Photoexcited Electrons Research Articles

Construction of triazine-heptazine-based carbon nitride heterojunctions boosts the selective photocatalytic C−C bond cleavage of lignin models

Photocatalytic lignin depolymerization emerges as a sustainable and cost-competitive strategy to produce low-molecular-weight aromatic chemicals from renewable resources. Significant efforts have been devoted to engineering C−C bond cleavage photocatalysts with diverse compositional and morphologic characteristics in the past decade. We herein present a facile photocatalytic strategy of promoting C−C bond cleavage in lignin models to achieve high-yield aromatic monomers over triazine-heptazine-based carbon nitride heterojunctions, exceeding the triazine- or heptazine-based counterparts. Mechanistic investigations reveal that the photo-excited electron and hole synergistically trigger the C−C bond cleavage. A combination of experimental results and theoretical calculations confirms that the improved photocatalytic performance is primarily attributed to the accelerated charge carriers separation and migration induced by the built-in electric field at the heterojunction interface, and the facilitated Cβ-radical generation. These findings highlight the effectiveness of interfacial engineering of intramolecular heterostructures towards the rational promotion of photocatalytic cleavage of C−C bond in lignin models.

A novel scheme to improve the photo-Fenton performance of iron oxychloride by carbon: Three existent states and roles of carbon in the degradation of tetracycline in water

The photo-Fenton process is promising for sincerely treating contaminated water. In this work, carbon-decorated iron oxychloride (C-FeOCl) is synthesized as a photo-Fenton catalyst for removing tetracycline (TC) from water. Three actual states of carbon are identified and their different roles in enhancing photo-Fenton performance are revealed. All carbon on/in FeOCl, including graphite carbon, carbon dots and lattice carbon, enhance visible light adsorption. More importantly, a homogeneous graphite carbon on the outer surface of FeOCl accelerates the transportation-separation of photo-excited electrons along the horizontal direction of FeOCl. Meanwhile, the interlayered carbon dots offer a FeOC bridge in helping the transportation-separation of photo-excited electrons along the vertical direction of FeOCl. In this way, C-FeOCl acquires isotropy in conduction electrons to ensure an efficient Fe(II)/Fe(III) cycle. These interlayered carbon dots extend the layer spacing (d) of FeOCl to about 1.10 nm, exposing the internal iron centers. The lattice carbon significantly increases the amounts of coordinatively unsaturated iron sites (CUISs) in activating hydrogen peroxide (H2O2) to hydroxyl radical (OH). Density functional theory (DFT) calculations confirm this activation on inner and external CUISs with a significantly low activation energy of about 0.33 eV.

Controllably solar-driven C‒C coupling organic synthesis integrated with H2 production over P-doped g-C3N4 with NiS nanoparticles modification

The development of mild and environmental method for direct transformation of aromatic alcohol into hydrobenzoin via controlled C‒C coupling is a highly attractive but challenging goal. In this paper, a P-doped g-C3N4 photocatalyst with NiS nanoparticles modification is first reported to apply the visible-light-driven C‒C coupling of aromatic alcohol into hydrobenzoin, as well as integrating with the production of clean H2 fuel. The synergistic effect of doped P atoms and formed type-II heterojunction between PCN and NiS improves the light absorption ability of g-C3N4 and greatly suppresses the charge recombination. Optimized 2.0% NiS/PCN composite achieves the complete conversion of aromatic alcohol within 6 h reaction time, as far as we known, which is the highest efficiency so far for aromatic alcohol conversion via photocatalytic strategy. Hydrobenzoin is controllably formed with 68% selectivity, together with a highly-efficient H2 production rate of 994.8 μmol·g−1·h−1. In-situ EPR studies reveal a preferential activation of C‒H bond than O‒H bond in aromatic alcohol by photoexcited holes, forming C6H5ĊH2OH radicals for subsequent coupling. The residual protons interact with photoexcited electrons to generate H2. Our study not only offers an efficient g-C3N4-based photocatalyst for the synthesis of hydrobenzoin under mild conditions, but also opens up a new avenue for manipulating the activation of C‒H or O‒H bonds for high selectivity of hydrobenzoin product.

