typical Z-scheme, and leads to the hydrogen evolution reaction on AlN with strong reduction ability. It is worth noting that the AlN/GaO heterojunction shows a high absorption coefficient in the visible light absorption range and has an excellent solar-to-hydrogen efficiency of 60.1%. These advantages demonstrate that the AlN/GaO heterojunction, as a promising photocatalyst, has significant application potential and offers a novel approach to address the energy crisis and environmental pollution challenges.

In situ SEIRAS analysis of enhanced photocatalytic carrier transfer to a Pt cocatalyst induced by sacrificial reagents

In situ SEIRAS analyses revealed a peak shift of adsorbed CO on Pt cocatalysts supported on TiO2 photocatalysts in the presence of sacrificial reagents. This observation suggests that charge separation from the photocatalysts to the cocatalysts was enhanced, leading to negative potential shifts that promote hydrogen evolution.

Design and Construction of D-A-Extended 3D Covalent-Organic Frameworks for Boosting Photocatalytic Hydrogen Evolution

The development of donor-acceptor (D-A) covalent-organic frameworks (COFs) has emerged as a promising strategy for enhancing photocatalytic performance. Although most studies have concentrated on 2D COFs, research into their 3D counterparts remains limited. In this study, we rationally designed and synthesized a carbazoyl dicyanobenzene derivative (TBFCC) as an intrinsic D-A building block. By selecting TAPA, TAPB, and TAPT as the donor, acceptor-π, and acceptor donors, respectively, we synthesized three distinct D-A-extended COF materials: D-D-A, A-π-D-A, and A-D-A. Among these, 3D-TAPT-COF, featuring an A-D-A structure, exhibited the highest hydrogen evolution rate of 31.3 mmol g-1 h-1, surpassing most previously reported 3D COF-based photocatalysts. This superior performance is attributed to its A-D-A configuration, which provides multiple charge transfer pathways in 3D space, overcoming the electron transport limitations inherent in 2D COFs. Consequently, this feature facilitates efficient separation of photogenerated charges within the framework and reduces carrier recombination, thereby optimizing photocatalytic efficiency.

High-Entropy Design Boosts Visible-Light-Induced Photocatalytic Hydrogen Production on Perovskite Oxynitrides

Semiconducting oxynitrides are attractive candidates for producing solar hydrogen, while the abundant defects evolved during harsh nitridation synthesis and the unfavorable charge transfer properties of oxynitrides restrict the solar-to-hydrogen conversion. Herein, by virtue of high-entropy design, a single-phase high-entropy oxynitride {LaSmPrNdGd}TiO2N (HE-LnTiO2N) is presented toward alleviating these issues for the first time. It is found that the HE-LnTiO2N can be obtained at milder nitridation conditions than those of the conventional one-element oxynitrides, which is beneficial to inhibiting the formation of reduced Ti3+ defects that act as recombination centers. Moreover, the combined contribution of the multiple lanthanide elements modifies the electronic structures of HE-LnTiO2N, thus enhancing the charge transfer efficiency. Consequently, the photocatalytic hydrogen evolution activity achieved on HE-LnTiO2N is two times that of the representative one-element oxynitride SmTiO2N under visible light irradiation. This study highlights the efficacy and great potential of high-entropy design toward optimizing photocatalytic materials for enhanced solar energy conversion.

Layered double hydroxide modified bismuth vanadate as an efficient photoanode for enhancing photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting has attracted significant interest as a promising approach for producing clean and sustainable hydrogen fuel. An efficient photoanode is critical for enhancing PEC water splitting. Bismuth vanadate (BiVO4) is a widely recognized photoanode for PEC applications due to its visible light absorption, suitable valence band position for water oxidation, and outstanding potential for modifications. Nevertheless, sluggish water oxidation rates, severe charge recombination, limited hole diffusion length, and inadequate electron transport properties restrict the PEC performance of BiVO4. To surmount these constraints, incorporating layered double hydroxides (LDHs) onto BiVO4 photoanodes has emerged as a promising approach for enhancing the performance. Herein, the latest advancements in employing LDHs to decorate BiVO4 photoanodes for enhancing PEC water splitting have been thoroughly studied and outlined. Initially, the fundamental principles of PEC water splitting and the roles of LDHs are summarized. Secondly, it covers the development of different composite structures, including BiVO4 combined with bimetallic and trimetallic LDHs, as well as other BiVO4-based composites such as BiVO4/metal oxide, metal sulfide, and various charge transport layers integrated with LDHs. Additionally, LDH composites incorporating materials like graphene, carbon dots, quantum dots, single-atom catalysts, and techniques for surface engineering and LDH exfoliation with BiVO4 are discussed. The research analyzes the design principles of these composites, with a specific focus on how LDHs enhance the performance of BiVO4 by increasing the efficiency and stability through synergistic effects. Finally, challenges and perspectives in future research toward developing efficient and stable BiVO4/LDHs photoelectrodes for PEC water splitting are described.

Narrow Bandgap Perovskite Enabled by Heterovalent Co-Doping for Visible-NIR Light Photocatalytic CO2 Reduction

Metal halide perovskites have garnered significant attention due to their vast potential in various optoelectronic applications. While their tunable bandgap properties allow for light absorption across the ultraviolet and much of the visible spectrum, the coverage in the near-infrared (NIR) region remains limited. Here, we demonstrate a heterovalent co-doping method for synthesizing Ag and Bi doped CsSnBr3 crystals with absorption edge up to 1300 nm, making it one of the narrowest bandgap perovskite materials. The incorporation of trivalent Bi (p) orbitals is responsible for the band narrowing, while the monovalent Ag stabilizes the entire perovskite lattice. Taking advantage of the new energy states within the bandgap, the absorption edge of the co-dopants is extended to NIR region, so they can efficiently utilize sunlight. Moreover, the co-dopants exhibit significantly better antioxidation capability than the pristine CsSnBr3. When applied to CO2 photoreduction, the co-dopants achieved highly selective CO production performance, with an apparent quantum yield (AQY) of 7.56 % at 700 nm, representing a 94 % improvement over CsSnBr3. Overall, this study provides effective strategies for optimizing tin-based perovskites and holds significant implications for future research in enhancing stability, reducing toxicity, and optimizing optoelectronic performance.

Conduction Band and Defect Engineering for the Prominent Visible-Light Responsive Photocatalysts

Controlling trap depth is crucial to improve photocatalytic activity, but designing such crystal structures has been challenging. In this study, we discovered that in 2D materials like BiOCl and Bi4NbO8Cl, composed of interleaved [Bi2O2]2+ and Cl- slabs, the trap depth can be controlled by manipulating the slab stacking structure. In BiOCl, oxygen vacancies (VO) create deep electron traps, while chlorine vacancies (VCl) produce shallow traps. The depth is determined by the coordination around anion vacancies: VO forms strong σ bonds with Bi-6p dangling bonds below the conduction band minimum (CBM), while those around Cl are parallel, forming weak π-bonding. The strong re-hybridization makes the trap depth deeper. In Bi4NbO8Cl, VCl also creates shallow traps, but VO does not produce deep traps although Bi-6p orbitals are also forming strong σ bonding. This difference is attributed to the difference of the energy level of CBM. In both cases, the CBM consists of Bi-6p orbitals extending into the Cl layers. However, these orbitals are isolated in BiOCl, but those in Bi4NbO8Cl are bonded with each other between neighboring [Bi2O2]2+ layers. This unique bonding-based CBM prevents the formation of deep electron traps, and significantly enhances H2 evolution activity by prolonging the lifetime of highly reactive free electrons.

