Two-dimensional Graphitic Carbon Nitride Nanosheets Research Articles

Pyrolysis-assisted synthesis of two-dimensional graphitic carbon nitride nanosheets embedded with transition metal oxide (Ni or Fe) for high-performance asymmetric supercapacitors

This study employed a one-step pyrolysis-assisted technique to successfully synthesized with two different transition metal oxides (M = Ni, Fe) embedded on graphitic carbon nitride nanosheets (g-C3N4-NS). The resulting nanocomposites exhibit exceptional electrochemical performance in supercapacitor applications due to various parameters such as morphology, specific surface area and crystallinity. Notably, the NiO/g-C3N4-NS and Fe2O3/g-C3N4-NS electrodes simplify the Faradaic reactions and achieve the maximum capacitance of 816 F g−1 and 703 F g−1 at 0.5 A g−1, respectively. Additionally, these electrodes demonstrate superior cycling stability, retaining approximately 96 % of their capacity retention after 5000 cycles. Furthermore, the NiO/g-C3N4-NS//AC and Fe2O3/g-C3N4-NS//AC devices exhibit promising supercapacitor device performance, yielding respectable specific capacity of 53 F g−1 (NiO/g-C3N4-NS//AC) and 43.5 F g−1 (Fe2O3/g-C3N4-NS//AC) at 0.5 A g−1, underscoring the commendable rate capability of the asymmetric electrodes and the energy densities of 19 Wh kg−1 and 16 Wh kg−1 at a power density of 400 W kg−1, respectively. These findings underscore the potential of metal oxide/g-C3N4-NS composites as an electrode material for power storing applications, as demonstrated by these asymmetric supercapacitor devices.

Laser-Shock-Driven In Situ Evolution of Atomic Defect and Piezoelectricity in Graphitic Carbon Nitride for the Ionization in Mass Spectrometry.

Nanostructures─coupled with mass spectrometry─have been intensively investigated to improve the detection sensitivity and reproducibility of small biomolecules in laser desorption/ionization mass spectrometry (LDI-MS). However, the impact of laser-induced shock wave on the ionization of the nanostructures has rarely been reported. Herein, we systematically elucidate the laser shock wave effect on the ionization in terms of the in situ development of atomic defects and piezoelectricity in two-dimensional graphitic carbon nitride nanosheets (g-C3N4 NS) by short laser pulses. The mass analysis results of immunosuppressive drugs verify the enhanced LDI-MS performance, structurally originating from anisotropic lattice distortions in g-C3N4 NS, i.e., in-plane extension (contraction) and out-of-plane contraction (extension) that modulate the charge carrier motion. Along with the experimental investigations, density functional theory calculations on Mulliken charges and dipole moments demonstrate the contribution of defect and piezoelectricity to the ionization. The results of this study provide a mechanistic understanding of the underlying ionization processes, which is crucial for revealing the full potential of laser shock waves in LDI-MS.

Photocatalytic elimination of moxifloxacin by two-dimensional graphitic carbon nitride nanosheets: Enhanced activity, degradation mechanism and potential practical application

Residuals of antibacterial drugs (ADs) threaten human health and ecological equilibrium, whereas few efficient treatments have been developed. Using a photocatalyst of two-dimensional (2D) g-C3N4 nanosheets (CNNS) fabricated by the method of ammonium chloride assisted chemical blowing, a high-efficiency photocatalytic treatment was reported to eliminate moxifloxacin (MOX) as a fourth-generation quinolone. The characterization results indicated that the high activity of CNNS originated from its 2D morphology, large specific surface area and high separation efficiency of photogenerated charges. Furthermore, the photocatalyst dosage, MOX concentration and the pH of solution were optimized. Based on the detection of reactive oxygen species (ROS) and intermediates in the photocatalytic process, the plausible photocatalytic mechanism and the degradation pathways of MOX were proposed. The toxicity assessment implied that antimicrobial activity of the photocatalytic degradation products were weakened significantly. The synthetic CNNS demonstrated excellent stability and reusability during five cycles. Finally, we carried out photocatalytic degradation experiments in the simulated real scenarios of tap water, lake water and sunlight. This work suggested the CNNS had great potential for purifying ADs-containing wastewater.