Ultra-thin carbon doped TiO2 nanotube arrays for enhanced visible-light photoelectrochemical water splitting

TiO2 has been widely employed as a photocatalyst for water splitting owing to its high activity, low cost, abundance, safety, and stability. However, the further utilization of TiO2 is still confined to the wide band gap and the rapid recombination speed. Carbon has metallic conductivity and a large electron storage capacity, which can help to absorb photoexcited electrons and enhance charge separation and transfer. Herein, we fabricated the ultra-thin carbon-doped TiO2 nanotube arrays (TNTAs). The as-prepared UTC-doped TiO2@TNT exhibited high photoelectrochemical (PEC) activity, realizing a high H2 evolution rate up to 41.3 μmol cm-2 h−1 (AM 1.5G) and 1.3 μmol cm-2 h−1 (visible light), which exhibit significantly narrowed band gaps and decreased charge resistance. Using ultra-thin carbon doping in TiO2 nanotube arrays opens up a new avenue for optimizing photocatalysts for PEC water splitting.

Enhancement of bifunctional photocatalytic activity of boron-doped g-C3N4/SnO2 heterojunction driven by plasmonic Ag quantum dots

Enhancement of photocatalytic charge transfer with reduced electron–hole (e− + h+) recombination toward the targeted chemical reaction is a challenging task. In this study, we utilized boron (B) dopant as impurity levels, and the plasmonic Ag quantum dots (QDs), and g-C3N4/SnO2 heterojunction nanocomposite under visible light (λ = 385–740 nm) as a nanocomposite photocatalytic system for energy and environmental applications. The introduction of B dopant with optimal level (BCN1.0) of 1 wt% resulted in the fast migration of photoexcited electrons from valence band to the conduction band of g-C3N4 and reduced the migration distance of the electrons from valence band to the conduction band and improved surface redox reactions. The heterojunction formed with SnO2 nanorods and nanoparticles enhanced the electron–hole transfer rate across the interface of the heterojunction (BCNS15) with 15 wt% and improved the photocatalytic activity during redox reactions. The introduction of plasmonic Ag QDs (1 wt%) as a co-catalyst improved the H2 generation efficiency (BCNS–Ag1.0). Ultraviolet photoelectron spectroscopy results confirmed that the charge transfer process was initiated via the Z-scheme mechanism. Photoluminescence spectra identified the reduction of electron–hole recombination that was responsible for improved catalytic efficiency in the optimized heterojunction nanocomposite. The synergetic effect of B dopant, the visible light sensitization effect and the co-catalytic effect of the Ag QDs, the formation of a heterojunction of the B-g-C3N4/SnO2/Ag (BCNS–Ag1.0) nanocomposite resulted in 2.5 times higher methyl orange dye degradation efficiency which is 65.6% compared to pristine g-C3N4 (CN) 25.9%. Further, the photocatalysts were tested for photocatalytic H2 generation, the optimized BCNS–Ag1.0 nanocomposite heterojunction showed 3.2 times higher H2 generation activity (10.2 mmol/h/gcat) than pristine CN(3.1 mmol/h/gcat) through Z-scheme mechanism. Finally, the BCNS–Ag1.0 nanocomposite demonstrated excellent stability toward methyl orange degradation as well as H2 generation for at least 4 cycles. Therefore, the BCNS–Ag1.0 nanocomposite is a promising photocatalytic system for scale-up synthesis.

