Novel g-C3N4 nanosheets/CDs/BiOCl photocatalysts with exceptional activity under visible light

We fabricated novel ternary nanocomposites through integration of C-dots (carbon dots), BiOCl, and nanosheets of graphitic carbon nitride (g-C₃N₄ nanosheets) by a cost-effective route. The fabricated photocatalysts were subsequently characterized by XRD, EDX, TEM, HRTEM, XPS, FT-IR, UV-vis DRS, TGA, BET, and PL methods to gain their structure, purity, morphology, optical, textural, and thermal properties. In addition, the degradation intermediates were identified by gas chromatography-mass spectroscopy (GC-MS). Photocatalytic performance of the synthesized samples was studied by photodegradations of three cationic (RhB, MB, and fuchsine), one anionic (MO) dyes, one colorless (phenol) pollutant and removal of an inorganic pollutant (Cr(VI)) under visible light. It was revealed that the ternary nanocomposite with loading 20% of BiOCl illustrated superlative performances in the selected photocatalytic reactions compared with the corresponding bare and binary photocatalysts. Visible-light photocatalytic activity of the g-C₃N₄ nanosheets/CDs/BiOCl (20%) nanocomposite was 42.6, 27.8, 24.8, 20.2, and 15.9 times higher than the pure g-C₃N₄ for removal of RhB, MB, MO, fuchsine, and phenol, respectively. Likewise, the ternary photocatalyst showed enhanced activity of 15.3 times relative to the g-C₃N₄ in photoreduction of Cr(VI). Moreover, the ternary nanocomposite exhibited excellent chemical stability and recyclability after five cycles. Finally, the mechanism for improved photocatalytic performance was discussed based on the band potential positions.     

Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation

A novel molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) composite photocatalyst was synthesized using a low temperature hydrothermal method. MoS₂ nanoparticles formed on g-C₃N₄ nanosheets greatly enhanced the photocatalytic activity of g-C₃N₄. The photocatalyst was tested for the degradation of methyl orange (MO) under simulated solar light. Composite 3.0 wt.% MoS₂/g-C₃N₄ showed the highest photocatalytic activity for MO decomposition. MoS₂ nanoparticles can increase the interfacial charge transfer and thus prevent the recombination of photo-generated electron–hole pairs. The novel MoS₂/g-C₃N₄ composite is therefore shown as a promising catalyst for photocatalytic degradation of organic pollutants using solar energy.     

Ultrathin graphitic carbon nitride nanosheets and graphene composite material as high-performance PtRu catalyst support for methanol electro-oxidation

Graphitic carbon nitride (g-C₃N₄) has been demonstrated as an advanced support material for Pt nanoparticles (NPs) due to its excellent stability and abundant Lewis acid for anchoring metal NPs. However, its non-conductive nature and low surface areas still impede its application in electrochemical fields. Herein, a π–π stacking method is presented to prepare graphene/ultrathin g-C₃N₄ nanosheets composite support for PtRu catalyst. The weaknesses of g-C₃N₄ are greatly overcome by establishing a 2D layered structure. The significantly enhanced performance for this novel PtRu catalyst is ascribed to reasons as follows: the homogeneous dispersion of PtRu NPs on g-C₃N₄ nanosheets due to its abundant Lewis acid sites for anchoring PtRu NPs; the excellent mechanical resistance and stability of g-C₃N₄ nanosheets in acidic and oxidative environments; the increased electron conductivity of support by forming a layered structure and the strong metal-support interaction (SMSI) between metal NPs and g-C₃N₄ NS.     

