Polymeric Graphitic Carbon Nitride for Heterogeneous Photocatalysis

Graphene-analogue carbon nitride: novel exfoliation synthesis and its application in photocatalysis and photoelectrochemical selective detection of trace amount of Cu²⁺

Graphene-analogue nanostructures defined as a new kind of promising materials with unique electronic, surface and optical properties have received much attention in the fields of catalysis, energy storage, sensing and electronic devices. Due to the distinctive structure characteristics of the graphene-analogue materials, they brought novel and amazing properties. Herein, graphene-analogue carbon nitride (GA-C₃N₄) was synthesized by high-yield, large-scale thermal exfoliation from the graphitic C₃N₄-based intercalation compound. Graphene-analogue carbon nitride exhibited 2D thin-layer structure with 6-9 atomic thickness, a high specific surface area of 30.1 m(2) g(-1), increased photocurrent responses and improved electron transport ability, which could give rise to enhancing the photocatalytic activity and stability. The graphene-analogue carbon nitride had a new features that could make it suitable as a sensor for Cu(2+) determination. So GA-C₃N₄ is a new but promising candidate for heavy metal ions (Cu(2+)) determination in water environment. The photocatalytic mechanism and photoelectrochemical selective sensing of Cu(2+) were also discussed.

Adsorption and photocatalytic splitting of water on graphitic carbon nitride: a combined first principles and semiempirical study

Water adsorption on graphitic carbon nitride is studied by means of first principles and semiempirical calculations. Using a thermodynamic model, the photocatalytic water oxidation reaction is found to be hindered by a very large overpotential.

Polycondensation of guanidine hydrochloride into a graphitic carbon nitride semiconductor with a large surface area as a visible light photocatalyst

g-C₃N₄ prepared from guanidine hydrochloride exhibited a large surface area and a reduced recombination rate of electrons and holes, leading to improved photocatalytic activity for degrading RhB under visible light.

Nanosheets of graphitic carbon nitride as metal-free environmental photocatalysts

Nanosheets of g-C₃N₄ with a surface area of 109.9 m² g⁻¹ exhibit better optical properties and enhanced photocatalytic activity.

Hybrid photocatalysts using graphitic carbon nitride/cadmium sulfide/reduced graphene oxide (g-C3N4/CdS/RGO) for superior photodegradation of organic pollutants under UV and visible light

Schematic of the electron transport from g-C₃N₄ to the CdS nanoparticles and RGO sheets during RhB photodegradation.

A simple and efficient method to prepare a phosphorus modified g-C3N4 visible light photocatalyst

Interstitial P doping is more effective in improving the photocatalytic activity compared with substitutional P doping.

Facile synthesis of organic–inorganic layered nanojunctions of g-C3N4/(BiO)2CO3 as efficient visible light photocatalyst

2D g-C₃N₄/(BiO)₂CO₃ organic–inorganic nanojunctions were constructed by in situ depositing (BiO)₂CO₃ nanoflakes on the surface of g-C₃N₄ nanosheets for highly active visible light photocatalysis.

Ultrathin graphitic carbon nitride nanosheets: a novel peroxidase mimetic, Fe doping-mediated catalytic performance enhancement and application to rapid, highly sensitive optical detection of glucose

In this article, we demonstrate for the first time that ultrathin graphitic carbon nitride nanosheets (g-C3N4) possess peroxidase activity. Fe doping of the nanosheets leads to peroxidase mimetics with greatly enhanced catalytic performance and the mechanism involved is proposed. We further demonstrate the novel use of such Fe-g-C3N4 as a cheap nanosensor for simple, rapid, highly selective and sensitive optical detection of glucose with a pretty low detection limit of 0.5 μM.

In situ construction of g-C3N4/g-C3N4 metal-free heterojunction for enhanced visible-light photocatalysis

