Carbon Nitride-based Materials Research Articles

Electronic Structure and Functions of Carbon Nitride in Frontier Green Catalysis.

ConspectusGraphitic carbon nitride-based materials have emerged as promising photocatalysts for a variety of energy and environmental applications owing to their "earth-abundant" nature, structural versatility, tunable electronic and optical properties, and chemical stability. Optimizing carbon nitride's physicochemical properties encompasses a variety of approaches, including the regulation of inherent structural defects, morphology control, heterostructure construction, and heteroatom and metal-atom doping. These strategies are pivotal in ultimately enhancing their photocatalytic activities. Previous reviews with extensive examples have mainly focused on the synthesis, modification, and application of carbon nitride-based materials in photocatalysis. However, there has been a lack of straightforward and in-depth discussion to understand the electronic characteristics and functions of various engineered carbon nitrides as well as their precise tailoring strategies and ultimately to explain the regularity and specificity of their improved performance in targeted photocatalytic systems. In the past ten years, our group has conducted extensive investigations on carbon nitride-based materials and their application in photocatalysis. These studies demonstrate the close yet intricate relationship between the electronic structure of carbon nitride materials and their photocatalytic reactivity. Understanding the electronic structure and functions of carbon nitride, as well as different engineering strategies, is essential for the improvement of photocatalytic processes from fundamental study to practical applications.To this end, in this Account, we first delve into the nature of the electronic properties of carbon nitride, highlighting the electronic structures, including band structure, density of states, molecular orbitals, and band center, as well as its electronic functions, such as the charge distribution, internal electric field, and external electric force. Subsequently, based on recent research in our group, we present a detailed discussion of the strategic modifications of carbon nitride and the consequential impacts on the physicochemical properties, particularly the optical properties and intrinsic electronic characteristics, for enhancing the photocatalytic performance. These modifications are categorized as follows: (i) component changing, which involves intralayer and interface heterojunctions as well as homojunctions, to modulate the band-edge potentials and reactivity of photoinduced electrons and holes toward surface redox reactions; (ii) dimensional tuning, which engineers the dimensional structure of carbon nitride, to influence the electron transfer direction; (iii) defect and heteroatom modification, which introduces a symmetry break in the carbon nitride framework, to promote charge redistribution for altering the charge density and electronic structure; and (iv) anchoring of single-atom metals to facilitate orbital hybridization and charge transfer enhancement through the unique metal-N coordination configurations. Finally, we propose an appraisal of the prospects and challenges in the precise manipulation and characterization of the electronic structure and functions of carbon nitride. The integration of in situ electronic structure analysis, theoretical calculation based on machine learning, and precise mechanism study may propel its substantial development in the light-driven circular economy. We hope this Account aspires to offer novel insights and perspectives into the operational mechanisms and tailored structure of carbon nitride-based materials in photocatalysis.

Emerging Roles of Graphitic Carbon Nitride-based Materials in Biomedical Applications.

Graphite carbon nitride (g-C3N4) is a two-dimensional conjugated polymer with a unique energy band structure similar to graphene. Due to its outstanding analytical advantages, such as relatively small band gap (2.7 eV), low-cost synthesis, high thermal stability, excellent photocatalytic ability, and good biocompatibility, g-C3N4 has attracted the interest of researchers and industry, especially in the medical field. This paper summarizes the latest research on g-C3N4-based composites in various biomedical applications, including therapy, diagnostic imaging, biosensors, antibacterial, and wearable devices. In addition, the application prospects and possible challenges of g-C3N4 in nanomedicine are also discussed in detail. This review is expected to inspire emerging biomedical applications based on g-C3N4.