Promoted charge separation and specific surface area via interlacing of N-doped titanium dioxide nanotubes on carbon nitride nanosheets for photocatalytic degradation of Rhodamine B

Abstract Titanium dioxide (TiO2) has been regarded as a promising catalyst owing to its superior charge transport properties in photocatalytic degradation of organic pollutants and photocatalytic hydrogen generation. However, a major bottleneck toward the utilization of TiO2 photocatalysts is inefficient exploitation of visible light and low adsorption behavior. To address this issue, we fabricated a hybrid nanocomposite composed of one-dimensional N-doped TiO2 nanotubes (N-TNTs) and two-dimensional graphitic carbon nitride nanosheets (g-CNNs) to improve photocatalytic behavior. Furthermore, photogenerated electron–hole pairs in the hybrid N-TNT/g-CNN composites were efficiently separated by introducing g-CNNs. In addition, the improved specific surface area provided many active sites, resulting in higher photocatalytic reactions in kinetics. Based on these features, the Rhodamine B photocatalytic degradation efficiency was the highest, ∼85%, under solar-light irradiation in the N-TNT/g-CNN composites (7 wt% of the g-CNN content), which is two times higher than that of the N-TNT. Moreover, excellent durability and stability were observed after four cycles, which can be attributed to the extended optical absorption range and enhanced separation of the photogenerated electron–hole pairs.

Photocatalytic Elimination of Moxifloxacin by Two-Dimensional Graphitic Carbon Nitride Nanosheets: Enhanced Activity, Degradation Mechanism and Potential Practical Application

Photocatalytic Elimination of Moxifloxacin by Two-Dimensional Graphitic Carbon Nitride Nanosheets: Enhanced Activity, Degradation Mechanism and Potential Practical Application

Synthesis of large area graphitic carbon nitride nanosheet by chemical vapor deposition

The polymerization of graphitic carbon nitride (g-C3N4) into large single crystals has been particularly challenging. This study presents a quick and simple method to grow high quality two-dimensional graphitic carbon nitride nanosheets with a large domain size (up to 40 µm) on copper (Cu) foils. The chemical vapor deposition (CVD) method was used with melamine (C₃H₆N₆) as the source. Electron backscatter diffraction (EBSD) revealed that graphitic carbon nitride prefers a Cu(111) surface to a Cu(211) surface, which is consistent with the theoretical calculations. Moreover, it was demonstrated that the carrier gas is critical for the growth of graphitic carbon nitride. The use of noble Ar gas is recommended because it has a weaker etching effect compared to that of the more commonly used hydrogen (H2) gas. Furthermore, CVD-grown high-quality graphitic carbon nitride films can be easily transferred onto other substrates for various applications, such as photodetectors or metal-free photocatalysts.

Synthesis of a novel ternary (g-C3N4 nanosheets loaded with Mo doped ZnOnanoparticles) nanocomposite for superior photocatalytic and antibacterial applications