The photocatalytic performance of the star photocatalyst g-C3N4 was restricted by the low efficiency because of the fast charge recombination. The present work developed a facile in situ method to construct g-C3N4/g-C3N4 metal-free isotype heterojunction with molecular composite precursors with the aim to greatly promote the charge separation. Considering the fact that g-C3N4 samples prepared from urea and thiourea separately have different band structure, the molecular composite precursors of urea and thiourea were treated simultaneously under the same thermal conditions, in situ creating a novel layered g-C3N4/g-C3N4 metal-free heterojunction (g-g CN heterojunction). This synthesis method is facile, economic, and environmentally benign using easily available earth-abundant green precursors. The confirmation of isotype g-g CN heterojunction was based on XRD, HRTEM, valence band XPS, ns-level PL, photocurrent, and EIS measurement. Upon visible-light irradiation, the photogenerated electrons transfer from g-C3N4 (thiourea) to g-C3N4 (urea) driven by the conduction band offset of 0.10 eV, whereas the photogenerated holes transfer from g-C3N4 (urea) to g-C3N4 (thiourea) driven by the valence band offset of 0.40 eV. The potential difference between the two g-C3N4 components in the heterojunction is the main driving force for efficient charge separation and transfer. For the removal of NO in air, the g-g CN heterojunction exhibited significantly enhanced visible light photocatalytic activity over g-C3N4 alone and physical mixture of g-C3N4 samples. The enhanced photocatalytic performance of g-g CN isotype heterojunction can be directly ascribed to efficient charge separation and transfer across the heterojunction interface as well as prolonged lifetime of charge carriers. This work demonstrated that rational design and construction of isotype heterojunction could open up a new avenue for the development of new efficient visible-light photocatalysts.

Preparation and enhanced visible-light photocatalytic activity of graphitic carbon nitride/bismuth niobate heterojunctions

A series of graphitic carbon nitride/bismuth niobate (g-C3N4/Bi5Nb3O15) heterojunctions with g-C3N4 doping level of 10-90 wt% were prepared by a facile milling-heat treatment method. The phase and chemical structures, surface compositions, electronic and optical properties as well as morphologies of the prepared g-C3N4/Bi5Nb3O15 were well-characterized. Subsequently, the photocatalytic activity and stability of g-C3N4/Bi5Nb3O15 were evaluated by the degradation of aqueous methyl orange (MO) and 4-chlorophenol (4-CP) under the visible-light irradiation. At suitable g-C3N4 doping levels, g-C3N4/Bi5Nb3O15 exhibited enhanced visible-light photocatalytic activity compared with pure g-C3N4 or Bi5Nb3O15. This excellent photocatalytic activity was revealed in terms of the extension of visible-light response and efficient separation and transportation of the photogenerated electrons and holes due to coupling of g-C3N4 and Bi5Nb3O15. Additionally, the active species yielded in the pure g-C3N4- and g-C3N4/Bi5Nb3O15-catalyzed 4-CP photodegradation systems were investigated by the free radical and hole scavenging experiments.

Ultrathin graphitic carbon nitride nanosheets: a low-cost, green, and highly efficient electrocatalyst toward the reduction of hydrogen peroxide and its glucose biosensing application

In this communication, we demonstrate for the first time that ultrathin graphitic carbon nitride (g-C₃N₄) nanosheets can serve as a low-cost, green, and highly efficient electrocatalyst toward the reduction of hydrogen peroxide. We further demonstrate its application for electrochemical glucose biosensing in both buffer solution and human serum medium with a detection limit of 11 μM and 45 μM, respectively.

Preparation of graphitic carbon nitride (g-C₃N₄)/WO₃ composites and enhanced visible-light-driven photodegradation of acetaldehyde gas

Novel visible-light-driven graphitic carbon nitride (g-C₃N₄)/WO₃ composite photocatalysts were prepared, and the acetaldehyde (CH₃CHO) degradation activity of these composites was evaluated. The prepared g-C₃N₄/WO₃ composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible diffuse reflection spectroscopy (UV-vis), and the N₂ gas adsorption Brunauer-Emmett-Teller (BET) method (N₃-BET). The WO₃ particles, which were 100-300 nm in size, were in direct contact with the g-C₃N₄ sheet surface. The optical band gap and specific surface area of the g-C₃N₄/WO₃ composites were in the range of 2.65-2.75 eV and 4-7 m(2)/g, respectively. The g-C₃N₄/WO₃ composites exhibited higher activity for the photodegradation of CH₃CHO under visible light irradiation compared to g-C₃N₄. The optimal WO₃ content for the CH₃CHO photodegradation activity of the heterojunction structures was determined. The synergistic effect of g-C₃N₄ and WO₃ was considered to lead to improved photogenerated carrier separation. A possible degradation mechanism of CH₃CHO over the g-C₃N₄/WO₃ composite photocatalyst under visible light irradiation was proposed. These results should usefully expand applications of g-C₃N₄ as a visible-light-driven photocatalyst.

