g-C3N4 Films Research Articles

Fabrication and high visible-light-driven photocurrent response of g-C3N4 film: The role of thiourea

We report on a convenient CVD fabrication of the uniform, compact and reproducible g-C3N4 solid films on indium-tin oxide substrates. It is found that mixing quantitative thiourea into melamine as co-precursor prompts the deposition of greenish-yellow, transparent and smooth g-C3N4 thin films. The thiourea apparently affects the crystalline, the surface morphologies and the energy band structures of g-C3N4 films by modulating the polymerization process of the precursors, and simultaneously introduces S dopants into the g-C3N4 films. Due to these roles of thiourea, the obtained S-doped g-C3N4 films as a photoelectrode show a high and stable visible-light-driven photocurrent response. To further improve the photocurrent, the construction of three heterojunction structure types based on g-C3N4 films is proposed and the corresponding charge transfer mechanisms are well discussed. The successful fabrication of high quality g-C3N4 films in this work provides a footstone to construct the heterojunction film structures based on the carbon nitrides for the photoelectrochemical overall water splitting.

Fabrication and Enhanced Photoelectrochemical Performance of MoS₂/S-Doped g-C₃N₄ Heterojunction Film.

We report on a novel MoS2/S-doped g-C3N4 heterojunction film with high visible-light photoelectrochemical (PEC) performance. The heterojunction films are prepared by CVD growth of S-doped g-C3N4 film on indium-tin oxide (ITO) glass substrates, with subsequent deposition of a low bandgap, 1.69 eV, visible-light response MoS2 layer by hydrothermal synthesis. Adding thiourea into melamine as the coprecursor not only facilitates the growth of g-C3N4 films but also introduces S dopants into the films, which significantly improves the PEC performance. The fabricated MoS2/S-doped g-C3N4 heterojunction film offers an enhanced anodic photocurrent of as high as ∼1.2 × 10(-4) A/cm(2) at an applied potential of +0.5 V vs Ag/AgCl under the visible light irradiation. The enhanced PEC performance of MoS2/S-doped g-C3N4 film is believed due to the improved light absorption and the efficient charge separation of the photogenerated charge at the MoS2/S-doped g-C3N4 interface. The convenient preparation of carbon nitride based heterojunction films in this work can be widely used to design new heterojunction photoelectrodes or photocatalysts with high performance for H2 evolution.

Optical properties of graphitic carbon nitride films prepared by evaporation

Graphitic carbon nitride (g-C3N4) consists of two-dimensional sheets of carbon and nitrogen atoms. Films of g-C3N4 were prepared by evaporating guanidine carbonate at four different substrate temperatures. The optical absorption band of the films appears at 3.3eV and the optical energy gaps are calculated to be 2.83–2.90eV. Band intensity increases with increasing substrate temperature, but the energetic band position does not shift. The photocurrent of g-C3N4 films can be observed by irradiation with monochromatic light. While the photosensitivity spectra are in almost complete correspondence with the optical absorption spectra, it is also found that the photocurrent is generated by irradiation at photon energies below the optical energy gap down to 2.5eV.

Electropolymerization as a new route to g-C3N4 coatings on TiO2 nanotubes for solar applications

A simple procedure comprising of electropolymerization followed by heat treatment allows conductive 3D structures, such TiO2 nanotubes, to be coated with thin and uniformly distributed g-C3N4 films.

Mechanical properties and thermal conductivity of graphitic carbon nitride: A molecular dynamics study

Graphitic carbon nitride (g-C3N4) nanosheets are among 2D attractive materials due to presenting unusual physicochemical properties. Nevertheless, no adequate information exists about their mechanical and thermal properties. Therefore, we used classical molecular dynamics simulations to explore the thermal conductivity and mechanical response of two main structures of single-layer triazine-based g-C3N4 films. By performing uniaxial tensile modeling, we found remarkable elastic modulus of 320 and 210GPa for two different structures of g-C3N4 sheets. Using equilibrium molecular dynamics simulations, the thermal conductivity of free-standing g-C3N4 structures were also predicted to be around 7.6W/mK and 3.5W/mK. Our study suggests the g-C3N4 films as exciting candidate for reinforcement of polymeric materials mechanical properties.

