Mild Deoxygenation of Sulfoxides over Plasmonic Molybdenum Oxide Hybrid with Dramatic Activity Enhancement under Visible Light

Reductive amination of triglycerides to fatty amines over a titanium oxide-supported Pt-Mo catalyst

The reductive amination of naturally abundant triglycerides is a promising approach for the synthesis of fatty amines. However, existing catalytic systems for this transformation typically require harsh reaction conditions. Herein, we present a titanium oxide-supported platinum-molybdenum (Pt-Mo/TiO2) catalyst that promotes the reductive amination of triglycerides to fatty amines. The Pt-Mo/TiO2 catalyst exhibits a high activity under milder conditions, specifically at 1 MPa of H2, surpassing the performance of previously reported catalysts. A wide range of triglycerides, including cooking oils, are successfully converted into the corresponding fatty amines in high yields. The Pt-Mo/TiO2 catalyst is reusable and applicable to gram-scale reactions, demonstrating the high potential of Pt-Mo/TiO2 for green and sustainable fatty amine production.

In-Situ Dynamic Carburization of Mo Oxide with Unprecedented High CO Formation Rate in Reverse Water-Gas Shift Reaction

In situ construction of active structure under reaction conditions is highly desired but still remains challenging in many important catalytic processes. Herein, we observe structural evolution of molybdenum oxide (MoOx) into highly active molybdenum carbide (MoCx) during reverse water-gas shift (RWGS) reaction. Surface oxygen atoms in various Mo-based catalysts are removed in H2-containing atmospheres and then carbon atoms can accumulate on surface to form MoCx phase with the RWGS reaction going on, both of which are enhanced by the presence of intercalated H species or Pt-dopants in MoOx. The structural evolution from MoOx to MoCx is accompanied by enhanced CO2 conversion, which is positively correlated with the surface C/Mo ratio but negatively with the surface O/Mo ratio. As a result, an unprecedented CO formation rate of 7544.6 mmol ⋅ gcatal -1 ⋅ h-1 at 600 °C has been achieved over in situ carbonized H-intercalated MoO3 catalyst, which is even higher than those from noble metal catalysts. During 100 h stability test only a minimal deactivation rate of 2.3 % is observed.

Full-spectrum plasmonic semiconductors for photocatalysis

Localized surface plasmon resonance (LSPR) of noble metal nanoparticles can focus surrounding light onto the particle surface to boost photochemical reactions and solar energy utilization. However, the rarity and high cost of noble metals limit their applications in plasmonic photocatalysis, forcing researchers to seek low-cost alternatives. Recently, some heavily doped semiconductors with high free carrier density have garnered attention due to their metal-like LSPR properties. However, plasmonic semiconductors have complex surface structures characterized by the presence of a depletion layer, which poses challenges for active site exposure and hot carrier transfer, resulting in low photocatalytic activity. In this review, we introduce the essential characteristics and types, synthesis methods, and characterization techniques of full-spectrum plasmonic semiconductors, elucidate the mechanism of full-spectrum nonmetallic plasmonic photocatalysis, including the local electromagnetic field, hot carrier generation and transfer, the photothermal effect, and the solutions for the surface depletion layer, and summarize the applications of plasmonic semiconductors in photocatalytic environmental remediation, CO2 reduction, H2 generation, and organic transformations. Finally, we provide a perspective on full-spectrum plasmonic photocatalysis, aiming to guide the design and development of plasmonic photocatalysts.

Mixed-Metal Alloying in Hybrid Bronzes

We show that substitutional alloying during the aqueous self-assembly of layered organic-templated metal oxides produces single-phase mixed-metal hybrids. Single-crystal X-ray diffraction, bulk elemental analyses, and vibrational and electronic spectroscopies corroborate a solid solution of Mo and W atoms at lattice sites within the two-dimensional metal oxide layers. Mild postsynthetic reduction then introduces relatively delocalized electrons to afford mixed-metal hybrid bronzes. To our knowledge, this represents the first demonstration of mixed-metal alloying in a hybrid metal oxide and a rare example of solid-solution formation at low temperature. We show this approach yields mixed-metal congeners with optical band gaps over 130 meV smaller than those of single-metal analogs, while achieving activation energies (Ea) of conduction as low as 78.4(2) meV. Further, metal substitution appears to tune collective electronic phenomena by suppressing the non-Arrhenius behavior observed for Mo-based hybrids. This work considerably expands the nascent hybrid bronze platform to help address energy-related challenges and fundamental solid-state physical questions.

Constructing High-Active Surface of Plasmonic Tungsten Oxide for Photocatalytic Alcohol Dehydration

Plasmonic semiconductors with broad spectral response hold significant promise for sustainable solar energy utilization. However, the surface inertness limits the photocatalytic activity. Herein, a novel approach is proposed to improve the body crystallinity and increase the surface oxygen vacancies of plasmonic tungsten oxide by the combination of hydrochloric acid (HCl) regulation and light irradiation, which can promote the adsorption of tert-butyl alcohol (TBA) on plasmonic tungsten oxide and overcome the hindrance of the surface depletion layer in photocatalytic alcohol dehydration. Additionally, this process can concentrate electrons for strong plasmonic electron oscillation on the near surface, facilitating rapid electron transfer within the adsorbed TBA molecules for C-O bond cleavage. As a result, the activation barrier for TBA dehydration is significantly reduced by 93% to 6.0 kJ mol-1, much lower than that of thermocatalysis (91 kJ mol-1). Therefore, an optimal isobutylene generation rate of 1.8 mol g-1 h-1 (selectivity of 99.9%) is achieved. A small flow reaction system is further constructed, which shows an isobutylene generation rate of 12 mmol h-1 under natural sunlight irradiation. This work highlights the potential of plasmonic semiconductors for efficient photocatalytic alcohol dehydration, thereby promoting the sustainable utilization of solar energy.

