Two-dimensional g-C3N4 Research Articles

Molten salt-assisted synthesis of nitrogen-vacancy crystalline graphitic carbon nitride with tunable band structures for efficient photocatalytic overall water splitting

The photocatalytic overall water splitting performance of graphitic carbon nitride (g-C3N4) has still been restricted by its inefficient charge separation efficiency. Herein, nitrogen-vacancy crystalline g-C3N4 nanosheets (g-C3N4-D) with tunable band structures were successfully prepared by the alkali-molten salt-assisted method for efficient photocatalytic overall water splitting. Among them, g-C3N4-D2 not only combines the advantages of the amorphous and crystalline state of two-dimensional g-C3N4 nanosheets, but also introduces nitrogen vacancy to adjust the bandgap structures of crystalline g-C3N4 by an alkali etching, thus improving the light energy utilization and charge separation efficiency. TEM and EPR spectrum prove the existence of N defects in the crystalline g-C3N4. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 with Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a significant quantum efficiency of 11.94 % at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48 %. The photocatalytic water oxidation activity of Pt/g-C3N4-D2/5%Co3O4 NRs is 42.34 μmol g−1 h−1. Additionally, the potential mechanism of photocatalytic overall water splitting was testified by in-situ XPS. This work provides a simple strategy for further advancing the potential application of g-C3N4 by molten salt-assisted alkali etching to introduce N vacancies to regulate the band gap of crystalline g-C3N4 for photocatalytic overall water splitting.

Efficient photocatalytic H2 production and ofloxacin degradation based on heterodimensional Z-scheme P-C3N4/MIL-88A(Fe) heterojunctions

The production of effective photocatalyst to generate H2 and eliminate pollutants is still a challenge. A simple solvothermal approach is demonstrated for synthesizing a coupled P-C3N4/MIL-88A(Fe) composite wherein two-dimensional phosphorus-doped g-C3N4 nanosheets are attached to three-dimensional MIL-88A. The P-CN/MIL-88A composite shows superior photocatalytic ability with a high hydrogen generation rate of 34.53 mmol/(g·h) and an ofloxacin degradation rate of 95.6%. The H2 evolution rate of the composite is approximately 38.3 times that of bulk g-C3N4 (B-CN). The enhancement mechanisms resulting in high efficiency and adaptability are attributed to the Z-scheme (2D/3D) P-CN/MIL-88A heterojunction, which has unique synergistic interface properties, good photoinduced electron mobility, and good electron-hole pair separation ability. This work provides insights into the design of 2D/3D heterostructure photocatalysts for highly efficient and simultaneous photocatalytic H2 production and antibiotic degradation.

Constructing Z-scheme g-C3N4/TiO2 heterostructure for promoting degradation of the hazardous dye pollutants

The use of dyes and segments has increased widely in recent years, but it poses a serious health risk to ecosystems. In this work, TiO2 and two-dimensional g-C3N4 nanosheets (g-CN) were fabricated through co-precipitation and thermal polymerization technique, respectively. The g–CN–TiO2 photocatalyst (1: 3, 2: 2, 3: 1) in various weight percentages was prepared using a simple impregnation process. The photocatalytic behaviour of the g-CN, TiO2 NPs, and different weight percentages of g–CN–TiO2 photocatalyst was evaluated against methylene blue (MB) dye under UV–visible light illumination. Compared to pristine and other weight percentages of the g–CN–TiO2 nanocomposite, the optimized g–CN–TiO2 nanocomposite (3:1) showed promoted performance against MB dye. The enriched catalytic efficiency can be accredited to the low amount of TiO2 nanoparticles deposited on gCN nanosheets, possibly due to the boosted transport properties of the electron-hole pairs. The enriched photocatalytic behaviour can be attributed to the development of the Z-scheme system between TiO2 and g-CN. The current study is an outstanding demonstration of the development of maximum catalytic efficiency for destroying hazardous chemical dyes.

