Development of novel Ag modified BiOF squares/g-C3N4 composite for photocatalytic applications

A novel Ag modified BiOF/g-C₃N₄ (Ag-BiOF/g-C₃N₄) organic–inorganic hybrid photocatalysts have been synthesized by a facile solvothermal route. The photocatalyst was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (UV-DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic studies reveals that the as-prepared Ag-BiOF/g-C₃N₄ photocatalyst exhibited significantly enhanced photocatalytic activity than the pure BiOF and BiOF/g-C₃N₄ photocatalysts toward degrading methylene blue (MB) under visible light irradiation. The heterostructured combination of Ag, g-C₃N₄ and BiOF micro squares provides synergistic photocatalytic performance through an efficient electron transport mechanism.     

Significant improvement of photocatalytic activity of porous graphitic-carbon nitride/bismuth oxybromide microspheres synthesized in an ionic liquid by microwave-assisted processing

Graphitic-carbon nitride/bismuth oxybromide (g-C₃N₄/BiOBr) porous microspheres have been successfully synthesized by a one-pot ethylene glycol (EG) assisted microwave process in the presence of 1-hexadecyl-3-methylimidazolium bromine ([C₁₆mim]Br). The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). During the reaction process, the ionic liquid acts not only as solvent and Br source but also as a template for fabrication of g-C₃N₄/BiOBr porous microspheres. In addition, the photocatalytic activity of the g-C₃N₄/BiOBr is evaluated by degrading Rhodamine B (RhB) and ciprofloxacin (CIP) under visible-light irradiation. It is found that 12.75 wt% g-C₃N₄/BiOBr microspheres exhibit higher photocatalytic activity than that of the as-prepared BiOBr. A possible photocatalytic mechanism based on the relative band positions of g-C₃N₄/BiOBr has been proposed.     

Enhanced photo-induced charge separation and solar-driven photocatalytic activity of g-C3N4 decorated by SO42−

SO₄²⁻ decorated g-C₃N₄ with enhanced photocatalytic performance was prepared by a facile pore impregnating method using (NH₄)₂S₂O₈ solution. The photocatalysts were characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and surface photovoltage (SPV) spectroscopy, respectively. The separation efficiency of photo-generated charge was investigated using benzoquinone as scavenger. The results demonstrate that sulfating of g-C₃N₄ increases the adsorption of rhodamine B on g-C₃N₄, the hydroxyl content and the separation efficiency of photo-generated charge. The photocatalytic activity of SO₄²⁻/g-C₃N₄ for decolorization of rhodamine B and methyl orange (MO) aqueous solution was evaluated. The result shows that loading of 6.0 wt% SO₄²⁻ results in the best photocatalytic activity under simulated solar irradiation and SO₄²⁻ play an important role in boosting the photocatalytic activity.     

Fabrication of Bi2MoO6 nanoplates hybridized with g-C3N4 nanosheets as highly efficient visible light responsive heterojunction photocatalysts for Rhodamine B degradation

The Bi₂MoO₆/g-C₃N₄ heterojunction photocatalysts have been successfully fabricated using a simple liquid chemisorptions and thermal post-treatment. These nanostructured Bi₂MoO₆/g-C₃N₄ composites were extensively characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR),UV–vis diffuse reflectance spectra (UV–vis DRS) and Photoluminescence (PL). The photocatalytic results show that 20 wt% Bi₂MoO₆/g-C₃N₄ sample exhibits efficient visible light activity and excellent photo-stability. The kinetic constant of RhB degradation over 20 wt% Bi₂MoO₆/g-C₃N₄ is about 5 and 2.5 times higher than that over pure Bi₂MoO₆ and g-C₃N₄ nanosheets, respectively. The enhanced photocatalytic performance is attributed to the construction of heterogeneous interface to promote photo-induced charge carrier pairs separation.     

