Photocatalytic Activity Of g-C3N4 Research Articles

Theoretical Study of p-Block Metal Single-Atom-Loaded Carbon Nitride Catalyst for Photocatalytic Water Splitting.

Graphitic carbon nitride (g-C3N4), recognized for its considerable potential as a heterogeneous photocatalyst in water splitting, has attracted extensive research interest. By using density functional theory (DFT) calculations, the regulatory role of p-block metal (PM) single atoms on the photocatalytic activity of g-C3N4 in overall water splitting was systematically explored. The incorporation of PM atoms (Ge, Sn and Pb) led to a reduction in the overpotentials required for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Combined with the electronic structures analysis via hybrid functional, it was found that the introduction of Ge, Sn or Pb optimizes the positions of the valence band maximum (VBM) and the conduction band minimum (CBM), providing a robust driving force for HER and ensuring substantial driving force for OER. Meanwhile, the presence of these three PMs induces the spatial separation of VBM and CBM, inhibiting the recombination of carriers. These findings have significant implications for the design and preparation of efficient photocatalysts.

Template-Free Synthesis of Boron-Doped Graphitic Carbon Nitride Porous Nanotubes for Enhanced Photocatalytic Hydrogen Evolution.

The photocatalytic activity of g-C3N4 can be enhanced by improving photoinduced carrier separation and exposing sufficient reactive sites. In this study, we synthesized B-doped porous tubular g-C3N4 (BCNT) using a H3BO3-assisted supramolecular self-template method, wherein H3BO3 helped in B-doping, building a porous structure, and maintaining one-dimensional nanotubes. The tubular structure had an ultrathin tube wall and large aspect ratio, which are conducive to the directional transmission and separation of photogenerated carriers; moreover, the abundant pore structure of the tube wall could fully expose the reactive sites. The introduction of B and the cyano group modulated the bandgap of g-C3N4 and elevated the position of the conduction band, thus enhancing the photoreduction ability and effectively improving the hydrogen evolution performance. Consequently, the hydrogen evolution of BCNT-2 (220.8, 53.2 μmol·h-1) was 1.82 and 1.54 times that of ultrathin g-C3N4 nanosheets (CNN, 121.3, 34.6 μmol·h-1) under simulated sunlight and LED lamp irradiation, respectively. Thus, this work provides in-depth insights into the rational design of one-dimensional g-C3N4 nanotubes with high hydrogen evolution activity under visible irradiation.

Co-optimization of g-C3N4 with prolonging exciton lifetime strategy and co-catalyst strategy for enhanced photocatalytic H2 evolution activity

In this work, the photocatalytic activity of g-C3N4 is co-optimized for the first time using a strategy of prolonging exciton lifetime and a co-catalyst strategy. Amorphous CoB nanoparticles are loaded on OCN-K-CN, which is an O, K doped g-C3N4 material with van der Waals heterojunctions inside. The optimized OCN-K-CN-CoB sample, containing 12 wt% CoB and 1.25% K2SO4 in precursors, show photocatalytic H2 evolution rate approximately 27 times higher than that of GCN. The mechanism of co-optimization is detailedly investigated through comparative experiments on light absorption, charge separation performance, and HER activity, with optimization strategy and CoB loading ratio as controlled variables. New roles of the two strategies have been revealed: "flux-limited reduction activity sites" for CoB and ''buffer-enhancer'' for OCN-K-CN. These new roles illustrate a hidden relationship between the optimizing effects of the two strategies and can explain a surprising advantage of this co-optimization: achieving near-optimal hydrogen evolution activity with significantly reduced co-catalyst loading ratio.