RETRACTED: Ionic liquid-assisted preparation of g-C3N4/RGO co-intercalated CuBi2O4 hierarchical nanoflower and enhancement of the photocatalytic activity

A new p-n type CBO/CN/RGO ternary heterojunction photocatalyst combining three-dimensional multi-stage rosette CuBi2O4 and two-dimensional g-C3N4 and RGO flakes was successfully prepared by ionic liquid-assisted hydrothermal method. The successful construction of p-n heterojunctions of CBO/CN/RGO composites was verified by means of UV–vis diffuse reflection, Mott Schottky curves and TEM, and construction the heterojunctions significantly improved that of the transfer and transport speed of photogenerated carriers. The photocatalytic degradation of MO by CBO/CN/RGO-6% reached 91.83% within 150 min, while the kinetic constants of degradation k were 9.7 and 7.9 times greater than those of single-phase CBO and g-C3N4, respectively. Three cycles of experiments demonstrated that the degradation efficiency of CBO/CN/RGO-6% composites remained above 88% for RhB, which fully proved that the CBO/CN/RGO-6% composites possessed good chemical stability. Based on its excellent photocatalytic performance and good stability, CBO/CN/RGO-6% is expected to be the preferred material for environmental wastewater treatment.

Snowball flower-like g-C3N4/ZnFe2O4 mesoporous hollow microspheres with enhanced triethylamine sensing properties

Herein, the snowball flower-like g-C3N4/ZnFe2O4 mesoporous hollow microspheres, in which two-dimensional (2D) g-C3N4 nanolayers were loaded onto the surface of ZnFe2O4 hollow microspheres, were constructed by a simple solid phase reaction. The effect of the g-C3N4 concentration on the structure, morphology and gas-sensing performance of the g-C3N4/ZnFe2O4 composites had been explored. On the basis of gas sensitivity test results, the composites owned lower working temperature (160 ℃) and better selectivity toward TEA in comparison with pure ZnFe2O4. Notably, the sensor based on the g-C3N4/ZnFe2O4-15 hollow microspheres (adding 15 ml of g-C3N4 aqueous solution) exhibited outstanding sensing properties, including superior response (18.3) toward 100 ppm TEA at optimum work temperature of 160 ℃, speedy response-recovery time (33, 30 s) and outstanding stability. And the sensor maintained high response of 4.3 to low concentration TEA (5 ppm). The improved gas-sensing performance of the composites could be attributed to the porous ZnFe2O4 hollow microspheres loaded by 2D g-C3N4 nanolayers with large specific surface area and the heterostructure formed between them. Hence, a potential application of the g-C3N4/ZnFe2O4 microspheres might be achieved in detecting TEA at a low optimum work temperature.

Energetic two-dimensional g-C3N4 nanosheets combined with ZnO nanoparticles as effectual catalyst for degradation of MB dye under UV–Visible-light irradiation

Energetic two-dimensional g-C3N4 nanosheets combined with ZnO nanoparticles as effectual catalyst for degradation of MB dye under UV–Visible-light irradiation

Review of 2D Graphitic Carbon Nitride-Based Membranes: Principles, Syntheses, and Applications

Membrane separation is a central area of research in chemical engineering because of its important status as the key technology in chemical separation and water treatment processes. Recently, polymeric graphitic carbon nitride (g-C3N4) has emerged as a candidate material for membrane applications because of its appealing physiochemical properties and ease of fabrication. Herein we review the progress of g-C3N4-based membranes, including the peculiarity of two-dimensional (2D) g-C3N4, the tailoring of functionality, and integration into membrane stacks for practical applications in gas separation, water purification, pervaporation, photocatalytic water filtration, oil-in-water separation, and polymer electrolyte membranes. Moreover, possible development directions of g-C3N4-based membranes are discussed along with the current challenges and future perspectives.

