다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Photoreduction of N₂ is among the most interesting and challenging methods for N₂ fixation under mild conditions. In this study, we determined that nitrogen vacancies (NVs) could endow graphitic carbon nitride (g-C₃N₄) with the photocatalytic N₂ fixation ability. Photocatalytic N₂ fixation induced by NVs is free from the interference of other gases. The reason is that NVs could selectively adsorb and activate N₂ because NVs have the same shape and size as the nitrogen atom in N₂. In addition to this, NVs could also improve many other properties of g-C₃N₄ to support photocatalytic N₂ fixation. These new findings could elucidate the design of efficient photocatalysts for photocatalytic N₂ fixation.

Selective photocatalytic N₂ fixation dependent on g-C₃N₄ induced by nitrogen vacancies

Electro-, photo-, and photoelectrocatalysis play a critical role toward the realization of a sustainable energy economy. They facilitate numerous redox reactions in energy storage and conversion systems, enabling the production of chemical feedstock and clean fuels from abundant resources like water, carbon dioxide, and nitrogen. One major obstacle for their large-scale implementation is the scarcity of cost-effective, durable, and efficient catalysts. A family of two-dimensional transition metal carbides, nitrides, and carbonitrides (MXenes) has recently emerged as promising earth-abundant candidates for large-area catalytic energy storage and conversion due to their unique properties of hydrophilicity, high metallic conductivity, and ease of production by solution processing. To take full advantage of these desirable properties, MXenes have been combined with other materials to form MXene hybrids with significantly enhanced catalytic performances beyond the sum of their individual components. MXene hybridization tunes the electronic structure toward optimal binding of redox active species to improve intrinsic activity while increasing the density and accessibility of active sites. This review outlines recent strategies in the design of MXene hybrids for industrially relevant electrocatalytic, photocatalytic, and photoelectrocatalytic applications such as water splitting, metal-air/sulfur batteries, carbon dioxide reduction, and nitrogen reduction. By clarifying the roles of individual material components in the MXene hybrids, we provide design strategies to synergistically couple MXenes with associated materials for highly efficient and durable catalytic applications. We conclude by highlighting key gaps in the current understanding of MXene hybrids to guide future MXene hybrid designs in catalytic energy storage and conversion applications.

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Rational Design of Two-Dimensional Transition Metal Carbide/Nitride (MXene) Hybrids and Nanocomposites for Catalytic Energy Storage and Conversion

In 2011, with the successful isolation of Ti3C2, a door of 2D layered MXene has been opened and received growing attention from researchers. MXene refers to a family of two-dimensional (2D) materials made up of atomic layers of the transition metal, carbide, nitrides, or carbonitrides. Given the large surface area, adjustable surface terminal groups, and excellent conductivity of MXene, it has shown exciting potential in photocatalysis, energy conversion, and many other fields. Among many 2D MXene, Ti3C2 was the most studied for its availability, low cost, facile modification procedure, and outstanding electronic properties. In previous investigations, Ti3C2 has shown huge potential in the photocatalysis area. Ti3C2 in a photocatalysis system can enhance the separation of photoinduced electrons and holes, reduce charge recombination, and thus improve the photocatalysis performance in many systems. To adjust the performance of Ti3C2 in different applications, the properties of Ti3C2 including morphology, structures, and stability are tunable by different post-processing method in the hybridized materials. In this review, an all-around understanding of the fabrication and modification methods of Ti3C2 and their connection to photocatalytic applications of Ti3C2 MXene based materials are presented. Moreover, a summary and our perspectives of Ti3C2 are given for further investigation.

Ti3C2 2D MXene: Recent Progress and Perspectives in Photocatalysis.