Improving the photocatalytic activity of graphitic carbon nitride through ionic liquid-mediated thermal annealing

Graphitic carbon nitride (g-C3N4) has shown a great promise in photocatalytic hydrogen evolution. However, the catalytic activity of g-C3N4 derived from nitrogen-rich compounds is still limited by fast charge carrier recombination and slow surface reaction dynamics. Herein, a series of primary g-C3N4 materials were prepared by thermal polymerization of melamine and/or urea, and then thermally treated with the involvement of different ionic liquids under altering heat conditions. Imidazole-containing ionic liquids, such as 1-propyl-3-methylimidazolium chloride ([PMIm]Cl), acted as an effective additive to mediate the thermal annealing behavior of primary g-C3N4, leading to the dissociation of aggregates into porous nanosheets with varying element compositions and with increased surface area. Regardless of little change in optical absorption and electronic structure, the resulting porous g-C3N4 nanosheets promoted the separation and transfer of photogenerated charges and modified surface hydrogen desorption. Hydrogen evolution tests confirmed that the catalytic activity of g-C3N4 from the co-polymerization of melamine and urea was enhanced by ∼3.4 and ∼7.4 times upon [PMIm]Cl-free and -mediated thermal annealing, respectively. This work suggests the potential effect of the additive involvement in the thermal annealing on the photocatalytic activity of g-C3N4.

Enhanced visible-light-driven photocatalysis via magnetic nanocomposites: A comparative study of g-C3N4, g-C3N4/Fe3O4, and g-C3N4/Fe3O4/ZnO

In this study, the photocatalytic activity of g-C3N4/Fe3O4/ZnO, g-C3N4/Fe3O4, and g-C3N4 catalysts when exposed to visible light was thoroughly examined. We deliberately take advantage of visible light potential to create electron-hole (e/h+) pairs with exceptional lifetimes. The g-C3N4/Fe3O4/ZnO nanocomposite stands out among the tested catalysts as the undisputed champion thanks to its excellent degrading efficiency. This remarkable result is due to the formation of an interface between g-C3N4 and ZnO, which increases the response to visible light and makes it easier to separate photo-induced electrons and holes, completely. Furthermore, the nanocomposite including Fe3O4 phase addressed the challenge of catalyst recovery and magnetic separation from the solution.

Facile synthesis of g-C3N4 nanosheets for effective degradation of organic pollutants via ball milling

Abstract Graphitic carbon nitride (g-C3N4) has attracted extensive research interest in pollutants remediation. However, the photocatalytic activity of g-C3N4 was significantly limited by its small specific surface area. In this work, a green, high-energy ball milling method was used to fabricate g-C3N4 nanosheets. The structure, morphology, and optical properties of the prepared g-C3N4 nanosheets were characterized. The effect of ball milling parameters on the photocatalytic performance evaluated by Rhodamine B (RhB) and tetracycline (TC) was investigated systemically. Among the tested samples, the g-C3N4 sample milled with a 4 mL isopropanol solution at a rotation speed of 420 rpm, ball-to-powder weight ratio of 10:1, and milling time of 24 h exhibited the highest RhB degradation efficiency of 91.4% and TC degradation efficiency of 70.2%. The enhanced photocatalytic activity after ball milling was ascribed to the increase in specific surface area and efficient separation of electron–hole pairs. The trapping experiment indicated that holes and superoxide radicals were the main active species in the degradation reaction. Moreover, the photocatalytic degradation mechanism of organic pollutants on g-C3N4 nanosheets was also discussed in detail.

Efficient Photocatalytic Degradation of Aqueous Atrazine over Graphene-Promoted g-C3N4 Nanosheets

Atrazine is a systemic herbicide widely used in weed control. In recent years, it has been largely detected in surface and groundwater in several locations all over the world. Photocatalysis is a green and sustainable technology with huge application prospects in pollution control and the degradation of organic water pollutants. In this work, photodegradation of aqueous atrazine was investigated over pristine graphitic carbon nitride (g-C3N4) synthesized via urea pyrolysis and graphene/g-C3N4 composite synthesized via the in situ growth method involving direct deposition of g-C3N4 nanosheets on the graphene surface. The obtained photocatalysts were characterized using transmission and scanning electron microscopy, Fourier-transformed infrared spectroscopy, UV-visible spectroscopy, photoluminescence spectroscopy, X-ray diffraction, and surface area measurements. It was demonstrated that the composite material exhibited remarkable photocatalytic properties for the efficient degradation of aqueous atrazine under visible light at ambient temperature. After 5 h of reaction, atrazine conversion reached 100% in the presence of graphene/g-C3N4 composite, while the pristine g-C3N4 allowed 40% conversion under the same conditions, thus demonstrating the positive effect of graphene on the photocatalytic activity of g-C3N4. Moreover, graphene/g-C3N4 was shown to keep its activity even when it was recycled five times, thus proving its stability and its potential to be used at the industrial scale.