Triethyl amine as an effective reducing agent for sulfoxide deoxygenation

Enabled by triethyl amine (Et3N) and thionyl chloride (SOCl2), an efficient and practical protocol for deoxygenation of sulfoxide to sulfide was developed. This new method features a wide range of substrate scope, including diaryl, dialkyl and aryl alkyl substituted sulfoxides. Detailed mechanistic investigations reveal the crucial role played by Et3N as an electron-donating reductant rather than a hydrogen-atom donor.

Dual-plasmonic Au@Cu7S4 yolk@shell nanocrystals for photocatalytic hydrogen production across visible to near infrared spectral region

Near infrared energy remains untapped toward the maneuvering of entire solar spectrum harvesting for fulfilling the nuts and bolts of solar hydrogen production. We report the use of Au@Cu7S4 yolk@shell nanocrystals as dual-plasmonic photocatalysts to achieve remarkable hydrogen production under visible and near infrared illumination. Ultrafast spectroscopic data reveal the prevalence of long-lived charge separation states for Au@Cu7S4 under both visible and near infrared excitation. Combined with the advantageous features of yolk@shell nanostructures, Au@Cu7S4 achieves a peak quantum yield of 9.4% at 500 nm and a record-breaking quantum yield of 7.3% at 2200 nm for hydrogen production in the absence of additional co-catalysts. The design of a sustainable visible- and near infrared-responsive photocatalytic system is expected to inspire further widespread applications in solar fuel generation. In this work, the feasibility of exploiting the localized surface plasmon resonance property of self-doped, nonstoichiometric semiconductor nanocrystals for the realization of wide-spectrum-driven photocatalysis is highlighted.

Hybrid bronzes: mixed-valence organic-inorganic metal oxides as a tunable material platform

We demonstrate that mixed-valence layered organic-inorganic metal oxides of the form (L)zHxMO3 (L = neutral ligand; M = Mo, W; z = 0.5, 1; 0 < x < 2), which we call hybrid bronzes, can be readily synthesized through mild solution-state self-assembly reactions to integrate the stability and electronic utility of inorganic metal oxide bronzes with the chemical diversity and functionality of organic molecules. We use single-crystal and powder X-ray diffraction coupled with X-ray, electronic, and vibrational spectroscopies to show that the products of aqueous pre-, mid-, or post-synthetic reduction are mixed-valence versions of highly crystalline layered hybrid oxides. Pillaring, bilayered, or canted bilayered arrangements of molecular arrays relative to inorganic sheets are dictated by judicious choice of organic ligands that can also incorporate chemical, redox, or photoactive handles. Significantly, bond-valence sum analysis and diffuse reflectance spectroscopy indicate relatively delocalized electronic behavior and four-point variable-temperature electrical transport measurements show that hybrid bronzes have comparable conductivity to their all-inorganic parent compounds. This work establishes a solution-processable, inexpensive, air- and water-stable, and non-toxic material family whose electronic bands can be readily tuned and doped, thereby positioning hybrid bronzes to address myriad material challenges.

High-Density Formation of Ir/MoOx Interface through Hybrid Clustering for Chemoselective Nitrostyrene Hydrogenation

To form high-density metal/oxide interfacial active sites, we developed a catalyst preparation method based on hybrid clustering. An iridium-molybdenum (Ir-Mo) hybrid clustering catalyst was prepared by using the hybrid cluster [(IrCp*)4Mo4O16] (Cp* = η5-C5Me5) as the precursor. The Ir-Mo hybrid clustering catalyst selectively reduced the nitro group in the hydrogenation of 4-nitrostyrene, whereas the coimpregnated Ir-Mo catalyst reduced both the nitro and vinyl groups nonselectively. The hybrid clustering catalyst also exhibited high selectivity, even at a high Ir loading (5 wt %), in contrast to Ir/MoO3, which exhibited high selectivity only at low Ir loadings (<0.3 wt %). In situ X-ray absorption spectroscopy analysis revealed that oxygen vacancies were formed at the Ir/MoOx interface in the presence of H2. We concluded that a high-density Ir/MoOx interface contributes to the preferential adsorption of nitro groups on vacant sites, promoting the selective hydrogenation of nitro groups.