Simultaneously Tuning Band Structure and Oxygen Reduction Pathway toward High-Efficient Photocatalytic Hydrogen Peroxide Production Using Cyano-Rich Graphitic Carbon Nitride

The demands for green production of hydrogen peroxide have triggered extensive studies in the photocatalytic synthesis, but most photocatalysts suffer from rapid charge recombination and poor 2e⁻ oxygen reduction reaction (ORR) selectivity. Here, a novel composite photocatalyst of cyano-rich graphitic carbon nitride g-C₃N₄ is fabricated in a facile manner by sodium chloride-assisted calcination on dicyandiamide. The obtained photocatalysts exhibit superior activity (7.01 mm  h⁻¹ under λ  ≥  420 nm, 16.05 mm  h⁻¹ under simulated sun conditions) for H₂O₂ production and 93% selectivity for 2e⁻ ORR, much higher than that of the state-of-the-art photocatalyst. The porous g-C₃N₄ with Na dopants and cyano groups simultaneously optimize two limiting steps of the photocatalytic 2e⁻ ORR: photoactivity, and selectivity. The cyano groups can adjust the band structure of g-C₃N₄ to achieve high activity. They also serve as oxygen adsorption sites, in which local charge polarization facilitates O₂ adsorption and protonation. With the aid of Na⁺, the O₂ is reduced to produce more superoxide radicals as the intermediate products for H₂O₂ synthesis. This work provides a facile approach to simultaneously tune photocatalytic activity and 2e⁻ ORR selectivity for boosting H₂O₂ production, and then paves the way for the practical application of g-C₃N₄ in environmental remediation and energy supply.     

Dual Functions of CO2 Molecular Activation and 4f Levels as Electron Transport Bridge in Dysprosium Single Atom Composite Photocatalysts with Enhanced Visible-Light Photoactivities

The effect of rare earth (RE) single atoms on photocatalytic activity is very complex due to its special electronic configuration, which leads to few reports on the RE single atoms. Here, Dy³⁺ single atom composite photocatalysts are successfully constructed based on both the special role of Dy³⁺ and the special advantages of CdS/g-C₃N₄ heterojunction in the field of photocatalysis. The results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO₂ molecular activation of rare-earth single atom and 4f levels as electron transport bridge are fully exploited. It is exciting that under visible-light irradiation, the catalytic performance of CdS:Dy³⁺/g-C₃N₄ is ≈ 6.9 times higher than that of pure g-C₃N₄. The catalytic performance of CdS:Dy³⁺ and CdS:Dy³⁺/g-C₃N₄ are ≈ 7 and ≈ 13.7 times higher than those of pure CdS, respectively. Besides, not all RE ions are suitable for charge transfer bridges, which is not only related to the 4f levels of RE ions but also related to the bandgap structure of CdS and g-C₃N₄. The pattern of combining single-atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.     

Synthesis and characterization of g-C3N4/BiFeO3 composites with an enhanced visible light photocatalytic activity

The novel visible light-induced g-C₃N₄/BiFeO₃ composites were successfully synthesized by introducing BiFeO₃ into polymeric g-C₃N₄. The structures and optical properties of composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), field-emission transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), respectively. For the degradation of Rhodamine B (RhB), the g-C₃N₄/BiFeO₃ composites exhibited significantly higher visible light photocatalytic activity than that of a single semiconductor. The optimal percentage of doped g-C₃N₄ was 50%. Both photooxidation and photoreduction processes follow first order kinetics. In addition, the stability of the prepared photocatalyst in the photocatalytic process was also investigated. The enhanced photocatalytic performance could be due to the high separation efficiency of the photogenerated electron–holes pairs. The possible photocatalytic mechanism of g-C₃N₄/BiFeO₃ was proposed to guide the further improvement of their photocatalytic activity.     

g-C3N4/Ag3PO4 composites with synergistic effect for increased photocatalytic activity under the visible light irradiation

The g-C₃N₄ was synthesized by a hydrothermal method and the g-C₃N₄/Ag₃PO₄ composites were prepared by a ordinary precipitation method. Microstructures, morphologies and optical properties of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that the Ag₃PO₄ nanoparticles were dispersed on the surface of the flake-like g-C₃N₄, and the heterojunction was formed on the interface. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst presented the highest photocatalytic activity for organic dye methylene blue (MB) degradation, and its photocurrent intensity was approximately 2 times than that of the pure Ag₃PO₄. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst also exhibited photocatalytic performance in the decomposition of colorless antibiotic ciprofloxacin (CIP). The capture experiment confirmed that holes acted as the main active species during the photocatalytic reaction.     

