g-C3N4 Film Research Articles

Bandgap modulations and promoted carrier separation in crystalline g-C3N4 thin films via chemical vapor deposition

The preparation of high-quality graphite-like phase carbon nitride (g-C3N4) films is challenging, which limits the potential optoelectronic and photocatalytic applications. Here, we report the growth of crystalline g-C3N4 films with thicknesses of approximately 100–200 nm on the indium tin oxide substrates by chemical vapor deposition. The films show high crystalline quality and uniformity as suggested by the appearance of interference fringes in the transmission spectra and the existence of exciton peak. The optimized growth conditions for high-quality g-C3N4 films deposition have been obtained through combined optical characterizations and detailed electronic structure analyses using x-ray spectroscopies. The as-grown g-C3N4 films exhibit a bandgap value of 3.05 eV as well as an enhanced fluorescence lifetime of ∼12.43 ns. By adding thiourea to the melamine precursors, N vacancies have been formed in the main heptazine structure, achieving the modulation of the bandgap and the promoted carrier separation. This work provides guidelines for understanding the property–structure relationships during g-C3N4 film deposition. The deposition of high crystallinity g-C3N4 films therein further extends the applications in the fields of optoelectronic and photocatalytic devices.

Fabrication of g-C3N4 films with enhanced mechanical and charge transfer properties by electrophoretic deposition and subsequent citric acid modification

A low-cost 2D metal-free material based on a graphitic carbon nitride (g-C3N4) film functionalized with a citric acid molecule has been successfully fabricated by Electrophoretic Deposition (EPD) and thermal techniques, aiming to evaluate its suitability for optoelectronic devices. The thickness-controlled g-C3N4 film having a good mechanical property was successfully performed. The chemical stability and photostability of the citric-modified g-C3N4 films deposited on indium tin oxide (ITO) glass were investigated. New chemical links were clarified such that it could possibly become a bridge for enhancing charge transport. The modified samples exhibited a significant increase in their photocurrent response, reaching 25 μA/cm2 at a thickness of about 20 μm. Electrochemical impedance spectra (EIS) verified the enhanced conductivity, efficient charge transfer, and reduced electron-hole recombination rate. This research revealed a facile synthetic route and environmentally benign materials, thereby suggesting promising prospects for their application in the optoelectronic field.

Oxidized Graphitic-C3N4 with an Extended π-System for Enhanced Photoelectrochemical Property and Behavior

In this work, an oxidized g-C3N4 film was successfully synthesized using a two-step acid treatment and electrophoretic deposition method. The delocalized π-system of the oxidized g-C3N4 film was extended via an annealing treatment. We investigated the influence of hydrogen bonding reversibility and the oxidation treatment of g-C3N4 on the photoelectrochemical property and photocathodic protection for 304 stainless steel (304 SS). The resulting oxidized g-C3N4 photoelectrode with an extended π-system presents a remarkably enhanced photogenerated electron transfer capability from the photoelectrode to 304 SS (photoinduced OCP negative shift of −0.55 VAgCl) compared with oxidized g-C3N4 and protonated g-C3N4. The oxidation of g-C3N4 facilitates the formation of a porous structure and the introduction of abundant oxygen functional groups, which could promote the effective separation and transport of photogenerated electron–hole pairs. The hydrogen bonding reversibility contributes to the extension of the delocalized π-conjugation system, which could enhance light absorption efficiency. Meanwhile, the annealing treatment is beneficial for prolonging the lifetime of photoelectrons, which could reduce the recombination rate of charge carriers. In addition, to understand how the oxidation treatment and annealing treatment affect the charge transfer behavior, the electronic band structure was investigated, and we found that the oxidized g-C3N4 film with an extended π-system possesses a more negative conduction band position, which could reduce the energy barrier of the photogenerated electron transfer.

Hydrogen production on g-C3N4 nanoflakes via photoelectrochemical water splitting

Graphitic carbon nitride (g-C3N4) is an emerging non oxide wide band gap semiconductor which has been investigated for hydrogen production through photoelectrochemical (PEC) water splitting. In this study, g-C3N4 nanoflakes film was fabricated by the thermal pyrolysis process and its PEC water splitting performance was investigated. The nanoflakes morphology and graphitic phase of C3N4 with an average crystallite size of 8.49 nm were confirmed with FESEM and XRD analysis respectively. A UV–visible spectrophotometer was used to estimate the band gap of the fabricated photoanode film (2.7 eV). Furthermore, the fabricated g-C3N4 film has shown a significant photocurrent density of 0.87 µA/cm2 under UV light illumination.

