Photocatalytic Formamide Synthesis via Coupling of Electrophilic and Nucleophilic Radicals over Atomically Dispersed Bi Sites.

Formamide (HCONH2) plays a pivotal role in the manufacture of a diverse array of chemicals, fertilizers, and pharmaceuticals. Photocatalysis holds great promise for green fabrication of carbon-nitrogen (C-N) compounds owing to its environmental friendliness and mild redox capability. However, the selective formation of the C-N bond presents a significant challenge in the photocatalytic synthesis of C-N compounds. This work developed a photocatalytic radical coupling method for the formamide synthesis from co-oxidation of ammonia (NH3) and methanol (CH3OH). An exceptional formamide yield rate of 5.47 ± 0.03 mmol·gcat-1·h-1 (911.87 ± 0.05 mmol·gBi-1·h-1) was achieved over atomically dispersed Bi sites (BiSAs) on TiO2. An accumulation of 45.0 mmol·gcat-1 (0.2 g·gcat-1) of formamide was achieved after long-term illumination, representing the highest level of photocatalytic C-N compounds synthesis. The critical C-N coupling for formamide formation originated from the "σ-σ" interaction between electrophilic ●CH2OH with nucleophilic ●NH2 radical. The  BiSAs sites facilitated the electron transfer between reactants and photocatalysts and enhanced the nucleophilic attack of â—NH2 radical at the â—CH2OH radical, thereby advancing the selective C-N bond formation. This work deepens the understanding of the C-N coupling mechanism and offers an alternative and intriguing photocatalytic approach for the efficient and sustainable production of C-N compounds.

Mechanically treated Mn2O3 triggers peracetic acid activation for superior non-radical oxidation of micropollutants: Identification of reactive complexes.

This study used a simple mechanical ball milling strategy to significantly improve the ability of Mn2O3 to activate peracetic acid (PAA) for sustainable and efficient degradation of organic micropollutant (like bisphenol A, BPA). BPA was successfully removed and detoxified via PAA activation by the bm-Mn2O3 within 30 min under neutral environment, with the BPA degradation kinetic rate improved by 3.4 times. Satisfactory BPA removal efficiency can still be achieved over a wide pH range, in actual water and after reuse of bm-Mn2O3 for four cycles. The change in hydrophilicity of Mn2O3 after ball milling evidently elevated the affinity of Mn2O3 for binding to PAA, while the reduction in particle size exposed more active sites contributing partially to catalytic oxidation. Further analysis revealed that BPA oxidation in the ball mill-treated Mn2O3 (bm-Mn2O3)/PAA process mainly depends on the bm-Mn2O3-PAA complex (i.e., Mn(III)-OO(O)CCH3) mediated non-radical pathway rather than R-O• and Mn(IV). Especially, the existence of the Mn(III)-PAA complex was definitely verified by in situ Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Simultaneously, density functional theory calculations determined that PAA adsorbs readily on manganese sites thereby favoring the formation of Mn(III)-OO(O)CCH3 complexes. This study advances an in-depth understanding of the underlying mechanisms involved in the manganese oxide-catalyzed activation of PAA for superior non-radical oxidation of micropollutants.

Regulating the Selectivity of Nitrate Photoreduction for Purification or Ammonia Production by Cooperating Oxidative Half-Reactions.

The removal and conversion of nitrate (NO3-) from wastewater has become an important environmental and health topic. The NO3- can be reduced to nontoxic nitrogen (N2) for environmental remediation or ammonia (NH3) for recovery, in which the tailoring of the selectivity is greatly challenging. Here, by construction of the CuOx@TiO2 photocatalyst, the NO3- conversion efficiency is enhanced to ∼100%. Moreover, the precise regulation of selectivity to NH3 (∼100%) or N2 (92.67%) is accomplished by the synergy of cooperative redox reactions. It is identified that the selectivity of the NO3- photoreduction is determined by the combination of different oxidative reactions. The key roles of intermediates and reactive radicals are revealed by comprehensive in situ characterizations, providing direct evidence for the regulated selectivity of the NO3- photoreduction. Different active radicals are produced by the interaction of oxidative reactants and light-generated holes. Specifically, the introduction of CH3CHO as the oxidative reactant results in the generation of formate radicals, which drives selective NO3- reduction into N2 for its remediation. The alkyl radicals, contributed to by the (CH2OH)2 oxidation, facilitate the deep reduction of NO3- to NH3 for its upcycling. This work provides a technological basis for radical-directed NO3- reduction for its purification and resource recovery.

