Among the diverse graphitic carbon nitride (CN) nanostructures, CN nanotubes (CNNTs) are currently attracting increasing interest due to the appealing properties of CN and the geometric advantages of one-dimensional (1D) nanotubes. CN is a metal-free photocatalyst and has the advantages of exceptional electronic band structure, rich nitrogen content, and high physicochemical stability. Nanotubes have a unique 1D hollow nanostructure, and they provide large surface area, high aspect ratio, electron mobility along the axial direction, and quantum confinement effects. Therefore, CNNTs and CNNT-based materials have been extensively explored in many energy- and environment-related fields. In this review, the functional merits of CNNTs and recent progress in the precursor-based synthesis of CNNTs are discussed. Besides, the corresponding applications of CNNT-based nanomaterials are summarized, such as photocatalytic H2 production, pollutant degradation, and CO2 reduction. Moreover, the modification strategies of CNNTs using elemental doping, texture tailoring, and heterojunction engineering are comprehensively discussed. Finally, the future challenges and opportunities of CNNT-based nanostructures are proposed. With the rapid development of materials science and technology, more efforts need to be devoted toward promoting the advanced functionalities and promising applications of CNNT-based materials.

Carbon nitride nanotube-based materials for energy and environmental applications: a review of recent progresses

Splitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve high-yield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties has received much attention in this field. Owing to the recent developments in high-end computation and advanced electronic structure theories, first principles studies offer powerful tools to screen photocatalytic systems reliably and efficiently. This review is organized to highlight the essential properties of 2D photocatalysts and the recent advances in the theoretical engineering of 2D materials for the improvement in photocatalytic overall water-splitting. The advancement in the strategies including (i) single-atom catalysts, (ii) defect engineering, (iii) strain engineering, (iv) Janus structures, (v) type-II heterostructures (vi) Z-scheme heterostructures (vii) multilayer configurations (viii) edge-modification in nanoribbons and (ix) the effect of pH in overall water-splitting are summarized to improve the existing problems for a photocatalytic catalytic reaction such as overcoming large overpotential to trigger the water-splitting reactions without using cocatalysts. This review could serve as a bridge between theoretical and experimental research on next-generation 2D photocatalysts.

/pdf/engineering-2d-materials-for-photocatalytic-water-splitting-34razs5p.pdf

Engineering 2D Materials for Photocatalytic Water-Splitting from a Theoretical Perspective

Nanocomposites based on 3D honeycomb-like carbon nitride with Cd0·5Zn0·5S quantum dots for efficient photocatalytic hydrogen evolution

Solar-driven water splitting is an appealing strategy to produce hydrogen energy. However, the non-negligible chance of reverse reactions due to a mixture of hydrogen molecules (H2) with oxygen species poses challenges for safe H2 collection and delivery, which hinders its applications. Using first-principles simulations, we propose a hybrid structure design where metal clusters of TM4 (TM = Au/Pt) are encapsulated in boron-carbon-nitride nanotube (BCNNT) decorated with CuN3 group. It can readily absorb ultraviolet-visible solar light to generate charge carriers. The energetic electrons and holes would be separately delivered to the reduction site of TM4 and the oxidation site of the BCNNT layer. Then, protons generated by water dissociation at the BCNNT layer will penetrate through BCNNT and consequently meet electrons at the TM4 site to be reduced into H2. As a selective sieve, BCNNT prevents oxygen species from going inside and H2 from crossing out so that H2 can be completely isolated. Further, the sufficient space of the tubular cavity endows the transportation feasibility of the produced H2 along the nanotube for collection. This proposed design combines photocatalytic hydrogen production and safe delivery, which may help in developing a practical solution for a photodriven hydrogen production.

Theoretical Calculation of Hydrogen Generation and Delivery via Photocatalytic Water Splitting in Boron-Carbon-Nitride Nanotube/Metal Cluster Hybrid.

As it is a promising clean energy source, the production and storage of hydrogen are crucial techniques. Here, based on first-principles calculations, we proposed an integral strategy for the production and storage of hydrogen in carbon nanotubes via photocatalytic processes. We considered a core–shell structure formed by placing a carbon nitride nanowire inside a carbon nanotube to achieve this goal. Photo-generated holes on the carbon nanotube surface promote water splitting. Driven by intrinsic electrostatic field in the core–shell structures, protons produced by water splitting penetrate the carbon nanotube and react with photo-generated electrons on the carbon nitride nanowire to produce hydrogen molecules in the carbon nanotube. Because carbon nanotubes have high hydrogen storage capacity, this core–shell structure can serve as a candidate system for photocatalytic water splitting and safe hydrogen storage.

