Metal-Free Graphitic Carbon Nitride Photocatalyst Goes Into Two-Dimensional Time

Doping and strain modulation of the electronic, optical and photocatalytic properties of the GaN/C2N heterostructure

The electronic, optical and photocatalytic properties of GaN/C2N van der Waals heterostructures are investigated using the first-principles theory, and effective regulation through element doping or strain is achieved further. The results show that the GaN/C2N heterostructure exhibits a type-II band alignment with an indirect band gap of 2.25 eV, which benefits photocatalytic water splitting. In this study, both type-I and type-II band alignments can be obtained through doping or strain modulation. Doping with P or As atoms reduces the band gap of the GaN/C2N heterostructure and transforms it to a type-I direct bandgap semiconductor, which makes the doped GaN/C2N heterostructure more suitable for optoelectronic devices. In addition, the GaN/C2N heterostructure retains type-II band alignment and has a decreased band gap under tensile strain (0 to +4%), which is more favorable for photocatalytic water splitting. Compressive strain (0 to -4%) converts the type-II band alignment to type-I, resulting in a wider light absorption range, making the GaN/C2N heterostructure more suitable for optoelectronic devices. These theoretical results are helpful for the design of GaN/C2N vdW heterostructures in the fields of optoelectronic devices and photocatalysts.

Transition metals-doped g-C3N4 nanostructures as advanced photocatalysts for energy and environmental applications

Graphitic carbon nitride (g-C3N4)-based heterostructured photocatalysts have received significant attention for its potential applications in the treatment of wastewater and hydrogen evolution. The utilization of semiconductor materials in heterogeneous photocatalysis has recently received great attention due to their potential and eco-friendly properties. Doping with metal ions plays a crucial role in altering the photochemical characteristics of g-C3N4, effectively enhancing photoabsorption into the visible range and thus improving the photocatalytic performance of doped photocatalysts. As an emerging nanomaterial, nanostructured g-C3N4 represents a visible light-active semiconducting photocatalyst that has attracted significant interest in the photocatalysis field, particularly for its practical water treatment applications. To the best of our knowledge, investigations of functionalized photocatalytic (PC) materials on 3d transition metal-doped g-C3N4 remain unexplored in the existing literature. g-C3N4 based heterohybrid photocatalysts have demonstrated excellent reusability, making them highly promising for wastewater treatment applications. This paper describes the overview of numerous studies conducted on the heterostructured g-C3N4 photocatalysts with various 3d metals. Research studies have revealed that the introduction of element doping with various 3d transition metals (e.g., Ti, Mn, Fe, Co, Ni, Cu, Zn, etc.) into g-C3N4 is an efficient approach to enhance degradation efficacy and boost photocatalytic activity (PCA) of doped g-C3N4 catalysts. Moreover, the significance of g-C3N4 heterostructured nanohybrids is highlighted, particularly in the context of wastewater treatment applications. The study concludes by providing insights into future perspectives in this developing area of research, with a specific focus on the degradation of various organic contaminants.

Insight on the structural, electronic and optical properties of Zn, Ga-doped/dual-doped graphitic carbon nitride for visible-light applications

The density functional theory (DFT) was applied for the first time to study the doping and co-doping of Ga and Zn metals on graphitic carbon nitride (g-C3N4). The doping of these metal impurities into g-C3N4 leads to a significant decrease in the bandgap energy. Moreover, the co-doping leads to even lower bandgap energy than either individual Zn or Ga-doped g-C3N4. The theoretical electronic and optical properties including the density of state (DOS), energy levels of the frontier orbital, excited state lifetime, and molecular electrostatic potential of the doped and co-doped g-C3N4 support their application in UV-visible light-based technologies. The quantum mechanical parameters (energy band gap, binding energy, exciton energy, softness, hardness) and dipole moment exhibit higher values (ranging from 1.36 to 4.94 D) compared to the bare g-C3N4 (0.29 D), indicating better solubility in the water solvent. The time-dependent DFT (TD-DFT) calculations showed absorption maxima in between the UV-Vis region (309-878 nm). Additionally, charge transfer characteristics, transition density matrix (TDM), excited state lifetime and light harvesting efficiency (LHE) were investigated. Overall, these theoretical studies suggest that doped and co-doped g-C3N4 are excellent candidates for electronic semiconductor devices, light-emitting diodes (LEDs), solar cells, and photodetectors.