Dynamic in situ Formation of Cu2 O Sub-Nanoclusters through Photoinduced pseudo-Fehling's Reaction for Selective and Efficient Nitrate-to-Ammonia Photosynthesis.

Copper (Cu) is evidenced to be effective for constructing advanced catalysts. In particular, Cu2 O is identified to be active for general catalytic reactions. However, conflicting results regarding the true structure-activity correlations between Cu2 O-based active sites and efficiencies are usually reported. The structure of Cu2 O undergoes dynamic evolution rather than remaining stable under working conditions, in which the actual reaction cannot proceed over the prefabricated Cu2 O sites. Therefore, the dynamic construction of Cu2 O active sites can be developed to promote catalytic efficiency and reveal the true structure-activity correlations. Herein, by introducing the redox pairs of Cu2+ and reducing sugar into a photocatalysis system, it is clarified that the Cu2 O sub-nanoclusters (NCs), working as novel active sites, are on-site constructed on the substrate via a photoinduced pseudo-Fehling's route. The realistic interfacial charge separation and transformation capacities are remarkably promoted by the dynamic Cu2 O NCs under the actual catalysis condition, which achieves a milestone efficiency for nitrate-to-ammonia photosynthesis, including the targets of production rate (1.98±0.04 mol gCu -1 h-1 ), conversion ratio (94.2±0.91 %), and selectivity (98.6 %±0.55 %). The current work develops an effective strategy for integrating the active site construction into realistic reactions, providing new opportunities for Cu-based chemistry and catalysis sciences research.

Promoting the efficiency and selectivity of NO3--to-NH3 reduction on Cu-O-Ti active sites via preferential glycol oxidation with holes.

The combined reductive and oxidative reaction is the essence of a solar-driven photoredox system. Unfortunately, most of these efforts focus on the specific half-reactions, and the key roles of complete photoredox reactions have been overlooked. Taking the nitrate reduction reaction (NO3-RR) as a typical multiple-electrons involved process, the selective reduction of the NO3- into ammonia (NH3) synthesis with high efficiency is still a grand challenge. Herein, a rational oxidative half-reaction is tailored to achieve the selective conversion of NO3- to NH3 on Cu-O-Ti active sites. Through the coupled NO3-RR with glycol oxidation reaction system, a superior NH3 photosynthesis rate of 16.04 ± 0.40 mmol gcat-1 h-1 with NO3- conversion ratio of 100% and almost 100% of NH3 selectivity is reached on Cu-O-Ti bimetallic oxide cluster-anchored TiO2 nanosheets (CuOx@TNS) catalyst. A combination of comprehensive in situ characterizations and theoretical calculations reveals the molecular mechanism of the synergistic interaction between NO3-RR and glycol oxidation pair on CuOx@TNS. The introduction of glycol accelerates the h+ consumption for the formation of alkoxy (•R) radicals to avoid the production of •OH radicals. The construction of Cu-O-Ti sites facilitates the preferential oxidation of glycol with h+ and enhances the production of e- to participate in NO3-RR. The efficiency and selectivity of NO3--to-NH3 synthesis are thus highly promoted on Cu-O-Ti active sites with the accelerated glycol oxidative half-reaction. This work upgrades the conventional half photocatalysis into a complete photoredox system, demonstrating the tremendous potential for the precise regulation of reaction pathway and product selectivity.

Continuous NO Upcycling into Ammonia Promoted by SO2 in Flue Gas: Poison Can Be a Gift.