Interfacial self-assembled dual-functional nanocomposite films for SERS monitoring of visible-light photocatalytic degradation of organic dye pollutants

Photocatalytic degradation by visible-light responsive photocatalysts is an efficient strategy to treat organic dye pollutants and monitoring of the photocatalytic reaction mechanisms and kinetics is important to the design of high-performance photocatalysts. Herein, a dual-functional graphitic carbon nitride/gold nanoparticles (g-C3N4/AuNPs) nanocomposite film is introduced to monitor the photocatalytic reactions by surface-enhanced Raman scattering (SERS) while degrading organic dyes photocatalytically. The nanocomposite film fabricated by two-step interfacial self-assembly consists of orderly arranged g-C3N4 film anchored on a closely packed AuNPs monolayer film. The nanoplatform has excellent SERS characteristics such as a rhodamine 6G (R6G) detection limit of 8.8 × 10−10 M, and good SERS detection uniformity with a relative standard deviation (RSD) of 9.62%, which is crucial to quantitative determination and accurate monitoring of the photocatalytic reactions. The nanoplatform is employed in visible-light photocatalytic degradation of organic dyes including R6G, methylene blue, acid orange II, and acid orange 74. The reactions follow the pseudo-first-order kinetics as revealed by SERS and the photocatalytic degradation mechanism is postulated to be the promoted charge separation. The results reveal a high-performance dual-functional nanoplatform suitable for visible-light photocatalytic degradation of organic dye pollutants and SERS monitoring of the reactions.

Preparation of C3N4 Thin Films for Photo-/Electrocatalytic CO2 Reduction to Produce Liquid Hydrocarbons

Thermal vapor condensation of melamine at various temperatures was used to fabricate thin graphitic carbon nitride (g-C3N4) films on fluorine-doped tin oxide (FTO) coated glass substrates. Photoanodic (n-type) and photocathodic (p-type) responses were observed simultaneously in the g-C3N4 films. The g-C3N4 film formed at 520 °C with the longest average lifetime of the photo-excited electrons shows the best cathodic photocurrent performance, which was then chosen for electrochemical and photoelectrochemical reduction of CO2. When the basic electrolyte (CO2-saturated 0.5 M KHCO3, pH = 7.6) was adopted, CO2 was electrochemically converted into formaldehyde ((54.6 μM/h)) in the liquid product. When the acidic electrolyte (CO2-saturated 0.5 M KCl, pH = 4.1) was adopted, formaldehyde (39.5 μM/h) and ethanol (15.7 μM/h) were generated through photoelectrochemical reduction, stimulated by the presence of sufficient protons from the electrolyte in the reduction process. Therefore, the pure g-C3N4 film has a great potential for CO2 reduction to value-added liquid hydrocarbons products via electrochemical or photoelectrochemical ways.

Developing high-quality g-C3N4 film electrode for the photoelectrocatalytic degradation of methylene blue in water

Developing a high-quality photoelectrode for photoelectrochemical applications is still an ongoing challenge. In this study, we prepared the g-C3N4 film on the indium tin oxide (ITO) glass through conventional coating, liquid-based growth, in-situ calcination, and vapor deposition methods, respectively. These electrodes were characterized and used as photoanodes to degrade methylene blue (MB) in water. Among these methods, the in-situ calcination method was most appropriate for preparing the continuous and organized g-C3N4 film electrodes with uniform g-C3N4 coverage and strong adhesion to the ITO substrate. It also had the highest activity in the photocatalytic (PC), electrochemical (EC), and photoelectrocatalytic (PEC) degradation processes of MB. In the PEC reaction, at an applied potential of 1.0 V and a light intensity of 0.96 W/cm2, the removal rate of MB was 62.5%, which was much higher than those in the PC and EC reactions. The high degradation rate was due to the synergistic effect of PEC degradation, wherein the PC and EC reactions promote and optimize each other. In the PC reaction, MB was degraded by −CH3 elimination, while the EC degradation pathway mainly included the conversion of sulfhydryl into sulfoxide and the opening of the central aromatic ring. Both methyl loss and aromatic ring opening occurred in the PEC reaction. Moreover, some monocyclic compounds were formed, and MB showed more complete degradation in the PEC reaction.

