Engineering Spatially Adjacent Redox Sites with Synergistic Spin Polarization Effect to Boost Photocatalytic CO2 Methanation.

The integration of oxidation and reduction half-reactions to amplify their synergy presents a considerable challenge in CO2 photoconversion. Addressing this challenge requires the construction of spatially adjacent redox sites while suppressing charge recombination at these sites. This study introduces an innovative approach that utilizes spatial synergy to enable synergistic redox reactions within atomic proximity and employs spin polarization to inhibit charge recombination. We incorporate Mn into Co3O4 as a catalyst, in which Mn sites tend to enrich holes as water activation sites, while adjacent Co sites preferentially capture electrons to activate CO2, forming a spatial synergy. The direct H transfer from H2O at Mn sites facilitates the formation of *COOH on adjacent Co sites with remarkably favorable thermodynamic energy. Notably, the incorporation of Mn induces spin polarization in the system, significantly suppressing the recombination of photogenerated charges at redox sites. This effect is further enhanced by applying an external magnetic field. By synergizing spatial synergy and spin polarization, Mn/Co3O4 exhibits a CH4 production rate of 23.4 µmol g-1 h-1 from CO2 photoreduction, showcasing a 28.8 times enhancement over Co3O4. This study first introduces spin polarization to address charge recombination issues at spatially adjacent redox sites, offering novel insights for synergistic redox photocatalytic systems.

Single-Atom Alloys Materials for CO2 and CH4 Catalytic Conversion.

The catalytic conversion of greenhouse gases CH4 and CO2 constitutes an effective approach for alleviating the greenhouse effect and generating valuable chemical products. However, the intricate molecular characteristics characterized by high symmetry and bond energies, coupled with the complexity of associated reactions, pose challenges for conventional catalysts to attain high activity, product selectivity, and enduring stability. Single-atom alloys (SAAs) materials, distinguished by their tunable composition and unique electronic structures, confer versatile physicochemical properties and modulable functionalities. In recent years, SAAs materials demonstrate pronounced advantages and expansive prospects in catalytic conversion of CH4 and CO2. This review begins by introducing the challenges entailed in catalytic conversion of CH4 and CO2 and the advantages offered by SAAs. Subsequently, the intricacies of synthesis strategies employed for SAAs are presented and characterization techniques and methodologies are introduced. The subsequent section furnishes a meticulous and inclusive overview of research endeavors concerning SAAs in CO2 catalytic conversion, CH4 conversion, and synergy CH4 and CO2 conversion. The particular emphasis is directed toward scrutinizing the intricate mechanisms underlying the influence of SAAs on reaction activity and product selectivity. Finally, insights are presented on the development and future challenges of SAAs in CH4 and CO2 conversion reactions.

High-density frustrated Lewis pairs based on Lamellar Nb2O5 for photocatalytic non-oxidative methane coupling.

Photocatalytic methane conversion requires a strong polarization environment composed of abundant activation sites with the robust stretching ability for C-H scissoring. High-density frustrated Lewis pairs consisting of low-valence Lewis acid Nb and Lewis base Nb-OH are fabricated on lamellar Nb2O5 through a thermal-reduction promoted phase-transition process. Benefitting from the planar atomic arrangement of lamellar Nb2O5, the frustrated Lewis pairs sites are highly exposed and accessible to reactants, which results in a superior methane conversion rate of 1456 µmol g-1 h-1 for photocatalytic non-oxidative methane coupling without the assistance of noble metals. The time-dependent DFT calculation demonstrates the photo-induced electron transfer from LA to LB sites enhances their intensities in a concerted way, promoting the C-H cleavage through the coupling of LA and LB. This work provides in-depth insight into designing and constructing a polarization micro-environment for photocatalytic C-H activation of methane without the assistance of noble metals.

Selective Photocatalytic CO2 Reduction to CH4 on Tri-s-triazine-Based Carbon Nitride via Defects and Crystal Regulation: Synergistic Effect of Thermodynamics and Kinetics.