This article reports the synthesis of a novel ternary Visible-Light-Driven (VLD) photocatalyst and antibacterial agent. The two-dimensional graphitic carbon nitride nanosheets (g-C3N4 NSs) and 7% molybdenum doped zinc oxide nanoparticles (Mo doped ZnO NPs) were used for the synthesis of the 65% g-C3N4 hybridized with 7% Mo doped ZnO novel ternary nanocomposite (Mo doped ZnO/g-C3N4 ternary NC). The synthesis process, as well as the structures, morphologies, photocatalytic and antibacterial properties of the synthesized ternary NC and constituents, were investigated by using several spectroscopic and microscopic techniques. It was revealed through the Transmission Electron Microscopy (TEM) characterization of the synthesized NC that the Mo doped ZnO NPs were found uniformly embedded upon the well-stacked g-C3N4NSs. It was further discovered by the bandgap analysis that the light absorbance ability of the ternary NC exists in the visible region of the light spectrum. The photocatalytic degradation of the methylene blue (MB) by the use of novel ternary NC in an aqueous medium was analyzed while using Ultra Violet-Visible (UV-Visible) spectroscopy. Trapping experiments of active species during the photodegradation and Electron Spin Resonance (ESR) experiment revealed that the superoxide and hydroxyl radicals were the leading species liable for MB deterioration. The ternary NC exhibited superior photocatalytic performance as compared with binary doped or hybridized nanomaterials (NMs) and mono photocatalysts due to the facility of effective migration and separation of the charge carriers across the (Mo doped ZnO NPs)/g-C3N4 NSs interface of the heterojunction. The increased generation of the reactive oxygen species (ROS), O2−, and •OH radicals the photogenerated charge carriers within the Mo doped ZnO/g-C3N4 NC were found responsible for its enhanced antibacterial performance.

Effect of a novel one-dimensional zinc tungsten oxide nanorods anchored two-dimensional graphitic carbon nitride nanosheets for improved solar-light-driven photocatalytic removal of toxic pollutants and photoelectrochemical water splitting

In this study, one-dimensional zinc tungsten oxide (ZnWO4) was prepared by a simple hydrothermal procedure, and two-dimensional graphitic carbon nitride (g-C3N4) was prepared by a solid-state reaction method. The g-C3N4/ZnWO4 (CZO) heterostructure was prepared by a hydrothermal approach. Further, TEM, HRTEM, XRD, DRS, and electrochemical investigations were used to describe the formation of CZO heterostructure. The photocatalytic performance of a CZO nanocomposite shows promising properties for the degradation of tetracycline (TC). Further, the CZO nanocomposite was also used for the photoelectrochemical (PEC) water oxidation. The morphology and structural analysis demonstrated the successful dispersion of ZnWO4 nanorods over the g-C3N4 nanosheets. The tuning of CZO nanocomposite bandgap confirms the establishment of heterostructure. From the photocatalytic investigations, the CZO nanocomposite degrades the antibiotic TC within 70 min under solar-light irradiation. The detailed PEC investigations notify the CZO nanocomposite has lesser charge-transfer resistance, high response of photocurrent with good stability. The CZO electrolyte shows improved photocurrent density of 0.162 mA/cm2 vs. Ag/AgCl in 0.1 M Na2SO3 electrolyte under solar-light illumination. The detailed mechanisms of photocatalytic degradation of TC and PEC water oxidation were discussed with possible graphical diagrams.

Two-dimensional graphitic carbon nitrides: Strain-tunable ferromagnetic ordering

Using first-principle calculations, we systematically study strain tuning of the electronic properties of two-dimensional graphitic carbon nitride nanosheets with empirical formula ${C}_{n}{N}_{m}$. We found the following: (i) the ferromagnetic ordered state in the metal-free systems $(n,m)=(4,3)$, (10,9), and (14,12) remains stable in the presence of strain of about $6%$. However, the system (9,7) loses its ferromagnetic ordering when increasing strain. This is due to the presence of topological defects in the (9,7) system, which eliminates the asymmetry between spin up and spin down of the ${p}_{z}$ orbitals when strain is applied. (ii) By applying uniaxial strain, a band gap opens in systems which are initially gapless. (iii) In semiconducting systems which have an initial gap of about 1 eV, the band gap is closed with applying uniaxial strain.

Two-dimensional graphitic carbon nitride nanosheets: a novel platform for flexible, robust and optically active triboelectric nanogenerators.