NIR-II driven photocatalytic hydrogen peroxide-supply on metallic copper-nickel selenide (Cu-Ni0.85Se) nanoparticle for synergistic therapy

Currently, finite intratumoral H2O2 content has restricted the efficacy of chemodynamic therapy (CDT). Here, Cu-Ni0.85Se@PEG nanoparticles are constructed to display intracellular NIR-II photocatalytic H2O2 supplement. The formation mechanism is explored to discover that H2O2 generation is dominated by photo-excited electrons and dissolved O2 via a typical sequential single-electron transfer process. Both density functional theory calculation and experimental data confirm its metallic feature that endows the great NIR-II absorption and photothermal conversion efficiency (59.6 %, 1064 nm). Furthermore, the photothermal-assisting consecutive interband and intraband transition in metallic catalyst contributes to the high redox capacity and efficient separation/transfer ability of photo-generated charges, boosting H2O2 production under 1064 nm laser irradiation. In addition, Cu-Ni0.85Se@PEG possess mimic peroxidase and catalase activity, leading to in-situ H2O2 activation to produce ∙OH and O2 for the enhanced CDT and hypoxia relief. What’s more, the nanomaterials reveal novel biodegradation that is derived from oxidation from insolvable selenide into soluble selenate, resulting in elimination via feces and urine within 2 weeks. Synergistic CDT and photothermal therapy (PTT) further lead to great tumor inhibition and immune response for anti-tumor. The antitumor mechanism and the potential biological process also are investigated by high-throughput sequencing of expressed transcripts (RNAseq). The great treatment performance is responsible for the regulation of related oxidative stress and stimulus genes to induce organelle (mitochondrial) and membrane dysfunction. Besides, the synergistic therapy also can efficiently evoke immune response to further fight against tumor.

Polarity‐Driven Atomic Displacements at the 2D Mg2TiO4‐MgO (001) Oxide Interface for Hosting Potential Interlayer Excitons

AbstractInterlayer excitons in solid‐state systems have emerged as candidates for realizing novel platforms ranging from excitonic transistors and optical qubits to exciton condensates. Interlayer excitons have been discovered in 2D transition metal dichalcogenides, with large exciton binding energies and the ability to form various van der Waals heterostructures. Here, an oxide system consisting of a single unit cell of Mg2TiO4 on MgO (001) is proposed as a platform for hosting interlayer excitons. Using a combination of density functional theory (DFT) calculations, molecular beam epitaxy growth, and in situ crystal truncation rod measurements, it is shown that the Mg2TiO4‐MgO interface can be precisely controlled to yield an internal electric field suitable for hosting interlayer excitons. The atoms in the polar Mg2TiO4 layers are observed to be displaced to reduce polarity at the interface with the non‐polar MgO (001) surface. Such polarity‐driven atomic displacements strongly affect electrostatics of the film and the interface, resulting in localization of filled and empty band‐edge states in different layers of the Mg2TiO4 film. The DFT calculations suggest that the electronic structure is favorable for localization of photoexcited electrons in the bottom layer and holes in the top layer, which may bind to form interlayer exciton states.

Impact of organic amine cations on photoluminescence and magnetic properties in Dion-Jacobson hybrid manganese halide perovskites

A strenuous effort has been made to design multifunctional lead-free organic–inorganic hybrid (OIH) halide compounds, which are envisioned as next generation solar cell materials. However, it is challenging to design OIH halides that can exhibit both long-range magnetic ordering and high photoluminescence quantum yield (PLQY) since the dimensionality of the compounds has a contrasting effect on them. In this article, we have shown an approach to enhance PLQY in two-dimensional (2D) Heisenberg antiferromagnets by increasing the alkylene chain length of [H3N–(CH2)m–NH3]MnCl4 (m = 2, 3, and 4) compounds. All these compounds exhibit 2D layers of corner-sharing MnCl6 octahedra where the organic cations are intercalated between them. These compounds exhibit long-range antiferromagnetic ordering confirmed by the DC magnetic susceptibility and heat capacity measurements. The Néel temperature (TN) decreases with increasing the length of spacer cations due to a decrease in interlayer exchange interactions; however, interestingly, the lifetime of photoexcited electrons and PLQY enhances from 24 to 56 µs and 8% to 23%, respectively. Furthermore, the temperature-dependent photoluminescence measurements provide insight into thermal quenching and exciton binding energy. We believe this study can help to design new OIH halides with long-range magnetic ordering and high PLQY.