Gas template mediated exfoliation of polymeric graphitic carbon nitride; what contributes more to hydrogen production, a higher specific surface area, or defect sites?

Polymeric graphitic carbon nitride (g-C3N4) has emerged as a promising photocatalyst for various applications; however, the optimization of its performance remains a challenge. In this study, we investigate the influence of specific surface area and nitrogen content on the photocatalytic activity of g-C3N4. Our findings reveal that a highly nitrogen-deficient g-C3N4 demonstrates superior photocatalytic activity in the absence of a co-catalyst. Conversely, a g-C3N4 sample with a higher surface area and reduced nitrogen deficiency performs better when coupled with a co-catalyst such as platinum. We attribute these differences to the concurrent introduction of nitrogen defects and oxygen species, which modify the conduction band position and improve the separation efficiency of photogenerated charge carriers. These outcomes suggest that the optimization of specific surface area and nitrogen defects could be a promising strategy for tailoring g-C3N4 performance in photocatalytic applications. Such an approach holds significant implications for developing highly efficient photocatalytic systems.

Alkaline metal derived secondary thermal polymerization for superior thin g-C3N4 nanosheets with efficient photocatalytic performance

The thermal polymerization controlled the thickness and composition of graphic carbon nitride (g-C3N4) to affect the photocatalytic performance. In this paper, potassium and sodium ions were firstly incorporated in bulk g-C3N4 prepared using melamine through a mechano-chemical pre-reaction. After a two-step thermal polymerization treatment at 500 and 550 °C, respectively, superior thin g-C3N4 nanosheets were created because K or Na ions implanted between g-C3N4 layers, in which activated cites were remained in the nanosheets. The results revealed that potassium or sodium ion doping revealed an important impact on the photocatalytic activity of g-C3N4. With an optimized K loading of 3%, the hydrogen evolution rate of potassium doped g-C3N4 superior thin nanosheets was 18.1 times of that of bulk g-C3N4. For the degradation of the degradation rate of Rhodamine B (Rh B), K-doped g-C3N4 sample revealed 3.8 times increase compared with pure g-C3N4. To indicate the role of alkaline metal ions, Na-doped samples were also used for H2 generation and Rh B degradation. Meanwhile, the hydrogen generation and Rh B degradation rate of sodium doped g-C3N4 nanosheets improved to 3.6 and 1.75 times higher than those of pure g-C3N4, respectively. The result suggested a mechano-chemical pre-treatment helped K and Na ions to improve the microstructure of g-C3N4 nanosheets and increase activated cites for photocatalysis.

Synthesis of mediator free hollow BiFeO3 spheres/porous g-C3N4 Z-scheme photocatalysts for CO2 conversion and Alizarin Red S degradation

In this current research work, we fruitfully prepared a mediator-free BiFeO3 hollow spheres/porous g-C3N4 Z-scheme based photocatalysts and utilized it for CO2 conversion and Alizarin Red S degradation. Remarkably, the porous g-C3N4 are prepared by acidic treatment and double calcination method, while BiFeO3 hollow spheres are prepared by employing carbon nanospheres as hard templates. Our results demonstrated that porosity and hollow spheres efficiently upgraded the surface area, light absorption capacity, and photocatalytic activities of g-C3N4 and BiFeO3. Based on electrochemical impedance spectroscopy (EIS), SPS, TEM, FS spectrum associated with the formed •OH amount, and UV-absorbance spectra, it is confirmed that coupling of BiFeO3 hollow spheres with porous g-C3N4 not only thermodynamically provide a suitable platform for receiving the high energy level electrons but also enhanced charge separation. Compared to pristine P–CN, the most optimal sample, 6HBFO/P–CN, showed a 3.5-times enhancement in activities for Alizarin Red S decontamination and CO2 conversion under visible light irradiation. Finally, our present work will open a new gateway to synthesize BiFeO3 hollow spheres/porous g-C3N4 Z-scheme materials as effective photocatalysts for organic contaminants decontamination and CO2 conversion.