/pdf/photocatalytic-hydrogen-production-and-storage-in-carbon-2u64yyoa.pdf

Photocatalytic hydrogen production and storage in carbon nanotubes: a first-principles study

The localization of photoexcitation leads to the proximity of photocatalytic reduction and oxidation sites, causing unfavorable side reactions. To address this issue, we designed a double-walled na...

Physically Close yet Chemically Separate Reduction and Oxidation Sites in Double-Walled Nanotubes for Photocatalytic Hydrogen Generation

The invention belongs to the field of composite materials and application, and particularly relates to a carbon/carbon-nitrogen (CxNy) composite nanotube composite material, and a preparation method and application thereof. The composite material of the present invention is composed of an inner layer of carbon-nitrogen (CxNy) nanotubes and carbon nanotubes coating the inner layer material, and theinner layer of carbon-nitrogen nanotubes and the outer layer of carbon nanotubes are combined via Van der Waals' force. The composite material of the invention has good light absorption capability and can efficiently capture solar energy, so the composite material can be used in the field of photocatalysis. At the same time, carbon nanotubes have high-efficiency selective penetration for protons,allows only protons to pass through the outer layer of carbon nanotubes to move to the carbon-nitrogen material under the action of electrostatical attraction, and inhibits detachment of newly generated H2 and entering of molecules such as OH and O , thereby achieving safe hydrogen storage, and thus the composite material is also suitable for hydrogen storage.

Carbon/carbon-nitrogen (CxNy) composite nanotube composite material, and preparation method and application thereof

The invention belongs to the field of composite materials, and in particular relates to a carbon quantum dot embedded g-C3N composite material as well as a preparation method and application of the carbon quantum dot embedded g-C3N composite material. The carbon quantum dot embedded g-C3N composite material provided by the invention comprises a single-layer two-dimensional material g-C3N and carbon quantum dots bonded to one side of the single-layer two-dimensional material g-C3N by Van der Waals force. The composite material provided by the invention has good light absorption capability in the ultraviolet, visible and partial near-infrared light ranges of solar energy, and can efficiently collect solar energy, so that the composite material is suitable in the field of photocatalysis; andhigh-efficient selective permeability of the g-C3N is utilized, the composite material provided by the invention allows protons to penetrate the g-C3N to participate in a reaction to generate hydrogen, the generated hydrogen cannot penetrate the g-C3N to escape, and meanwhile the g-C3N blocks OH and O2 from entering the system to inhibit occurrence of reverse reactions, so that effective purification and safe storage of the hydrogen are realized, and the composite material is also suitable in the field of hydrogen storage.

Carbon quantum dot embedded g-C3N composite material as well as preparation method and application of carbon quantum dot embedded g-C3N composite material

The invention discloses a two-dimensional carbon-nitrogen-based compound photocatalyst and a preparation method and an application thereof and relates to the technical field of photocatalytic materials. The two-dimensional carbon-nitrogen-based compound photocatalyst is prepared by loading transitional metal elements onto the surface of two-dimensional carbon-nitrogen materials. The prepared two-dimensional carbon-nitrogen-based compound photocatalyst can reduce band gap to form a Z-scheme system, of which the valence-band maximum is lower than oxidation potential of water and the conduction band minimum higher than reduction potential of water. According to the two-dimensional carbon-nitrogen-based compound photocatalyst, electrons can be effectively transferred inside the Z-scheme systemcomposed of the two-dimensional carbon-nitrogen-based compound photocatalyst; the two-dimensional carbon-nitrogen-based compound photocatalyst ensures hydrogen production and oxygen production on tworeaction sites simultaneously; due to the fact that the band gap of the two-dimensional carbon-nitrogen-based compound photocatalyst is reduced after loading the transitional metal ions, so that thetwo-dimensional carbon-nitrogen-based compound photocatalyst can make effective use of the light energy within the visible light range and solve the problem of interfacial transfer difficulty of existing reaction electrons.

Two-dimensional carbon-nitrogen-based compound photocatalyst and preparation method and application thereof

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Physically Close yet Chemically Separate Reduction and Oxidation Sites in Double-Walled Nanotubes for Photocatalytic Hydrogen Generation

Carbon/carbon-nitrogen (CxNy) composite nanotube composite material, and preparation method and application thereof

Carbon quantum dot embedded g-C3N composite material as well as preparation method and application of carbon quantum dot embedded g-C3N composite material

Two-dimensional carbon-nitrogen-based compound photocatalyst and preparation method and application thereof