Although ammonia (NH3) synthesis efficiency from the NO reduction reaction (NORR) is significantly promoted in recent years, one should note that NO is one of the major air pollutants in the flue gas. The limited NO conversion ratio is still the key challenge for the sustainable development of the NORR route, which potentially contributes more to contaminant emissions rather than its upcycling. Herein, we provide a simple but effective approach for continuous NO reduction into NH3, promoted by coexisting SO2 poison as a gift in the flue gas. It is significant to discover that SO2 plays a decisive role in elevating the capacity of NO absorption and reduction. A unique redox pair of SO2-NO is constructed, which contributes to the exceptionally high conversion ratio for both NO (97.59 ± 1.42%) and SO2 (99.24 ± 0.49%) in a continuous flow. The ultrahigh selectivity for both NO-to-NH3 upcycling (97.14 ± 0.55%) and SO2-to-SO42- purification (92.44 ± 0.71%) is achieved synchronously, demonstrating strong practicability for the value-added conversion of air contaminants. The molecular mechanism is revealed by comprehensive in situ technologies to identify the essential contribution of SO2 to NO upcycling. Besides, realistic practicality is realized by the efficient product recovery and resistance ability against various poisoning effects. The proposed strategy in this work not only achieves a milestone efficiency for NH3 synthesis from the NORR but also raises great concerns about contaminant resourcing in realistic conditions.

Efficient purification of a nitrate and chlorate mixture in water via photoredox activated intermediate coupling-decoupling pathway.

Nitrate (NO3-) is a widespread contaminant that threatens human health and ecological safety. Meanwhile, the disinfection byproducts chlorate (ClO3-) is generated inevitably in conventional wastewater treatment. Therefore, the contaminants mixture of NO3- and ClO3- are universal in common emission units. Photocatalysis technology is a feasible approach for the synergistic abatement of contaminant mixture, where matching suitable oxidation reactions is a potential strategy to improve the photocatalytic reduction reactions. Herein, formate (HCOOH) oxidation is introduced to facilitate the photocatalytic reduction of the NO3- and ClO3- mixture. As a result, high purification efficiency of NO3- and ClO3- mixture are achieved, evidenced by 84.6% e--dependent removal of the mixture at a reaction time of 30 min, with 94.5% N2 selectivity and 100% Cl- selectivity, respectively. Specifically, by the close combination of in-situ characterizations and theoretical calculations, the detailed reaction mechanism is revealed, in which the intermediate coupling-decoupling route from NO3- reduction and HCOOH oxidation is established by the chlorate-induced photoredox activation, leading to the significantly enhanced efficiency for the wastewater mixture purification. The practical application of this pathway is established for simulated wastewater to show its wide applicability. This work provides new insights into photoredox catalysis technology for its environmental application.

Activation of Sphingomyelin Phosphodiesterase 3 in Liver Regeneration Impedes the Progression of Colorectal Cancer Liver Metastasis Via Exosome-Bound Intercellular Transfer of Ceramides.

BACKGROUND & AIMS: The machinery that prevents colorectal cancer liver metastasis (CRLM) in the context of liver regeneration (LR) remains elusive. Ceramide (CER) is a potent anti-cancer lipid involved in intercellular interaction. Here, we investigated the role of CER metabolism in mediating the interaction between hepatocytes and metastatic colorectal cancer (CRC) cells to regulate CRLM in the context of LR. METHODS: Mice were intrasplenically injected with CRC cells. LR was induced by 2/3 partial hepatectomy (PH) to mimic the CRLM in the context of LR. The alteration of corresponding CER-metabolizing genes was examined. The biological roles of CER metabolism in vitro and in vivo were examined by performing a series of functional experiments. RESULTS: Induction of LR augmented apoptosis but promoted matrix metalloproteinase 2 (MMP2) expression and epithelial-mesenchymal transition (EMT) to increase the invasiveness of metastatic CRC cells, resulting in aggressive CRLM. Up-regulation of sphingomyelin phosphodiesterase 3 (SMPD3) was determined in the regenerating hepatocytes after LR induction and persisted in the CRLM-adjacent hepatocytes after CRLM formation. Hepatic Smpd3 knockdown was found to further promote CRLM in the context of LR by abolishing mitochondrial apoptosis and augmenting the invasiveness in metastatic CRC cells by up-regulating MMP2 and EMT through promoting the nuclear translocation of ß-catenin. Mechanistically, we found that hepatic SMPD3 controlled the generation of exosomal CER in the regenerating hepatocytes and the CRLM-adjacent hepatocytes. The SMPD3-produced exosomal CER critically conducted the intercellular transfer of CER from the hepatocytes to metastatic CRC cells and impeded CRLM by inducing mitochondrial apoptosis and restricting the invasiveness in metastatic CRC cells. The administration of nanoliposomal CER was found to suppress CRLM in the context of LR substantially. CONCLUSIONS: SMPD3-produced exosomal CER constitutes a critical anti-CRLM mechanism in LR to impede CRLM, offering the promise of using CER as a therapeutic agent to prevent the recurrence of CRLM after PH.