Facile one-step synthesis of pellet-press-assisted saddle-curl-edge-like g-C3N4 nanosheets for improved visible-light photocatalytic activity

Graphitic carbon nitride (g-C₃N₄) has attracted increasing interest as a visible-light-active photocatalyst. In this study, saddle-curl-edge-like g-C₃N₄ nanosheets were prepared using a pellet presser (referred to as g-CN P nanosheets). Urea was used as the precursor for the preparation of g-C₃N₄. Thermal polymerization of urea in a pellet form significantly affected the properties of g-C₃N₄. Systematic investigations were performed, and the results for the modified g-C₃N₄ nanosheets are presented herein. These results were compared with those for pristine g-C₃N₄ to identify the factors that affected the fundamental properties. X-ray diffraction analysis and high-resolution transmission electron microscopy revealed a crystallinity improvement in the g-CN P nanosheets. Fourier-transform infrared spectroscopy provided clear information regarding the fundamental modes of g-C₃N₄, and X-ray photoelectron spectroscopy (XPS) peak-fitting investigations revealed the variations of C and N in detail. The light-harvesting property and separation efficiency of the photogenerated charge carriers were examined via optical absorption and photoluminescence studies. The valence band edge and conduction band edge potentials were calculated using XPS, and the results indicated a significant reduction in the bandgap for the g-CN P nanosheets. The Brunauer–Emmett–Teller surface area increased for the g-CN P nanosheets. The photocatalytic degradation performance of the g-CN P nanosheets was tested by applying a potential and using the classical dye Rhodamine B (RhB). The RhB dye solution was almost completely degraded within 28 min. The rate constant of the g-CN P nanosheets was increased by a factor of 3.8 compared with the pristine g-C₃N₄ nanosheets. The high crystallinity, enhanced light absorption, reduced bandgap, and increased surface area of the saddle-curl-edge-like morphology boosted the photocatalytic performance of the g-CN P nanosheets.     

Tungsten-doped foam g-C3N4 with improved photocatalytic properties for degradation of pollutant and hydrogen evolution

As a potential material applied in the photocatalytic field, graphitic carbon nitride (g-C₃N₄) has attracted extensive attention for its advantages of visible-light response, excellent thermodynamic, and chemical stability. However, the photocatalytic performance of g-C₃N₄ is still limited in practical applications. Here, using a facile thermal polymerization method, unique W-doped foam g-C₃N₄ was synthesized to realize enhanced photocatalytic performance for the degradation of Rhodamine B and the evolution of hydrogen. Compared with pure foam g-C₃N₄, tungsten doping modified the foam g-C₃N₄ and efficiently improved its specific surface area, leading to enhanced photocatalytic performance. The average rate of hydrogen evolution was as high as 8818 μmol·h⁻¹·g⁻¹, which was better than most photocatalysts. This work proposes a new effective method and idea to modify g-C₃N₄ for improving its photocatalytic performance.     

Tailoring the bandgap of N-rich graphitic carbon nitride for enhanced photocatalytic activity

Nitrogen - rich graphitic carbon nitride (Ng-C₃N₄) with improved photocatalytic activity was engineered using a facile post-annealing treatment of pristine g-C₃N₄ in N₂ atmosphere. The thermal annealing did not modify the crystal structure, vibrational modes, or morphology of the N-rich g-C₃N₄ (Ng-C₃N₄). However, it decreased the crystallinity by broadening the dominant X-ray diffraction (XRD) peak and increased the surface area and mesoporous nature because of the formation of carbon vacancies. Diffuse reflectance spectroscopy indicated that the bandgap of the annealed Ng-C₃N₄ decreased from 2.82 to 2.77 eV compared to pristine g-C₃N₄. The increase of nitrogen content in the annealed Ng-C₃N₄ was quantified by X-ray photoelectron spectroscopy (XPS), which was also used to examine the formation of carbon vacancies. Photocurrent and electrochemical impedance spectroscopy measurements showed that the annealed Ng-C₃N₄ had higher light absorption capacity than the pristine g-C₃N₄. The photocatalytic performance of the samples was investigated for the degradation of crystal violet (CV) under ultra-violet light irradiation. The annealed Ng-C₃N₄ sample exhibited superior photodegradation of CV over pristine g-C₃N₄.     