Near-Field Drives Long-Lived Shallow Trapping of Polymeric C3N4 for Efficient Photocatalytic Hydrogen Evolution

Undesired photoelectronic dormancy through active species decay is adverse to photoactivity enhancement. An insufficient extrinsic driving force leads to ultrafast deep charge trapping and photoactive species depopulation in carbon nitride (g-C₃N₄). Excitation of shallow trapping in g-C₃N₄ with long-lived excited states opens up the possibility of pursuing high-efficiency photocatalysis. Herein, a near-field-assisted model is constructed consisting of an In₂O₃-cube/g-C₃N₄ heterojunction associated with ultrafast photodynamic coupling. This In₂O₃-cube-induced near-field assistance system provides catalytic “hot areas”, efficiently enhances the lifetimes of excited states and shallow trapping in g-C₃N₄ and this favors an increased active species density. Optical simulations combined with time-resolved transient absorption spectroscopy shows there is a built-in charge transfer and the active species lifetimes are longer in the In₂O₃-cube/g-C₃N₄ hybrid. Besides these properties, the estimated overpotential and interfacial kinetics of the In₂O₃-cube/g-C₃N₄ hybrid co-promotes the liquid phase reaction and also helps in boosting the photocatalytic performance. The photocatalytic results exhibit a tremendous improvement (34-fold) for visible-light-driven hydrogen production. Near-field-assisted long-lived active species and the influences of trap states is a novel finding for enhancing (g-C₃N₄)-based photocatalytic performance.     

Enhanced Photocatalytic Activity of Lead-Free Cs2TeBr6/g-C3N4 Heterojunction Photocatalyst and Its Mechanism

In this study, a new type of lead-free double perovskite Cs₂TeBr₆ combined with metal-free semiconductor g-C₃N₄ heterojunction is constructed and used for photocatalytic CO₂ reduction for the first time. The S-scheme charge transfer mechanism between Cs₂TeBr₆ and g-C₃N₄ is systematically verified by X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and in situ Fourier infrared spectroscopy(FT-IR). The formation of S-type heterojunction makes the photocatalyst have higher charge separation ability and highest redox ability. The results show that 5%-CTB/CN heterojunction material has the best photocatalytic reduction effect on CO₂ under visible light irradiation. After 3 h of illumination, the yield of CO and CH₄ are 468.9 µmol g⁻¹ and 61.31 µmol g⁻¹, respectively. The yield of CO is 1.5 times and 32 times that of pure Cs₂TeBr₆ and g-C₃N₄, and the yield of CH₄ is doubled compared with pure Cs₂TeBr₆. However, g-C₃N₄ almost does not produce CH₄, which indicates that the construction of heterojunction helps to further improve the photocatalytic performance of the material. This study provides a new idea for the preparation of Cs₂TeBr₆/g-C₃N₄ heterojunction and its effective interfacial charge separation.     

Wood-Inspired Binder Enabled Vertical 3D Printing of g-C3N4/CNT Arrays for Highly Efficient Photoelectrochemical Hydrogen Evolution