We report on the characteristics of mechanically flexible, stable and photoactive triboelectric nanogenerators based on two-dimensional graphitic carbon nitride (g-C3N4) nanosheets. The performance of nanogenerator devices has been studied with varying frictional surfaces (such as polypropylene, aluminium oxide, Teflon and polyethylene terephthalate). Energy band diagrams have been used to explain the mechanism of triboelectric charge transfer in pristine and doped g-C3N4, with the former showing better characteristics. An optimized device has been found to be responsive to external stimuli to generate an output voltage of 10 V upon simple biomechanical impulses. To demonstrate the efficacy for practical applications of g-C3N4-based triboelectric nanogenerators, output voltages have been recorded for different common activities like walking, water showering, using as a writing/drawing pad, etc. Repetitive finger tapping on a device could charge a capacitor to as high as 55 V within ∼50 s, while that under UV illumination is found to be much faster (∼14 s) due to photoinduced carrier generations in g-C3N4. The exhibition of a superior photoresponsivity of ∼117 V W-1 under UV illumination demonstrates the dual functionality of g-C3N4-based triboelectric devices as a nanogenerator as well as an active flexible photosensor, which is hitherto unreported. Excellent mechanical flexibility, stability and photoinduced enhancement of output characteristics make g-C3N4 an attractive candidate for nanogenerator devices for future applications.

Defects Promote Ultrafast Charge Separation in Graphitic Carbon Nitride for Enhanced Visible-Light-Driven CO2 Reduction Activity.

Fundamental photocatalytic limitations of solar CO2 reduction remain due to low efficiency, serious charge recombination, and short lifetime of catalysts. Herein, two-dimensional graphitic carbon nitride nanosheets with nitrogen vacancies (g-C3 Nx ) located at both three-coordinate N atoms and uncondensed terminal NHx species were prepared by one-step tartaric acid-assistant thermal polymerization of dicyandiamide. Transient absorption spectra revealed that the defects in g-C3 N4 act as trapped states of charges to result in prolonged lifetimes of photoexcited charge carriers. Time-resolved photoluminescence spectroscopy revealed that the faster decay of charges is due to the decreased interlayer stacking distance in g-C3 Nx in favor of hopping transition and mobility of charge carriers to the surface of the material. Owing to the synergic virtues of strong visible-light absorption, large surface area, and efficient charge separation, the g-C3 Nx nanosheets with negligible loss after 15 h of photocatalysis exhibited a CO evolution rate of 56.9 μmol g-1 h-1 under visible-light irradiation, which is roughly eight times higher than that of pristine g-C3 N4 . This work presents the role of defects in modulating light absorption and charge separation, which opens an avenue to robust solar-energy conversion performance.

Research Progress in Preparation and Photocatalysis of Two-Dimensional Graphitic Carbon Nitride Nanosheets

Research Progress in Preparation and Photocatalysis of Two-Dimensional Graphitic Carbon Nitride Nanosheets

Amphiphilic two-dimensional graphitic carbon nitride nanosheets for visible-light-driven phase-boundary photocatalysis

Amphiphilic two-dimensional graphitic carbon nitride nanosheets exhibit improved performance for visible-light-driven phase-boundary photocatalytic reduction of nitrobenzene to aniline.

Preparation of protonated, two-dimensional graphitic carbon nitride nanosheets by exfoliation, and their application as a fluorescent probe for trace analysis of copper(II)

Bulk graphitic carbon nitride (g-C3N4) was obtained by pyrolysis of urea at 600 °C. The material was then subjected to protonation and exfoliation to obtain strongly fluorescent g-C3N4 nanosheets. These nanosheets are representing a two-dimensional layered material that emits strong blue fluorescence peaking at 434 nm, and their quantum yield of up to 10.3 % is much higher than that of bulk g-C3N4 (6.0 %). It was found that Cu(II) ions quench the fluorescence of the nanosheets due to photo-induced electron transfer (PET), probably the result of the stronger binding affinity between Cu(II) and the nitrogen and oxygen functional groups of the nanosheets. The probe responds to Cu(II) in the 0.01 to 0.4 nM concentration range, with a 8 pM detection limit. The method was applied to the determination of Cu(II) in spiked water samples.