Facile one-step synthesis of onion-like carbon modified ultrathin g-C3N4 2D nanosheets with enhanced visible-light photocatalytic performance

Synergistic effect of adsorption and photocatalytic degradation of oilfield-produced water by electrospun photocatalytic fibers of Polystyrene/Nanorod-Graphitic carbon nitride

Graphitic carbon nitride with nanorod structure (Nr-GCN) was synthesized using melamine as a precursor without any other reagents by hydrothermal pretreatment method. XRD, FTIR, SEM, N2 adsorption-desorption from BET, UV-Vis DRS spectroscopy, and photoluminescence were used to characterize the prepared samples. Also, the photoelectrochemical behavior of nanoparticles was studied by photocurrent transient response and cyclic voltammetry analysis. Polystyrene (PS) fibrous mat was fabricated by electrospinning technique and used as a support for the stabilization of the nanoparticles. The performance of the synthesized nanoparticles and photocatalytic fibers (PS/Nr-GCN) was evaluated in oilfield-produced water treatment under visible light irradiation. During this process, oil contaminants were adsorbed by hydrophobic polystyrene fibers and simultaneously degraded by Nr-GCN. The removal efficiency of chemical oxygen demand (COD) has been obtained 96.6% and 98.4% by Nr-GCN and PS/Nr-GCN, respectively, at the optimum conditions of pH 4, photocatalyst dosage 0.5 g/L, COD initial concentration 550 mg/L, and illumination time 150 min. The gas chromatography-mass spectroscopy analysis results showed 99.3% removal of total petroleum hydrocarbons using photocatalytic fibers of PS/Nr-GCN. The results demonstrated that the GCN has outstanding features like controllable morphology, visible-light-driven, and showing high potential in oily wastewater remediation. Moreover, the synergistic effect of adsorption and photocatalytic degradation is an effective technique in oilfield-produced water treatment.

Composite Foams of the Graphitic Carbon Nitride@Carbon Nanofibrils Conferred a Superamphiphilic Property and Reinforced Thermal Stability

Herein, we demonstrated the preparation of novel three-dimensional (3D) superamphiphilic g-C3N4@carbon nanofibers foam (g-C3N4@CNFs) via a two-step approach: liquid nitrogen treatment-freeze-drying; the foams possessed good thermal stability. In this approach, melamine acted as a nitrogen source, and nanofibrillated cellulose (NFCs) functioned as a 3D skeleton. The thermal stability of the as-prepared g-C3N4@CNFs-3 foam was much higher than that of g-C3N4@CNFs-1, as indicated by thermogravimetric data, including an increase of the onset weight loss point (Tonset) by 238.6 °C and an improvement of the maximal weight loss rate (Tmax) by 258.8 °C. The combination of g-C3N4 with CNFs conferred a reduction in the heat release rate (ca. -86%) and the total heat release (ca. -75%). Furthermore, the composition of the hydrophilically oxygenated functional groups and hydrophobic triazine domains in g-C3N4@CNFs rendered it a unique amphiphilic property (contact angle close to 0° within 1.0 s for water and 0° within 12 ms for hexane). A high storage capacity for water and various organic solvents of the superamphiphilic g-C3N4@CNFs foam was found, up to 40-50 times its original weight. The discovery of these superamphiphilic foams is of great significance for the development of superwetting materials and may find their applications in oil emulsion purification and catalyst support fields.

Design strategies and mechanisms of g-C3N4-based photoanodes for photoelectrocatalytic degradation of organic pollutants in water

Emerging photoelectrocatalytic (PEC) systems integrate the advantages of photocatalysis and electrocatalysis and are considered as a promising technology for solving the global organic pollution problem in water environments. Among the photoelectrocatalytic materials applied for organic pollutant degradation, graphitic carbon nitride (CN) has the combined advantages of environmental compatibility, stability, low cost, and visible light response. However, pristine CN has disadvantages such as low specific surface area, low electrical conductivity, and high charge complexation rate, and how to improve the degradation efficiency of PEC reaction and the mineralization rate of organic matter is the main problem faced in this field. Therefore, this paper reviews the progress of various functionalized CN used for PEC reaction in recent years, and the degradation efficiency of these CN-based materials is critically evaluated. First, the basic principles of PEC degradation of organic pollutants are outlined. Then, engineering strategies to enhance the PEC activity of CN (including morphology control, elemental doping, and heterojunction construction) are focused on, and the structure-activity relationships between these engineering strategies and PEC activity are discussed. In addition, the important role of influencing factors on the PEC system is summarized in terms of mechanism, to provide guidance for the subsequent research. Finally, suggestions and perspectives are provided for the preparation of efficient and stable CN-based photoelectrocatalysts for practical wastewater treatment applications.