Ce-mediated molecular tailoring on gigantic polyoxometalate {Mo132} into half-closed {Ce11Mo96} for high proton conduction

Precise synthesis of polyoxometalates (POMs) is important for the fundamental understanding of the relationship between the structure and function of each building motif. However, it is a great challenge to realize the atomic-level tailoring of specific sites in POMs without altering the major framework. Herein, we report the case of Ce-mediated molecular tailoring on gigantic {Mo132}, which has a closed structural motif involving a never seen {Mo110} decamer. Such capped wheel {Mo132} undergoes a quasi-isomerism with known {Mo132} ball displaying different optical behaviors. Experiencing an 'Inner-On-Outer' binding process with the substituent of {Mo2} reactive sites in {Mo132}, the site-specific Ce ions drive the dissociation of {Mo2*} clipping sites and finally give rise to a predictable half-closed product {Ce11Mo96}. By virtue of the tailor-made open cavity, the {Ce11Mo96} achieves high proton conduction, nearly two orders of magnitude than that of {Mo132}. This work offers a significant step toward the controllable assembly of POM clusters through a Ce-mediated molecular tailoring process for desirable properties.

Emergence of Dynamically-Disordered Phases During Fast Oxygen Deintercalation Reaction of Layered Perovskite

Determination of a reaction pathway is an important issue for the optimization of reactions. However, reactions in solid-state compounds have remained poorly understood because of their complexity and technical limitations. Here, using state-of-the-art high-speed time-resolved synchrotron X-ray techniques, the topochemical solid-gas reduction mechanisms in layered perovskite Sr₃ Fe₂ O_{7- δ} (from δ ∼ 0.4 to δ = 1.0), which is promising for an environmental catalyst material is revealed. Pristine Sr₃ Fe₂ O_{7- δ} shows a gradual single-phase structural evolution during reduction, indicating that the reaction continuously proceeds through thermodynamically stable phases. In contrast, a nonequilibrium dynamically-disordered phase emerges a few seconds before a first-order transition during the reduction of a Pd-loaded sample. This drastic change in the reaction pathway can be explained by a change in the rate-determining step. The synchrotron X-ray technique can be applied to various solid-gas reactions and provides an opportunity for gaining a better understanding and optimizing reactions in solid-state compounds.

Research Progress of Tungsten Oxide-Based Catalysts in Photocatalytic Reactions

Photocatalysis technology is a potential solution to solve the problem of environmental pollution and energy shortage, but its wide application is limited by the low efficiency of solar energy conversion. As a non-toxic and inexpensive n-type semiconductor, WO3 can absorb approximately 12% of sunlight which is considered one of the most attractive photocatalytic candidates. However, the narrow light absorption range and the high recombination rate of photogenerated electrons and holes restrict the further development of WO3-based catalysts. Herein, the studies on preparation and modification methods such as doping element, regulating defects and constructing heterojunctions to enlarge the range of excitation light to the visible region and slow down the recombination of carriers on WO3-based catalysts so as to improve their photocatalytic performance are reviewed. The mechanism and application of WO3-based catalysts in the dissociation of water, the degradation of organic pollutants, as well as the hydrogen reduction of N2 and CO2 are emphatically investigated and discussed. It is clear that WO3-based catalysts will play a positive role in the field of future photocatalysis. This paper could also provide guidance for the rational design of other metallic oxide (MOx) catalysts for the increasing conversion efficiency of solar energy.

Electrocatalytic Reduction of Nitrate to Ammonia via a Au/Cu Single Atom Alloy Catalyst

Electrocatalytic ammonia (NH₃) synthesis from the reduction of nitrate (NO₃^-) is one of the effective and mild methods to treat nitrogen-containing wastewater from stationary sources and to obtain NH₃ readily compared with the Haber-Bosch process. However, the low efficiency of electrocatalytic NO₃^- reduction to NH₃ on traditional Cu-based catalysts hinders their practical application. Here, we prepare a Au/Cu single atom (SA) alloy (Au/Cu SAA) that shows a high performance of NH₃ synthesis with 99.69% Faradaic efficiency at -0.80 V vs RHE. The structures of Au SAs and alloyed Au/Cu are confirmed by the detailed characterizations. Online differential electrochemical mass spectrometry confirms the occurrence of key reaction intermediates (*NO₂, *NO, and *NH₃). Density functional theory calculations demonstrate that Au SAs efficiently reduce the adsorption energy of *NO₃^-, and the newly formed Au-Cu bonds boost the reduction process of *NO₂ to *NO. Meanwhile, Au/Cu SAAs produce significantly less N₂ and N₂O byproducts due to the prohibition of N-N coupling on single atoms, which finally leads to excellent Faradaic efficiency and NH₃ selectivity.

Elucidation of a Photothermal Energy Conversion Mechanism in Hydrogenated Molybdenum Suboxide: Interplay of Trapped Charges and Their Dielectric Interactions

Hydrogenated molybdenum suboxide (H_xMoO_3-y) is a promising photothermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/H_xMoO_3-y composite. The charge recombination of H₂-reduced Pt/H_xMoO_3-y was 2-3 orders of magnitude faster than that of Pt/MoO₃, indicating efficient PEC. A complex photoconductivity study revealed that Pt/H_xMoO_3-y has two types of trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, depending on the reduction temperature. Pt/H_xMoO_3-y reduced at 100 °C exhibited a dominant NPE owing to the electrical interaction of trapped charges with the surrounding ions and/or OH base. This polaronic trapped state retarded the PEC process. We found Pt/H_xMoO_3-y reduced at 200 °C to be optimal owing to the balanced suppression of the NPE and charge diffusion. This is the first report revealing the charge dynamics in hydrogenated metal oxides and their impacts on PEC processes.