A kind of 2D-layered material, Ti3C2 MXenes, was successfully used as a new and efficient co-catalyst to improve the photocatalytic NH3 synthesis performance of P25, due to its large surface area/2D-layered structure, large electric capacity, excellent electrical conductivity and effective chemisorption/activation of N2 molecules. The generation yield of NH3 was improved by five times on the optimized sample of 6% Ti3C2 MXenes–P25 compared with pure P25 under full spectrum light irradiation, consistent with the measured both photocurrent densities and charge lifetime. The further mechanistic study showed that Ti3C2 MXenes played an important role in the separation of photogenerated electron–hole pairs by accumulating the excited electrons from the excited P25. Most importantly, Ti3C2 MXenes could dramatically improve chemisorption and activation of N2 as demonstrated by ESR spectra and DFT calculations. In addition, Ti3C2 MXenes loading on P25 could introduce oxygen vacancies in P25, also beneficial for photocatalytic NH3 synthesis. Thus this study provides an efficient and promising co-catalyst for the photocatalytic NH3 synthesis process from N2 in air

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2D-layered Ti3C2 MXenes for promoted synthesis of NH3 on P25 photocatalysts

This paper considers pole assignment and robust pole assignment problems for discrete-time linear periodic systems by using linear periodic state feedback. The monodromy matrix of the closed-loop system is represented in a special form. By combining this special form with our recent result on solutions to a class of generalized Sylvester matrix equations, a complete parametric approach for pole assignment via periodic state feedback is proposed. The free parameters existing in the solutions to pole assignment are further used to achieve robustness performances. The robust pole assignment problem is converted into a nonconvex optimization problem. Numerical examples illustrate the effectiveness of the proposed approaches.

Parametric Pole Assignment and Robust Pole Assignment for Discrete-Time Linear Periodic Systems

Electrocatalytic reduction of nitrates (NO3RR) selectively generating ammonia (NH3) opens up a new idea for treating nitrates in wastewater, which not only reduces nitrates but also obtains the valuable product ammonia. By first-principles calculations, we explore the activity and selectivity for NO3RR to NH3 of TM/g-C3N4 single-atom catalysts. Six TM/g-C3N4 catalysts (TM = Ti, Os, Ru, Cr, Mn, and Pt) are selected by a four-step screening method. Ru/g-C3N4 is the most promising of these six TM/g-C3N4 catalysts because of its lowest energy barrier and extraordinary selectivity. The origin of the NO3RR activity of Ru/g-C3N4 is explained from the viewpoint of NO3- adsorption. In addition, the hydrogen evolution reaction has also been implied to be uncompetitive for the poor adsorption on H atoms. This work provides a screening mechanism for finding new catalysts for NO3RR to NH3, promotes the development of NO3RR, and provides a stimulating impetus for further experimental exploration.

Computational Screening of High Activity and Selectivity TM/g-C3N4 Single-Atom Catalysts for Electrocatalytic Reduction of Nitrates to Ammonia.

Photocatalytic Nitrogen Reduction by Ti3C2 MXene Derived Oxygen Vacancy-Rich C/TiO2

The investigations of two-dimensional photocatalysts are promising subjects in clean and renewable energy. Herein, we proposed a novel two-dimensional GeN3 monolayer. The stability of GeN3 monolayer was examined via formation energy, phonon calculations and ab initio molecular dynamics simulations. Excellent photocatalytic properties are revealed: (a) GeN3 monolayer is a semiconductor with appropriate band gap of 1.962 eV that the valence and conduction bands straddle the redox potential of water. (b) GeN3 monolayer has extremely high carrier mobility with anisotropic character (its electron mobility is 1.55 × 104 cm2 V−1 s−1 along the armchair direction, whereas the hole mobility reaches 1.6 × 103 cm2 V−1 s−1 along the zigzag direction), which boost the separation of electron-hole pairs. (c) The GeN3 monolayer shows strong light absorption coefficients (up to 105 cm−1) in the visible regions, leading to high solar-to-hydrogen efficiency (12.63 %). (d) Furthermore, the band gap of the GeN3 monolayer could be engineered from indirect to direct under external strain and electric field. This work discloses a novel 2D GeN3 monolayer whose fascinating properties make it a promising photocatalyst for hydrolyzing to produce hydrogen.

Lingling Lv

Papers

2D-layered Ti3C2 MXenes for promoted synthesis of NH3 on P25 photocatalysts

Parametric Pole Assignment and Robust Pole Assignment for Discrete-Time Linear Periodic Systems

Computational Screening of High Activity and Selectivity TM/g-C3N4 Single-Atom Catalysts for Electrocatalytic Reduction of Nitrates to Ammonia.

Photocatalytic Nitrogen Reduction by Ti3C2 MXene Derived Oxygen Vacancy-Rich C/TiO2

GeN3 monolayer: A promising 2D high-efficiency photo- hydrolytic catalyst with High carrier mobility transport anisotropy