Tailoring 2D carbides and nitrides based photo-catalytic nanomaterials for energy production and storage: a review

2D carbides and nitrides-based nanomaterials because of their unusual physical and chemical properties and a vast range of energy-storage applications have attracted tremendous attention. However, 2D carbides and nitrides-based nanomaterials and their corresponding composites have many intrinsic constraints in terms of energy-storage applications. The nano-engineering of these 2D materials is widely investigated, to improve their performance for practical application. In this Review article, the current progress and research on 2D carbides and nitrides-based nanostructures are presented and debated, concentrating on their methods of preparation, and energy conservation applications for example Lithium-ion-battery, supercapacitors, and Sodium-ion-battery. In conclusion, the problems, and recommendations essential to be discussed for the progress of these 2D nanomaterials for energy-storage applications based on carbides and nitrides are displayed.

Semiconductor-metal-semiconductor TiO2@Au/g-C3N4 interfacial heterojunction for high performance Z-scheme photocatalyst

We designed an edge-sites 2D/0D/2D based TiO2@Au/g-C3N4 Z-scheme photocatalytic system consists of highly exposed (001) TNSs@Au edge-site heterojunction, and the Au/g-C3N4 interfacial heterojunction. The designed photocatalyst was prepared by a facile and controlled hydrothermal synthesis strategy via in-situ nanoclusters-to-nanoparticles deposition technique and programable calcination in N2 atmosphere to get edge-site well-crystalline interface, followed by chemically bonded thin overlay of g-C3N4. Photocatalytic performance of the prepared TNSs@Au/g-C3N4 catalyst was evaluated by the photocatalytic degradation of organic pollutants in water under visible light irradiation. The results obtained from structural and chemical characterization conclude that the inter-facet junction between highly exposed (001) and (101) TNSs surface, and TNSs@Au interfacial heterojunction formed by a direct contact between highly crystalline TNSs and Au, are the key factors to enhance the separation efficiency of photogenerated electrons/holes. On coupling with overlay of g-C3N4 2D NSs synergistically offer tremendous reactive sites for the potential photocatalytic dye degradation in the Z-scheme photocatalyst. Particularly in the designed photocatalyst, Au nanoparticles accumulates and transfer the photo-stimulated electrons originated from anatase TNSs to g-C3N4via semiconductor-metal heterojunction. Because of the large exposed reactive 2D surface, overlay g-C3N4 sheets not only trap photoelectrons, but also provide a potential platform for increased adsorption capacities for organic contaminants. This work establishes a foundation for the development of high-performance Z-scheme photocatalytic systems.

Nonadiabatic Molecular Dynamics with Extended Density Functional Tight-Binding: Application to Nanocrystals and Periodic Solids

In this work, we report a new methodology for nonadiabatic molecular dynamics calculations within the extended tight-binding (xTB) framework. We demonstrate the applicability of the developed approach to finite and periodic systems with thousands of atoms by modeling "hot" electron relaxation dynamics in silicon nanocrystals and electron-hole recombination in both a graphitic carbon nitride monolayer and a titanium-based metal-organic framework (MOF). This work reports the nonadiabatic dynamic simulations in the largest Si nanocrystals studied so far by the xTB framework, with diameters up to 3.5 nm. For silicon nanocrystals, we find a non-monotonic dependence of "hot" electron relaxation rates on the nanocrystal size, in agreement with available experimental reports. We rationalize this relationship by a combination of decreasing nonadiabatic couplings related to system size and the increase of available coherent transfer pathways in systems with higher densities of states. We emphasize the importance of proper treatment of coherences for obtaining such non-monotonic dependences. We characterize the electron-hole recombination dynamics in the graphitic carbon nitride monolayer and the Ti-containing MOF. We demonstrate the importance of spin-adaptation and proper sampling of surface hopping trajectories in modeling such processes. We also assess several trajectory surface hopping schemes and highlight their distinct qualitative behavior in modeling the excited-state dynamics in superexchange-like models depending on how they handle coherences between nearly parallel states.