Plasmonic metal oxides and their biological applications

Metal oxides modified with dopants and defects are an emerging class of novel materials supporting the localized surface plasmon resonance across a wide range of optical wavelengths, which have attracted tremendous research interest particularly in biological applications in the past decade. Compared to conventional noble metal-based plasmonic materials, plasmonic metal oxides are particularly favored for their cost efficiency, flexible plasmonic properties, and improved biocompatibility, which can be important to accelerate their practical implementation. In this review, we first explicate the origin of plasmonics in dopant/defect-enabled metal oxides and their associated tunable localized surface plasmon resonance through the conventional Mie-Gans model. The research progress of dopant incorporation and defect generation in metal oxide hosts, including both in situ and ex situ approaches, is critically discussed. The implementation of plasmonic metal oxides in biological applications in terms of therapy, imaging, and sensing is summarized, in which the uniqueness of dopant/defect-driven plasmonics for inducing novel functionalities is particularly emphasized. This review may provide insightful guidance for developing next-generation plasmonic devices for human health monitoring, diagnosis and therapy.

Development of defective molybdenum oxides for photocatalysis, thermal catalysis, and photothermal catalysis

The localized surface plasmon resonance (LSPR) of noble metals has been investigated for decades for applications in various catalysis reactions and optical research studies, but its development has been hampered by inefficient light absorption and high costs. In comparison, the creation of less expensive semiconductors (metal oxides) with strong plasmonic absorption is an appealing option, particularly defective molybdenum oxide (H_xMoO_3-y) has received considerable attention and investigation as a promising plasmonic material for a variety of catalytic reactions (photocatalysis, thermocatalysis, photothermal catalysis, etc.).The LSPR effect of H_xMoO_3-y can be tuned throughout a broad spectrum range from visible to near-infrared (NIR) by altering the doping amount by electrochemical control, chemical reduction, or photochemical control. Notably, defects (oxygen vacancies) in H_xMoO_3-y arise in conjunction with the LSPR effect, resulting in the formation of unique and useful active sites in a range of catalytic processes. In this review, we explore the formation mechanism of H_xMoO_3-y with plasmonic features and discuss its applications in photocatalysis, thermocatalysis, and photothermal catalysis.

Hydrogenated Molybdenum Oxide Overlayers Formed on Mo Nitride Nanosheets in Ambient-Pressure CO2/H2 Gases

Transition metal nitrides (TMN_x) often exhibit high catalytic activity in many important reactions. Due to their low stability in a reaction environment, it remains as a crucial issue to reveal surface active structures in catalytic reactions, particularly for the cases containing both oxidative and reductive gases. Herein, MoN and Mo₂N nanosheets have been constructed on Al₂O₃(0001) and Au foil surfaces, and in situ surface characterizations are performed on the model catalysts in ambient-pressure CO₂, H₂, and CO₂ + H₂ gases. In situ Raman spectroscopy and quasi in situ X-ray photoelectron spectroscopy (XPS) analysis indicate that MoO₃ and defective MoO_3-x overlayers form on both MoN and Mo₂N surfaces in CO₂, and the surface oxidation occurs under a milder condition on Mo₂N than on MoN. Further, a hydrogenated Mo oxide (H_zMoO_3-y) overlayer forms in a CO₂ + H₂ atmosphere, as confirmed using quasi in situ XPS and time-of-flight secondary ion mass spectroscopy. The surface analysis over the model nitride catalysts suggests that O and/or H atoms may be incorporated into surface layers to form the active structure in many O and H-containing reactions.

Reduction of Sulfoxides in Multigram Scale, an Alternative to the Use of Chlorinated Solvents

In this manuscript, we describe the use of ethyl vinyl ether/oxalyl chloride as the reducing mixture for sulfoxides. The reaction is based on the high electrophilic character of chlorosulfonium salts, formed in situ by the reaction of oxalyl chloride and the sulfoxide. Thereafter, the nucleophilic vinyl ether acts as a chlorine scavenger, affording the corresponding sulfide. The method is applicable on a big scale and may be applied to highly functionalized sulfoxides. Chromatographic purification is only needed in exceptional cases of unstable substrates, and the final sulfide or the corresponding salt is usually obtained after simple evaporation of volatiles. The sole contaminants of this method are carbon dioxide, carbon monoxide and small (five-carbon maximum) aldol products, which are formed during the reaction process.

Non-Noble Plasmonic Metal-Based Photocatalysts

Solar-to-chemical energy conversion via heterogeneous photocatalysis is one of the sustainable approaches to tackle the growing environmental and energy challenges. Among various promising photocatalytic materials, plasmonic-driven photocatalysts feature prominent solar-driven surface plasmon resonance (SPR). Non-noble plasmonic metals (NNPMs)-based photocatalysts have been identified as a unique alternative to noble metal-based ones due to their advantages like earth-abundance, cost-effectiveness, and large-scale application capability. This review comprehensively summarizes the most recent advances in the synthesis, characterization, and properties of NNPMs-based photocatalysts. After introducing the fundamental principles of SPR, the attributes and functionalities of NNPMs in governing surface/interfacial photocatalytic processes are presented. Next, the utilization of NNPMs-based photocatalytic materials for the removal of pollutants, water splitting, CO₂ reduction, and organic transformations is discussed. The review concludes with current challenges and perspectives in advancing the NNPMs-based photocatalysts, which are timely and important to plasmon-based photocatalysis, a truly interdisciplinary field across materials science, chemistry, and physics.