Combined Photoredox Catalysis for Value-Added Conversion of Contaminants at Spatially Separated Dual Active Sites.

As 2 indispensable counterparts in one catalysis system, the independent reduction and oxidation reactions require synergetic regulation for cooperatively promoting redox efficiency. Despite the current success in promoting the catalytic efficiency of half reduction or oxidation reactions, the lack of redox integration leads to low energy efficiency and unsatisfied catalytic performance. Here, we exploit an emerging photoredox catalysis system by combining the reactions of nitrate reduction for ammonia synthesis and formaldehyde oxidation for formic acid production, in which superior photoredox efficiency is achieved on the spatially separated dual active sites of Ba single atoms and Ti3+. High catalytic redox rates are accomplished for respective ammonia synthesis (31.99 ± 0.79 mmol gcat -1 h-1) and formic acid production (54.11 ± 1.12 mmol gcat -1 h-1), reaching a photoredox apparent quantum efficiency of 10.3%. Then, the critical roles of the spatially separated dual active sites are revealed, where Ba single atoms as the oxidation site using h+ and Ti3+ as the reduction site using e- are identified, respectively. The efficient photoredox conversion of contaminants is accomplished with environmental importance and competitive economic value. This study also represents a new opportunity to upgrade the conventional half photocatalysis into the complete paradigm for sustainable solar energy utilization.

Beyond Purification: Highly Efficient and Selective Conversion of NO into Ammonia by Coupling Continuous Absorption and Photoreduction under Ambient Conditions.

Although the selective catalytic reduction technology has been confirmed to be effective for nitrogen oxide (NOx) removal, green and sustainable NOx re-utilization under ambient conditions is still a great challenge. Herein, we develop an on-site system by coupling the continuous chemical absorption and photocatalytic reduction of NO in simulated flue gas (CNO = 500 ppm, GHSV = 18,000 h-1), which accomplishes an exceptional NO conversion into value-added ammonia with competitive conversion efficiency (89.05 ± 0.71%), ammonia production selectivity (95.58 ± 0.95%), and ammonia recovery efficiency (>90%) under ambient conditions. The anti-poisoning capacities, including the resistance against factors of H2O, SO2, and alkali/alkaline/heavy metals, are also achieved, which presents strong environmental practicability for treating NOx in flue gas. In addition, the critical roles of corresponding chemical absorption and catalytic reduction components are also revealed by in situ characterizations. The emerging strategy herein not only achieves a milestone efficiency for sustainable NO purification but also opens a new route for contaminant resourcing in the near future of carbon neutrality.

Chemical Discrimination of Benzene Series and Molecular Recognition of the Sensing Process over Ti-Doped Co3O4.

This work achieved the chemical discrimination of benzene series (toluene, xylene isomers, and ethylbenzene gases) based on the Ti-doped Co3O4 sensor. Benzene series gases presented different gas-response features due to the differences in redox rate on the surface of the Ti-doped Co3O4 sensor, which created an opportunity to discriminate benzene series via the algorithm analysis. Excellent groupings were obtained via the principal component analysis. High prediction accuracies were acquired via k-nearest neighbors, linear discrimination analysis (LDA), and support vector machine classifiers. With the confusion matrix for the data set using the LDA classifier, the benzene series have been well classified with 100% accuracy. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory calculations were conducted to investigate the molecular gas-solid interfacial sensing mechanism. Ti-doped Co3O4 showed strong Lewis acid sites and adsorption capability toward reaction species, which benefited the toluene gas-sensing reaction and resulted in the highly boosted gas-sensing performance. Our research proposed a facile distinction methodology to recognize similar gases and provided new insights into the recognition of gas-solid interfacial sensing mechanisms.