Photoinduced Dynamics of Spin Centers in Carbon-Modified Titanium Dioxide Nanotubes

Arrays of titanium dioxide (TiO2) nanotubes with different chemical compositions have been synthesized; their structural properties have been studied, and the characteristics of spin centers (defects) have been determined. All samples have appeared to contain carbon. It has been established that the main type of spin centers in TiO2 nanotubes are dangling carbon bonds, and their concentration correlates with the carbon content in the obtained structures. Under illumination, a reversible increase in the concentration of defects occurs, which is caused by their photoinduced recharging in the process of impurity absorption. This process is accompanied by an increase in the concentration of photoexcited electrons in the conduction band. The originality and novelty of the work are determined by the development of a method for controlling the density of defects and, accordingly, the concentration of photoinduced electrons by thermal treatment of samples under various conditions. The results open up new possibilities for the development of photocatalysts based on titanium dioxide nanotubes with a controlled electron concentration in the conduction band that function in the visible range of the spectrum.

Gallium Oxide Assisting Ag-Loaded Calcium Titanate Photocatalyst for Carbon Dioxide Reduction with Water

An efficient and highly selective photocatalytic conversion of carbon dioxide (CO2) into valuable chemicals such as carbon monoxide (CO) using water (H2O) as an electron donor has been much attractive and deeply desired, which requires the development of advanced photocatalysts based on a functional design. As the Ag-loaded calcium titanate (CaTiO3, CTO) photocatalyst showed a high selectivity to CO2 reduction in aqueous solution and the Ag-loaded gallium oxide (Ga2O3) photocatalyst showed a higher activity for both H2O splitting and CO2 reduction, herein, a series of composite photocatalyst samples consisting of Ga2O3 and CTO were simply fabricated by calcination of the physical mixtures, followed by loading of a Ag cocatalyst with a photodeposition method. The optimized sample with the Ag cocatalyst exhibited both a high CO formation rate of 56.9 μmol h–1 (higher than that of Ag/Ga2O3) and a high selectivity of 95.0% (comparable to Ag/CTO) in the photocatalytic CO2 reduction with H2O. In this composite photocatalyst, most of the electrons generated in the photoexcited Ga2O3 part migrated to the minor CTO particles to contribute to the selective CO2 reduction reaction, which was evidenced by the selective photodeposition of Ag species on the CTO part. The selective CO formation originates from the property of Ag-loaded CTO photocatalyst as the active part in the composite photocatalyst. The Ga2O3 part functions as an antenna to receive the light and donate the photoexcited electrons to the much decorated Ag/CTO part, where the concentrated electrons would promote CO2 reduction with high efficiency.

Photocatalytic CO2 reduction to CH4 mediated by MoS2@NH2-MIL-68 heterojunction with water vapor

Construction of heterojunction-based photocatalyst is a fascinating approach to improve the conversion efficiency of CO2 photoreduction. Herein, we report a series of low-cost heterojunction catalysts (x% MSNM) assembled by 1T MoS2 nanosheets and NH2-MIL-68 for photocatalytic CO2 reduction conjugated with H2O oxidation under visible-light irradiation. Notably, 8% MSNM exhibits enhanced photocatalytic activity for the photoreduction of CO2 to CH4 in the absence of organic solvent, sacrificial agent and photosensitizer. The evolution rate of CH4 can reach to 12.56 ​μmol ​g−1, higher than that of isolated MoS2 and NH2-MIL-68. Systematic investigations demonstrate that the 1T MoS2 fragments are uniformly dispersed on the NH2-MIL-68 surface during the assembly and crystallization process of NH2-MIL-68. Under light conditions, the NH2-MIL-68 crystals serve as light collectors to absorb visible light and generate electron-hole pairs, and the photo-excited electrons rapidly transferred to the surface of 1T MoS2, prolonging the lifetime of the photo-induced excitons. This work provides a new direction for the rational design of composite catalysts in artificial photosynthesis.