Divalent Cation Doping into SrTiO3 for Enhancing the Photocatalytic Performance of Water Splitting

Perovskite SrTiO3 (STO) is a widely used semiconductor photocatalyst whose photocatalytic activity is significantly influenced by cation doping. In this work, we explore effective divalent dopants to improve the photocatalytic performance of water splitting through both theoretical and experimental approaches. First-principles calculations suggest that divalent Mg2+ and Zn2+ are promising dopants replacing Ti4+ sites of STO to help mitigate charge recombination processes associated with defect levels caused by oxygen vacancies. Experimental analysis of synthesized STO confirms the photocatalytic performance, consistent with the theoretical predictions.

Strain Engineering the Optoelectronic and HER Behavior of MoS2/ZnO Heterojunction: A DFT Investigation

The rational design of heterojunctions by coupling two or more two-dimensional (2D) materials is regarded as a feasible strategy to efficiently enhance photocatalytic-hydrogen performance by capturing solar energy to address the increasing global energy crisis. In this work, a functional MoS2/ZnO heterojunction is proposed based on first-principles simulation. Our results reveal that the photogenerated electrons and holes in the MoS2/ZnO heterojunction follow a specific Z-scheme pathway, highly facilitating redox reactions and optimizing optical properties in the visible-light region. Under external strain, the MoS2/ZnO heterojunction demonstrates improved HER performance and remarkable optical-harvesting capabilities. Interestingly, the HER free energy for the heterojunction is only -0.04 eV under -5% compressive strain, highlighting its promising potential for photocatalytic hydrogen production. We observe that the absorption edge of the spectrum shifts gradually to the infrared region with increasing tensile biaxial strains, whereas compressive biaxial strains result in a blue-shift absorption spectrum. Additionally, all heterojunctions achieve excellent solar-to-hydrogen (STH) efficiencies exceeding 10%, demonstrating their capability to store sufficient solar energy. Our work offers a novel strategy for exploring highly efficient photocatalysts in the field of hydrogen energy with the ability to modulate their activity through external strain.

Metalloporphyrins in bio-inspired photocatalytic conversions

Numerous natural systems contain porphyrin derivatives that facilitate important catalytic processes; thus, developing biomimetic photocatalytic systems based on synthetic metalloporphyrins constitutes a rapidly advancing and fascinating research field. Additionally, porphyrins are widely investigated in a plethora of applications due to their highly versatile structure, presenting advantageous photoredox, photophysical and photochemical properties. Consequently, such metallated tetrapyrrolic macrocycles play a prominent role as photosensitizers and catalysts in developing artificial photosynthetic systems that can store and distribute energy through fuel forming reactions. This review highlights the advances in the field of metalloporphyrin-based biomimetic photocatalysis, particularly targeting water splitting, including both hydrogen and oxygen evolution reactions, carbon dioxide reduction and alcohol oxidation. For each photocatalytic system different approaches are discussed, concerning either structural modifications of the porphyrin derivatives or the phase in which the process takes place, i.e. homogenous or heterogenous. The most important findings for each porphyrin-based photocatalytic reaction are presented and accompanied by the analysis of mechanistic aspects when possible. Finally, the perspectives and limitations are discussed, providing future guidelines for the development of highly efficient metalloporphyrin-based biomimetic systems towards energy and environmental applications.

Heterophase Junction Effect on Photogenerated Charge Separation in Photocatalysis and Photoelectrocatalysis

ConspectusThe conversion of solar energy into chemical energy is promising to address energy and environmental crises. For solar conversion processes, such as photocatalysis and photoelectrocatalysis, a deep understanding of the separation of photogenerated charges is pivotal for advancing material design and efficiency enhancement in solar energy conversion. Formation of a heterophase junction is an efficient strategy to improve photogenerated charge separation of photo(electro)catalysts for solar energy conversion processes. A heterophase junction is formed at the interface between the semiconductors possessing the same chemical composition with similar crystalline phase structures but slightly different energy bands. Despite the small offset of Fermi levels between the different phases, a built-in electric field is established at the interface of the heterophase junction, which can be the driving force for the photogenerated charge separation at the nanometer scale. Notably, slight variations in the energy band of the two crystalline phases result in small energy barriers for the photogenerated carrier transfer. Moreover, the structural similarity of the two different crystalline phases of a semiconductor could minimize the lattice mismatch at the heterophase junction, distinguishing it from a p/n junction or heterojunction formed between two very different semiconductors.This Account provides an overview of the understanding, design, and application of heterophase junctions in photocatalysis and photoelectrocatalysis. It begins with a conceptualization of the heterophase junction and reviews recent advances in the synthesis of semiconductors with a heterophase junction. The phase transformation method with the advantage of forming a heterophase junction with an atomically matched interface and the secondary seed growth method for unique structures with excellent electronic and optoelectronic properties are described. Furthermore, the mechanism of the heterophase junction for improving the photogenerated charge separation is discussed, followed by a comprehensive discussion of the structure-activity relationship for the heterophase junction. The home-built spatially resolved and time-resolved spectroscopies offer direct imaging of the built-in electric field across the heterophase junction and then the direct detection of the photogenerated charge transfer between the two crystalline phases driven by the built-in electric field. Such an efficient interfacial charge transfer results in the improvement of the photogenerated charge separation, a higher yield of long-lived charges, and thus the inhibition of the charge recombination. Benefiting from these insights, structural design strategies for the heterophase junction, such as precise tuning of band alignment, exposed heterophase amounts, phase alignment, and interface structure, have been developed. Finally, the challenges, opportunities, and perspectives of heterophase junctions in the design of advanced photo(electro)catalyst systems for solar energy to chemical energy conversion will be discussed.

Metal-free Amorphous Cross-Linked Porous Organic Polymers for Photocatalytic Hydrogen Evolution and Carbon Dioxide Reduction

The use of solar energy to produce valuable chemicals has gained significant attention in recent years. In this area, photocatalytic hydrogen evolution and carbon dioxide reduction have become key focal points. Recently, amorphous cross-linked porous organic polymers (CPOPs) have emerged as promising photocatalysts due to their tunable band gaps, broad light absorption range, and high porosity. In this article, we highlight recent advancements in cutting-edge metal-free amorphous CPOPs for photocatalytic hydrogen evolution and carbon dioxide reduction. We examine the design principles, synthetic strategies, and structure-property relationships of various cross-linked porous polymers to achieve high photocatalytic performance. Additionally, we propose future research directions and offer insights to further advance CPOP-based photocatalysts for efficient solar-driven hydrogen evolution and carbon dioxide reduction.