Photocatalytic Activities of g-C3N4 (CN) Treated with Nitric Acid Vapor for the Degradation of Pollutants in Wastewater

In this article, we reported a novel setup treatment using nitric acid vapor to treat g-C3N4 (CN). By treatment with nitric acid vapour, the basic structure of the CN has not been destroyed. These adoptive treatments enhanced the photocatalytic performance of CN and were reflected in the elimination of rhodamine B (RhB) as well as tetracycline hydrochloride (TC). In comparison to CN, CN-6 demonstrated the highest photocatalytic yield for the breakdown of RhB (99%, in 20 min). Moreover, the excellent reuse of CN-6 for breaking down RhB was also demonstrated. This clearly demonstrated that treatment with nitric acid vapor promoted a blue shift, positively extended its valence band position, and increased the oxidizability of the holes. This also caused CN to disperse better into the aqueous phase, introducing more oxygen-containing functional groups. Thus, treatment with nitric acid vapor has the potential to be applied to delaminate the CN in order to enhance photocatalytic activity.

Single-Step Synthesis of Graphitic Carbon Nitride Nanomaterials by Directly Calcining the Mixture of Urea and Thiourea: Application for Rhodamine B (RhB) Dye Degradation

Recently, polymeric graphitic carbon nitride (g-C3N4) has been explored as a potential catalytic material for the removal of organic pollutants in wastewater. In this work, graphitic carbon nitride (g-C3N4) photocatalysts were synthesized using mixtures of low-cost, environment-friendly urea and thiourea as precursors by varying calcination temperatures ranging from 500 to 650 °C for 3 h in an air medium. Different analytical methods were used to characterize prepared g-C3N4 samples. The effects of different calcination temperatures on the structural, morphological, optical, and physiochemical properties of g-C3N4 photocatalysts were investigated. The results showed that rhodamine B (RhB) dye removal efficiency of g-C3N4 prepared at a calcination temperature of 600 °C exhibited 94.83% within 180 min visible LED light irradiation. Photocatalytic activity of g-C3N4 was enhanced by calcination at higher temperatures, possibly by increasing crystallinity that ameliorated the separation of photoinduced charge carriers. Thus, controlling the type of precursors and calcination temperatures has a great impact on the photocatalytic performance of g-C3N4 towards the photodegradation of RhB dye. This investigation provides useful information about the synthesis of novel polymeric g-C3N4 photocatalysts using a mixture of two different environmentally benign precursors at high calcination temperatures for the photodegradation of organic pollutants.

Synthesis and photocatalytic activity of g-C3N4/CdS materials under visible light

The g-C3N4/CdS composite photocatalysts consisting of cadmium sulfide (CdS) and graphitic carbon nitride g-C3N4) with a different mass ratio of CdS were successfully prepared and denoted as CNCS-1:1, CNCS-1:3, CNCS-1:5. The obtained materials were characterized by X-Ray diffraction (XRD), infrared spectra (IR), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The UV-vis DRS results showed that CNCS-1:1, CNCS-1:3 and CNCS-1:5 materials possess bandgap of around 2.31, 2.25 and 2.28 eV, respectively. The photocatalytic activity of the materials was assessed by degradation of methylene blue (MB) under visible light. Among the three materials, CNCS-1:3 exhibited the highest photocatalytic activity. The enhancement of photocatalytic activity of the CNCS-1:3 (or g-C3N4/CdS) composites compared to single components, g-C3N4 and CdS was observed, which can be attributed to the reduction of combination rate of photogenerated electron – hole pairs in the composites.