Controlled preparation of P-doped g-C3N4 nanosheets for efficient photocatalytic hydrogen production

Hydrogen production by photolysis of water by sunlight is an environmentally-friendly preparation technology for renewable energy. Graphitic carbon nitride (g-C₃N₄), despite with obvious catalytic effect, is still unsatisfactory for hydrogen production. In this work, phosphorus element is incorporated to tune g-C₃N₄'s property through calcinating the mixture of g-C₃N₄ and NaH₂PO_2, sacrificial agent and co-catalyst also been supplied to help efficient photocatalytic hydrogen production. Phosphorus (P) doped g-C₃N₄ samples (PCN-S) were prepared, and their catalytic properties were studied. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and ultraviolet diffuse reflection (UV-DRS) were used to study their structures and morphologies. The results show that the reaction rate of PCN-S is 318 μmol h⁻¹ g⁻¹, which is 2.98 times as high as pure carbon nitride nanosheets (CN) can do. Our study paves a new avenue, which is simple, environment-friendly and sustainable, to synthesize highly efficient P doping g-C₃N₄ nanosheets for solar energy conversion.     

Rapid synthesis and characterization of advanced ceramic-polymeric nanocomposites for efficient photocatalytic decontamination of hazardous organic pollutant under visible light and inhibition of microbial biofilm

Ceramic-polymeric 3C–silicon carbide-graphitic carbon nitride (3C–SiC@g-C₃N₄) nanocomposites were synthesized by decorating cubic phased, ceramic 3C-Silicon carbide (3C–SiC) on the framework of the nanosheets of metal free polymeric graphitic carbon nitride (g-C₃N₄) by single step pulsed laser ablation in liquid (PLAL) method. Morphological, structural, elemental and optical characterizations of the synthesized 3C–SiC@g-C₃N₄ nanocomposites were carried out. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) studies confirm the perfect anchoring of 3C–SiC on g-C₃N₄ nanosheets in 3C–SiC@g-C₃N₄ nanocomposites synthesized by PLAL method. Ultra-violet diffuse reflectance spectra (UV-DRS) of 3C–SiC@g-C₃N₄ indicated the enhancement of visible light absorption and also the narrowing down of band gap energy in 3C–SiC@g-C₃N₄ nanocomposites, as a result of the anchoring of 3C–SiC on g-C₃N₄. Also we noticed the decrease of photoluminescence (PL) emission intensities in the PL spectra of 3C–SiC@g-C₃N₄ with respect to pure g-C₃N₄, which indicates the reduced photo-induced charge recombination by the presence of 3C–SiC content on g-C₃N₄ nanosheets. In the application side, PLAL synthesized 3C–SiC@g-C₃N₄ nanocomposites exhibited enhanced visible light driven photocatalytic degradation of methylene blue dye in water, improved antibacterial activity against Pseudomonas aeruginosa (gram-negative) and Staphylococcus aureus (gram-positive) bacteria, and also served as better inhibiting agent for biofilm formation, compared to pure g-C₃N₄ nanosheets. It is quite obvious from our studies that this ceramic-polymeric nanocomposite, 3C–SiC@g-C₃N₄ has the potential application for antibacterial and anti-biofilm activities in addition to its remarkable photocatalytic performance.     

One-Step Synthesis of g-C3N4 Nanosheets with Enhanced Photocatalytic Performance for Organic Pollutants Degradation Under Visible Light Irradiation

Graphitic carbon nitride (g-C₃N₄) has received much interest as a visible-light-driven photocatalyst for degrading pollutants such as organic dyes and antibiotics. However, g-C₃N₄ bulk activity could not meet expectations due to its rapid recombination of photogenerated electron–hole pairs and low specific surface area. In our study, melamine was thermally treated one-step in the presence of NH₄Cl to produce g-C₃N₄ nanosheets. The characterizations of surface morphology and optical properties of all g-C₃N₄ samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrum (XPS), transmission electron microscopy (TEM), and UV–visible diffuse reflectance spectroscopy. Compared to bulk g-C₃N₄, g-C₃N₄ nanosheets demonstrated excellent photocatalytic activities, with approximately 98% RhB removal after 210 min of visible light irradiation. Furthermore, the effect of catalyst dosage, pH, and RhB concentration on the removal percentage dye of g-C₃N₄ nanosheets was also investigated. h⁺ and ^?O₂^? species were demonstrated as the key reactive species for the RhB. Besides, ECN exposed a tetracycline degradation efficiency of 80.5% under visible-light irradiation for 210 min, which is higher than BCN (60.8%). The improved photocatalytic activity of g-C₃N₄ nanosheets is due to the restriction of the recombination of photogenerated electrons/hole pairs, as provided by photoluminescence spectra and Nyquist plot. As a result, our research may offer an effective approach to fabricating g-C₃N₄ nanosheets with high photocatalytic activity and high stability for environmental decontamination.