Synthesis of graphene supported graphene-like C3N4 metal-free layered nanosheets for enhanced electrochemical performance and their biosensing for biomolecules

A new strategy for the assembly of graphene-like C3N4 on graphene is reported. Transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) clearly demonstrated that g-C3N4 was successful in the reduction of GO and the immobilization of g-C3N4 on the graphene surface. Investigation of their electrochemical behaviour for several redox systems was conducted, which indicated the unique electron structure endows the G–g-C3N4 with faster transfer and proper amount of g-C3N4 could make G–g-C3N4 advantageous in terms of improving the redox current and promoting electron transfer. Finally, several electroactive biomolecules, such as uric acid (UA), norepinephrine (NE), tyrosine (Tyr), tryptophan (Trp), acetaminophen (APAP) and rutin, were used to probe the biosensing capacity of G–g-C3N4 films by using the cyclic voltammetric method.

Solar hydrogen evolution using metal-free photocatalytic polymeric carbon nitride/CuInS2 composites as photocathodes

Polymeric carbon nitride (g-C3N4) films were synthesized on polycrystalline semiconductor CuInS2 chalcopyrite thin film electrodes by thermal polycondensation and were investigated as photocathodes for the hydrogen evolution reaction (HER) under photoelectrochemical conditions. The composite photocathode materials were compared to g-C3N4 powders and were characterized with grazing incidence X-ray diffraction and X-ray photoemission spectroscopy as well as Fourier transform infrared and Raman spectroscopies. Surface modification of polycrystalline CuInS2 semiconducting thin films with photocatalytically active g-C3N4 films revealed structural and chemical properties corresponding to the properties of g-C3N4 powders. The g-C3N4/CuInS2 composite photocathode material generates a cathodic photocurrent at potentials up to +0.36 V vs. RHE in 0.1 M H2SO4 aqueous solution (pH 1), which corresponds to a +0.15 V higher onset potential of cathodic photocurrent than the unmodified CuInS2 semiconducting thin film photocathodes. The cathodic photocurrent for the modified composite photocathode materials was reduced by almost 60% at the hydrogen redox potential. However, the photocurrent generated from the g-C3N4/CuInS2 composite electrode was stable for 22 h. Therefore, the presence of the polymeric g-C3N4 films composed of a network of nanoporous crystallites strongly protects the CuInS2 semiconducting substrate from degradation and photocorrosion under acidic conditions. Conversion of visible light to hydrogen by photoelectrochemical water splitting can thus be successfully achieved by g-C3N4 films synthesized on polycrystalline CuInS2 chalcopyrite electrodes.

Metal‐Free Photocatalytic Graphitic Carbon Nitride on p‐Type Chalcopyrite as a Composite Photocathode for Light‐Induced Hydrogen Evolution

Recently, it has been shown that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. We present herein the preparation and characterization of graphitic carbon nitride (g-C(3)N(4)) films on p-type semiconducting CuGaSe(2) chalcopyrite thin-film substrates by thermal condensation of a dicyandiamide precursor under inert-gas conditions. Structural and surface morphological studies of the carbon nitride films suggest a high porosity of g-C(3)N(4) thin films consisting of a network of nanocrystallites. Photoelectrochemical investigations show light-induced hydrogen evolution upon cathodic polarization for a wide range of proton concentrations in the aqueous electrolyte. Additionally, synchrotron radiation-based photoelectron spectroscopy has been applied to study the surface/near-surface chemical composition of the utilized g-C(3)N(4) film photocathodes. For the first time, it has been shown that g-C(3)N(4) films coated on p-type CuGaSe(2) thin films can be successfully applied as new photoelectrochemical composite photocathodes for light-induced hydrogen evolution.