Optimization of enzymatic synthesis of theaflavins from potato polyphenol oxidase.

Theaflavin (TF), a chemical component important in measuring the quality of fermented tea, has a strong natural antioxidant effect and many pharmacological functions. Enzymatic oxidation has become a widely used method for preparing TFs at the current research stage. Using plant exogenous polyphenol oxidase (PPO) to enzymatically synthesize TFs can significantly increase yield and purity. In this study, tea polyphenols were used as the reaction substrate to discuss the optimal synthesis conditions of potato PPO enzymatic synthesis of theaflavins and the main products of enzymatic synthesis of TFs. The optimal enzymatic synthesis conditions were as follows: pH of the reaction system was 5.5, reaction time was 150 min, substrate concentration was 6.0 mg/mL, reaction temperature was 20 °C, and the maximum amount of TFs produced was 651.75 µg/mL. At the same time, high-performance liquid chromatography was used to determine the content of theaflavins and catechins in the sample to be tested, and the dynamic changes and correlations of the main catechins and theaflavins in the optimal enzymatic system were analyzed. The results showed that epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) are all the main substrates synthesis of TFs. The main substrate of TFs and its strongest enzymatic catalytic effect on EGCG make theaflavin-3,3'-digallate (TFDG) the most important synthetic monomer. In this study, theaflavins were synthesized by polyphenol oxidase catalysis, which laid a foundation for industrialization of theaflavins.

Subnanometric alkaline-earth oxide clusters for sustainable nitrate to ammonia photosynthesis.

The limitation of inert N2 molecules with their high dissociation energy has ignited research interests in probing other nitrogen-containing species for ammonia synthesis. Nitrate ions, as an alternative feedstock with high solubility and proton affinity, can be facilely dissociated for sustainable ammonia production. Here we report a nitrate to ammonia photosynthesis route (NO3-RR) catalyzed by subnanometric alkaline-earth oxide clusters. The catalyst exhibits a high ammonia photosynthesis rate of 11.97 mol gmetal-1 h-1 (89.79 mmol gcat-1 h-1) with nearly 100% selectivity. A total ammonia yield of 0.78 mmol within 72 h is achieved, which exhibits a significant advantage in the area of photocatalytic NO3-RR. The investigation of the molecular-level reaction mechanism reveals that the unique active interface between the subnanometric clusters and TiO2 substrate is beneficial for the nitrate activation and dissociation, contributing to efficient and selective nitrate reduction for ammonia production with low energy input. The practical application of NO3-RR route in simulated wastewater is developed, which demonstrates great potential for its industrial application. These findings are of general knowledge for the functional development of clusters-based catalysts and could open up a path in the exploitation of advanced ammonia synthesis routes with low energy consumption and carbon emission.

Promote the activation and ring opening of intermediates for stable photocatalytic toluene degradation over Zn-Ti-LDH.

Improving the selectivity of photocatalysis and reducing the generation of toxic by-products are the two key challenges for the development of highly efficient and stable photocatalysts. In this work, it was revealed that Zn-Ti-layered double hydroxide (ZT-LDH) photocatalyst, which generated less intermediates, showed better toluene degradation efficiency (removal ratio, 75.2%) and stability, compared with P25 (removal ratio, 10.9%). During the photocatalytic toluene degradation, benzaldehyde and benzoic acid were the main intermediates existed in the gas phase and on the surface of the catalyst, respectively. By combining experiments with theoretical calculation, it was found that the hydrogen atoms on the hydroxyl groups in the LDH would selectively attract the oxygen atoms in the carbon-oxygen double bond of the two major intermediates, facilitating their adsorption and activation on ZT-LDH. Besides, the surface electronic structure of ZT-LDH was demonstrated to facilitate the ring-opening reaction of the two major intermediates, eventually maintaining high activity and stability. This work could provide new molecular perspectives for understanding the photocatalytic reactions in VOCs degradation and developing efficient and stable photocatalysts.