Construction of S-scheme heterojunction for enhanced photocatalytic conversation of NO over dual-defect CeO2−x/g-C3N4−x

An increasing amount of nitric oxide (NOx) is being discharged into the atmosphere due to the development of industry and combustion of fossil fuels. Photocatalysis, as a green and renewable technology, has attracted increasing attention from global researchers to address environmental pollution caused by excessive NOx in air. g-C3N4 is a metal-free organic polymer photocatalyst that has received widespread attention due to its unique physical and chemical properties. However, the photocatalytic activity of g-C3N4 under visible light irradiation is limited by high photocarrier recombination, poor conductivity, and low visible light utilization. The construction of novel S-scheme heterojunction semiconductors based on g-C3N4 is a promising strategy to enhance the photocatalytic activity. In this study, S-scheme CeO2−x/g-C3N4−x (Ce/CN) photocatalysts were synthesized by the thermal polymerization of melamine and Ce(NO3)4. The photocatalytic activity of the as-prepared photocatalysts was investigated for the removal of NO with visible-light irradiation. The photocatalytic efficiency of 4Ce/CN was about 1.7 times higher than that of g-C3N4 with a low NO2 yield. Material characterization and DFT analysis demonstrated that the enhanced photocatalytic activity was attributed to N and O dual defects, the excellent conductivity of CeO2, and the in-built field of the Ce/CN S-scheme heterojunction.

Synthesis and photocatalytic activity of g-C3N4/BiVO4/CNTs composites

g-C3N4 was prepared, and samples of different contents of BiVO4, CNTs and g-C3N4 were doped, characterized, and ternary composites were successfully prepared. RhB was selected as the pollutant to test the photocatalytic performance of the ternary composite (GCBC) sample. The photocatalytic activity was analyzed by degrading RhB under visible light (λ > 550 nm), combined the kinetic equation of the degradation reaction and the capture of free radicals for research. And elucidated the mechanism of GCBC active species capture and photocatalytic degradation.

Study on the synthesis of g-C3N4/CoFe2O4/Reduced graphene oxide material and its application as photocatalyst

In this study, the g-C3N4/CoFe2O4/Reduced graphene oxide composites were successfully synthesized by the co-precipitation method combined with mixed phase mixture. The obtained results from characterization methods such as XRD, SEM, FT-IR, EDX,… showed that the composite has a high structure and crystallinity, and spinel ferrite particles were dispersed fairly evenly onto reduced graphene oxide sheets as well as layers of g-C3N4. The existence of Co/Fe-O and Co-O-C bonds in materials was determined. The photocatalytic activity of g-C3N4/CoFe2O4/Reduced graphene oxide (GCN/CF-rGO) was estimated through the degradation of Tetracycline (TC) in aqueous solution. TC decomposition efficiency is up to 95% after 240 minutes of reaction and is higher than that of each component material. GCN/CF-rGO is a potential catalyst for effective application in TC decomposition reaction under visible light and has the ability to implement treatment in practice.

Construction of g-C3N4/Ag/TiO2 Z-scheme photocatalyst and Its improved photocatalytic U(VI) reduction application in water.