Effect of Band Bending in Photoactive MOF-Based Heterojunctions

Semiconductor/metal-organic framework (MOF) heterojunctions have demonstrated promising performance for the photoconversion of CO₂ into value-added chemicals. To further improve performance, we must understand better the factors which govern charge transfer across the heterojunction interface. However, the effects of interfacial electric fields, which can drive or hinder electron flow, are not commonly investigated in MOF-based heterojunctions. In this study, we highlight the importance of interfacial band bending using two carbon nitride/MOF heterojunctions with either Co-ZIF-L or Ti-MIL-125-NH₂. Direct measurement of the electronic structures using X-ray photoelectron spectroscopy (XPS), work function, valence band, and band gap measurements led to the construction of a simple band model at the heterojunction interface. This model, based on the heterojunction components and band bending, enabled us to rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. Using the insight gained from a promising band bending diagram, we developed a Type II carbon nitride/MOF heterojunction with a 2-fold enhanced CO₂ photoreduction activity compared to the physical mixture.

A 2D/1D heterojunction nanocomposite built from polymeric carbon nitride and MIL-88A(Fe) derived α-Fe2O3 for enhanced photocatalytic degradation of rhodamine B

2D/1D heterojunction α-Fe2O3/C3N4 photocatalysts containing α-Fe2O3 microrods and polymeric carbon nitride flakes are synthesised through the calcination of Fe-based metal-organic frameworks and boost the visible light photocatalytic degradation of rhodamine B.

Single-layer carbon nitride: synthesis, structure, photophysical/photochemical properties, and applications

This Perspective provides a critical summary of the current state of the art in the synthesis and properties of polyheptazine single-layer carbon nitride (SLCN). The summary combines the authors' research and literature reports on SLCN concerning the synthesis of single-layer polyheptazine sheets, light absorption and emission by SLCN, photochemical and photocatalytic properties of SLCN as well as examples of applications of SLCN sheets as "building blocks" in heterostructures with nanocrystalline semiconductors and metals. The Perspective is concluded with an outlook discussing the most promising directions for further studies and applications of SLCN and related composites.

Graphite Carbon Nitride and Its Composites for Medicine and Health Applications

With the progress of science and technology and the improvement of people's living standards, the performance of traditional materials can no longer fully meet the needs of social development. Graphitic phase carbon nitride (g-C₃ N₄ ), as a new type of nanomaterial, has good properties. Its unique graphite like structure and stable thermodynamic characteristics have led an increasing number of researchers to explore its diverse functions and use this as a basis to develop related energy and products for applications in various fields. Among them, applications in the field of medicine health have become popular in recent years. Therefore, this review summarizes the synthesis methods of g-C₃ N₄ and its composites, as well as their applications in food, medicine, environmental monitoring and disease treatment, in the hope of providing references and basis for further expanding the applications of g-C₃ N₄ in large health areas.

Ab initio quantum dynamics of charge carriers in graphitic carbon nitride nanosheets

Graphitic carbon nitride (g-C₃N₄), a metal-free and visible light responsive photocatalyst, has garnered much attention due to its wide range of applications. In order to elucidate the role of dimensionality on the properties of photo-generated charge carriers, we apply nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory to investigate nonradiative relaxation of hot electrons and holes, and electron-hole recombination in monolayer and bulk g-C₃N₄. The nonradiative charge recombination occurs on a nanosecond timescale and is faster in bulk than the nanosheet, in agreement with the experiment. The difference arises due to the smaller energy gap and participation of additional vibrations in the bulk system. The long carrier lifetimes are favored by small NA coupling and rapid phonon-induced loss of quantum coherence between the excited and ground electronic states. Decoherence is fast because g-C₃N₄ is soft and undergoes large scale vibrations. The NA coupling is small since electrons and holes are localized on different atoms, and the electron-hole overlap is relatively small. Phonon-driven relaxation of hot electrons and holes takes 100-200 fs and is slightly slower at higher initial energies due to participation of fewer vibrational modes. This feature of two-dimensional g-C₃N₄ contrasts traditional three-dimensional semiconductors, which exhibit faster relaxation at higher energies due to larger density of states, and can be used to extract hot carriers to perform useful functions. The ab initio quantum dynamics simulations present a comprehensive picture of the photo-induced charge carrier dynamics in g-C₃N₄, guiding design of photovoltaic and photocatalytic devices.