2D/2D Boron/g-C3N4 Nanosheet Heterojunction Boosts Photocatalytic Hydrogen Evolution Performance

Photocatalysis clean hydrogen production is a modern technology for simultaneously addressing and solving energy and environmental issues, of which the most critical part is to develop a highly efficient photocatalyst. In this work, we rationally designed and synthesized a metal-free 2D/2D boron/g-C3N4 nanosheet heterojunction (B-CN) through an electrostatic self-assembly thermal induction combined with ultrasound-assisted technology. The optimized photocatalyst 3.0B-CN possesses a hydrogen generation rate 35 times that of g-C3N4, which provided an impressive H2 evolution photocatalytic activity. The tight heterojunction architecture via the coupling of two-dimensional boron nanosheets and g-C3N4 nanosheets realizes the enhanced visible light absorption, the increasing carrier concentration, and the rapid transfer of interfacial charge and thus hinders the electron–hole recombination. The coupling of two 2D metal-free nanosheet materials for constructing a 2D/2D layered heterojunction in our work offers pioneering tactics for the design and synthesis of green nonmetal 2D photocatalytic HER materials in the future.

Brush-like gold nanowires-anchored g-C3N4 nanosheets with tunable geometry for ultrasensitive and regenerative SERS detection of gaseous molecules

Strapping plasmonic substrate with a reliable ability to anchor molecules and achieve reproducible result provides trustworthy opportunities for flourishing surface-enhanced Raman scattering (SERS) technique. Herein, a facile controllable in-situ anisotropic growth strategy was exploited to anchor gold nanowires (Au NWs) onto two-dimensional g-C3N4 nanosheets (g-C3N4/Au NWs), facilitating a sensitive and recyclable SERS sensor for gaseous analytes. Benefiting from the attractive enrichment effect of the brush-like surface formed by numerous small Au NWs as well as their rich nanotips-mediated enhancement capability, the hybrid substrate showed an outstanding performance in SERS-based detection of trace 4-Aminothiophenol (4-ATP) molecules, demonstrating a monitoring limitation down to 10−8 M even in atmosphere. Satisfyingly, under visible light illumination, the efficient green photocatalytic ability derived from the g-C3N4 supporting matrix rendered reusable capability for the substrate, whose SERS signal was kept at a persistent high level throughout 6 cycles. Attributed to the narrow line width of SERS spectrum, the 4-ATP assay under the interference of 2-naphthalenethiol (2-NAT) was acquired in gas phase and the dependable recovery rates from 85.4 to 93.9% were confirmed as well. Thanks to the intriguing features including excellent sensitivity and recyclability, the g-C3N4/Au NWs substrate proposed here will pave the way toward the potential application of SERS technique in multiplexed gaseous detection.

Au nanoparticles-modified S-scheme In2O3/H1.5CN heterojunction with enhanced photocatalytic CO2 reduction activity

The construction of S-scheme heterojunction is of great significance for the photocatalytic reduction of CO2. Here, we prepared two-dimensional (2D) ultra-thin g-C3N4 by acidifying the carbon nitride precursor, and used In2O3 to construct a S-scheme heterojunction with 2D g-C3N4, and finally In2O3/H1.5CN was modified with Au nanoparticles. The physicochemical properties of the prepared materials were studied by SEM/TEM, XPS, DRS, PL and photochemical test. Meantime, the S-scheme charge transfer mechanism was demonstrated by UPS and ESR. As a result, on the one hand, S-scheme heterojunction accelerated the transfer of electrons on the CB of In2O3 to the VB of g-C3N4, avoided the recombination of photon-generated carrier. On the other hand, Au, as an effective cocatalyst, promoted photoinduced electron transfer and provided more active sites for CO2 reduction and the local surface plasmon resonance phenomenon caused by Au NPs enhanced the visible light absorption capacity of the composite material. Moreover, 2D thin layer of g-C3N4 played a carrier effect to disperse In2O3 cube. Therefore, In2O3/H1.5CN/2Au had stable CO2 reduction products, and the yields of CO/CH4 reached 141.24/77.05 μmol/g.