The reduction of soluble U(VI) to insoluble U(IV) by photocatalytic technology is considered to be a valid method to remove U(VI) from water. Herein, g-C3N4/Ag/TiO2 Z-scheme heterojunction was synthesized for photocatalytic U(VI) reduction application. The SEM, XRD and XPS characterization results showed that a ternary g-C3N4/Ag/TiO2 composite photocatalyst was synthesized successfully. g-C3N4/Ag/TiO2 exhibited excellent photocatalytic reduction performance for U(VI) under visible light irradiation. After 30 min irradiation, the removal rate of U(VI) was above 99%. XPS indicated that the majority of U(VI) on the surface of g-C3N4/Ag/TiO2 was reduced to U(IV). In addition, the photocatalytic activity of g-C3N4/Ag/TiO2 has been kept significantly after five rounds of experiments, indicating good stability. g-C3N4/Ag/TiO2 exhibited better photocatalytic reduction of U(VI) under visible light irradiation, which is mainly ascribed to Z-scheme photocatalytic mechanism assisted by the LSPR effect (Local Surface Plasmon Resonance). Ag with plasmon resonance effect on the loading has a strong absorption of photon energy. In addition, an intermediate charge transfer channel is formed between Ag and the semiconductor to inhibit the combination of photogenerated electrons and holes, resulting in a significant increase in the photocatalytic activity of the photocatalyst. This idea has some significance in design of other composite photocatalytic systems.

Direct microwave heating synthesis and characterization of highly efficient g-C3N4 photocatalyst

Graphitic carbon nitride (g-C3N4) material was rapidly synthesized by direct microwave heating method with different microwave powers and irradiation reaction periods of time. Phase, functional group, surface morphology and optical properties of as-prepared g-C3N4 samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The samples synthesized by direct microwave heating at 600–800 W for 9–15 min were g-C3N4 single phase with typical CN stretching vibration and out-of-plane bending vibration of C–N heterocycle and good absorption in the visible light region. The photocatalytic activity of g-C3N4 was evaluated through the degradation of methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) under visible light irradiation. In this research, the g-C3N4 sample synthesized at 800 W microwave power for 15 min has the best photocatalytic performance in degrading of 91.82 % MB, 81.86% MO and 97.48% RhB within 60 min.

Boosting photocharge separation in Z-schemed g-C3N4/RGO/ln2S3 photocatalyst for H2 evolution and antibiotic degradation

Due to the high redox ability and effective separation of photocharges, Z-schemed photocatalysts have been extensively used to deal with energy crises and environmental pollution. Here, a novel Z-schemed g-C3N4/RGO/ln2S3 photocatalyst was designed and prepared for hydrogen generation and tetracycline hydrochloride degradation. The properties of optical absorption, separation, and transfer of photocharges and heterojunction on photocatalytic activity of g-C3N4/RGO/ln2S3 composite have been studied. The characterization results showed that the Z-scheme photocatalyst has high efficiency on the separation and transfer of photocharges, and the strong redox ability has also remained. Thus, the g-C3N4/RGO/ln2S3 composite exhibited superior photocatalytic performance than pristine ln2S3 and g-C3N4 in the same situations. The H2 evolution rate can reach up to 512.72 μmolg-1h−1 and the degradation of tetracycline hydrochloride can reach 95.6% in 60 min under visible light irradiation. This work provides a potential pathway for designing and preparing high-performance photocatalysts to produce clean energy and purify the environment.

Enhancement of photocatalytic activity of g-C3N4 under solar light by Nd3+ doping and HPA incorporation and its application in the degradation of ceftriaxone sodium

ABSTRACT Nd3+-doped graphitic carbon nitride nanosheets incorporated with heteropoly phosphotungstic acid (Nd3+-g-C3N4-HPA) were synthesised, and their optical response, band structure and charge separation efficiency were analysed. UV–vis diffuse reflectance spectral studies revealed that Nd3+ doping and HPA incorporation led to an increase in absorption intensity, which enhances the range of visible light absorption. Improved separation efficiency and reduction in the recombination rate of photogenerated electrons and holes are supported by photoluminescence studies. This novel photocatalyst was applied for the removal of the antibiotic, ceftriaxone sodium from water and attained complete degradation within 75 min of sunlight irradiation, demonstrating that the Nd3+-g-C3N4-HPA photocatalyst would be beneficial for eliminating persistent organic pollutants like dyes and pharmaceutical compounds from wastewater. Investigations revealed that superoxide anion radicals and holes play a significant role in the photocatalytic degradation of pollutants. Furthermore, a possible degradation pathway of ceftriaxone sodium was proposed using mass spectral analysis.