Promotion mechanism of -OH group intercalation for NOx purification on BiOI photocatalyst.

Bismuth oxyiodide (BiOI) is a traditional layered oxide photocatalyst that performs in a wide visible-light absorption band, owing to its appropriate band structure. Nevertheless, its photocatalytic efficiency is immensely inhibited due to the serious recombination of photogenerated charge carriers. Herein, this great challenge is addressed via a new strategy of intralayer modification by -OH groups in BiOI, which leads to enhancement of the reactants' activation capacity to promote photocatalytic activity and generate more active species. Furthermore, analysis via a combination of experimental and theoretical methods revealed that the -OH group-functionalized samples reduce the energy barriers for conversion of the main intermediate (NO2), which is easily transformed to NO2-, thus accelerating the oxidation of NO to the final product (NO3-). This study gives insight into NO oxidation, improving the photocatalytic efficiency, and mastering the photocatalysis reaction mechanism to curb air pollution.

Identification of deactivation-resistant origin of In(OH)3 for efficient and durable photodegradation of benzene, toluene and their mixtures.

Aromatic hydrocarbon is a representative type of VOCs, which causes adverse effects to human health. The degradation stability of aromatic hydrocarbon is of vital importance to commercializing a photocatalyst for its practical application. The most commonly used titanium dioxide photocatalyst (P25) was deactivated rapidly in the photocatalytic VOCs degradation process. In this work, the indium hydroxide (In(OH)3) photocatalyst was developed, which exhibited not only higher efficient activity but also ultra-stable stability for degradation of benzene, toluene and their mixtures. The origin of the activity difference between two catalysts was investigated by combined experimental and theoretical ways. Based on in situ DRIFTS and GC-MS, it was revealed that benzoic acid and carbonaceous byproducts were specifically formed and accumulated on P25, which were responsible for deactivation of photocatalyst. In contrast, as revealed by both DFT calculations and experimental results, the reaction pathway with byproducts blocking the active sites can be thermodynamically avoided on In(OH)3. This rendered high durability to In(OH)3 photocatalyst in degradations of aromatic pollutants. The elucidation of deactivation-resistant effect and reaction mechanism as an ideal photocatalyst for practical usage were provided.

Synergistic Effect of Cu Single Atoms and Au-Cu Alloy Nanoparticles on TiO2 for Efficient CO2 Photoreduction.

The synergy between metal alloy nanoparticles (NPs) and single atoms (SAs) should maximize the catalytic activity. However, there are no relevant reports on photocatalytic CO2 reduction via utilizing the synergy between SAs and alloy NPs. Herein, we developed a facile photodeposition method to coload the Cu SAs and Au-Cu alloy NPs on TiO2 for the photocatalytic synthesis of solar fuels with CO2 and H2O. The optimized photocatalyst achieved record-high performance with formation rates of 3578.9 for CH4 and 369.8 µmol g-1 h-1 for C2H4, making it significantly more realistic to implement sunlight-driven synthesis of value-added solar fuels. The combined in situ FT-IR spectra and DFT calculations revealed the molecular mechanisms of photocatalytic CO2 reduction and C-C coupling to form C2H4. We proposed that the synergistic function of Cu SAs and Au-Cu alloy NPs could enhance the adsorption activation of CO2 and H2O and lower the overall activation energy barrier (including the rate-determining step) for the CH4 and C2H4 formation. These factors all enable highly efficient and stable production of solar fuels of CH4 and C2H4. The concept of synergistic SAs and metal alloys cocatalysts can be extended to other systems, thus contributing to the development of more effective cocatalysts.

Efficient photocatalytic toluene degradation over heterojunction of GQDs@BiOCl ultrathin nanosheets with selective benzoic acid activation.