Intercalation-Activated Layered MoO3 Nanobelts as Biodegradable Nanozymes for Tumor-Specific Photo-Enhanced Catalytic Therapy

The existence of natural van der Waals gaps in layered materials allows them to be easily intercalated with varying guest species, offering an appealing strategy to optimize their physicochemical properties and application performance. Herein, we report the activation of layered MoO₃ nanobelts via aqueous intercalation as an efficient biodegradable nanozyme for tumor-specific photo-enhanced catalytic therapy. The long MoO₃ nanobelts are grinded and then intercalated with Na⁺ and H₂ O to obtain the short Na⁺ /H₂ O co-intercalated MoO_3-x (NH-MoO_3-x ) nanobelts. In contrast to the inert MoO₃ nanobelts, the NH-MoO_3-x nanobelts exhibit excellent enzyme-mimicking catalytic activity for generation of reactive oxygen species, which can be further enhanced by the photothermal effect under a 1064 nm laser irradiation. Thus, after bovine serum albumin modification, the NH-MoO_3-x nanobelts can efficiently kill cancer cells in vitro and eliminate tumors in vivo facilitating with 1064 nm laser irradiation.

Overturning CO2 Hydrogenation Selectivity with High Activity via Reaction-Induced Strong Metal-Support Interactions

Encapsulation of metal nanoparticles by support-derived materials known as the classical strong metal-support interaction (SMSI) often happens upon thermal treatment of supported metal catalysts at high temperatures (≥500 °C) and consequently lowers the catalytic performance due to blockage of metal active sites. Here, we show that this SMSI state can be constructed in a Ru-MoO₃ catalyst using CO₂ hydrogenation reaction gas and at a low temperature of 250 °C, which favors the selective CO₂ hydrogenation to CO. During the reaction, Ru nanoparticles facilitate reduction of MoO₃ to generate active MoO_3-x overlayers with oxygen vacancies, which migrate onto Ru nanoparticles' surface and form the encapsulated structure, that is, Ru@MoO_3-x. The formed SMSI state changes 100% CH₄ selectivity on fresh Ru particle surfaces to above 99.0% CO selectivity with excellent activity and long-term catalytic stability. The encapsulating oxide layers can be removed via O₂ treatment, switching back completely to the methanation. This work suggests that the encapsulation of metal nanocatalysts can be dynamically generated in real reactions, which helps to gain the target products with high activity.

Phosphorus-Alloying as a Powerful Method for Designing Highly Active and Durable Metal Nanoparticle Catalysts for the Deoxygenation of Sulfoxides: Ligand and Ensemble Effects of Phosphorus

The modification of metal nanoparticles (NPs) by incorporating additional metals is a key technique for developing novel catalysts. However, the effects of incorporating nonmetals into metal NPs have not been widely explored, particularly in the field of organic synthesis. In this study, we demonstrate that phosphorus (P)-alloying significantly increases the activity of precious metal NPs for the deoxygenation of sulfoxides into sulfides. In particular, ruthenium phosphide NPs exhibit an excellent catalytic activity and high durability against sulfur-poisoning, outperforming conventional catalysts. Various sulfoxides, including drug intermediates, were deoxygenated to sulfides with excellent yields. Detailed investigations into the structure-activity relationship revealed that P-alloying plays a dual role: it establishes a ligand effect on the electron transfer from Ru to P, facilitating the production of active hydrogen species, and has an ensemble effect on the formation of the Ru-P bond, preventing strong coordination with sulfide products. These effects combine to increase the catalytic performance of ruthenium phosphide NPs. These results demonstrate that P-alloying is an efficient method to improve the metal NP catalysis for diverse organic synthesis.

Crystal Facet Engineering and Hydrogen Spillover-Assisted Synthesis of Defective Pt/TiO2-x Nanorods with Enhanced Visible Light-Driven Photocatalytic Activity

Hydrogen spillover can assist the introduction of defects such as Ti³⁺ and concomitant oxygen vacancies (V_O) in a TiO₂ crystal, thereby inducing a new level below the conduction band to improve the conductivity of photogenerated electrons and the visible light absorption property of TiO₂. Meanwhile, crystal facet engineering offers a promising approach to achieve improved activity by influencing the recombination step of the photogenerated electrons and holes. In this study, with the aim of achieving enhanced visible light-driven photocatalytic activity, rutile TiO₂ nanorods with different aspect ratios were synthesized by crystal facet engineering, and Pt-deposited TiO_2-x nanorods (Pt/TNR) were then obtained via reduction treatment assisted by hydrogen spillover. The reduction treatment at 200 °C induced the formation of surface Ti³⁺ exclusively, whereas surface Ti³⁺ and V_O were formed by performing the reduction at 600 °C. The Pt/TNR with a higher aspect ratio reduced at 200 °C exhibited the highest activity in photocatalytic H₂ production under visible light irradiation owing to the synergistic effect of the introduction of Ti³⁺ defects and the spatial charge carrier separation induced by crystal facet engineering.