Realizing the high selectivity of CH4 from the photocatalytic CO2 reduction reaction (CO2 RR) remains a great challenge owing to the lower efficiency of multi-electron transfer and the similar thermodynamic properties of CH4 and CO. Herein, nitrogen-deficient carbon nitride two-dimensional (2D) nanosheets were prepared via the high-temperature crystalline phase transformation process. Optimizing crystallinity enhances the in-plane polarization along the a-axis. Owing to the increased electron density of the N defect, the kinetic possibilities of CH4 production have increased. Furthermore, the potential energy of the mid-gap states introduced by the N defect favors the thermodynamics of CH4 production. The selectivity values of CH4 based on yield and electrons are 87.1 and 96.4%. This work unravels the mechanism to selectively produce CH4 from CO2 photoreduction through the crystalline phase and defect regulation and provides significant guidance for the rational design of CO2 reduction photocatalysts for selective CH4 production.

Transthoracic minimally invasive closure for the treatment of ruptured sinus of Valsalva aneurysm: immediate and mid-term follow-up results.

BACKGROUND: We aimed to evaluate the immediate and mid-term outcomes of transthoracic minimally invasive closure (TMIC) of ruptured sinus of Valsalva aneurysm (RSVA), which is a rare and mostly congenital heart disease. METHODS: From January 2014 to November 2020, 19 patients (16 males, 3 females) with RSVA were selected for TMIC and were followed up at our centre. Data were analysed from our prospectively collected database and clinical mid-term follow-up was obtained. RESULTS: Among these 19 cases, transthoracic echocardiography showed rupture of the right coronary sinus to the right atrium in 9 patients, non-coronary sinus rupture to the right atrium in 7 patients, and right coronary sinus rupture to the right ventricle in 3 patients. Most (13/19) cases were New York Heart Association (NYHA) functional class III or IV. The mean diameters of the defect from the aortic end and ruptured site were 8.8±3.0 and 6.4±2.6 mm, respectively. TMIC was attempted using ventricular septal defect (VSD)/patent ductus arteriosus (PDA) occluders 2-7 mm larger than the aortic ends of the defects. All patients were successfully treated by TMIC and achieved complete closure at discharge after a mean hospital stay length of 6.2±2.5 days. Seventeen patients were NYHA class I while 2 patients were NYHA class II. No cases of residual shunts, device embolization, infective endocarditis, or aortic regurgitation were observed during a median follow-up of 36 months (range, 16-84 months). CONCLUSIONS: In appropriately selected cases with RSVA, TMIC is an attractive alternative to surgery, with a high technical success rate and encouraging short-term and mid-term outcomes. However, long-term follow-up is needed.

Non-oxidative Coupling of Methane: N-type Doping of Niobium Single Atoms in TiO2 -SiO2 Induces Electron Localization.

Photodriven nonoxidative coupling of CH4 (NOCM) is an attractive potential way to use abundant methane resources. Herein, an n-type doped photocatalyst for NOCM is created by doping single-atom Nb into hierarchical porous TiO2 -SiO2 (TS) microarray, which exhibits a high conversion rate of 3.57 µmol g-1 h-1 with good recyclability. The Nb dopant replaces the 6-coordinated titanium on the (1 0 1) plane and forms shallow electron-trapped surface polarons along [0 1 0] direction and the comparison of different models proves that the electron localization caused by the n-type doping is beneficial to both methane activation and ethane desorption. The positive effect of n-type dopant on CH4 conversion is further verified on Mo-, W- and Ta-doped composites. In contrast, the doping of p-type dopant (Ga, Cu, Fe) shows a less active influence.

Chemisorption-Induced and Plasmon-Promoted Photofixation of Nitrogen on Gold-Loaded Carbon Nitride Nanosheets.