Flux-assisted synthesis of bismuth nanoparticle decorated carbon nitride for efficient photocatalytic degradation of endocrine disrupting compound

Traditional approaches to synthesizing bismuth nanoparticle decorated carbon nitride (C₃N₄) materials suffer from the complex synthesis process and the addition of a surfactant, which is not conducive to environmental protection. To address these problems, we adopted a simple and green flux-assisted approach for the first time to fabricate metallic bismuth nanoparticle decorated C₃N₄ (BiCCN). Electron microscopy results suggested that bismuth vanadate was converted into small bismuth nanoparticles via the flux-assisted approach. Highly dispersed Bi nanoparticles dramatically intensify light absorption, facilitate spatial charge separation as electron acceptors, shorten the charge diffusion length, and reserve more active sites for generating reactive species via surface photo-redox reactions. Consequently, the derived optimized photocatalyst BiCCN-15 rendered around 26 times higher photocatalytic degradation efficiency toward an endocrine disrupting compound (bisphenol A) than C₃N₄. This work provides a novel approach for developing non-precious metal decorated photocatalytic materials for sustainable water decontamination.

CdS and Ag synergistically improved the performance of g-C3N4 on visible-light photocatalytic degradation of pollution

CdS-AgO@g-C₃N₄ nanocomposites were successfully synthesized and characterized by XRD, N₂ physical adsorption, XPS, SEM, TEM, EDX, and UV-Vis DRS (various technical means). The adsorption light range of as-prepared materials could extend to the whole visible light region with the addition of Ag. Silver can act as a bridge to facilitate the separation of electrons and holes, thereby greatly enhancing the photocatalytic activity of CdS-AgO@g-C₃N₄, enabling the maximum degradation efficiency of salicylic acid in water to reach 92.8% under visible light. Peroxy radical is the most important radical in the photocatalytic reaction process, followed by electron and hole, while hydroxyl radical has almost no effect. In addition, the mechanism of photocatalytic process was also explored.

Exfoliation method matters: The microstructure-dependent photoactivity of g-C3N4 nanosheets for water purification

Exfoliation of carbon nitride (g-C₃N₄) into an ultrathin nanostructure significantly improves its photoactivity. However, the effects of the exfoliation method on the microstructure and photocatalytic performance of g-C₃N₄ nanosheets remain largely unknown. Herein, several typical strategies, such as thermal, chemical, ultrasonic and one-step exfoliation, were applied to exfoliate g-C₃N₄ nanosheets for photocatalytic applications. A procedure capable of controlling the morphology, microstructure, light-absorption property, and visible light photoactivity of g-C₃N₄ nanosheets was attempted. We found that nanosheets prepared from one-step exfoliation present superior photocatalytic efficiency under visible light than those fabricated by thermal exfoliation and ultrasonic exfoliation. The kinetic constants for bisphenol A (BPA) photodegradation over these samples were determined to be 6.5, 4.5 and 2.3 times higher than bulk g-C₃N₄, respectively. For chemical exfoliation, excessive oxidation by H₂SO₄ can lead to the structural defects and deactivation of urea-derived g-C₃N₄ nanosheets. Carbon nitride nanosheets synthesized by one-step exfoliation exhibited high specific surface area, optimal band gap energy structure, and high charge separation efficiency, thereby increasing visible-light photoactivity. Enabling cost-effective production of ultrathin and robust g-C₃N₄ nanosheets, one-step exfoliation offers a potential strategy to exploit high-performance g-C₃N₄ for water purification applications.

Preparation of miscible CdS and homojunction C3N4 hybrids for efficient photocatalytic degradation of tetracycline

Preparation of high-performance photocatalysts for the degradation of organic pollutants by a simple method.

Facile synthesis of high-efficiency magnetic graphitic carbon nitride adsorbents for the selective removal of hazardous anionic dyes in wastewater

A novel composite adsorbent was successfully prepared by a simple impregnation method. The prepared adsorbent not only exhibits ultra-efficient and selective removal of anionic dyes, but also shows excellent performance in practical water samples.