     

Amino group-rich porous g-C3N4 nanosheet photocatalyst: Facile oxalic acid-induced synthesis and improved H2-evolution activity

The reasonable modulation of tri-s-triazine structure units of g-C₃N₄ is an effective method to optimize its intrinsic electronic and optical properties, thus boosting its photocatalytic hydrogen-evolution activity. Herein, amino groups are successfully introduced into the tri-s-triazine structure units of g-C₃N₄ nanosheets to improve their H₂-evolution activity via a facile oxalic acid-induced supramolecular assembly strategy. In this case, the resulting amino group-rich porous g-C₃N₄ nanosheets display a loose and fluffy structure with a large specific surface area (70.41 m² g^?1) and pore volume (0.50 cm³? g^??1), and enhanced visible-light absorption (450–800 nm). Photocatalytic tests reveal that the amino group-rich porous g-C₃N₄ nanosheets (AP-CN1.0 nanosheets) exhibit a significantly elevated photocatalytic H₂-production activity (130.7 μmol h^?1, AQE = 5.58%), which is much greater than that of bulk g-C₃N₄ by a factor of 4.9 times. The enhanced hydrogen-generation performance of amino group-rich porous g-C₃N₄ nanosheets can be mainly attributed to the introduction of more amino groups, which can reinforce the visible-light absorption and work as the interfacial hydrogen-generation active centers to boost the photocatalytic hydrogen production. The present facile and effective regulation of tri-s-triazine structure units may provide an ideal route for the exploitation of novel and highly efficient g-C₃N₄ photocatalysts.     

Influence of Hydrogenation on Morphology,Chemical Structure and Photocatalytic Efficiency of Graphitic Carbon Nitride

In this contribution, the effect of hydrogenation conditions atmosphere (temperature and time) on physicochemical properties and photocatalytic efficiency of graphitic carbon nitride (g-C₃N₄, gCN) was studied in great details. The changes in the morphology, chemical structure, optical and electrochemical properties were carefully investigated. Interestingly, the as-modified samples exhibited boosted photocatalytic degradation of Rhodamine B (RhB) with the assistance of visible light irradiation. Among modified gCN, the sample annealed at 500 °C for 4 h (500-4) in H₂ atmosphere exhibited the highest photocatalytic activity—1.76 times higher compared to pristine gCN. Additionally, this sample presented high stability and durability after four cycles. It was noticed that treating gCN with hydrogen at elevated temperatures caused the creation of nitrogen vacancies on gCN surfaces acting as highly active sites enhancing the specific surface area and improving the mobility of photogenerated charge carriers leading to accelerating the photocatalytic activity. Therefore, it is believed that detailed optimization of thermal treatment in a hydrogen atmosphere is a facile approach to boost the photoactivity of gCN.     

Method for the synthesis of water-soluble oxide of graphite-like carbon nitride

The new route to synthesize the oxygen containing carbon nitride is developed. In contrast to known methods, our approach does not require the preliminary preparation of g-C₃N₄: pyrolysis of melamine is carried out at the presence of oxygen. First alongside with the oxygen-doped (~ 8.1%) carbon nitride (O-g-C₃N₄) an oxide of carbon nitride (g-C₃N₄)O was obtained as a new substance that has a structure similar to the graphite oxide. Nanosized powder of (g-C₃N₄)O is easily dissolved and exfoliated in water with the formation of a flake-like solution, which can contain nanosheets from several heptazine layers.     

Graphene oxide-assisted production of carbon nitrides using a solution process and their photocatalytic activity

Graphitic carbon nitride (g-C₃N₄) and its derivatives are promising candidates as catalysts or supports for photocatalytic applications. Since they are typically produced by polymerization or condensation of monomers under high temperature and high pressure, development of a cost-effective, solution-based, low-temperature method of production is important. Herein, novel hybrid materials composed of g-C₃N₄ and reduced graphene oxide are produced using a simple reaction between graphene oxide and cyanamide using a solution-based process. During the reaction, reduction of graphene oxide and graphene oxide-assisted generation of g-C₃N₄ occurred simultaneously. These hybrids show good photocatalytic performance for the removal of organic dyes under one sun solar light illumination.     