Interfacial Bi-S chemical bond-coupled sulfur vacancy in Bi4NbO8Cl@ZnIn2S4-x S-scheme heterojunction for superior photocatalytic hydrogen generation

Strategies such as reducing charge transfer resistance and enhancing transmission driving force are considered effective in achieving higher photocatalytic performance. In this study, Bi4NbO8Cl@ZnIn2S4-x S-scheme heterojunction photocatalyst with atomic-level interface Bi-S chemical bond connection was successfully constructed through in-situ growth of ZnIn2S4-x nanosheets containing sulfur vacancies (Sv) on Bi4NbO8Cl microplates. Firstly, the S-scheme charge transfer mode effectively spatially separated photogenerated carriers while retaining their reactivity to the maximum extent. Secondly, the interfacial Bi-S bond served as a "bridge" to lessen the interface resistance and provide a high-speed channel for the transmission of photogenerated carriers. Lastly, Sv effectively expanded the Fermi level (Ef) difference between the two semiconductors in the heterojunction, so as to enlarge the built-in electric field (IEF) at the interface and reinforce the driving force for charge transfer. Owing to the synergistic effects of these advantages, the Bi4NbO8Cl@ZnIn2S4-x composite exhibited an average hydrogen production rate of up to 8.7 mmol g-1 h-1 under visible light, which was 4.0 and 14.5 times that of ZnIn2S4-x and Bi4NbO8Cl samples, respectively. This work presents a novel approach for designing interfacial chemically bonded S-scheme heterojunction photocatalysts with high catalytic activity.

Tunable Electronic Structure and Carrier Dynamics Modulation via Ferroelectric Polarization in a CuInP2S6/C7N6 Heterostructure

Enhancing the transfer and separation efficiency of photogenerated carriers in heterostructures is critical for the development of high-efficiency photocatalysts. In this study, we propose a novel ferroelectric-based van der Waals heterostructure (CuInP2S6/C7N6) and investigate its electronic properties and carrier dynamics using first-principles calculations and nonadiabatic molecular dynamics (NAMD) simulations. The results revealed that the incorporation of CuInP2S6 significantly modulated the electronic structure and enabled efficient separation of photogenerated carriers. NAMD simulations indicated that carrier transfer and recombination in the CuInP2S6/C7N6 system followed a Type-II mechanism, with the Up-CuInP2S6/C7N6 configuration meeting the potential requirements for overall water splitting. Moreover, switching the polarization direction of CuInP2S6 effectively tunes its interfacial properties, electronic structure, and nonadiabatic coupling, thereby controlling the carrier transfer dynamics. Notably, the Up-CuInP2S6/C7N6 system exhibits superior photogenerated carrier separation efficiency, making it a promising candidate for photocatalytic applications. This work provides a novel strategy for regulating carrier dynamics and offers valuable insights into designing ferroelectric-based heterostructures for high-performance photocatalytic and optoelectronic devices.

In-depth analysis of FeNi-based nanoparticles for the oxygen evolution reaction

This study investigates the effect of varying iron-to-nickel ratios on the catalytic performance of Fe-Ni oxide nanoparticles (NPs) for the oxygen evolution reaction (OER). Addressing the issue of high energy wastage due to large overpotentials in OER, we synthesized and characterized different NP catalysts with different Fe: Ni oxide ratios. Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD) were employed to determine the morphology, elemental and phase composition of the NPs. Furthermore, in-depth profiling with X-ray Photoelectron Spectroscopy (XPS) and Hard X-ray Photoelectron Spectroscopy (HAXPES) revealed that iron predominantly exists as oxide, while nickel exhibits both metallic and oxidic forms depending on the Fe content. XPS indicated an enrichment of iron at the NP surface, whereas HAXPES and EDS data agreed on the bulk stoichiometry. The assessment of the catalytic activity via cyclic voltammetry (CV) showed that the Fe: Ni ratio of 2:3 exhibited superior performance, characterized by lower overpotential and a smaller Tafel slope.

Reactive co-sputter deposition of Ta-doped tungsten oxide thin films for water splitting application

This study aimed to investigate the structural, optical, and electronic properties of WO3 thin films modified by Ta-doping, considering their potential application in photoelectrochemical (PEC) water splitting. Due to its unique physical and chemical properties, WO3 films have been commonly suggested as a promising photoanode for hydrogen production. However, the wide bandgap and unsuitable band edge positions of WO3 limit its PEC efficiency. Doping have been extensively applied as an effective strategy for bandgap engineering. Here, post-annealed WO3 films with different concentrations of Ta dopant were synthesized via reactive magnetron co-sputtering, while DC and RF sputtering powers were varied with the aim of achieving the desired properties. EDX analysis showed that Ta atoms were doped into WO3 in the range of 0-3.93 at%. As evident from SEM and AFM images, the surface morphology was significantly affected by increasing Ta doping, the formation of a granular structure with well-defined boundaries and increasing surface roughness (1.79-47.94 nm). XRD patterns confirmed that the incorporation of Ta atoms into a monoclinic WO3 improved the crystallinity, especially in the (002) direction. Most importantly, a decrease in the average transparency (92.82-74.27%), an increase in visible absorption, a red shift of the fundamental absorption edge corresponding to a favorable drop in the optical bandgap energy (3.07-2.61 eV) were found with increasing Ta concentration. Notably, the substitution of W6+ ions with Ta dopant (0-3.93 at%) led to an upward shift in the valence band maximum (3.62-3.31 eV) and a downward shift in the conduction band minimum (0.55-0.70 eV). The WO3 photoanode doped with 3.93 at% Ta exhibited the maximum photocurrent density of 0.65 mA/cm2 (at 1 V vs. Ag/AgCl) under simulated sunlight. Furthermore, WO3 photoanode doped with 3.93 at% Ta showed excellent photoresponsivity and slow electron-hole recombination. The obtained results predict the potential of Ta-doping coupled with post-annealing to optimize the structural and optoelectronic properties of sputtered WO3 thin films as photoanode for use in efficient PEC water splitting.

Analysis of the TiO2 Photoanode Process Using Intensity Modulated Photocurrent Spectroscopy and Distribution of Relaxation Times

Photoelectrochemical water splitting offers a promising pathway for green hydrogen production, but its efficiency is limited by electron-hole recombination. Overcoming this challenge requires detailed analysis of the relationship between charge separation and charge transfer kinetics under operando conditions. Here, we applied intensity-modulated photocurrent spectroscopy (IMPS) combined with distribution of relaxation times (DRT) analysis to the photoanodic process under varying light intensities. This approach revealed three distinct applied potential regions: a high-potential region with constant admittance independent of light intensity; a midpotential region strongly influenced by light intensity; and a low-potential region with back electron-hole recombination (BER). Crucially, our analysis demonstrated that what has traditionally been viewed as a single bulk recombination process can be resolved into distinct mechanisms based on light intensity dependence. Additionally, we identified satellite peaks in the slow kinetic regions for the first time. These peaks, influenced by light intensity and reaction conditions, revealed novel insights into surface-trapped hole dynamics. Based on these insights, we propose tailored band bending models for each kinetic scenario and discuss the implications of satellite peaks for reaction bottlenecks. These results offer new perspectives on understanding and optimizing photoelectrochemical systems.