Methane Activation by (MoO3 )5 O- Cluster Anions: The Importance of Orbital Orientation

The reactivity of the molybdenum oxide cluster anion (MoO₃ )₅ O^- , bearing an unpaired electron at a bridging oxygen atom (O_b ^.- ), towards methane under thermal collision conditions has been studied by mass spectrometry and density functional theory calculations. This reaction follows the mechanism of hydrogen atom transfer (HAT) and is facilitated by the O_b ^.- radical center. The reactivity of (MoO₃ )₅ O^- can be traced back to the appropriate orientation of the lowest unoccupied molecular orbitals (LUMO) that is essentially the 2p orbital of the O_b ^.- atom. This study not only makes up the blank of thermal methane activation by the O_b ^.- radical on negatively charged clusters but also yields new insights into methane activation by the atomic oxygen radical anions.

Defect Engineering of Pt/TiO2-x Photocatalysts via Reduction Treatment Assisted by Hydrogen Spillover

Defect engineering of metal oxides is a facile and promising strategy to improve their photocatalytic activity. In the present study, Pt/TiO_2-x was prepared by a reduction treatment assisted by hydrogen spillover to pure rutile, anatase, and brookite and was subsequently used for hydrogen production from an aqueous methanol solution. With increasing reduction temperature, the photocatalytic activity of the rutile Pt/TiO_2-x increased substantially, whereas the activity of anatase Pt/TiO_2-x decreased and that of brookite Pt/TiO_2-x was independent of the treatment temperature. Electron-spin resonance analysis revealed that rutile and brookite possess similar defect sites (Ti³⁺ and concomitant oxygen vacancy) after the reduction at 600 °C, whereas different resonance signals were observed for anatase after the reduction at 600 °C. During the reduction process, electrons donated from spillover hydrogen migrate between the conduction band and the inherent midgap states. This research demonstrates that the depth of the inherent midgap states, depending on the crystal phases, influences the generation of defects, which play a key role in the photocatalytic performance of Pt/TiO_2-x.

Photo-thermo catalytic selective oxidation of cyclohexane by In-situ prepared nonstoichiometric Molybdenum oxide and Silver-palladium alloy composite

The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oil) is one of the most challenging issues in the chemical industry. However, the difficulty in attaining high selectivity and high conversion rate in parallel for the existing catalysts limits its practical application. In this paper, a novel photo-thermo synergistic catalyst was reported for the aerobic oxidation of cyclohexane. The uniform blue MoO_3-x nanowires with small diameter stabilized by polyvinyl pyrrolidone (PVP) were synthesized by a hydrothermal method, and a series of MoO_3-x-AgPd composite materials of different proportions were prepared by an in-situ reduction process. The morphology, crystalline structure, surface chemical bonding, photoelectrochemical properties of MoO_3-x-AgPd composites are thoroughly characterized. The MoO_3-x-AgPd composites present significantly increased catalytic performance than MoO_3-x nanowires in the photo-thermo synergistic catalytic oxidation of cyclohexane under dry air. The high conversion rate of 11.3% with the KA oil selectivity of 99.0% was achieved by the MoO_3-x-Ag₂₀Pd₂₀ composites under photo-thermo catalytic process at 120 ℃, which is 1.5 times of that by MoO_3-x nanowires. Under photo-thermo catalytic process, a high cyclohexane conversion rate similar to that of higher temperature thermal catalysis can be obtained at lower reaction temperature, and more cyclohexanol can be produced with a ketone to alcohol (K/A) ratio of 0.254. The significantly enhanced catalytic activity can be attributed to the effective charge transfer in the AgPd alloy nanoparticles, the optimized band gap structure, the suppressed charge recombination, and the promoted photo-thermo synergetic catalytic effect. This work provides a new reference scheme for the design and preparation of high-efficiency photo-thermo catalysts for the selective oxidation of cyclohexane.

Advances in photothermal nanomaterials for biomedical, environmental and energy applications

Materials that exhibit photothermal effect have attracted enormous research interests due to their ability to strongly absorb light and effectively transform it into heat for a wide range of applications in biomedical, environmental and energy related fields. The past decade has witnessed significant advances in the preparation of a variety of photothermal materials, mainly due to the emergence of many nano-enabled new materials, such as plasmonic metals, stoichiometric/non-stoichiometric semiconductors, and the newly emerging MXenes. These photothermal nanomaterials can be hybridized with other constituents to form functional hybrids or composites for achieving enhanced photothermal performance. In this review, we present the fundamental insight of inorganic photothermal materials, including their photothermal conversion mechanisms/properties as well as their potential applications in various fields. Emphasis is placed on strategic approaches for improving their light harvesting and photothermal conversion capabilities through engineering their nanostructured size, shape, composition, bandgap and so on. Lastly, the underlying challenges and perspectives for future development of photothermal nanomaterials are proposed.