Recent progress in graphitic carbon nitride-based materials for antibacterial applications: synthesis, mechanistic insights, and utilization

Recent breakthroughs in graphitic carbon nitride (g-C3N4)-based materials have catalyzed the development of highly effective antibacterial strategies. This comprehensive review delves into the synthesis, mechanistic insights, and applications of g-C3N4 in the realm of antibacterial research. The introduction first highlights the importance of antibacterial materials, emphasizing the urgent need for innovative solutions in the face of bacterial infections and the escalating challenges posed by antibiotic resistance. Continuing, the structural attributes and distinctive characteristics of g-C3N4 are examined in detail, elucidating its inherent properties that make it a compelling candidate for antibacterial applications. Subsequently, we meticulously dissect various methods used in the synthesis of g-C3N4, encompassing both top-down and bottom-up approaches, offering valuable insights into the production of this promising nanomaterial. Furthermore, it delves deeper into the sterilization mechanisms of g-C3N4-based nanomaterials, encompassing a spectrum of strategies, including physical structure sterilization, photocatalytic antibacterial effects, enzymatic antibacterial processes, and the synergetic benefits that emerge from the fusion of these mechanisms. Then, it comprehensively examines the practical applications of g-C3N4-based nanomaterials in antibacterial endeavors, encompassing their pivotal roles in water purification, air purification, treatment of bacterial infections, and the development of antibacterial layers in diverse settings. In conclusion, we encapsulate the crux of our findings and provide a forward-looking perspective on the potential challenges and opportunities in the arena of g-C3N4-based materials for antibacterial applications. This review aspires to galvanize further exploration and innovation in the design of high-performance g-C3N4-based materials, thereby contributing to the progression of antibacterial solutions.

Phosphorylated g-C3N4/sulfur self-doped g-C3N4 homojunction carboxymethyl cellulose beads: An efficient photocatalyst for H2O2 production

The development of highly reusable, affordable, and durable photocatalysts for the production of hydrogen peroxide (H2O2) remained a challenge. In this study, a homojunction photocatalyst (SPGCN) is constructed between phosphorylated g-C3N4 (PCN) and sulfur self-doped g-C3N4 (SCN) using a simple wet impregnation method. Later, the obtained SPGCN homojunction is transformed into hydrogel beads using carboxymethyl cellulose via an effective cross-linking strategy (SPGCN/CMC). The photocatalytic beads displayed a phenomenal H2O2 production of 3.5 mM under visible light illumination for 60 min. The SPGCN/CMC hydrogel beads showed a maximum reusability of 10 cycles with a decline of 1.5 mM H2O2 production. The improved photocatalytic efficiency is indicated by strengthened utilization of visible light via tuning of the band gap, suppressed recombination of electron-hole pairs, and higher separation efficiency through the effective construction of Z-scheme between the phosphorylated carbon nitride and the sulfur-self-doped carbon nitride present in the SPGCN/CMC beads. The mechanistic studies affirmed the dominant role of superoxide radicals in H2O2 production. The photocatalytic H2O2 production followed a highly selective two-electron reduction reaction. Overall, this study highlights the efficient engineering of carbon nitride-based materials towards artificial photosynthesis.

Graphitic Carbon Nitride Meets Molecular Oxygen: New Sustainable Photocatalytic Ways for the Oxidation of Organic Molecules

In recent years, organic chemists have taken a resolute step toward green photocatalytic synthesis. In this regard, the oxidation of organic compounds with molecular oxygen is one of the most important classes of transformations, as it increases molecular complexity while avoiding the use of toxic and harmful oxidants. To this aim, the development of new and efficient photocatalysts capable of driving valuable oxidative reactions in a sustainable manner is highly desirable. These novel photocatalytic systems need to be metal-free, easy-to-prepare, and potentially recyclable. Carbon nitride (CN) fulfils all these requirements because of its outstanding physicochemical properties, thus emerging as a promising heterogeneous photocatalytic platform. The growing popularity of this material is also substantiated by its fast and facile preparation from readily available and inexpensive molecular precursors. This Review aims at highlighting the recent advances in synthesis of carbon nitride-based materials and their applications in organic photocatalysis for the oxidation of organic molecules in presence of molecular oxygen. Lastly, forward-looking opportunities within this intriguing research field are mentioned.

Efficient Strategies to Use β-Cationic Porphyrin-Imidazolium Derivatives in the Photoinactivation of Methicillin-Resistant Staphylococcus aureus.