From photocatalysis to photon-phonon co-driven catalysis for methanol reforming to hydrogen and valuable by-products

Hydrogen energy will play a dominant role in energy transition from fossil fuel to low carbon processes, while economical, efficient, and safe hydrogen storage and transportation technology has become one of the main bottlenecks that currently hinder the application of the hydrogen energy scale. Methanol has widely been regarded as a primary liquid H2 storage medium due to its high hydrogen content, easy storage and transportation and relatively low toxicity. Hydrogen release from methanol using photocatalysis has thus been the focus of intense research and recent years have witnessed its fast progress and drawbacks. This review offers a comprehensive overview of methanol-based hydrogen production via photocatalysis, spotlighting recent developments in photocatalysts referring to thermal catalysts, including efficient semiconductors and cocatalysts, followed by the discussion of mechanistic investigation via advanced techniques and their disadvantages. Beyond this, particular focus has been placed on the discussion of co-driven processes involving coupling of photons (photocatalysis) with phonons (thermal catalysis) - the concept of photon-phonon co-driven catalysis - for methanol reforming and cutting-edge reactor design strategies, in order to enhance the overall process efficiency and applicability. Concluding with forward-looking insights, this review aims to provide valuable guidance for future research on hydrogen release through methanol reforming.

Plasmonic Hot-Carrier Engineering at Bimetallic Nanoparticle/Semiconductor Interfaces: A Computational Perspective

Plasmonic catalysis employs plasmonic metals such as Ag, Au, Cu, and Al, typically in combination with semiconductors, to drive diverse redox chemical reactions. These metals are good at harnessing sunlight, owing to their strong absorption cross-sections and tunable absorption peaks within the visible range of the solar spectrum. Unfortunately, facilitating plasmon-induced hot-carrier separation and subsequently harvesting them to improve catalytic efficiencies has been a problem at monometallic particle-semiconductor interfaces. To overcome this issue, this perspective focuses on recent computational methods and studies to discuss the advantages of designing bimetallic particles (core-shell or core-satellite), with a plasmonic-metal core and a less-plasmonic-metal shell on top, and coupling them with semiconductors. The aim of this approach is to favorably modify the interface between the plasmonic-metal particle and the semiconductor by introducing a thin section of a non-plasmonic metal in between. This approach is expected to enhance hot-carrier separation at the interface, preventing fast electron-hole recombination within the plasmonic-metal particle. Through a careful design of such bimetal/semiconductor configurations, by varying the size and composition of the non-plasmonic metal for example, and through appropriate utilization of quantum-mechanical modeling and experimental techniques, it is anticipated that plasmonic hot-carrier generation and separation processes can be studied and controlled in such systems, thereby enabling more-efficient plasmonic devices.

Development of ZFO family nanophotocatalysts: Clean hydrogen production by a new high performance photoreactor

In this study, ZnFe2O4 (ZFO), Pd0.2Zn0.8Fe2O4 (PZFO), Ba0.1Ca0.1Mg0.1Sr0.1Zn0.6Fe2O4 (BCMSZFO), Ca0.2Co0.2Cu0.2Zn0.4Fe2O4 (CCCZFO), Mg0.2Mn0.2Zn0.6Fe2O4 (MMZFO), and Co0.1Cu0.1Mg0.1Mn0.1Ni0.1Zn0.5Fe2O4 (CCMMNZFO) nanospinels were synthesized via a hydrothermal method assisted by succinic acid. This material was evaluated for hydrogen production through photocatalytic water splitting under separate irradiation wavelengths of visible LED light. The chemical, physical, and photophysical properties of the ZFO family nanophotocatalysts were characterized using FT-IR, XRD, FESEM-EDX-MAP, UV-Vis DRS, and VSM. All synthesized nanospinels exhibited a pure spinel phase with no evidence of secondary crystalline phase. The direct band gap energies of ZFO, PZFO, BCMSZFO, CCCZFO, MMZFO, and CCMMNZFO were determined as 1.75, 1.51, 1.73, 1.50, 1.48, and 1.25 eV, respectively. Photocatalytic water splitting experiments were conducted under N₂ injection using a setup with operational parameters of 5 min irradiation time and 1 g of nanophotocatalyst mass. The hydrogen production rates of the nanophotocatalysts under identical conditions revealed significant differences, forming the basis for further investigations in this study.

Facing the "Cutting Edge:" Edge Site Engineering on 2D Materials for Electrocatalysis and Photocatalysis

The utilization of 2D materials as catalysts has garnered significant attention in recent years, primarily due to their exceptional features including high surface area, abundant exposed active sites, and tunable physicochemical properties. The unique geometry of 2D materials imparts them with versatile active sites for catalysis, including basal plane, interlayer, defect, and edge sites. Among these, edge sites hold particular significance as they not only enable the activation of inert 2D catalysts but also serve as platforms for engineering active sites to achieve enhanced catalytic performance. Here it is comprehensively aimed to summarize the state-of-the-art advancements in the utilization of edge sites on 2D materials for electrocatalysis and photocatalysis, with applications ranging from water splitting, oxygen reduction, and nitrogen reduction to CO2 reduction. Additionally, various approaches for harnessing and modifying edge sites are summarized and discussed. Here guidelines for the rational engineering of 2D materials for heterogeneous catalysis are provided.

Spontaneous adsorption of iridium chloride complex on oxychloride photocatalysts provides efficient and durable reaction site for water oxidation

The visible-light-driven O2 evolution on oxychloride photocatalysts, such as Bi4NbO8Cl, was significantly enhanced by stirring in an aqueous solution containing IrCl63- in the dark. Various characterizations indicated that highly dispersed IrOxHyClz-like species spontaneously formed on the oxychloride surface, serving as effective and stable cocatalysts for enhancing O2 evolution.

Review on the optical and electrical properties of chalcogenide thin films: challenges and applications

Thin films play an essential role in our daily lives as they are utilized in various applications. The deposition techniques used to create thin films are categorized into two main types: physical and chemical deposition. Many materials are available in thin film form, including chalcogenides, which are cost-effective and possess excellent structural, optical, and electrical properties, making them suitable for various applications. They can be fabricated in binary, ternary, and quaternary forms, either in an amorphous or crystalline state. The optical and electrical properties of chalcogenide thin films are affected by several factors, such as the type of deposition, compositional effect, thickness, and annealing temperature. This review aims to compile research on chalcogenide thin films, highlighting their significant importance, preparation processes, and structural characteristics. Additionally, the theoretical and experimental models commonly used in optical and electrical studies of chalcogenide thin films have been discussed, including their parameters, such as the absorption coefficient, refractive index, nonlinear optical parameters, and DC and AC conductivity. Lastly, some challenges faced to achieve good results in practical applications by utilizing thin films and highlighting some of these applications have been briefly addressed and discussed.