Applications of electron spin resonance spectroscopy in photoinduced nanomaterial charge separation and reactive oxygen species generation

Nano-metals, nano-metal oxides, and carbon-based nanomaterials exhibit superior solar-to-chemical/photo-electron transfer properties and are potential candidates for environmental remediations and energy transfer. Recent research effort focuses on enhancing the efficiency of photoinduced electron-hole separation to improve energy transfer in catalytic reactions. Electron spin resonance (ESR) spectroscopy has been used to monitor the generation of electron/hole and reactive oxygen species (ROS) during nanomaterial-mediated photocatalysis. Using ESR coupled with spin trapping and spin labeling techniques, the underlying photocatalytic mechanism involved in the nanomaterial-mediated photocatalysis was investigated. In this review, we briefly introduced ESR principle and summarized recent advancements using ESR spectroscopy to characterize electron-hole separation and ROS production by different types of nanomaterials.

Fabrication of AgCl/Ag3PO4/graphitic carbon nitride heterojunctions for enhanced visible light photocatalytic decomposition of methylene blue, methylparaben and E. coli

Herein, a novel ternary nanocomposite AgCl/Ag₃PO₄/g-C₃N₄ was successfully synthesized via sedimentation precipitation and ion exchange method. The photocatalytic performance of the as-prepared AgCl/Ag₃PO₄/g-C₃N₄ nanocomposite was investigated via photocatalytic degradation of methylene blue (MB), methylparaben (MPB) and inactivation of E. coli under visible light irradiation. The AgCl/Ag₃PO₄/g-C₃N₄ composite presented the optimal photocatalytic performance, degrading almost 100% MB and 100% MPB, respectively. The excellent stability of AgCl/Ag₃PO₄/g-C₃N₄ was also verified in the cycle operations; the degradation efficiency of MPB could still be maintained at 85.3% after five cycles of experiments. Moreover, the AgCl/Ag₃PO₄/g-C₃N₄ composite displayed more superior photocatalytic inactivation efficiency with 100% removal of E. coli (7-log) in 20 min under visible light irradiation. The efficient photo-generated charge separation originated from a strong interaction in the intimate contact interface, which was confirmed by the results of photocurrent and EIS measurements. In addition, radical trapping experiments revealed that hole (h⁺) was the predominant active species in the photocatalytic system. Based on the experimental results, a photocatalytic mechanism for the degradation of parabens over AgCl/Ag₃PO₄/g-C₃N₄ was also proposed. We believe that this work provides new insights into the multifunctional composite materials for the applications in solar photocatalytic degradation of harmful organic compounds and common pathogenic bacteria in wastewater.

A noval ternary nanocomposite AgCl/Ag₃PO₄/g-C₃N₄ was successfully synthesized for photocatalytic degradation of methylene blue, methylparaben and inactivation of E. coli under visible light irradiation, showing excellent photocatalytic degradation performance and stability.

Mesoporous magnetic g-C3N4 nanocomposites for photocatalytic environmental remediation under visible light

Mesoporous magnetic Fe₃O₄/g-C₃N₄ nanocomposites were synthesized by a facile precipitation method using deionized water as solution. And the prepared magnetic materials were characterized by mean of various detection methods. At the same time, the photocatalytic activity of the synthetic material as photocatalyst under visible light was tested by taking the degradation of rhodamine B in water as a mark. Results show that as-synthesized Fe₃O₄/g-C₃N₄ nanocomposites have high specific surface areas of about 5-10.5 times that of pure g-C₃N₄ and high saturation magnetizations, which can ensure the smooth recovery of used nanomaterials under the action of external magnetic field. The addition of Fe₃O₄ greatly extents the response range of g-C₃N₄ nanomaterials to visible light and reduces the recombination rate of photoinduced electron-hole pairs. Meanwhile, the photocatalytic activity of the synthetic materials increases so that the degradation ratio of rhodamine B in water reached 97.6% after 4 h visible light irradiation. Furthermore, prepared magnetic Fe₃O₄/g-C₃N₄ nanocomposites have also excellent stability so that the degradation ratio of rhodamine B was almost not reduce after 5 times of continuous reuse of photocatalyst. Free radical scavenging experiments shows that hydroxyl groups are the main free radicals of photocatalytic reaction, peroxyradicals and holes play the secondary role. Therefore, it can be predicted that the synthesized mesoporous magnetic Fe₃O₄/g-C₃N₄ nanomaterials will have a broad application prospect in environmental remediation.