Bacterial resistance to antibiotics is a critical global health issue and the development of alternatives to conventional antibiotics is of the upmost relevance. Antimicrobial photodynamic therapy (aPDT) is considered a promising and innovative approach for the photoinactivation of microorganisms, particularly in cases where traditional antibiotics may be less effective due to resistance or other limitations. In this study, two β-modified monocharged porphyrin-imidazolium derivatives were efficiently incorporated into polyvinylpyrrolidone (PVP) formulations and supported into graphitic carbon nitride materials. Both porphyrin-imidazolium derivatives displayed remarkable photostability and the ability to generate cytotoxic singlet oxygen. These properties, which have an important impact on achieving an efficient photodynamic effect, were not compromised after incorporation/immobilization. The prepared PVP-porphyrin formulations and the graphitic carbon nitride-based materials displayed excellent performance as photosensitizers to photoinactivate methicillin-resistant Staphylococcus aureus (MRSA) (99.9999% of bacteria) throughout the antimicrobial photodynamic therapy. In each matrix, the most rapid action against S. aureus was observed when using PS 2. The PVP-2 formulation needed 10 min of exposure to white light at 5.0 µm, while the graphitic carbon nitride hybrid GCNM-2 required 20 min at 25.0 µm to achieve a similar level of response. These findings suggest the potential of graphitic carbon nitride-porphyrinic hybrids to be used in the environmental or clinical fields, avoiding the use of organic solvents, and might allow for their recovery after treatment, improving their applicability for bacteria photoinactivation.

Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies.

The facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride-based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large-scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties.

Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies

AbstractThe facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride‐based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large‐scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties.

Fe Powder Catalytically Synthesized C3N3 toward High-Performance Anode Materials of Lithium-Ion Batteries

Recently, carbon nitrides and their carbon-based derivatives have been widely studied as anode materials of lithium-ion batteries due to their graphite-like structure and abundant nitrogen active sites. In this paper, a layered carbon nitride material C3N3 consisting of triazine rings with an ultrahigh theoretical specific capacity was designed and synthesized by an innovative method based on Fe powder-catalyzed carbon-carbon coupling polymerization of cyanuric chloride at 260 °C, with reference to the Ullmann reaction. The structural characterizations indicated that the as-synthesized material had a C/N ratio close to 1:1 and a layered structure and only contained one type of nitrogen, suggesting the successful synthesis of C3N3. When used as a lithium-ion battery anode, the C3N3 material showed a high reversible specific capacity up to 842.39 mAh g-1 at 0.1 A g-1, good rate capability, and excellent cycling stability attributed to abundant pyridine nitrogen active sites, large specific surface area, and good structure stability. Ex situ XPS results indicated that Li+ storage relies on the reversible transformation of -C=N- and -C-N- groups as well as the formation of bridge-connected -C=C- bonds. To further optimize the performance, the reaction temperature was further increased to synthesize a series of C3N3 derivatives for the enhanced specific surface area and conductivity. The resulting derivative prepared at 550 °C showed the best electrochemical performance, with an initial specific capacity close to 900 mAh g-1 at 0.1 A g-1 and good cycling stability (94.3% capacity retention after 500 cycles at 1 A g-1). This work will undoubtedly inspire the further study of high-capacity carbon nitride-based electrode materials for energy storage.

Single-atom cobalt-incorporating carbon nitride for photocatalytic solar hydrogen conversion: An X-ray spectromicroscopy study

The use of carbon nitride-based materials and light to drive catalytic water splitting has enormous potential for the production of hydrogen. Revealing the processes of molecular conjugation, nucleation, and crystallization in crystalline carbon nitride is expected to enhance the photocatalytic activity through the creation of isotype heterojunctions and active sites. In this work, the addition of cobalt salts in ionothermal synthesis was found to promote the phase transition of heptazine-based crystalline carbon nitride (CCN) to triazine-based poly (triazine imide) (PTI), resulting in the formation of a single-atom cobalt-doped coordinated isotype CCN/PTI heterojunction. The new hybrid orbital modulates the atomic/electronic structure and the band gap of the CCN/PTI heterojunction, and synergistically increases the absorption of visible light, accelerating the separation and transfer of photoexcited electrons and holes. Synchrotron-based X-ray spectroscopy and microscopy are used to identify the origin of the improved performance of the single-atom cobalt-doped CCN/PTI heterojunction in the photocatalytic hydrogen evolution reaction. This work demonstrates that synchrotron X-ray spectroscopy is a promising tool for designing materials aimed at enhancing photocatalytic activity in solar energy conversion applications.