Activation of photocatalytic CO2 reduction by loading hydrophobic thiolate-protected Au25 nanocluster cocatalyst

The photocatalytic carbon dioxide (CO2) reduction reaction (CO2RR), which reduces CO2 to various useful chemical compounds by light, has attracted attention to achieve carbon neutrality. In photocatalytic CO2RR, it is effective to load metal nanoparticles (NP) as cocatalysts on the surface of semiconductor photocatalysts to improve their activity and selectivity. In this study, we used ultrafine metal nanoclusters (NC) with a particle size of about 1 nm as cocatalysts to clarify the effect of surface ligands on the activity and selectivity of the photocatalytic CO2RR. As a result, it was shown that the introduction of hydrophobic ligands to the Au25 NC cocatalyst suppresses the competing hydrogen evolution reaction, thereby increasing the selectivity of CO2RR. In addition, the hydrophobic ligand-protected Au25 NC cocatalysts exhibited 66 times higher CO evolution rates per Au-loading weights than the Au NP cocatalysts with a particle size of about 7 nm. These results provide crucial insights into the creation of highly active metal NC cocatalysts for photocatalytic CO2RR.

Photoionization-induced charge separation for efficient solar energy conversion

The most important primary process in solar energy conversion systems is photo-induced charge separation. This Perspective summarizes our current understanding of the photoionization-induced charge separation process, which involves the transfer of an electron from a discrete to a continuous electronic state with particular emphasis on the threshold energy and efficiency of photoionization. Based on our understanding of alkane solutions and in aromatic organic crystals, the charge separation mechanism in dye-sensitized solar cells is discussed as a photoionization-induced solar energy conversion system.

Role of Metal Cocatalysts in the Photocatalytic Production of Hydrogen from Water Revisited

The use of photocatalysts to promote the production of molecular hydrogen from water, following the so-called water splitting reaction, continues to be a promising route for the green production of fuels. The molecular basis of this photocatalysis is the photoexcitation of electrons from the valence band of semiconductors to their conduction band, from which they can be transferred to chemical reactants, protons in the case of water, to promote a reduction reaction. The mechanism by which such a process takes place has been studied extensively using titanium oxide, a simple material that fulfills most requirements for water splitting. However, photocatalysis with TiO2 tends to be highly inefficient; a cocatalyst, commonly a late transition metal (Au, Pt) in nanoparticle form, needs to be added to facilitate the production of H2. The metal is widely believed to help with the scavenging of the excited electrons from the conduction band of the semiconductor in order to prevent their recombination with the accompanying hole formed in the valence band, a step that cancels the initial photon absorption and competes with the photolytic chemical reduction. Here we review and analyze the molecular basis for that mechanism and argue for an alternative explanation, that the role of the metal is to help with the recombination of the atomic hydrogen atoms produced by proton reduction on the semiconductor surface instead. First, we summarize what is known about the electronic structure of these photocatalysts and how the electronic levels need to line up for the reduction of protons in water to be feasible. Next, we review the current understanding of the dynamics of the steps associated with the absorption of photons, the de-excitation via electron-hole pair recombination and fluorescence decay, and the electronic transitions that lead to proton reduction, and contrast those with the rates of the chemical steps required to produce molecular hydrogen. The following section addresses the changes introduced by the addition of the metal cocatalyst, comparatively evaluating its role as either an electron scavenger or a promoter of the recombination of hydrogen atoms. A discussion of the viable chemical mechanisms for the latter pathway is included. Finally, we briefly mention other associated aspects of this photocatalysis, including the possible promotion of H2 production with visible light via resonant excitation of the surface plasmon of Au nanoparticles, the use of single-metal (Au, Pt) atom catalysts and of yolk-shell nanostructures, and the reduction of organic molecules. We end with a brief personal perspective on the possible generality of the concepts introduced in this Critical Review.

Interface engineering for photoelectrochemical oxygen evolution reaction

Photoelectrochemical (PEC) water splitting provides a promising approach for solving sustainable energy challenges and achieving carbon neutrality goals. The oxygen evolution reaction (OER), a key bottleneck in the PEC water-splitting system occurring at the photoanode/electrolyte interface, plays a fundamental role in sustainable solar fuel production. Proper surface or interface engineering strategies have been proven to be necessary to achieve efficient and stable PEC water oxidation. This review summarizes the recent advances in interface engineering, including junction formation, surface doping, surface passivation or protection, surface sensitization, and OER cocatalyst modification, while highlighting the remarkable research achievements in the field of PEC water splitting. The benefits of each interface engineering strategy and how it enhances the device performance are critically analyzed and compared. Finally, the outlook for the development of interface engineering for efficient PEC water splitting is briefly discussed. This review illustrates the importance of employing rational interface engineering in realizing efficient and stable PEC water splitting devices.

Noble-Metal-Free Cocatalysts Reinforcing Hole Consumption for Photocatalytic Hydrogen Evolution with Ultrahigh Apparent Quantum Efficiency

Achieving efficient and sustainable hydrogen production through photocatalysis is highly promising yet remains a significant challenge, especially when replacing costly noble metals with more abundant alternatives. Conversion efficiency with noble-metal-free alternatives is frequently limited by high charge recombination rates, mainly due to the sluggish transfer and inefficient consumption of photo-generated holes. To address these challenges, a rational design of noble-metal-free cocatalysts as oxidative sites is reported to facilitate hole consumption, leading to markedly increased H2 yield rates without relying on expensive noble metals. By integrating femtosecond transient absorption spectroscopy with in situ characterizations and theoretical calculations, the rapid hole consumption is compellingly confirmed, which in turn promotes the effective separation and migration of photo-generated carriers. The optimized catalyst delivers an impressive photocatalytic H2 yield rate of 57.84 mmol gcat -1 h-1, coupled with an ultrahigh apparent quantum efficiency reaching up to 65.8%. Additionally, a flow-type quartz microreactor is assembled using the optimal catalyst thin film, which achieves a notable H2 yield efficiency of 0.102 mL min-1 and maintains high stability over 1260 min of continuous operation. The strategy of reinforcing hole consumption through noble-metal-free cocatalysts establishes a promising pathway for scalable and economically viable solar H2 production.

Layer-by-Layer Nanoarchitectonics: A Method for Everything in Layered Structures

The development of functional materials and the use of nanotechnology are ongoing projects. These fields are closely linked, but there is a need to combine them more actively. Nanoarchitectonics, a concept that comes after nanotechnology, is ready to do this. Among the related research efforts, research into creating functional materials through the formation of thin layers on surfaces, molecular membranes, and multilayer structures of these materials have a lot of implications. Layered structures are especially important as a key part of nanoarchitectonics. The diversity of the components and materials used in layer-by-layer (LbL) assemblies is a notable feature. Examples of LbL assemblies introduced in this review article include quantum dots, nanoparticles, nanocrystals, nanowires, nanotubes, g-C3N4, graphene oxide, MXene, nanosheets, zeolites, nanoporous materials, sol-gel materials, layered double hydroxides, metal-organic frameworks, covalent organic frameworks, conducting polymers, dyes, DNAs, polysaccharides, nanocelluloses, peptides, proteins, lipid bilayers, photosystems, viruses, living cells, and tissues. These examples of LbL assembly show how useful and versatile it is. Finally, this review will consider future challenges in layer-by-layer nanoarchitectonics.