Controllable synthesis of Co nanoparticles with the assistance of cucurbit[6]uril and its efficient photoelectrochemical catalysis in water splitting on a g-C3N4 photoanode

An innovative photoanode was developed for efficient PEC water splitting by the deposition of a Co nano-catalyst on the surface of a g-C3N4 film, producing the significant photocurrent density of 393 μA cm−2 at 1.23 V vs. RHE.

Unveiling the Working Mechanism of g-C3N4 as a Protection Layer for Lithium- and Sodium-Metal Anode.

The practical application of lithium-/sodium-metal batteries is currently hindered by severe safety issues caused by uncontrolled continuous dendrite growth. Semiconductive nanoporous g-C3N4 film has been demonstrated to be an effective protection layer for lithium-/sodium-metal anode, which can suppress the growth of dendrite. However, the underlying mechanism of how this semiconductive flexible thin film works to suppress dendrite growth remains unclear. In this work, we investigate the detailed working mechanism of g-C3N4 protection layer employing both density functional theory calculations and ab initio molecular dynamics simulations. The calculation results indicate that g-C3N4 layers show strong adhesion toward the lithium-/sodium-metal surface. When contacting with lithium/sodium metal, the intrinsic triangular nanopores of g-C3N4 will be quickly filled with lithium/sodium atoms, turning the semiconductive g-C3N4 into a metallic material. Lithium/sodium atoms can migrate through the triangular nanopores of stacked g-C3N4 layers via a vacancy-mediated approach with moderate energy barriers of 0.42 and 0.61 eV, respectively. With a low current density, the newly deposited lithium/sodium atoms can permeate through the g-C3N4 protection layers, therefore resulting in a flat electrode surface with no dendrite; with a high current density, however, the newly deposited lithium/sodium atoms cannot transport across the protection layer timely, which will result in the aggregation of lithium/sodium atoms on the surface of the g-C3N4 protection layer.

Demonstration of electronic devices in graphitic carbon nitride crystalline film

Graphitic carbon nitride (g-C3N4) exhibits semiconducting properties and is a promising candidate for use as a metal-free functional material. Electronic transport in g-C3N4 depends on the crystal orientation, resulting in the anisotropic characteristics of low out-of-plane and high in-plane resistivity. We investigated a Schottky barrier diode (SBD) and a heterojunction diode (HJD) with out-of-plane transport properties and a top-gate device with in-plane transport properties. The SBD with a Cr/Au Schottky contact exhibited rectifying behavior with a turn-on voltage of ∼1.0 V and estimated series resistance and barrier height at the interface of 1.63 kΩ and 344 meV, respectively. The HJD comprises a g-C3N4 film and an n-type hexagonal silicon carbide (4H–SiC) substrate, with a turn-on voltage of 4.0 eV. The HJD belonged to a type-II band alignment with a staggered-gap; it had a thin insulator-based van der Waals gap at the interface, thereby inducing tunneling transport. In-plane carrier transport control was carried out by the top-gate device with a Parylene-C film gate dielectric and was achieved only when the negative bias voltage was applied along the out-of-plane direction, indicating the realization of the normally off switch that utilizes the intrinsic transport characteristics and a simple device structure.

Efficient photoelectrochemical overall water-splitting of MoS2/g-C3N4 n-n type heterojunction film.

The construction of heterojunctions has attracted considerable attention among the various strategies of water-splitting for hydrogen evolution due to their band structure advantages. In this research, we combined chemical vapor deposition and pulsed laser deposition to fabricate MoS2/g-C3N4 heterojunction films on indium-tin oxide glass substrates, and we studied the photoelectrochemical (PEC) performance. The x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and scanning electron microscope characterizations suggested the successful preparation of MoS2/g-C3N4 heterojunction films. In particular, the shifts of the peak positions in the XPS spectra indicated the formation of a strong interaction between the g-C3N4 and MoS2 films. After depositing MoS2 on the g-C3N4 film, the visible-light absorption was enhanced and broadened, the electrical conductivity improved, and the intensity of the photoluminescence peak decreased. As a result, the greater generation, faster transport, and lower recombination rate of electrons and holes caused the heterojunction films to show higher PEC performance. More importantly, the obtained MoS2/g-C3N4 film was confirmed to be an n-n type heterojunction and to have a typical type-II band structure, which could indeed suppress the recombination and promote the separation, transfer, and transport of photogenerated electron-holes. Finally, the obtained MoS2/g-C3N4 film successfully achieved the overall water-splitting and the H2 evolution rate when the visible-light radiation reached 252 µmol/h.

