As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.

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2D metal carbides and nitrides (MXenes) for energy storage

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

A review on g-C3N4-based photocatalysts

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

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Graphene in Photocatalysis: A Review

The layered graphene/g-C3N4 composites show high conductivity, electrocatalytic performance and visible light response and have potential applications in microelectronic devices and photocatalytic technology. In the present work, the stacking patterns and the correlations between electronic structures and related properties of graphene/g-C3N4 bilayers are investigated systematically by means of first-principles calculations. Our results indicate that the band gap of graphene/g-C3N4 bilayers can be up to 108.5 meV, which is large enough for the gap opening at room temperature. The calculated charge density difference unravels that the charge redistribution drives the interlayer charge transfer from graphene to g-C3N4. Interestingly, the investigation also shows that external electric field can tune the band gap of graphene/g-C3N4 bilayers effectively. Our research demonstrates that graphene on g-C3N4 with a tunable band gap and high carrier mobility may provide a novel way for fabricating high-performance graphene-based nanodevices.

Graphene/g-C3N4 bilayer: considerable band gap opening and effective band structure engineering.

A new family of Si-based pentagonal monolayers is constructed on the basis of the okayamalite structure by means of first principles calculations. Phonon spectra and ab initio molecular dynamics simulations provide eloquent examinations for the dynamical and thermal stabilities of p-SiX (X = B, C, and N) monolayers. Electronic structures show that p-SiC and p-SiN are indirect semiconductors with band gaps of 2.35 and 4.98 eV by HSE hybrid functional, respectively. The carrier mobilities up to 2500 cm2 V−1 s−1 are quantitatively investigated by using deformation potential theory with effective mass approximation. And the band structures can be modulated monotonically under proper isotropic strains. This indicates that p-SiX can be used as field effect transistors or other electronic devices. More intriguingly, the band gap of p-SiC corresponds to the wavelength of 528 nm, showing a semiconducting character absorption in the green region of the visible spectra. Enlightened by prominent photocatalytic behavior of g-C3N4, we demonstrate that both band gap and band edges of p-SiC can meet the requirement of the reduction and oxidation levels in water splitting. The new type of Si-based nanomaterial offers an interesting alternative to diverse nanodevices and paves way for new metal-free photocatalysts.

Stable Si-based pentagonal monolayers: high carrier mobilities and applications in photocatalytic water splitting

Plasmonic Bi2WO6 with strong localized surface plasmon resonance (LSPR) around the 500-1400 region is successfully constructed by electron doping Oxygen vacancies on W-O-W (V1) and Bi-O-Bi (V2) sites are precisely controlled to obtain Bi2WO6-V1 with LSPR and Bi2WO6-V2 with defect absorption Density functional theory (DFT) calculation demonstrates that the V1-induced energy state facilitates photoelectron collection for a long lifetime, resulting in LSPR of Bi2WO6 Photoelectron trapping on V1 sites is demonstrated by a single-particle photoluminescence (PL) study, and 93% PL quenching efficiency is observed With strong LSPR, plasmonic Bi2WO6-V1 exhibits highly selective methane generation with a rate of 995 μmol g-1 h-1 during the CO2 reduction reaction (CO2-RR), which is 26-fold higher than 037 μmol g-1 h-1 of BiWO3-V2 under UV-visible light irradiation LSPR-dependent methane generation is confirmed by various photocatalytic results of plasmonic Bi2WO6 with tunable LSPR and different light excitations Furthermore, the DFT-simulated pathway of CO2-RR and in situ Fourier transform infrared spectra on the surface of Bi2WO6 prove that V1 sites facilitate CH4 generation Our work provides a strategy to obtain nonmetallic plasmonic materials by electron doping

Constructing Surface Plasmon Resonance on Bi2WO6 to Boost High-Selective CO2 Reduction for Methane.

https://hal.archives-ouvertes.fr/hal-03103500/document

Rational band engineering and structural manipulations inducing high thermoelectric performance in n-type CoSb3 thin films

A number of graphene-like materials have been theoretically predicted and experimentally confirmed so far. Here, based on the first-principles calculations, we predict that stable BiTeX (X = Br and I) monolayers possess intrinsic large polar electric fields along the normal direction to the plane, making them two-dimensional polar systems. Moreover, we find that these novel monolayers with thicknesses of only 3.8 A can produce a giant Rashba spin splitting derived from their peculiarly polar atomic configurations. Furthermore, the Rashba parameters of BiTeX monolayers can be effectively modulated by applying strain, and are thus promising for wide applications in nanoelectronics.

Xinru Li

Papers

Graphene/g-C3N4 bilayer: considerable band gap opening and effective band structure engineering.

Stable Si-based pentagonal monolayers: high carrier mobilities and applications in photocatalytic water splitting

Constructing Surface Plasmon Resonance on Bi2WO6 to Boost High-Selective CO2 Reduction for Methane.

Rational band engineering and structural manipulations inducing high thermoelectric performance in n-type CoSb3 thin films

Emergence of electric polarity in BiTeX (X = Br and I) monolayers and the giant Rashba spin splitting.