Indium-Iron Oxide Nanosized Solid Solutions as Photocatalysts for the Degradation of Pollutants under Visible Radiation

A series of solid solutions of indium and iron oxides with different In/Fe ratios (InxFeyO3, with x + y = 2) were synthesized in the form of nanoparticles (diameter of ca. 30-40 nm) with the purpose of generating enhanced photocatalysts with an intermediate band gap compared to those of the monometallic oxides, In2O3 and Fe2O3. The materials were prepared by co-precipitation from an aqueous solution of iron and indium nitrates and extensively characterized with a combination of techniques. XRD analysis proved the formation of the desired InxFeyO3 solid solutions for Fe content in the range 5-25 mol%. UV-Vis absorption analysis showed that the substitution of In with Fe in the crystalline structure led to the anticipated gradual decrease of the band gap values compared to In2O3. The obtained semiconductors were tested as photocatalysts for the degradation of model organic pollutants (phenol and methylene blue) in water. Among the InxFeyO3 solid solutions, In1.7Fe0.3O3 displayed the highest photocatalytic activity in the degradation of the selected probe molecules under UV and visible radiation. Remarkably, In1.7Fe0.3O3 showed a significantly enhanced activity under visible light compared to monometallic indium oxide and iron oxide, and to the benchmark TiO2 P25. This demonstrates that our strategy consisting in engineering the band gap by tuning the composition of InxFeyO3 solid solutions was successful in improving the photocatalytic performance under visible light. Additionally, In1.7Fe0.3O3 fully retained its photocatalytic activity upon reuse in four consecutive cycles.

Unlocking the Key to Photocatalytic Hydrogen Production Using Electronic Mediators for Z-Scheme Water Splitting

A prevalent challenge in particulate photocatalytic water splitting lies in the fact that while numerous photocatalysts exhibit outstanding hydrogen evolution reaction (HER) activity in organic sacrificial reagents, their performance diminishes markedly in a Z-scheme water splitting system using electronic mediators. This underlying reason remains undefined, posing a long-standing issue in photocatalytic water splitting. Herein, we unveiled that the primary reason for the decreased HER activity in electronic mediators is due to the strong adsorption of shuttle ions on cocatalyst surfaces, which inhibits the initial proton reduction and results in a severe backward reaction of the oxidized shuttle ions. To address this, taking typical visible-light-responsive photocatalysts, BaTaO2N and SrTiO3:Rh, as examples, we have developed a strategy via selective surface modification of metal cocatalysts (such as Pt, Ru) with chromium oxide species (CrOx) to prevent the adsorption of shuttle ions. It is demonstrated that the photocatalytic HER activities of BaTaO2N and SrTiO3:Rh can be improved by one to two orders of magnitude in diverse shuttle ions. The introduced CrOx substantially weakens the interaction between the metal cocatalysts and shuttle ions, promotes proton adsorption for the HER reaction, and also suppresses the backward reaction between shuttle ions. Owing to the improved HER activity, the photocatalytic performance of Z-scheme water splitting is significantly enhanced, providing a feasible strategy for constructing efficient Z-scheme systems in heterogeneous photocatalysis.

Photogenerated charge carrier dynamics on Pt-loaded SrTiO3 nanoparticles studied via transient-absorption spectroscopy

Loading cocatalysts on semiconductor-based photocatalysts to create active reaction sites is a preferable method to enhance photocatalytic activity and a widely adopted strategy to achieve effective photocatalytic applications. Although theoretical calculations suggest that the broad density of states of noble metal cocatalysts, such as Pt, act as a recombination center, this has never been experimentally demonstrated. Herein, we employed pico-nano and nano-micro second transient absorption spectroscopy to investigate the often overlooked photogenerated holes, instead of the widely studied electrons on Pt- and Ni-loaded SrTiO3 to evaluate the effects of cocatalysts as a recombination center. It is demonstrated that Pt serves as the recombination center with no sacrificial agent; recombination can be suppressed by a hole scavenger, while recombination is not significant on Ni with localized density of states. It is also found that photo-generated holes in SrTiO3 tend to migrate to Pt within 400 ps, and photo-generated holes generated in the bulk gradually migrate to Pt cocatalysts in a micro-second regime.

Band structure engineering, optical, transport, and photocatalytic properties of pristine and doped Nb3O7(OH): a systematic DFT study

Nb3O2(OH) has emerged as a highly attractive photocatalyst based on its chemical stability, energetic band positions, and large active lattice sites. Compared to other various photocatalytic semiconductors, it can be synthesized easily. This study presents a systematic analysis of pristine and doped Nb3O7(OH) based on recent developments in related research. The current study summarizes the modeling approach and computationally used techniques for doped Nb3O7(OH) based photocatalysts, focusing on their structural properties, defects engineering, and band structure engineering. This study demonstrates that the Trans-Blaha modified Becke-Johnson approximation (TB-mBJ) is an effective approach for optoelectronic properties of pristine and Ta/Sb-doped Nb3O7(OH). The generalized gradient approximation is used for structure optimization of all systems studied. Spin-orbit (SO) coupling is also applied to deal with the Ta f orbital and Sb d orbital in the Ta/Sb-doped systems. Doping shifts the energetic band positions and relocates the Fermi level i.e. both the valence band maximum and the conduction band minimum are relocated, decreasing the band gap from 1.7 eV (pristine), to 1.266 eV (Ta-doped)/1.203 eV (Sb-doped). The band structures of pristine and doped systems reflect direct band behavior. Investigation of the partial density of states reveals that the O p orbital and Nb d/Ta d/Sb-d orbitals contributed to the valence and conduction bands, respectively. Optical properties like real and imaginary components of the dielectric function, reflectivity, and electron energy loss function are calculated using the OPTIC program implemented in the WIEN2k code. Moreover, doped systems shift the optical threshold to the visible region. Transport properties like effective mass and electrical conductivity are calculated, reflecting that the mobility of charge carriers increases with the doping of Ta/Sb atoms. The reduction in the band gap and red-shift in the optical properties of the Ta/Sb-doped Nb3O7(OH) to the visible region suggest their promising potential for photocatalytic activity and photoelectrochemical solar cells.

High Stability, Piezoelectric Response, and Promising Photocatalytic Activity on the New Pentagonal CGeP4 Monolayer

This study introduces the penta-structured semiconductor p-CGeP4 through density functional theory simulations, which possesses an indirect band gap transition of 3.20 eV. Mechanical analysis confirms the mechanical stability of p-CGeP4, satisfying Born-Huang criteria. Notably, p-CGeP4 has significant direct (e 31 = -11.27 and e 36 = -5.34 × 10-10 C/m) and converse (d 31 = -18.52 and d 36 = -13.18 pm/V) piezoelectric coefficients, surpassing other pentagon-based structures. Under tensile strain, the band gap energy increases to 3.31 eV at 4% strain, then decreases smoothly to 1.97 eV at maximum stretching, representing an ∼38% variation. Under compressive strain, the band gap decreases almost linearly to 2.65 eV at -8% strain and then drops sharply to 0.97 eV, an ∼69% variation. Strongly basic conditions result in a promising band alignment for the new p-CGeP4 monolayer. This suggests potential photocatalytic behavior across all tensile strain regimes and significant compression levels (ε = 0% to -8%). This study highlights the potential of p-CGeP4 for groundbreaking applications in nanoelectronic devices and materials engineering.