Photocatalytic fixation of nitrogen is a promising method for green conversion of solar light, but has been substantially limited by inefficient activation of the nonpolar N≡N bond and the poor utilization of visible light. In this study, carbon nitride nanosheet composites with abundant nitrogen vacancies and strong plasmonic resonance absorption of visible light have been fabricated through the combination of hydrogen treatment and loading of Au nanoparticles. Ammonia yields of 184 µmol g-1 and 93 µmol g-1 are obtained without any sacrificial agent under full-light and visible-light irradiation, respectively. In particular, the visible-light activity is enhanced tenfold with the help of Au. Combining the experimental results and theoretical calculations, both the hydrogen treatment and Au loading help form nitrogen vacancies on the carbon nitride nanosheets, which promote N2 activation by enhancing the chemisorption. Furthermore, the Au loading further improves the nitrogen reduction efficiency through charging the excited hot electrons formed from the surface plasmonic resonance to the adsorbed N2 molecules.

Ga-Doped and Pt-Loaded Porous TiO2-SiO2 for Photocatalytic Nonoxidative Coupling of Methane.

Photodriven nonoxidative coupling of CH4 (NOCM) is a potential alternative approach to clean hydrogen and hydrocarbon production. Herein, a Mott-Schottky photocatalyst for NOCM is fabricated by loading Pt nanoclusters on a Ga-doped hierarchical porous TiO2-SiO2 microarray with an anatase framework, which exhibits a CH4 conversion rate of 3.48 µmol g-1 h-1 with 90% selectivity toward C2H6. This activity is 13 times higher than those from microarrays without Pt and Ga. Moreover, a continuous H2 production (36 µmol g-1) with a high CH4 conversion rate of ∼28% can be achieved through a longtime irradiation (32 h). The influence of Ga on the chemical state of a surface oxygen vacancy (Vo) and deposited Pt is investigated through a combination of experimental analysis and first-principles density functional theory calculations. Ga substitutes for the five-coordinated Ti next to Vo, which tends to stabilize the single-electron trapped Vo and reduce the electron transfer from Vo to the adsorbed Pt, resulting in the formation of a higher amount of cationic Pt. The cationic Pt and electron-enriched metallic Pt form a cationic-anionic active pair, which is more efficient for the dissociation of C-H bonds. However, the presence of too much cationic Pt results in more C2+ product with a decrease in the CH4 conversion rate due to the reduced charge-carrier separation efficiency. This study provides deep insight into the effect of the doping/loading strategy on the photocatalytic NOCM reaction and is expected to shed substantial light on future structural design and modulation.

Nitrogen-Doped Mesoporous Carbon-Encapsulated MoO2 Nanobelts as a High-Capacity and Stable Host for Lithium-Ion Storage.

N-doped mesoporous carbon-capped MoO2 nanobelts (designated as MoO2 @NC) were synthesized and applied to lithium-ion storage. Owing to the stable core-shell structural framework and conductive mesoporous carbon matrix, the as-prepared MoO2 @NC shows a high specific capacity of around 700 mA h g-1 at a current of 0.5 A g-1 , excellent cycling stability up to 100 cycles, and superior rate performance. The N-doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core-shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO2 @NC to be a suitable and promising material for lithium ion battery.

Noble-Metal-Free Materials for Surface-Enhanced Raman Spectroscopy Detection.

Surface-enhanced Raman spectroscopy (SERS) is an attractive tool for the sensing of molecules in the fields of chemical and biochemical analysis as it enables the sensitive detection of molecular fingerprint information even at the single-molecule level. In addition to traditional coinage metals in SERS analysis, recent research on noble-metal-free materials has also yielded highly sensitive SERS activity. This Minireview presents the recent development of noble-metal-free materials as SERS substrates and their potential applications, especially semiconductors and emerging graphene-based nanostructures. Rather than providing an exhaustive review of this field, possible contributions from semiconductor substrates, characteristics of graphene enhanced Raman scattering, as well as effect factors such as surface plasmon resonance, structure and defects of the nanostructures that are considered essential for SERS activity are emphasized. The intention is to illustrate, through these examples, that the promise of noble-metal-free materials for enhancing detection sensitivity can further fuel the development of SERS-related applications.