Defect Engineering of Photocatalysts towards Elevated CO2 Reduction Performance

Photocatalytic CO₂ reduction provides a promising solution to address the crises of massive CO₂ emissions and fossil energy shortages. As one of the most effective strategies to promote CO₂ photoconversion, defect engineering shows great potential in modulating the electronic structure and light absorption properties of photocatalysts while increasing surface active sites for CO₂ activation and conversion. This Review summarizes the recent progress in defect engineering of photocatalysts to promote CO₂ reduction performances from the following four aspects: 1) Approaches to defect (mainly vacancy and dopant) generation in photocatalysts; 2) defect structure characterization techniques; 3) physical and chemical properties of defect-engineered photocatalysts; 4) CO₂ reduction performance enhancements in activity, selectivity, and stability of photocatalysts by defect engineering. This Review is expected to present readers with a comprehensive view of progress in the field of photocatalytic CO₂ reduction through defect engineering for elevated CO₂ -to-fuels conversion efficiency.

A quasi-stable molybdenum sub-oxide with abundant oxygen vacancies that promotes CO2 hydrogenation to methanol

Production of methanol from anthropogenic carbon dioxide (CO₂) is a promising chemical process that can alleviate both the environmental burden and the dependence on fossil fuels. In catalytic CO₂ hydrogenation to methanol, reduction of CO₂ to intermediate species is generally considered to be a crucial step. It is of great significance to design and develop advanced heterogeneous catalysts and to engineer the surface structures to promote CO₂-to-methanol conversion. We herein report an oxygen-defective molybdenum sub-oxide coupled with Pt nanoparticles (Pt/H_xMoO_3−y) which affords high methanol yield with a methanol formation rate of 1.53 mmol g_-cat⁻¹ h⁻¹ in liquid-phase CO₂ hydrogenation under relatively mild reaction conditions (total 4.0 MPa, 200 °C), outperforming other oxide-supported Pt catalysts in terms of both the yield and selectivity for methanol. Experiments and comprehensive analyses including in situ X-ray absorption fine structure (XAFS), in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and density functional theory (DFT) calculations reveal that both abundant surface oxygen vacancies (V_O) and the redox ability of Mo species in quasi-stable H_xMoO_3−y confer the catalyst with enhanced adsorption and activation capability to subsequently transform CO₂ to methanol. Moreover, the Pt NPs act as H₂ dissociation sites to regenerate oxygen vacancies and as hydrogenation sites for the CO intermediate to finally afford methanol. Based on the experimental and computational studies, an oxygen-vacancy-mediated “reverse Mars–van Krevelen (M–vK)” mechanism is proposed. This study affords a new strategy for the design and development of an efficient heterogeneous catalyst for CO₂ conversion.

Oxygen-defective molybdenum sub-oxide coupled with Pt nanoparticles affords high methanol yield in liquid-phase CO₂ hydrogenation via reverse Mars–van Krevelen mechanism.

Remarkable variation of visible light photocatalytic activities of M/Sn0.9Sb0.1O2/TiO2 (M=Au, Ag, Pt) heterostructures depending on the loaded metals

Sn_0.9Sb_0.1O₂/TiO₂ (ATO/TiO₂) heterostructure is a potential visible light photocatalysts that function via an inter-semiconductor hole-transport mechanism. Herein we selectively deposited Au, Ag, or Pt onto the ATO surface of ATO/TiO₂ to investigate charge-trapping behaviors of the noble metals and their effects on photocatalytic performance. We observed that Pt deposition greatly enhanced the photocatalytic activity whereas effects of Au or Ag depositions were not significant. The result of spectroscopic analysis also indicates that Pt is the most effective in scavenging the electrons from the ATO CB. Particularly, Pt/ATO/TiO₂ (ATO:TiO₂ = 15:85 in weight) produced CO₂ of 42 ppmv in 2 h, which is 16 times and 4.8 times that of bare ATO/TiO₂ and nitrogen-doped TiO₂, respectively. Pt deposition on the ATO seems to suppress two independent charge recombination pathways, that is, recombination of electron-hole pairs in ATO and electron transport from the ATO CB to TiO₂ VB.

Recent Advances in Plasmonic Nanostructures for Enhanced Photocatalysis and Electrocatalysis

Plasmonic nanomaterials coupled with catalytically active surfaces can provide unique opportunities for various catalysis applications, where surface plasmons produced upon proper light excitation can be adopted to drive and/or facilitate various chemical reactions. A brief introduction to the localized surface plasmon resonance and recent design and fabrication of highly efficient plasmonic nanostructures, including plasmonic metal nanostructures and metal/semiconductor heterostructures is given. Taking advantage of these plasmonic nanostructures, the following highlights summarize recent advances in plasmon-driven photochemical reactions (coupling reactions, O₂ dissociation and oxidation reactions, H₂ dissociation and hydrogenation reactions, N₂ fixation and NH₃ decomposition, and CO₂ reduction) and plasmon-enhanced electrocatalytic reactions (hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, alcohol oxidation reaction, and CO₂ reduction). Theoretical and experimental approaches for understanding the underlying mechanism of surface plasmon are discussed. A proper discussion and perspective of the remaining challenges and future opportunities for plasmonic nanomaterials and plasmon-related chemistry in the field of energy conversion and storage is given in conclusion.

Oxide-based composites: applications in thermo-photocatalysis

Recent progress on oxide-based thermo-photocatalytic composite systems. Role of plasmonic, defect-related, and thermal effects on the catalytic performance.