In Situ Infared Optical Fiber Sensor Monitoring Reactants and Products Changes during Photocatalytic Reaction

An in situ monitoring reaction can better obtain the variations during the progression of the photocatalytic reaction. However, the complexity of the apparatus and the limited applicability of substances are the common challenges faced by most in situ monitoring methods. Here, we invented an in situ infrared optical fiber sensor to monitor the reactants and products during photocatalytic reaction. The sensor, which has four tapered regions, demonstrates the best sensitivity of 0.71 au/vol %, 70 times higher than that of the fiber sensor without a tapered region. Then, this sensor was successfully used to in situ monitor the photocatalytic reaction between benzaldehyde and ethanol under the UV light and TiO2. The calibration plots of the reactants and products were established by sensing a series of designed concentration solutions. Based on the calibration plots, the real-time concentrations of four substances could be derived by converting the absorbance values, and the concentration changes of the reactants and products followed the first order kinetic mode. The equilibrium concentrations of reactants and products could be obtained from the fitting curves. With the increase in the UV light intensity, this sensor could detect a gradual increase in the rate of this photocatalytic reaction. The results show that this in situ infrared fiber sensor can monitor the progression of the photocatalytic reaction in real time, which will be helpful for unveiling the photocatalytic mechanism.

Enhancing deep visible-light photoelectrocatalysis with a single solid-state synthesis: Carbon nitride/TiO2 heterointerface

Visible-light responsive, stable, and abundant absorbers are required for the rapid integration of green, clean, and renewable technologies in a circular economy. Photoactive solid-solid heterojunctions enable multiple charge pathways, inhibiting recombination through efficient charge transfer across the interface. This study spotlights the physico-chemical synergy between titanium dioxide (TiO2) anatase and carbon nitride (CN) to form a hybrid material. The CN(10%)-TiO2(90%) hybrid outperforms TiO2 and CN references and literature homologs in four photo and photoelectrocatalytic reactions. CN-TiO2 achieved a four-fold increase in benzylamine conversion, with photooxidation conversion rates of 51, 97, and 100 % at 625, 535, and 465 nm, respectively. The associated energy transfer mechanism was elucidated. In photoelectrochemistry, CN-TiO2 exhibited 23 % photoactivity of the full-spectrum measurement when using a 410 nm filter. Our findings demonstrate that CN-TiO2 displayed a band gap of 2.9 eV, evidencing TiO2 photosensitization attributed to enhanced charge transfer at the heterointerface boundaries via staggered heterojunction type II.

Blue-LED assisted Photodegradation kinetics of rhodamine-6G dye, enhanced anticancer activity and cleavage of plasmids using Au-ZnO nanocomposite

The plasmonic metal doping on the UV-active metal oxide nanoparticle turns the resultant plasmonic metal-metal oxide (PMMO) into visible light active and upon exogenous illumination the photogenerated energetic charge carriers and the in situ generated reactive oxygen species (ROS, e.g. ·OH and O2 -·) authoritatively enhances its biological and catalytic activity. Herein, a hexagonal rod-shaped ZnO nanoparticles (NP) precursor was prepared using the sol-gel method, which in the presence of varying concentrations of gold (0.005M, 0.01M, and 0.015M) via a greener citrate reduction method afforded a nanocrystalline Au-ZnO nanocomposite. Using which, the visible-light driven photo-degradation kinetics investigation of rhodamine-6G (R6G) dye under blue LED irradiation were carried out. The use of 20 mg 0.015-Au-ZnO completes the degradation of R6G (97.0 %, k = 6.5 X 10-3s-1 at pH 7) within 55 min while 50 mg of 0.015-Au-ZnO catalyst improves the rate of R6G degradation (15 min 97.8 %, k = 14.8 × 10-3 s-1) and it is reusable up to three cycles. The LC-MS spectra of the remains of R6G (after 15 min) identified various low molecular ions (up m/z = 65). Further, the blue-LED assisted anti-cancer studies (MTT assay) using 0.015-Au-ZnO towards human lung cancer cells (A549), breast cancer cells (SKBr3) show high anti-proliferation rate and low cytotoxicity against healthy human embryonic kidney cells (HEK-293) with an IC50 value of 65, 53 and 124 μg/mL respectively. Also, the AO-EB dual staining and DCFH-DA analysis of SKBr3 and A549 cells revealed ROS-mediated cell death via apoptosis. Moreover, plasmid cleavage studies against supercoiled pBR322 DNA result in single-stranded linear DNA without traversing the nicked circular form, suggesting the possible DNA targeting activity of Au-ZnO nanozyme. Thus, the synthesized Au-ZnO nanocomposite shows excellent photocatalytic and biological activity.

Surface Oxygen Vacancies on Copper-Doped Titanium Dioxide for Photocatalytic Nitrate-to-Ammonia Reduction

Photocatalytic transformation of nitrate (NO3-) in wastewater into ammonia (NH3) is a challenge in the detoxification and recycling of limited nitrogen resources. In particular, previously reported photocatalysts cannot promote the reaction using water as an electron donor. Herein, we report that copper-doped titanium dioxide (Cu-TiO2) powders, prepared via the sol-gel method and subsequent calcination, promote NO3--to-NH3 reduction in water. The Cu2+ doping into TiO2 creates a large number of surface oxygen vacancies (OVsurf), which are stable even under aerated conditions. The Ti3+ and Cu2+ atoms adjacent to OVsurf behave as active sites for the NO3--to-NH3 reduction. Doping with an appropriate amount of Cu2+ and calcination at an appropriate temperature produce the catalysts with a large number of OVsurf, while maintaining a high conductivity, and exhibit a high photocatalytic activity.

Floating Photothermal Hydrogen Production

Solar-to-hydrogen (STH) is emerging as a promising approach for energy storage and conversion to contribute to carbon neutrality. The lack of efficient catalysts and sustainable reaction systems is stimulating the fast development of photothermal hydrogen production based on floating carriers to achieve unprecedented STH efficiency. This technology involves three major components: floating carriers with hierarchically porous structures, photothermal materials for solar-to-heat conversion and photocatalysts for hydrogen production. Under solar irradiation, the floating photothermal system realizes steam generation which quickly diffuses to the active site for sustainable hydrogen generation with the assistance of a hierarchically porous structure. Additionally, this technology is endowed with advantages in the high utilization of solar energy and catalyst retention, making it suitable for various scenarios, including domestic water supply, wastewater treatment, and desalination. A comprehensive overview of the photothermal hydrogen production system is present due to the economic feasibility for industrial application. The in-depth mechanism of a floating photothermal system, including the solar-to-heat effect, steam diffusion, and triple-phase interaction are highlighted by elucidating the logical relationship among buoyant carriers, photothermal materials, and catalysts for hydrogen production. Finally, the challenges and new opportunities facing current photothermal catalytic hydrogen production systems are analyzed.