Mini Review on the Structure and Properties (Photocatalysis), and Preparation Techniques of Graphitic Carbon Nitride Nano-Based Particle,and Its Applications

Graphite carbon nitride (g-C₃N₄) is well known as one of the most promising materials for photocatalytic activities, such as CO₂ reduction and water splitting, and environmental remediation through the removal of organic pollutants. On the other hand, carbon nitride also pose outstanding properties and extensive application forecasts in the aspect of field emission properties. In this mini review, the novel structure, synthesis and preparation techniques of full-bodied g-C₃N₄-based composite and films were revealed. This mini review discussed contemporary advancement in the structure, synthesis, and diverse methods used for preparing g-C₃N₄ nanostructured materials. The present study gives an account of full knowledge of the use of the exceptional structural and properties, and the preparation techniques of graphite carbon nitride (g-C₃N₄) and its applications.     

Visible light-activated degradation of microcystin-LR by ultrathin g-C3N4 nanosheets-based heterojunction photocatalyst

Microcystins (MCs) is a harmful toxin generated by blue-green algae in water, which has seriously threatened the ecological safety of water and human body. It is urgent to develop new catalysts and techniques for the degradation of MCs. A feasible electrostatic self-assembly method was carried out to synthesize BiVO₄/g-C₃N₄ heterojunction photocatalyst with highly efficient photocatalytic ability, where BiVO₄ nanoplates with exposed {010} facets anchored to the g-C₃N₄ ultrathin nanosheets. The morphology and microstructure of the heterojunction photocatalysts were identified by XRD, SEM, TEM, XPS, and BET. The g-C₃N₄ nanosheets have huge surface area over 200 m²/g and abundant mesoporous ranging from 2-20 nm, which provides tremendous contact area for BiVO₄ nanoplates. Meanwhile, the introduction of BiVO₄ led to red-shift of the absorption spectrum of photocatalyst, which was characterized by UV-vis diffuse reflection spectroscopy (DRS). Compared with pure BiVO₄ and g-C₃N₄, the BiVO₄/g-C₃N₄ heterojunction shows a drastically enhanced photocatalytic activity in degradation of microcystin-LR (MC-LR) in water. The MC-LR could be removed within 15 minutes under the optimal ratio of BiVO₄/g-C₃N₄. The outstanding performance of the photocatalyst is attributed to synergetic effect of interface Z-scheme heterojunction and high active facets {010} of BiVO₄ nanoplates, which provides an efficient transfer pathway to separate photoinduced carriers meanwhile endows the photocatalysts with strong redox ability.     

Enhanced antipressure ability through graphene oxide membrane by intercalating g-C3N4 nanosheets for water purification

Graphene oxide (GO) membranes have shown great potential for water purification, but their permeability and antipressure ability are poor, which limits their practical applications. In this study, two-dimensional graphitic carbon nitride (g-C₃N₄) nanosheet-intercalated GO (GOCN) membranes were developed to improve the separation performance of GO membranes, especially under high operating pressure. After incorporation of the g-C₃N₄ nanosheets, the amount of permeable nanochannels (wrinkles or corrugation) in the membrane increased; hence, the water permeance was effectively improved (twice as high as that of GO membranes). Moreover, the antipressure performance of the GOCN membranes was significantly enhanced (even below 0.5 MPa pressure) as the nanochannels in the composite membranes become stable and rigid due to the support of the pressure-resistant g-C₃N₄ nanosheets. The good separation performance demonstrates that the intercalation of g-C₃N₄ is an effective strategy to improve the GO-based membrane properties, which can promote their application in water purification.     