Au-nanoparticle-loaded graphitic carbon nitride nanosheets: green photocatalytic synthesis and application toward the degradation of organic pollutants

Au nanoparticles (AuNPs) were loaded on graphitic carbon nitride (g-C3N4) nanosheets prepared by ultrasonication-assisted liquid exfoliation of bulk g-C3N4 via green photoreduction of Au(III) under visible light irradiation using g-C3N4 as an effective photocatalyst. The nanohybrids show superior photocatalytic activities for the decomposition of methyl orange under visible-light irradiation to bulk g-C3N4, g-C3N4 nanosheets, and AuNP/bulk g-C3N4 hybrids.

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

Since the beginning of the century, N-hydroxyphthalimide and related compounds have been revealed to be efficient organocatalysts for free-radical processes and have found ample application in promoting the aerobic oxidation of a wide range of organic substrates. When combined with different co-catalysts, they are activated to the corresponding N-oxyl radical species and become able to promote radical chains, involving molecular oxygen, directly or indirectly. Most of the examples reported in the literature describe the use of these N-hydroxy derivatives in the presence of transition-metal complexes. However, eco-friendly standards, including the demand for highly selective transformations, impose the development of metal-free processes, especially for large-scale productions, as in the case of the oxygenation of hydrocarbons. For this reason, many efforts have been devoted in the past decade to the design of new protocols for the activation of N-hydroxy imides in the presence of nonmetal initiators. Herein we provide a concise overview of the most significant and successful examples in this field, with the final aim to furnish a useful instrument for all scientists actively involved in the O₂-mediated selective oxidation of organic compounds and looking for environmentally safe alternatives to metal catalysis.

Ultrathin graphitic carbon nitride nanosheet: a highly efficient fluorosensor for rapid, ultrasensitive detection of Cu(2+)

A highly efficient fluorosensor based on ultrathin graphitic carbon nitride (g-C₃N₄) nanosheets for Cu(2+) was developed. In the absence of metal ions, the nanosheets exhibit high fluorescence; the strong coordination of the Lewis basic sites on them to metal ions, however, causes fluorescence quenching via photoinduced electron transfer leading to the qualitative and semiquantitative detection of metal ions. This fluorosensor exhibits high selectivity toward Cu(2+). The whole detection process can be completed within 10 min with a detection limit as low as 0.5 nM. The use of test paper enables the naked-eye detection of Cu(2+) with a detection limit of 0.1 nmol. The practical use of this sensor for Cu(2+) determination in real water samples was also demonstrated.

Graphene supported Co-g-C3N4 as a novel metal-macrocyclic electrocatalyst for the oxygen reduction reaction in fuel cells

Graphitic carbon nitride (g-C3N4) polymer was doped with cobalt species and supported on a similar sp(2) structure graphene, to form a novel nitrogen-metal macrocyclic catalyst for the oxygen reduction reaction (ORR) in alkaline fuel cells. The structural characterizations confirmed the formation of Co-N bonds and the close electron coupling between Co-g-C3N4 and graphene sheets. The electrocatalytic measurements demonstrated Co-g-C3N4-catalyzed reduction of oxygen mainly in a four electron pathway. The improvement of ORR activity is closely related to the abundant accessible Co-Nx active sites and fast charge transfer at the interfaces of Co-g-C3N4/graphene. Also, Co-g-C3N4@graphene exhibited comparable ORR activity, better durability, and methanol tolerance ability in comparison to Pt/C, and bodes well for a promising non-noble cathode catalyst for the application of direct methanol fuel cells. The chemical doping strategy in this work would be helpful to improve other present catalysts for fuel cell applications.

Patterning Graphitic C-N Sheets into a Kagome Lattice for Magnetic Materials

We propose porous C-N-based structures for biocompatible magnetic materials that do not contain even a single metal ion. Using first-principles calculations based on density functional theory, we show that when patterned in the form of a kagome lattice, nonmagnetic g-C3N4 not only becomes ferromagnetic but also its magnetic properties can be further enhanced by applying external strain. Similarly, the magnetic moment per atom in ferromagnetic g-C4N3 is increased three fold when patterned into a kagome lattice. The Curie temperature of g-C3N4 kagome lattice is 100 K, while that of g-C4N3 kagome lattice is much higher, namely, 520 K. To date, all of the synthesized two- and three-dimensional magnetic kagome structures contain metal ions and are toxic. The objective of our work is to stimulate an experimental effort to develop nanopatterning techniques for the synthesis of g-C3N4- and g-C4N3-based kagome lattices.