Surface Sulfurization of Cubic Cu2O to Form Cu2S Nanostructure-Decorated Catalysts for Light-Enhanced Electrocatalytic H2 Evolution and Photocatalytic CO2 Reduction

Developing highly efficient bifunctional catalysts for electrocatalysis and photocatalysis suffers from sluggish charge transfer and poor photo-to-electric conversion rate. Herein, micro-sized Cu2O cubes were initially prepared for subsequent transformation into Cu2O@Cu2S core-shell structures by a slight surface sulfurization. The formation of nanostructured Cu2S thin layer at Cu2O surface can endow an immediate charge separation and migration under light irradiation, leading to high surface photovoltages (SPV, 18-30 mV). As a result, the as-prepared Cu2O@Cu2S catalysts exhibited reduced overpotentials (η, only 86 mV is required for the optimized sample to achieve a current density of 10 mA cm-2) for H2 evolution with good cycling stability in electrocatalytic water splitting. Meanwhile, a high methane (CH4) production rate of 30.3 μmol h-1 g-1 can be delivered from the optimized Cu2O@Cu2S sample when used for photocatalytic CO2 reduction. This work has provided a strategy to prepare bifunctional catalysts with improved photoelectric properties for photo/electrocatalytic applications.

Improved conversion of carbon dioxide to methane via photohydrogenation using Gd2NiMnO6 with a dendritic fibrous architecture

The conversion of diluted CO₂ into high-energy fuels is increasingly central to renewable energy research. This study investigates the efficacy of a Gd₂NiMnO₆ dendritic nanofibrous (DNF) photocatalyst in transforming carbon dioxide to methane through photoreduction. Gd₂NiMnO₆ DNF was found to provide active adsorption sites and control the strand dimensions for metal groups, facilitating the chemical absorption of CO₂. The light-driven photoreduction of CO₂ to CH₄ through biomass valorization has become a sustainable focus area, with photocatalytic CO₂ reduction recognized as a key strategy to mitigate greenhouse gases and achieve carbon neutrality. However, designing active sites with enhanced selectivity and efficiency for CO₂ photoreduction remains challenging. Reducing carbon dioxide is especially crucial in the era of petroleum refineries. This work introduces a reusable, magnetically responsive nanocatalyst for the targeted light reduction of CO₂ to CH₄, utilizing eco-friendly methods, mild thermal conditions, ambient pressure, and sustainable dehydrating agents. This approach provides significant economic benefits and compatibility with functional groups, highlighting the potential of combining 3D nanoparticle structures with sustainable chemistry to create highly efficient catalytic systems for CO₂ to CH₄ conversion.

Simultaneous Structural and Electronic Engineering on Bi- and Rh-co-doped SrTiO3 for Promoting Photocatalytic Water Splitting

Activating metal ion-doped oxides as visible-light-responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)-molten (dopants) reaction to synthesize Bi- and Rh-codoped SrTiO3 (SrTiO3 : Bi,Rh) particles. Our investigation reveals that SrTiO3 : Bi,Rh manifests as single-crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well-stabilized Rh3+ energy state for visible-light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high-concentration and long-lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3 : Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9 % at 420 nm, setting a new benchmark among Rh-doped-based SrTiO3 materials. Furthermore, when integrated into an all-solid-state Z-Scheme system with Mo-doped BiVO4 and reduced graphene oxide, SrTiO3 : Bi,Rh enabled water splitting with an AQY of 7.1 % at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid-molten reaction as a viable approach for this purpose.

Water and seawater splitting with MgB2 plasmonic metal-based photocatalyst

Plasmonic nanostructures can help to drive chemical photocatalytic reactions powered by sunlight. These reactions involve excitation of plasmon resonances and subsequent charge transfer to molecular orbitals under study. Here we engineered photoactive plasmonic nanostructures with enhanced photocatalytic performance using non-noble metallic MgB2 high-temperature superconductor which represents a new family of photocatalysts. Ellipsometric study of fabricated MgB2 nanostructures demonstrates that this covalent binary metal with layered graphite-like structure could effectively absorb visible and infrared light by excitation of multi-wavelengths surface plasmon resonances. We show that a MgB2 plasmonic metal-based photocatalyst exhibit fundamentally different behaviour compared to that of a semiconductor photocatalyst and provides several advantages in photovoltaics applications. Excitation of localised surface plasmon resonances in MgB2 nanostructures allows one to overcome the limiting factors of photocatalytic efficiency observed in semiconductors with a wide energy bandgap due to the usage of a broader spectrum range of solar radiation for water splitting catalytic reactions conditioned by enhanced local electromagnetic fields of localised plasmons. Excitation of localised surface plasmon resonances induced by absorption of light in MgB2 nanosheets could help to achieve near full-solar spectrum harvesting in this photocatalytic system. We demonstrate a conversion efficiency of ~ 5% at bias voltage of V bias  = 0.3 V for magnesium diboride working as a catalyst for the case of plasmon-photoinduced seawater splitting. Our work could result in inexpensive and stable photocatalysts that can be produced in large quantities using a mechanical rolling mill procedure.

Natural Sunlight-Driven Photocatalytic Overall Water Splitting with 5.5% Quantum Yield Promoted by Porphyrin-Sensitized Zn Poly(heptazine imide)

Meso-tetrakis(4-carboxyphenyl)porphyrin (H4TCPP) has been loaded on a partially exchanged Zn2+ poly(heptazine imide) (PHI), changing the light harvesting properties of the system, without altering the PHI structure. At the optimal loading (20 wt %), the photosensitized (Zn/K)-PHI is able to produce 1.06 mmolH2/g and 0.46 mmolO2/g after 12 h of reaction irradiation of Milli-Q water under visible light by a 100 mW/cm2 white LED. The apparent quantum yield for the overall water splitting reaction was 5.5% at 400 nm and 2% at 700 nm. Outdoor water splitting irradiation with natural sunlight shows the feasibility of the process. The photocatalytic performance of TCPP20%@(Zn/K)-PHI is considerably higher than that of analyzed reference samples such as graphitic carbon nitride, poly(triazine imide), and potassium PHI with H4TCPP photosensitization. These relative photocatalytic activities point out the relevance of the PHI structure and the presence of Zn2+. It is proposed that Zn2+ simultaneously binds PHI and H4TCPP. Transient absorption spectroscopy supports the occurrence of photoinduced electron transfer in which electrons are located at the H4TCPP and holes at the PHI moiety. Transient photocurrent measurements show a higher charge separation efficiency on TCPP20%@-(Zn/K)-PHI compared to (Zn/K)-PHI, and measurement of the frontier orbitals indicates an adequate energy alignment of the HOMO/LUMO levels of TCPP4- with respect to (Zn/K)-PHI. The results show the possibility of developing efficient noble metal-free photocatalytic systems based on PHI dye sensitization.

Molecular Heterogeneous Photocatalysts for Visible-Light-Driven CO2 Reduction

Photoreduction of CO2 to high-value chemical fuels presents an effective strategy to reduce reliance on fossil fuels and mitigate climate change. The development of a photocatalyst characterized by superior activity, high selectivity, and good stability is a critical issue for PCR. Molecular heterogeneous photocatalytic systems integrate the advantages of both homogeneous and heterogeneous catalysts, creating a synergistic enhancement effect that increases photocatalytic performance. This review summarizes recent advancements in molecular heterogeneous photocatalysts for CO2 reduction. Much of the discussion focuses on the types of molecular heterogeneous photocatalysts, and their photocatalytic performance in CO2 reduction is summarized. The synthesis strategies for molecular heterogeneous photocatalysts are thoroughly discussed. Finally, the challenges and future prospects of molecular heterogeneous photocatalysts for PCR are addressed.