Photocatalytic toluene degradation has attracted tremendous attention because of the growing environmental problem. However, conventional photocatalytic materials used for toluene degradation usually suffer from low carrier separation efficiency and poor stability which will degrade the catalytic performance. Herein, we report the synthesis of a novel heterostructure of GQDs@BiOCl ultrathin nanosheets where the GQDs can rapidly capture and transport photogenerated electrons for effective charge separation, promoting the generation of more reactive oxygen species (·O2- and ·OH radicals) for toluene degradation. In situ DRIFTS measurement and theoretical calculation are performed to unveil the reaction intermediates and the underlying toluene oxidation mechanism. The GQDs@BiOCl heterojunction could facilitate the adsorption and conversion of toluene and the reaction intermediates. Especially, the heterojunction greatly enhances the activation and conversion of benzoic acid and thus expedites the complete toluene degradation. This work presents a new insight on the design of high-performance photocatalysts for efficient degradation of typical air pollutants.

Co and Pt Dual-Single-Atoms with Oxygen-Coordinated Co-O-Pt Dimer Sites for Ultrahigh Photocatalytic Hydrogen Evolution Efficiency.

The platinum single-atom-catalyst is verified as a very successful route to approach the size limit of Pt catalysts, while how to further improve the catalytic efficiency of Pt is a fundamental scientific question and is challenging because the size issue of Pt is approached at the ultimate ceiling as single atoms. Here, a new route for further improving Pt catalytic efficiency by cobalt (Co) and Pt dual-single-atoms on titanium dioxide (TiO2 ) surfaces, which contains a fraction of nonbonding oxygen-coordinated Co-O-Pt dimers, is reported. These Co-Pt dimer sites originate from loading high-density Pt single-atoms and Co single-atoms, with them anchoring randomly on the TiO2 substrate. This dual-single-atom catalyst yields 13.4% dimer sites and exhibits an ultrahigh and stable photocatalytic activity with a rate of 43.467 mmol g-1 h-1 and external quantum efficiency of ≈83.4% at 365 nm. This activity far exceeds those of equal amounts of Pt single-atom and typical Pt clustered catalysts by 1.92 and 1.64 times, respectively. The enhancement mechanism relies on the oxygen-coordinated Co-O-Pt dimer coupling, which can mutually optimize the electronic states of both Pt and Co sites to weaken H* binding. Namely, the "mute" Co single-atom is activated by Pt single-atom and the activity of the Pt atom is further enhanced through the dimer interaction. This strategy of nonbonding interactive dimer sites and the oxygen-mediated catalytic mechanisms provide emerging rich opportunities for greatly improving the catalytic efficiency and developing novel catalysts with creating new electronic states.

Surface Lattice Oxygen Activation on Sr2Sb2O7 Enhances the Photocatalytic Mineralization of Toluene: from Reactant Activation, Intermediate Conversion to Product Desorption.

Transition-metal oxide photocatalysis has attracted increasing attention in environmental remediation and solar energy conversion. Surface lattice oxygen is the key active site on the metal oxide, but its role and activation mechanism in the photocatalytic VOC mineralization are still unclear. In this work, we have demonstrated that Sr2Sb2O7 exhibits an excellent photocatalytic activity and stability compared to TiO2 (P25) in gaseous toluene mineralization because the lattice oxygen on Sr2Sb2O7 can be activated efficiently. The lattice oxygen of Sr2Sb2O7 promotes the adsorption and activation of O2 and H2O molecules and enhances the production of •O2- and •OH radicals, as confirmed by the electron spin resonance and DFT calculations. The in situ diffuse reflectance infrared Fourier transform spectroscopy spectra are applied to dynamically monitor the intermediate activation and selective conversion. Combined with DFT calculation, the role and the mechanism of lattice oxygen in photocatalysis have been revealed. Owing to the promoted surface lattice oxygen, the selectivity for benzoic acid formation is enhanced and final product desorption is promoted, which could largely advance the ring opening and mineralization of toluene. This work reveals the origin of lattice oxygen activation and the role for efficient VOC degradation at the atomic scale.