2D nanomaterials are very attractive for photoelectrochemical applications due to their ultra-thin structure, excellent physicochemical properties of large surface-area-to-volume ratios, and the resulting abundant active sites and high charge transport capacity. However, the application of commonly used 2D nanomaterials with disordered-stacking is always limited by high photoelectrode tortuosity, few surface-active sites, and low mass transfer efficiency. Herein, inspired by wood structures, a vertical 3D printing strategy is developed to rapidly build vertically aligned and hierarchically porous graphitic carbon nitride/carbon nanotube (g-C₃N₄/CNT) arrays by using lignin as a binder for efficient photoelectrochemical hydrogen evolution. Arising from the directional electron transport and multiple light scattering in the out-of-plane aligned and porous architecture, the resulting g-C₃N₄/CNT arrays display an outstanding hydrogen evolution performance, with the hydrogen yield up to 4.36 µmol (cm⁻² h⁻¹) at a bias of −0.5 V versus RHE, 12.7 and 41.6 times higher than traditional thick g-C₃N₄/CNT and g-C₃N₄ films, respectively. Moreover, this 3D printed structure can overcome the agglomeration problem of the commonly used g-C₃N₄ with powder configuration and shows desirable recyclability and stability. This facile and scalable vertical 3D printing strategy will open a new avenue to highly enhance the photoelectrochemical performance of 2D nanomaterials for sustainably production of clean energy.     

Experimental Strategy and Mechanistic View to Boost the Photocatalytic Activity of Cs3Bi2Br9 Lead-Free Perovskite Derivative by g-C3N4 Composite Engineering

The rational design of heterojunctions based on metal halide perovskites (MHPs) is an effective route to create novel photocatalysts to run relevant solar-driven reactions. In this work, an experimental and computational study on the synergic coupling between a lead-free Cs₃Bi₂Br₉ perovskite derivative and g-C₃N₄ is presented. A relevant boost of the hydrogen photogeneration by more than one order of magnitude is recorded when going from pure g-C₃N₄ to the Cs₃Bi₂Br₉/g-C₃N₄ system. Effective catalytic activity is also achieved in the degradation of the organic pollutant with methylene blue as a model molecule. Based upon complementary experimental outputs and advanced computational modeling, a rationale is provided to understand the heterojunction functionality as well as the trend of hydrogen production as a function of perovskite loading. This work adds further solid evidence for the possible application of MHPs in photocatalysis, which is emerging as an extremely appealing and promising field of application of these superior semiconductors.     

A review on photocatalytic application of g-C3N4/semiconductor (CNS) nanocomposites towards the erasure of dyeing wastewater

Widespread concerns about the impacts of exposure to chemical substances with textile dyeing activities continue to be raised. Hitherto, the percolation of synthetic colourants into the groundwater and surface water supply remains an intricate challenge abroad the nations. With the revolution of graphitic carbon nitride (g-C₃N₄), there has been a gradually increasing attention in this research area. Recent advancements have been demonstrated that g-C₃N₄/semiconductor (CNS) nanocomposites can be envisioned as the most privileged and promising novel catalysts in the photocatalytic destruction of industrial effluents. The paper presents a review of current state of art on photocatalytic destruction of dyestuff effluents via CNS nanocomposites. Numerous techniques used to synthesize the CNS nanocomposites together with their representative examples have been reviewed. In addition, the recent research progresses on the efficacy of these nanocomposites in removing of selected dye pollutants are also summarized. This review paper ends with a summary and several future prospects on the challenges in expanding g-C₃N₄-based advanced nanocomposites in the possible enhancement of environmental conservation.     

2D Graphitic Carbon Nitride for Energy Conversion and Storage

Graphitic carbon nitride (g-C₃N₄) have attracted great attention in the field of energy conversion and storage due to its unique layered structure, tunable bandgap, metal-free characteristic, high physicochemical stability, and easy accessibility. 2D g-C₃N₄ nanosheets have the features of short charge/mass transfer path, abundant reactive sites and easy functionalization, which are beneficial to optimizing their performance in different fields. However, the reviews of the comprehensive applications of 2D g-C₃N₄ for energy conversion and storage are rare. Herein, this review first introduces the physicochemical properties of bulk g-C₃N₄ and g-C₃N₄ nanosheets, and then summarizes the synthetic strategies of 2D g-C₃N₄ nanosheets in detail, such as thermal oxidation etching, chemical exfoliation, ultrasonication-assisted liquid phase exfoliation, chemical vapor deposition, and others. Emphasis is focused on the rational design and development of 2D g-C₃N₄ nanosheets for the diversified applications in energy conversion and storage, including photocatalytic H₂ evolution, CO₂ reduction, electrocatalytic H₂ evolution, O₂ evolution, O₂ reduction, alkali-metal ion batteries, lithium-metal batteries, lithium–sulfur batteries, metal-air batteries, and supercapacitors. Finally, the current challenges and perspectives of 2D g-C₃N₄ nanosheets for energy conversion and storage applications are discussed.     