Biowaste derived hydroxyapatite embedded on two-dimensional g-C3N4 nanosheets for degradation of hazardous dye and pharmacological drug via Z-scheme charge transfer

In recent years, there has been an increase in demand for inexpensive biowaste-derived photocatalysts for the degradation of hazardous dyes and pharmacological drugs. Here, we developed eggshell derived hydroxyapatite nanoparticles entrenched on two-dimensional g-C3N4 nanosheets. The structural, morphological and photophysical behavior of the materials is confirmed through various analytical techniques. The photocatalytic performance of the highly efficient HAp/gC3N4 photocatalyst is evaluated against methylene blue (MB) and doxycycline drug contaminates under UV–visible light exposure. The HAp/gC3N4 photocatalyst exhibit excellent photocatalytic performance for MB dye (93.69%) and doxycycline drug (83.08%) compared to bare HAp and g-C3N4 nanosheets. The ultimate point to note is that the HAp/gC3N4 photocatalyst was recycled in four consecutive cycles without any degradation performance. Superoxide radicals play an important role in degradation performance, which has been confirmed by scavenger experiments. Therefore, the biowaste-derived HAp combined with gC3N4 nanosheets is a promising photocatalyst for the degradation of hazardous dyes and pharmacological drug wastes.

Significance of g-C3N4 nanosheets for enhancing tribological performance of epoxy subjected to starved lubrication

It is of great interest to realize controllable tribo-designs of a large variety of motion components operating under starved lubrication conditions. In this work, g-C3N4 nanosheets were prepared and uniformly dispersed into pure epoxy (EP) matrix. Especially for sliding with only 5 μL oil supply. In comparison to neat EP, friction coefficient and wear rate are reduced by up to 27% and 83% with addition of only 1% g-C3N4. Research illustrates a small amount of two-dimensional g-C3N4 nanosheets promote the growth of robust tribofilm on oil starved interface. The carbonous top layer of tribofilm benefits the boundary lubrication effect of the sliding pair, whereas the beneath layer confers a high load-bearing ability to tribofilm. It is anticipated that this work will pave a route for designing new polymer nanocomposites serving under oil starved conditions.

Step-scheme heterojunction g-C3N4/TiO2 for efficient photocatalytic degradation of tetracycline hydrochloride under UV light

Construction of heterojunction between semiconductors is considered an effective strategy for enhancing photocatalytic capability. Herein, this work prepared an abundant porous g-C3N4/TiO2 photocatalyst, with the two-dimensional (2D) nanosheet g-C3N4 and nanoparticle TiO2. The heterojunction both enhanced the ultraviolet (UV) light absorption ability, and inhibited the recombination of photogenerated electron-hole (h+) pairs. As expected, the optimal 4 % g-C3N4/TiO2 (g-C3N4:TiO2 = 1:25) exhibited a prominent degradation efficiency of 96.53 % in the photocatalytic performance of tetracycline hydrochloride (TCH) under UV irradiation. The recycling of the heterojunction photocatalyst g-C3N4/TiO2 remained stability and reusability. The main active species were·O2-, h+ and·OH, and the formation of internal electric field on the step-scheme (S-scheme) heterojunction interface accelerated the migration of photogenerated carriers. Moreover, several environmental factors on degradation such as dose, pH, and the initial concentration of TCH were investigated. This work could be spread to the conceive of other S-scheme heterojunction photocatalysts in application to different environmental demands.