One Stone Two Birds: Utilization of Solar Light for Simultaneous Selective Phenylcarbinol Oxidation and H2 Production over 0D/2D-3D Pt/In2S3 Schottky Junction

Precise regulation and control solar-light-driven charges photoexcited on photocatalysts for separation-transfer and target redox reactions is an attractive and challenging pathway toward sustainability. Herein, 0D/2D-3D Pt/In2S3 Schottky junction was fabricated for simultaneous selective phenylcarbinol conversion into value-added aldehydes and production of clean energy H2 by directly utilizing photoexcited holes and electrons in one reaction system under mild reaction conditions. In contrast to pure water splitting and pure In2S3, the reaction thermodynamics and kinetics of H2 evolution on the Pt/In2S3 were significantly enhanced. The optimized 0.3% Pt/In2S3 exhibited the highest and most stable photocatalytic activity with 22.1 mmol g−1 h−1 of H2 production rate and almost 100% selectivity of benzaldehyde production. Notably, this dual-function photocatalysis also exhibited superiority in contrast to sacrificial-agent H2 evolution reactions such as lactic acid, Na2S, methanol and triethanolamine. The turnover frequency (TOF) could reach up to ~2394 h−1. The Pt clusters anchored at the electron location and strong metal-support interactions (SMSI) between Pt and In2S3 synergistically improved the spatial charge separation and directional transportation (~90.1% of the charge transport efficiency could be achieved over the Pt/In2S3 hybrid), and thus result in significant enhancement of photocatalytic H2 evolution with simultaneous benzaldehyde production.

Perspective on functional metal-oxide plasmonic metastructures

Plasmonic nanostructures and metasurfaces are appealing hosts for investigation of novel optical devices and exploration of new frontiers in physical/optical processes and materials research. Recent studies have shown that these structures hold the promise of greater control over the optical and electronic properties of quantum emitters, offering a unique horizon for ultra-fast spin-controlled optical devices, quantum computation, laser systems, and sensitive photodetectors. In this Perspective, we discuss how heterostructures consisting of metal oxides, metallic nanoantennas, and dielectrics can offer a material platform wherein one can use the decay of plasmons and their near fields to passivate the defect sites of semiconductor quantum dots while enhancing their radiative decay rates. Such a platform, called functional metal-oxide plasmonic metasubstrates (FMOPs), relies on formation of two junctions at very close vicinity of each other. These include an Au/Si Schottky junction and an Si/Al oxide charge barrier. Such a double junction allows one to use hot electrons to generate a field-passivation effect, preventing migration of photo-excited electrons from quantum dots to the defect sites. Prospects of FMOP, including impact of enhancement exciton–plasmon coupling, collective transport of excitation energy, and suppression of quantum dot fluorescence blinking, are discussed.

Mechanistic insights into efficient photocatalytic H2O2 production of 2D/2D g-C3N4/In2S3 photocatalyst by tracking charge flow direction

Understanding the charge flow direction within semiconductor heterojunction is of crucial importance for designing and constructing next generation photocatalysts for fundamental perspective as well as efficient production of fuels such as hydrogen and hydrogen peroxide (H2O2). Here, two-dimensional (2D)/2D g-C3N4/In2S3 heterostructures are explored for photocatalytic H2O2 production in organic electron donor-free condition for the first time. The substantially augmented photocatalytic performance is unveiled by charge flow tracking realized through in situ reduction of Au ions by electron into Au and oxidation of Pb ions by hole into PbO2, revealing that photoinduced electrons of g-C3N4 move to In2S3 and holes remain in g-C3N4, prompting effective separation of charges. The experiments of radical trapping confirm that the photoexcited electrons accumulated on the conduction band of In2S3 in g-C3N4/In2S3 heterostructures generate H2O2 through a two-step one-electron reduction reaction of O2. This work not only identifies In2S3 as a new promising material for the photocatalytic H2O2 production but also provides a new approach for rational design of heterojunction photocatalyst via tracking charge flow direction to boost H2O2 production.