Controllable Approach to Carbon-Deficient and Oxygen-Doped Graphitic Carbon Nitride: Robust Photocatalyst Against Recalcitrant Organic Pollutants and the Mechanism Insight

Polymeric g-C₃N₄ is a promising visible-light-responsive photocatalyst; however, the fast recombination of charge carriers and moderate oxidation ability remarkably restrict its photocatalytic oxidation efficiency towards organic pollutants. To overcome these drawbacks, a self-modification strategy of one-step formaldehyde-assisted thermal polycondensation of molten urea to prepare carbon-deficient and oxygen-doped g-C₃N₄ (V_C-OCN) is developed, and the carbon vacancy concentration is well-controlled by changing formaldehyde dosage. The V_C-OCN catalysts exhibit interesting carbon vacancy concentration-dependent photocatalytic removal efficiency to p-nitrophenol (PNP) and atrazine (ATN), in which V_C-OCN₁₅ with appropriate carbon vacancy concentration displays significantly higher pollutant removal efficiency than bulk g-C₃N₄. The apparent first-order rate constant of V_C-OCN₁₅ for PNP and ATN removal is 4.4 and 5.2 times higher than that of bulk g-C₃N₄. A combination of the experimental results and theoretic calculations confirm that the synergetic effect of carbon vacancies and oxygen doping sites can not only delay the recombination of charge carriers but also facilitate adsorption of oxygen molecules on the carbon vacancies, which leads to the generation of plentiful active oxygen species including not only superoxide anion radicals but also indirectly formed hydroxyl radicals and singlet oxygen. These active oxygen species play a dominant role in the removal of target pollutants.     

Effective Prevention of Charge Trapping in Graphitic Carbon Nitride with Nanosized Red Phosphorus Modification for Superior Photo(electro)catalysis

The high occurrence of trapped unreactive charges due to chemical defects seriously affects the performance of g‐C₃N₄ in photocatalytic applications. This problem can be overcome by introducing ultrasmall red phosphorus (red P) crystals on g‐C₃N₄ sheets. The elemental red P atoms reduce the number of defects in the g‐C₃N₄ structure by forming new chemical bonds for much more effective charge separation. The product shows significantly enhanced photocatalytic activity toward hydrogen production. To the best of our knowledge, the hydrogen evolution rate obtained on this hybrid should be the highest among all P‐containing g‐C₃N₄ photocatalysts reported so far. The trapping and detrapping processes in this red P/g‐C₃N₄ system are thoroughly revealed by using time‐resolved transient absorption spectroscopy.     

Nanocellulose-Assisted Molecularly Engineering of Nitrogen Deficient Graphitic Carbon Nitride for Selective Biomass Photo-Oxidation

Structural modulation of graphitic carbon nitride (g-C₃N₄) remains a major challenge in rational catalyst design for artificial photosynthesis of valuable chemicals. Herein, a cellulose nanofiber (CNF) assisted polymerization is utilized to prepare 1D holey g-C₃N₄ nanorods (HCN) with nitrogen vacancies and oxygen dopants for photochemical synthesis of lactic acid via monosaccharide photooxidation. The HCN exhibits a remarkable yield of 75.5% for lactic acid from a wide assortment of sugars such as hexose (C5) to pentose (C6), together with an excellent hydrogen production rate of 2.8 mmol h⁻¹ g⁻¹. Mechanistic studies confirm the rapid generation of superoxide radical is responsible for the superior activity, enjoying the synergetic effect between nitrogen vacancies and oxygen dopants. This work provides new directions for the design of green and efficient photocatalysts for biomass upgrading.     