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications.

Enhanced photocatalytic degradation of organic pollutants using carbon nanotube mediated CuO and Bi2WO6 sandwich flaky structures

CuO/CNT/Bi2WO6 composites were synthesized with a solvothermal and impregnation-calcination method. This material combines the advantages of CuO, carbon nanotubes (CNTs) and Bi2WO6. The photocatalytic activity of the catalyst was evaluated by degrading phenolic organic pollutants such as p-nitrophenol and phenol under visible light. Compared with pure Bi2WO6, the photocatalytic activity of CuO/CNT/Bi2WO6 composites is significantly increased by a factor of 3.52. The main reason for the increased activity is that the doped CNTs and CuO promote the separation of photogenerated hole and electron pairs. In addition, the coupling of π-π electrons on the CNT surface with the pollutants promotes the adsorption of the pollutants on the photocatalyst surface. The degradation rate of pure photocatalytic degradation of phenol can reach 60%. Under the synergistic effect of H2O2, the degradation rate of phenol can reach 94%, which is 1.56 times higher than that of pure photocatalysis. The UV-vis absorption spectrum shows that CuO/CNT/Bi2WO6 has stronger light absorption ability in both visible and ultraviolet light regions. The trapping experiments of active species show that h + and • OH are the main active substances for photocatalytic degradation of phenol. This paper proposes a Z scheme mechanism to improve the photocatalytic performance.

Visible-near-infrared-responsive g-C3N4Hx+ reduced decatungstate with excellent performance for photocatalytic removal of petroleum hydrocarbon

The development of photocatalysts making full use of natural light sources is highly desired for the remediation of marine oil spill pollution, which is full of challenges. Herein, we demonstrate a well-defined visible-near-infrared-responsive g-C₃N₄H_x⁺ reduced decatungstate charge-transfer salt (RCD-CTS), which possess efficient light-absorption ability ranging from visible light to the near infrared region. The RCD-CTS photocatalyst exhibits excellent performance for photocatalytic removal of petroleum hydrocarbon. The structural characterization and theoretical calculation confirmed strong chemical interaction between components and partly reduction of decatungstate results in the plasmonic properties and the absorption of near infrared light. As a results, it is proposed that"hot electrons"transfer process generated by plasmon effect promotes the efficient separation of charge-carriers. Ultimately, this work sheds light on the discovery and application of visible-near-infrared-responsive optical materials that may be exploited further in artificial photosynthesis, solar energy conversion, and phototherapy.

Synthesis of hollow donut-like carbon nitride for the visible light-driven highly efficient photocatalytic production of hydrogen and degradation of pollutants

Design and synthesis of highly effective, hollow, erythrocyte-like g-C₃N₄ photocatalysts towards the degradation of environmental pollutants.

Polymeric structure optimization of g-C3N4 by using confined argon-assisted highly-ionized ammonia plasma for improved photocatalytic activity

The optimization of the polymeric structure and the modulation of surface amino groups in graphitic carbon nitride (g-CN) are critical but challenging in improving the photoelectric and photocatalytic performances of this polymer semiconductor. Ammonia plasma treatment may provide a fast and useful approach to optimize g-CN materials yet is seriously restricted by the low ionization ability of ammonia. Herein, a confined fast and environmental-friendly ammonia plasma method based on argon-assisted high ionization of NH₃ was developed for efficient modification of raw g-CN. Compared with the weakly-ionized pure ammonia plasma which can only introduce amino group onto the surface g-CN, the argon-assisted highly-ionized ammonia plasma treatment obviously contributes to the comprehensively polymeric structure optimization of g-CN, and thus plays a key role in enhancing its light-harvesting and decelerating the recombination of the photogenerated charge carriers. As a result, the argon-assisted highly-ionized ammonia plasma-treated g-CN-Ar+NH₃ outperformed the raw g-CN by a 2.5-fold higher photocatalytic reduction of hexavalent chromium and a remarkable 3.8-fold higher photocatalytic H₂ evolution activity (up to 957.8 μmol·h^-1·g^-1) under visible light irradiation. Our findings suggest the great prospects of this novel highly-ionized ammonia plasma treatment method in the controllable modification of semiconductors and polymers.