Measuring Photoexcited Electron and Hole Dynamics in ZnTe and Modeling Excited State Core-Valence Effects in Transient Extreme Ultraviolet Reflection Spectroscopy

Transient extreme ultraviolet (XUV) spectroscopy is becoming a valuable tool for characterizing solar energy materials because it can separate photoexcited electron and hole dynamics with element specificity. Here, we use surface-sensitive femtosecond XUV reflection spectroscopy to separately measure photoexcited electron, hole, and band gap dynamics of ZnTe, a promising photocathode for CO2 reduction. We develop an ab initio theoretical framework based on density functional theory and the Bethe-Salpeter equation to robustly assign the complex transient XUV spectra to the material's electronic states. Applying this framework, we identify the relaxation pathways and quantify their time scales in photoexcited ZnTe, including subpicosecond hot electron and hole thermalization, surface carrier diffusion, ultrafast band gap renormalization, and evidence of acoustic phonon oscillations.

Particle Size Dependent Trap States of Photoexcited Carriers in Anatase TiO2 Nanoparticles

Heterogeneous photocatalysis is a promising technology for artificial photosynthesis and environmental remediation. The development of efficient photocatalysts requires a better understanding of trap states of photoexcited carriers since it determines the reactivity of the carriers. Although the surface morphology as well as coordination environment of surface atoms should depend on the size of photocatalyst nanoparticles, how the trap states change with the particle size remains unclear. Here we found that the depth of electron traps on anatase TiO2 particles decreases with increasing their particle size. It was shown that most photoexcited electrons are deeply trapped in the midgap states (3.1 to 0.7 eV from the conduction band minimum) in ultrafine nanoparticles (6.3 nm), but a part of electrons survived as free electrons in the conduction band when particle size was increased to 14.5 nm by annealing. Further increase to 28.6 nm exhibits only free electrons. These results show that an increase in the particle size decrease the density of deep electron traps, allowing photoexcited electrons to survive without being trapped even in the microsecond region. Our results identify particle size as a determining factor of trap states of photoexcited carriers in anatase TiO2 nanoparticles.

Role of Pi-Electron Density at the Interface of Small Molecule-Sensitized Solar Cells

Conventional dye-sensitized solar cells (DSSCs) involving charge-transfer interfaces face charge injection losses and offsets for TiO2-sensitizer band alignment. The direct charge-transfer mechanism in DSSCs with catechol (CT, 1,2-benzenediol)-based compounds minimizes the injection losses and eliminates band alignment issues, although the photovoltaic performance of the corresponding device is very poor due to the ultrafast (picosecond) recombination of photoexcited electrons. Just as in a natural photosystem, structural selectivity toward inhibition of this recombination needs to be defined. The interfacial electron density and back electron transfer kinetics at the molecular sensitizer–TiO2 interface play a significant role in the overall energy conversion efficiency. Herein, we identified, for the first time, that the π-electron cloud at the sensitizer–TiO2 interface facilitates the degree of recombination. Comparative density functional theory analyses confirmed that these electron clouds act as large recombination sites. Luminol (LM) and isoluminol (ILM) were employed as “small molecule” sensitizers without the cloud, having a secondary amine linker, which increased the photoenergy conversion efficiency of the single-step sensitization-based photovoltaic cell (type-II DSSC) by reducing the recombination. The device with LM exhibited a power-conversion efficiency (PCE) of ca. 1.11% (representing 363% improvement when compared to CT), the highest ever reported in this category. This understanding is insightful for the design of novel small molecular sensitizers for future DSSCs.