Engineering the Photocatalytic Behaviors of g/C3N4‐Based Metal‐Free Materials for Degradation of a Representative Antibiotic

Graphitic carbon nitride (g/C₃N₄) is of promise as a highly efficient metal‐free photocatalyst, yet engineering the photocatalytic behaviours for efficiently and selectively degrading complicated molecules is still challenging. Herein, the photocatalytic behaviors of g/C₃N₄ are modified by tuning the energy band, optimizing the charge extraction, and decorating the cocatalyst. The combination shows a synergistic effect for boosting the photocatalytic degradation of a representative antibiotic, lincomycin, both in the degradation rate and the degree of decomposition. In comparison with the intrinsic g/C₃N₄, the structurally optimized photocatalyst shows a tenfold enhancement in degradation rate. Interestingly, various methods and experiments demonstrate the specific catalytic mechanisms for the multiple systems of g/C₃N₄‐based photocatalysts. In the degradation, the active species, including ·O₂^?, ·OH, and h⁺, have different contributions in the different photocatalysts. The intermediate, H₂O₂, plays an important role in the photocatalytic process, and the detailed functions and originations are clarified for the first time.     

In Situ Bond Modulation of Graphitic Carbon Nitride to Construct p–n Homojunctions for Enhanced Photocatalytic Hydrogen Production

Graphitic carbon nitride (g‐C₃N₄) has recently emerged as an attractive photocatalyst for solar energy conversion. However, the photocatalytic activities of g‐C₃N₄ remain moderate because of the insufficient solar‐light absorption and the fast electron–hole recombination. Here, defect‐modified g‐C₃N₄ (DCN) photocatalysts, which are easily prepared under mild conditions and show much extended light absorption with band gaps decreased from 2.75 to 2.00 eV, are reported. More importantly, cyano terminal C?N groups, acting as electron acceptors, are introduced into the DCN sheet edge, which endows the DCN with both n‐ and p‐type conductivities, consequently giving rise to the generation of p–n homojunctions. This homojunction structure is demonstrated to be highly efficient in charge transfer and separation, and results in a fivefold enhanced photocatalytic H₂ evolution activity. The findings deepen the understanding on the defect‐related issues of g‐C₃N₄‐based materials. Additionally, the ability to build homojunction structures by the defect‐induced self‐functionalization presents a promising strategy to realize precise band engineering of g‐C₃N₄ and related polymer semiconductors for more efficient solar energy conversion applications.     

Modulation of Charge Trapping by Island-like Single-Atom Cobalt Catalyst for Enhanced Photo-Fenton-Like reaction

Composites-based photocatalysis relies on the interfacial electron transfer between the metallic cocatalyst and photosensitizer (the semiconductor) to realize spatial separation of charge carriers. Herein, an ingenious heterojunction between Co-CN single atom catalysts (SACs) and g-C₃N₄ is constructed for heterogeneous photo-Fenton-like reactions. Driven by built-in electric field across the heterojunctions, the separation and migration of the photogenerated charge carriers is promoted, leading to the fast electron transfer from the g-C₃N₄ to the Co-CN SACs. Theoretical calculations and transient absorption spectroscopy reveal the modulated charge transfer and trapping in the SA-Co-CN/g-C₃N₄ heterostructure, resulting in the remarkably enhanced generation of reactive oxygen species via peroxymonosulfate activation under light irradiation. This ingenious SA-Co-CN/g-C₃N₄/PMS/vis system is efficient for the oxidation of various antibiotics with high removal efficiency (>98%), a wide operating pH range (pH 3–11) and excellent stability in long-term operation. This study provides a new tactic for rational design of SACs-based heterojunctions to bridge photocatalysis and heterogeneous catalysis, attaining superior photoredox activity via interfacial coupling.