PES-Ag3PO4/g-C3N4 Mixed Matrix Film Photocatalyst for Degradation of Methyl Orange Dye.

In the present study, we explored the effectiveness of PES-Ag3PO4/g-C3N4 film photocatalyst in degrading methyl orange dye under visible light irradiation. The PES-Ag3PO4/g-C3N4 film photocatalyst was prepared via a non-solvent-induced phase inversion process and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser scanning microscopy (LSM), X-ray photoelectron spectra (XPS), UV-diffuse reflectance (DRS), and water contact angle. The incorporation of the Ag3PO4/g-C3N4 composite into the PES matrix improved the pristine PES film’s hydrophilicity, as evidenced by the reduction of water contact angle from 79.03° to 54.33° for a film containing 15 wt % of Ag3PO4/g-C3N4 composite. The film’s photoactivity showed that 13 wt % was the best loading of Ag3PO4/g-C3N4 composite, and the degradation performance was maintained up to three cycles. The •O2− and h+ were the predominant species responsible for the methyl orange degradation.

Visible-Light-Driven Photocatalytic Water Disinfection Toward Escherichia coli by Nanowired g-C3N4 Film

Graphitic carbon nitride (g-C3N4) as metal-free visible light photocatalyst has recently emerged as a promising candidate for water disinfection. Herein, a nanowire-rich superhydrophilic g-C3N4 film was prepared by a vapor-assisted confined deposition method. With a disinfection efficiency of over 99.99% in 4 h under visible light irradiation, this nanowire-rich g-C3N4 film was found to perform better than conventional g-C3N4 film. Control experiments showed that the disinfection performance of the g-C3N4 film reduced significantly after hydrophobic treatment. The potential disinfection mechanism was investigated through scavenger-quenching experiments, which indicate that H2O2 was the main active specie and played an important role in bacteria inactivation. Due to the metal-free composition and excellent performance, photocatalytic disinfection by nanowire-rich g-C3N4 film would be a promising and cost-effective way for safe drinking water production.

Graphitic Carbon Nitride Films: Emerging Paradigm for Versatile Applications.

Graphitic carbon nitride (g-C3N4) is a well-known two-dimensional conjugated polymer semiconductor that has been broadly applied in photocatalysis-related fields. However, further developments of g-C3N4, especially in device applications, have been constrained by the inherent limitations of its insoluble nature and particulate properties. Recent breakthroughs in fabrication methods of g-C3N4 films have led to innovative and inspiring applications in many fields. In this review, we first summarize the fabrication of continuous and thin films, either supported on substrates or as free-standing membranes. Then, the novel properties and application of g-C3N4 films are the focus of the current review. Finally, some underlying challenges and the future developments of g-C3N4 films are tentatively discussed. This review is expected to provide a comprehensive and timely summary of g-C3N4 film research to the wide audience in the field of conjugated polymer semiconductor-based materials.

Electronic transport and device application of crystalline graphitic carbon nitride film

The electronic transport characteristics of crystalline g-C3N4 film and its device application were investigated. Crystalline g-C3N4 films ordered along the c-axis were formed via thermal chemical vapor deposition using melamine source. The chemical bonds of the film were confirmed to be the bond states that constitutes g-C3N4. In addition, the stoichiometric N/C ratio was estimated as 1.17 from the C1s and N1s signal intensities of X-ray photoelectron spectroscopy. A typical photoluminescence and Raman spectra of the g-C3N4 film was detected. Anisotropic transport characteristics with a dependence on the crystal orientation were observed, resulting in a high out-of-plane conductivity and a low in-plane conductivity. A Schottky barrier diode with a Au anode and Ti/Au cathode was fabricated as a vertical electronic device. Rectifying behavior was achieved for the diode, suggesting possibilities of electronic device applications of g-C3N4.

Graphite-like C3N4-coated transparent superhydrophilic glass with controllable superwettability and high stability

In this study, transparent superhydrophilic glass is prepared by doping g-C3N4(g-C3N4-TSG) using a facile evaporation process. The obtained g-C3N4-TSG exhibited excellent superhydrophilicity, transmittance with high stability, wearability, and weatherability, and novel features including photocatalytic and antibacterial activity, anti-ultraviolet and adsorption properties, and electrical conductivity. This material is promising for use in diverse everyday scenarios. The high surface energy of 78.4 mN·m−1 and thinness (2 μm) of the deposited g-C3N4 film endow the glass with exceptional performance, but also cause rapid performance decay in high-dust environments due to adsorbate contamination. Lowering the surface energy and roughening the surface microstructure can effectively extend the service life of g-C3N4-TSG to more than 120 days. This multifunctional glass is a useful material and provides a novel strategy for preparing superhydrophilic surfaces.