Functionalized two-dimensional g-C3N4 nanosheets in PIM-1 mixed matrix membranes for gas separation

The virtuous of two-dimensional (2D) nanomaterials in high aspect ratio and tunable surface functionality have geared towards their implementation in mixed matrix membranes (MMMs) for advanced gas separation. In this study, the effects of functionalized 2D nanosheets in the MMMs for gas separation were investigated. The graphitic carbon nitride (g-C3N4) nanosheets were modified with various functional groups namely sulfuric acid group, aliphatic amino group, aromatic amino group, and sulfonic group via four different synthesis approaches. Polymers of intrinsic microporosity (PIMs, e.g., PIM-1) was selected as the continuous polymer phase due to its intrinsic high permeability and comparable selectivity towards different gas pair. The sulfonic acid functionalized g-C3N4 MMMs (e.g., PIM-1/g-C3N4-D) imparted high separation properties ascribed to the great CO2 affinity induced by the sulfonic acid groups. In particular, PIM-1/g-C3N4-D (99:1) MMM demonstrated promising CO2 separation performance, with CO2 permeability of 3740 Barrer and CO2/N2 selectivity of 19.8. Moreover, at 5 wt% loading of g-C3N4-D, the H2/N2 and O2/N2 separation of the MMMs had exceeded the 2008 Robeson upper bound, thanks to the periodic triangular ultramicropores in g-C3N4 that favor precise sieving of small gases. These results pave the way in using the developed membranes in practical H2 purification, air separation and CO2 capture.

Construction of a 3D/2D plasmonic Z-scheme heterojunction with electrostatic self-assembly for full-spectrum solar-light driven photocatalytic protons reduction

A key solution for high-efficiency solar-to-fuel conversion is fabrication of semiconductor photocatalysts with ultra-broad spectral absorption and high charge-carriers utilization efficiency. Here, we report a non-metallic plasmonic Z-scheme photocatalyst with three-dimensional (3D) W18O49 hierarchical microflowers and two-dimensional (2D) g-C3N4 nanosheets constructed by an electrostatic self-assembly method. The hydrogen production performance of the heterojunction is three times that of pure g-C3N4. This is ascribed to the efficient harvesting of photon energy from the ultraviolet to near-infrared region and the improved charge-carrier transfer on the tight-contact heterojunction interface. This work not only provides an effective reference for the construction of heterostructure based on W18O49 and g-C3N4, but also helps design materials for satisfactory solar energy conversion performance through electrostatic self-assembly methods.

Exfoliation of graphitic carbon nitride and homogeneous loading of Cu2O catalyst

In order to get desired Cu2O catalyst on two-dimensional (2D) g-C3N4, bulk melamine-derived g-C3N4 with a very small specific surface area was exfoliated first and then Cu2O catalyst was loaded using solvothermal method. X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Electrochemical impedance spectroscopy (EIS), N2 adsorption/desorption and Fourier transform infrared (FT-IR) techniques as well as catalytic evaluation were performed to investigate the structure-properties relationship of the composite catalyst. The results show that the as-prepared Cu2O catalyst with the exfoliated g-C3N4 as support not only exhibits a uniform dispersion of Cu2O nanoparticles with ultrafine particle size, but also inherits a large specific surface area up to 165.3 m2/g that hasn't been reported before for transition metal oxide being supported on 2D g-C3N4 with high loading, in the meantime improved catalytic performance towards the removal of some organic pollutants is obtained.

α-Bi2(MoO4)3 nanorods decorated with two-dimensional g-C3N4 nanosheets for efficient degradation of doxycycline under visible light illumination