Facile synthesis of Y-doped graphitic carbon nitride with enhanced photocatalytic performance

Yttrium-doped graphitic carbon nitride (Y/g-C₃N₄) catalysts were prepared via a facile pyrolysis method with urea used as a precursor and yttrium nitrate as the Y source. Characterization results show that an appropriate doping ratio of Y can be embedded into in-planes of g-C₃N₄. The Y/g-C₃N₄ catalysts are characterized by hierarchical porosity, large specific surface area, and large pore volume. Introduction of Y species effectively extends the spectral response of g-C₃N₄ from ultraviolet to visible region and decelerates the recombination of photogenerated electrons and holes. Because of these properties, the Y/g-C₃N₄ catalysts show an enhanced photocatalytic performance in rhodamine B degradation under visible light.     

Carbon nitride nanowires/nanofibers: A novel template-free synthesis from a cyanuric chloride–melamine precursor towards enhanced adsorption and visible-light photocatalytic performance

The development of a graphitic carbon nitride (g-C₃N₄) photocatalyst is of great importance to a variety of visible utilization application fields. The desired high efficiency can be achieved by employing well-controlled g-C₃N₄ nanostructures. In this study, we successfully synthesized high surface area g-C₃N₄ nanowires and nanofibers using a cyanuric chloride and melamine precursor dispersed in a solvothermal reaction and with a subsequent calcination step. The obtained novel nanowire product had a diameter of 10–20 nm and a length of several hundreds of nanometers, while the nanofibers revealed fibrous nanostructures of randomly dispersed fibers with an average diameter of ~15 nm. The adsorption and photocatalytic experimental results indicated that the as-prepared nanowires and nanofibers showed enhanced activities compared with bulk g-C₃N₄. Based on our experimental results, a possible photocatalytic mechanism with hydroxyl and superoxide radical species as the main active species in photocatalysis was proposed. Moreover, our strategy may provide progress toward the design and practical application of 1D g-C₃N₄ nanostructures in the adsorption and photocatalytic degradation of pollutants.     

Enhanced interfacial electronic transfer of BiVO4 coupled with 2D g-C3N4 for visible-light photocatalytic performance

A BiVO₄/2D g-C₃N₄ direct dual semiconductor photocatalytic system has been fabricated via electrostatic self-assembly method of BiVO₄ microparticle and g-C₃N₄ nanosheet. According to experimental measurements and first-principle calculations, the formation of built-in electric field and the opposite band bending around the interface region in BiVO₄/2D g-C₃N₄ as well as the intimate contact between BiVO₄ and 2D g-C₃N₄ will lead to high separation efficiency of charge carriers. More importantly, the intensity of bulid-in electric field is greatly enhanced due to the ultrathin nanosheet structure of 2D g-C₃N₄. As a result, BiVO₄/2D g-C₃N₄ exhibits excellent photocatalytic performance with the 93.0% Rhodamine B (RhB) removal after 40 min visible light irradiation, and the photocatalytic reaction rate is about 22.7 and 10.3 times as high as that of BiVO₄ and 2D g-C₃N₄, respectively. In addition, BiVO₄/2D g-C₃N₄ also displays enhanced photocatalytic performance in the degradation of tetracycline (TC). It is expected that this work may provide insights into the understanding the significant role of built-in electric field in heterostructure and fabricating highly efficient direct dual semiconductor systems.     

Mechanical and thermal performances of epoxy resin/graphitic carbon nitride composites

In this paper, a series of graphitic carbon nitride (g-C₃N₄) was synthesized under different thermal oxidation etching temperatures and epoxy/g-C₃N₄ composites were prepared via solution blending. The morphology and structure of g-C₃N₄ were investigated by transmission electron microscope, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The tensile fracture morphology and structure of epoxy resin (EP) composites were demonstrated by scanning electron microscopy and XRD, respectively. Mechanical properties of EP composites were characterized by tensile testing, and the thermal performances were investigated by dynamic mechanical thermal analysis and thermal gravimetric analysis. The results revealed that the active groups on g-C₃N₄ sheets increased under thermal oxidation etching and the C to N ratio of g-C₃N₄ decreased from 0.94 to 0.76 with the increasing etching temperature. Noticeably, the tensile strength of EP composites was enhanced by 58% with the addition of C₃N₄-NS-500 and the thermal properties were also improved significantly, including T_0.5 (the decomposition temperature at the mass loss of 50%) increased by 21.5 °C and glass transition temperature improved by 8 °C. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48598.