Nickel phosphide nanoalloy catalyst for the selective deoxygenation of sulfoxides to sulfides under ambient H2 pressure

Exploring novel catalysis by less common, metal-non-metal nanoalloys is of great interest in organic synthesis. We herein report a titanium-dioxide-supported nickel phosphide nanoalloy (nano-Ni2P/TiO2) that exhibits high catalytic activity for the deoxygenation of sulfoxides. nano-Ni2P/TiO2 deoxygenated various sulfoxides to sulfides under 1 bar of H2, representing the first non-noble metal catalyst for sulfoxide deoxygenation under ambient H2 pressure. Spectroscopic analyses revealed that this high activity is due to cooperative catalysis by nano-Ni2P and TiO2.

Electrophilic Chlorine from Chlorosulfonium Salts: A Highly Chemoselective Reduction of Sulfoxides

Herein, we describe a selective late-stage deoxygenation of sulfoxides based on a novel application of chlorosulfonium salts and demonstrate a new process using these species generated in situ from sulfoxides as the source of electrophilic chlorine. The use of highly nucleophilic 1,3,5-trimethoxybenzene (TMB) as the reducing agent is described for the first time and applied in the deoxygenation of simple and functionalized sulfoxides. The method is easy to handle, economic, suitable for gram-scale operations, and readily applied for poly-functionalized molecules, as demonstrated with more than 45 examples, including commercial medicines and analogues. We also report the results of competition experiments that define the more reactive sulfoxide and we present a mechanistic proposal based on substrate and product observations.

A Hydrogenated Metal Oxide with Full Solar Spectrum Absorption for Highly Efficient Photothermal Water Evaporation

Searching for cost-effective photothermal material that can harvest the full solar spectrum is critically important for solar-driven water evaporation. Metal oxides are cheap materials but cannot cover the full solar spectrum. Here we prepared a hydrogenated metal oxide (H_1.68MoO₃) material, in which H-doping causes the insulator-to-metal phase transition of the originally semiconductive MoO₃. It offers a blackbody-like solar absorption of ≥95% over the entire visible-to-near-infrared solar spectrum, owing to its unusual quasi-metallic energy band, and high solar-to-heat conversion rate due to quick relaxation of excited electrons. Using a self-floating H_1.68MoO₃/airlaid paper photothermal film, we achieved a stable and high water vapor generation rate of 1.37 kg m^-2 h^-1, a superb solar-to-vapor efficiency of 84.8% under 1 sun illumination, and daily production of 12.4 L of sanitary water/m² from seawater under natural sunlight. This thus opens a new avenue of designing cost-effective photothermal materials based on metal oxides.

Facile Fabrication of Amorphous Molybdenum Oxide as a Sensitive and Stable SERS Substrate under Redox Treatment

Amorphous MoO_3-x nanosheets were fabricated by the room-temperature oxidation of molybdenum powder with H₂ O₂ , followed by light-irradiation reduction in methanol. When applied as a substrate for surface-enhanced Raman spectroscopy (SERS), these nanosheets exhibit higher sensitivity than the crystalline counterpart for a wide range of analytes. Moreover, the SERS activity remains stable on repeated oxygen insertion/extraction. In contrast, the performance of crystalline MoO_3-x continuously deteriorates on successive redox treatments. This unique SERS activity allows the recycling of the substrate through an H₂ O₂ -based Fenton-like reaction. More importantly, the non-invasive SERS was unprecedentedly used for the self-diagnosis of amorphous MoO_3-x as a more selective photocatalyst than its crystalline counterpart.

Top-down fabrication of colloidal plasmonic MoO3−x nanocrystals via solution chemistry hydrogenation

The top-town fabrication of colloidal α-MoO_3−x nanocrystals via the synergistic effect of oleic acid and oleylamine is proposed in this study.

Properties, fabrication and applications of plasmonic semiconductor nanocrystals

We highlight three widely explored oxide-based plasmonic materials, including H_xMoO_3−y, H_xWO_3−y, and Mo_xW_1−xO_3−y, and their applications in catalysis.

Distance-dependent plasmon-enhanced electrochemiluminescence biosensor based on MoS2 nanosheets

Nonmetallic plasmonic MoS₂ nanosheets were synthesized by hydrothermal top-down method. MoS₂ nanosheets had shown strong surface plasmon coupling (SPC) light absorption in the visible and near-infrared region. Herein, the nonmetallic plasmonic MoS₂ nanosheets were employed to enhance the electrochemiluminescence (ECL) signal of sulfur doped boron nitrogen QDs (S-BN QDs) in this work. It is important to regulate the distance between ECL luminophore and plasmonic nanoparticles. On one hand, too closed distance can cause energy or electron transfer, which could quench the ECL intensity of nano-luminophore. On the other hand, plasmonic nanostructure cannot significantly affect the luminescence in the far distance. Therefore, we discussed the distance-dependent plasmon-enhanced ECL in detail with different length DNA chains. Furthermore, we constructed a hybridization chain reaction (HCR) amplification ECL sensing mode with the SPC-ECL strategy. The proposed DNA sensor can quantify hepatitis C virus (HCV) gene from 0.5 pmoL/L to 1 nmoL/L with a limit of detection (LOD) of 0.17 pmoL/L.