Water pollution caused by pharmaceutical and personal care products (PPCPs) has been significant stress on the water management system. The development of effective and recyclable material for PPCPs removal has become essential. In the present work, a highly efficient g-C3N4/α-Bi2(MoO4)3 nanocomposites was prepared by a simple wet impregnation method and investigated as a catalyst for the photocatalytic degradation of doxycycline under visible light irradiation. The as-prepared catalysts with various mass ratios were systematically characterized with XRD, FT-IR, UV−vis, FE-SEM, EDX, FE-TEM, and XPS. The equal weight ratio (50:50) of g-C3N4/α-Bi2(MoO4)3 nanocomposite exhibits excellent visible light absorption and outstanding doxycycline photodegradation due to the improved separation efficiency of photo-generated charge carriers. After four consecutive cycles, the equal weight ratio (50:50) of g-C3N4/α-Bi2(MoO4)3 nanocomposite shows superior photostability. The scavenger study was carried out to investigate the role of active species in photodegradation activity. More superoxide radicals present on the surface of g-C3N4/α-Bi2(MoO4)3 nanocomposites can significantly enhance the photocatalytic performance. Therefore, a simple wet impregnation method was used to produce a low-cost g-C3N4/α-Bi2(MoO4)3 photocatalyst with the influential effects of removing pharmaceutical contaminants in water bodies.

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.

Highly Efficient Photocatalytic Hydrogen Production Performance for 2D/0D g-C3N4/Zn0.5Cd0.5S with g-C3N4 as a Transport Medium for Photogenerated Charge Carriers

Two-dimensional g-C3N4 nanosheets are synthesized by high-temperature calcination. The prepared g-C3N4 is used further to synthesize a 2D/0D composite series based on g-C3N4/Zn0.5Cd0.5S heterojunction composite with varied amounts of g-C3N4. The structure, microscopic morphology, photoelectric and photocatalytic performance, and the mechanism for enhancement of photocatalytic performance of the samples are studied through various characterization methods. Microstructural studies revealed that 0D Zn0.5Cd0.5S nanoparticles (ca. 3 ∼ 5 nm) were uniformly dispersed over the surface of the g-C3N4 and thus the formation of a heterostructure. The photo-electrochemical test shows that an appropriate amount of g-C3N4 modification (10%-C3N4/Zn0.5Cd0.5S) can effectively improve photogenerated carriers’ separation and transfer efficiency. Besides, the hydrogen production performance of the g-C3N4/Zn0.5Cd0.5S samples first increased and then decreased with the amount of g-C3N4. The photocatalytic activity of the 10%-C3N4/Zn0.5Cd0.5S showed the highest hydrogen production of 3.53 mmol·g−1·h−1, which is 2.8 times than that of pure Zn0.5Cd0.5S (1.26 mmol·g−1·h−1). The enhanced photocatalytic performance is attributed to the introduced g-C3N4 that can supply more activity sites and lead to the formation of the heterojunction across the interface, which effectively improves the separation and migration of photogenerated charges. Designing this kind of sustainable, low cost, and efficient photocatalytic hydrogen production method that avoids the application of precious metals will provide a feasible solution to meet the increasing global energy demand and a sustainable future.

Engineering of 2D/3D architectures type II heterojunction with high-crystalline g-C3N4 nanosheets on yolk-shell ZnFe2O4 for enhanced photocatalytic tetracycline degradation

Heterostructures constructed in various dimensions have received considerable attention as promising platforms for improving activity of photocatalytic materials. Herein, two-dimensional (2D) high crystalline g-C3N4 (HCCN) nanosheets were loaded onto the surface of three-dimensional (3D) yolk-shell ZnFe2O4 (ZFO) to construct 2D/3D HCCN/ZFO heterojunction by a simple two-step process consisting of a solvothermal method and a calcination process. It is found that the formation of heterojunction can effectively enhance photo-absorption and separation efficiency of carriers. In contrast to pure HCCN and ZFO, the tetracycline (TC, 30 mg/L) degradation rate of optimal 20% HCCN/ZFO heterojunction can be reached 85%, and degradation rate constant is 0.0133 min−1, which is 3.8 and 4.9 times higher than HCCN (0.0035 min−1) and ZFO (0.0027 min−1), respectively. Besides, the reasonable mechanism of photocatalytic degradation of TC and possible intermediates products were discussed based on the results of capture experiments, electron spin resonance (ESR) and liquid chromatography-mass spectrometry (LC-MS).