Heterostructured thin LaFeO3/g-C3N4 films for efficient photoelectrochemical hydrogen evolution

The deposition of LaFeO3 at the surface of a graphitic carbon nitride (g-C3N4) film via magnetron sputtering followed by oxidation for photoelectrochemical (PEC) water splitting is reported. The LaFeO3/g-C3N4 film was investigated by various characterization techniques including SEM, XRD, Raman spectroscopy, XPS and photo-electrochemical measurements. Our results show that the hydrogen production rate of a g-C3N4 film covered by a LaFeO3 film, exhibiting both a thickness of ca. 50 nm, is of 10.8 μmol h−1 cm−2 under visible light irradiation. This value is ca. 70% higher than that measured for pure LaFeO3 and g-C3N4 films and confirms the effective separation of electron-hole pairs at the interface of LaFeO3/g-C3N4 films. Moreover, the LaFeO3/g-C3N4 films were demonstrated to be stable and retained a high activity (ca. 70%) after the third reuse.

High-sensitivity resistive humidity sensor based on graphitic carbon nitride nanosheets and its application

Currently, most humidity sensors have problems such as narrow measurement range, long response time and poor reversibility. In this work, we developed a resistive humidity sensor based on graphitic carbon nitride (g-C3N4) nanosheet film on epoxy substrate with Cu/Ni electrodes. The structure, morphology and composition properties of the g-C3N4 were analyzed by XRD, SEM, TEM, FTIR and XPS. The humidity sensing results show that the g-C3N4 film sensor has the advantages of high sensitivity (6457548.8 Ω/%RH), good reversibility and fast response/recovery time (0.3/8.5 s). The humidity sensing performance of g-C3N4 overpasses the other sensors based on graphene oxide (GO), ZnO, anodic aluminum oxide (AAO), SnO2, Bi6S2O15 and common composites. The g-C3N4 film sensor exhibits great application prospect in humidity alarm device, automatic diaper alarm and non-contact testing of cultural relics, which have advantages such as strong anti-interference capability, low cost and easy to use.

Excellent Photocatalytic Efficiency of t-ZrO2/g-C3N4 Photocatalyst for Pollutants Degradation: Experiment and theory

The large work function difference between two semiconductors will effectively adjust the interfacial electronic distribution and catalytic performances of heterojunction. In this work, a novel t-ZrO2/g-C3N4 composite photocatalyst was prepared by integrating t-ZrO2 nanoparticle with graphitic carbon nitride (g-C3N4) film considering the large work function of tetragonal ZrO2 (t-ZrO2). With the aid of experimental measurements and density functional theory calculations, the electronic distributions of g-C3N4 film were explicitly adjusted by the supporting t-ZrO2 nanoparticle on account of the large interfacial internal electric field, which leaded to the improvement of photogenerated carriers mobility and lifetime, the enhancement of reduction ability and the increase of oxidation active sites. Results showed that the photocatalytic activity of the composite sample was increased by 9.4 and 2.9 times compared with g-C3N4 sample for Rhodamine B and tetracycline hydrochloride degradation under visible-light. This modification strategy shall be applied to devise other high-efficient catalysts by selecting semiconductor with suitable work function.

Graphitic carbon nitride homojunction films for photocathodic protection of 316 stainless steel and Q235 carbon steel

Constructing homojunction of the same semiconductors is another new effective method to promote charge separation and thus to improve the photocathodic protection performance. In this work, we prepared graphic carbon nitride (g-C3N4) homojunction films on Indium tin oxide (ITO) substrate by simultaneously calcining mixture precursors containing melamine and thiourea of different proportions. Photocurrent density and open circuit potential (OCP) results indicate the photocathodic protection performance for 316 stainless steel (316 SS) and Q235 carbon steel in 3.5 wt% NaCl solution under 300 W Xe lamp enhanced with the combination of different g-C3N4 photoanode films, and g-C3N4 film with 40% thiourea/melamine weight ratio has the optimal photocathodic protection effect. The mechanism of enhancement may be result from the narrowed band gap and the small difference potentials between n-n homojunctions which promote the separation of photogenerated electron-holes, and improve the photon-to-electron conversion efficiency.