Promoted photocatalytic hydrogen evolution via double-electron migration in Ag@g-C3N4 heterojunction

The unsaturated edge Ag introduced on the surface of photocatalysts plays an important role in boosting photo-excited electrons for the photoreduction H2O reaction. However, a moderate and tractable strategy to efficiently expose edge Ag remains an enormous challenge. For this purpose, a core skeleton with ‘Ag conductive nanosphere array’ inside and a two-dimensional sheet structure with g-C3N4 layer outside are formed. The introduction of Ag nanospheres into g-C3N4 not only enlarges the distance between g-C3N4 nanolayers, but also increases the exposure of Ag nanospheres. When Ag intimately contacts with g-C3N4, the electrons of g-C3N4 voluntarily flow to the Ag. Consequently, a built-in electric field (IEF) has been formed at interface of Ag@g-C3N4 heterojunction, which prevents the continuous flow of electrons from g-C3N4 to Ag. Under irradiation, the e− accumulated in Ag tend to recombine with the h+ in the valence band of g-C3N4 which is driven by Coulomb interaction and IEF. Ag nanospheres are fabricated as a co-catalyst to decorate the g-C3N4 nanolayer, which hinder the conglomeration of g-C3N4 nanolayers. Moreover, Ag@g-C3N4 heterojunction provides polyunsaturated edge Ag as active sites, inducing prolonged lifetime of photogenerated electrons and formed the unique charge transfer channels. In addition, abundant nitrogen vacancies are formed, which strengthens the chemisorption of H2O. As a result, supreme Ag@g-C3N4 realizes a high H2 evolution of 312.5 μmol and preserves a good sustainability. This paper emphasizes the importance of unique electron transfer pathway and chemisorption of water for photoreduction H2O.

Dual-functional photocatalysis boosted by electrostatic assembly of porphyrinic metal-organic framework heterojunction composites with CdS quantum dots

Photocatalytic dual-functional reaction under visible light irradiation represents a sustainable development strategy. In detail, H2 production coupled with benzylamine oxidation can remarkably lower the cost by replacing sacrificial agents. In this work, CdS quantum dots (CdS QDs) were successfully loaded onto the surface of a porphyrinic metal-organic framework (Pd-PCN-222) by the electrostatic self-assembly at room temperature. The consequent Pd-PCN-222/CdS heterojunction composites displayed superb photocatalytic activity under visible light irradiation, achieving a H2 production and benzylamine oxidation rate of 5069 and 3717 µmol g−1 h−1 with >99% selectivity in 3 h. There is no noticeable loss of catalytic capability during three successive runs. Mechanistic studies by in situ electron spin resonance and X-ray photoelectron spectroscopy disclosed that CdS QDs injected photoexcited electrons to Pd-PCN-222 and then Zr6 clusters under visible-light irradiation, and thus CdS QDs and Zr6 clusters behave as the photocatalytic oxidation and reduction centers, respectively.

Synchronous fabrication of Ru single atoms and RuO2 on hierarchical TiO2 spheres for enhanced photocatalytic coproduction of H2 and benzaldehyde

Photocatalytic water splitting coupled with selective organic oxidation can simultaneously produce clean H2 fuel and value-added chemicals by effective utilization of photoexcited electrons and holes. However, significant challenges remain in developing the dual-function photocatalysts with high performance. Herein, well-dispersed Ru single atoms (RuSA) and RuO2 nanoparticles are synchronously anchored on hierarchical TiO2 sub-microspheres to fabricate a superb dual-function photocatalyst (RuSA-RuO2/TiO2) for accelerating the coproduction of hydrogen and benzaldehyde from benzyl-alcohol aqueous solution. The hierarchical TiO2 spheres with a high specific surface area act not only a light-harvesting material but also a favorable support for exposing more catalytic sites. The one-step modification of dual cocatalysts on semiconductor is more attractive than the complicated multi-step process. Under a simulated sunlight, the yield rates of hydrogen and benzaldehyde reach up to 2.91 and 1.42 mmol·gcat-1·h−1, respectively, much higher than those obtained from the prepared photocatalysts with other modifications. Mechanistic investigations by control experiments, detailed characterizations and theoretical calculations elucidate the synergetic catalysis of Ru single atoms and RuO2 nanoparticles on TiO2, which facilitates the separation of photo-generated charge carriers as well as affords the specific active sites for hydrogen evolution and benzaldehyde production. This work provides a facile strategy to develop high-performance photocatalysts for sustainable energy conversion as well as a new insight into the synergistic catalysis of different active sites.