Interface tweaking of perovskite solar cells with carbon nitride-based 2D materials

Two-dimensional van der Waals layered materials display strong Coulomb interactions, which in turn give rise to large exciton binding energies. Tuning the interface is the basis of devices including optoelectrical, and their delineation is of paramount importance. The developed 2D-carbon nitrides, display graphene-like atomic structures, and the variation in synthetic protocols impact their properties. Engineering the interface with carbon nitride at hole transport layers and perovskite, can eliminate defective charge build-up and suppress the charge carrier recombination rate to induce accelerated photo-induced charge transfer. The fabricated solar cells with L-C3N4 or g-C3N4 interface layers gave an improved performance with boosted open-circuit voltage and fill factor. The developed interface layers avoid the direct contact of NiOx with perovskite, overcoming the possible instability of the active layer via iodide oxidation and deprotonation of cationic amines. The carbon nitride-based 2D materials will serve as an effective interfacial layer for long-term reliability in photovoltaics.

Interface Tweaking of Perovskite Solar Cells with Carbon Nitride-based 2D Materials

Interface Tweaking of Perovskite Solar Cells with Carbon Nitride-based 2D Materials

Interface engineering of a hole-transport layer/perovskite with low-band-gap 2D-carbon nitrides for solar cell fabrication

Carbon nitride-based 2D materials, such as C3N3 and C3N5, and their role as an interlayer in perovskite solar cells to stabilize NiOx hole selectivity are investigated.

Realizing a strong visible-light absorption band in piezoelectric 2D carbon nitride sheets for enhanced piezocatalysis

Piezoelectric photocatalytic water splitting is a viable approach to generate renewable energy and carbon nitride sheets (CNs) has emerged as a promising material. However, the narrow solar absorption range of CNs due to its wide-band-gap hinders its further development and practical applications. In this study, CNs with a strong visible-light absorption band and a sharp absorption edge beyond 574 nm are successfully prepared by developing a fluorination and defluorination strategy. Experimental results show that introducing cyano groups into the framework of CNs as well as the accompanied nitrogen vacancies at the edges maintains high piezoelectricity and that the separation of photo-generated electron-hole pairs by the piezo-polarization charges is enhanced in the modulated CNs. Under simultaneous visible-light exposure and the ultrasonic irradiation, the modulated CNs loaded with Pt cocatalyst as a photocatalyst show a superior photocatalytic hydrogen evolution rate of 13.53 mmol g−1 h−1, which is one of the highest record reported so far for carbon nitride-based materials. Theoretical calculations reveal that the introduction of cyano into CNs leads to a suitable band gap for visible light, which dramatically improves the photocatalytic ability. This study advances the investigation of piezoelectric photocatalytic water splitting, and is also an enabling technology for piezoelectric semiconductors for their practical applications.

Magnetically recyclable CoS-modified graphitic carbon nitride-based materials for efficient immobilization of gaseous elemental mercury

• The CoS/g-C 3 N 4 composite was prepared by ultrasonic mechanical mixing method. • The Hg 0 adsorption capacity and durability of CoS modified g-C 3 N 4 are significantly improved in the low temperature range. • 20CoS/CN has excellent magnetic and recycling ability. • The S substances on the surface of the CoS/g-C 3 N 4 adsorbent were the main active sites for capturing Hg 0 . Mercury pollution from coal-fired power plants poses a serious threat to human health and the ecological environment. In this work, a novel cobalt sulfide (CoS) modified graphite carbon nitride (g-C 3 N 4 ) adsorbent was developed to capture Hg 0 in flue gas at low temperature, aiming at the shortcomings of poor adsorption performance and slow adsorption rate of most traditional adsorbents. It was found that the addition of CoS can greatly improve the Hg 0 removal effect of g-C 3 N 4 monomer. Meanwhile, due to the magnetic characteristics of CoS, it can be recycled and reused under the action of an external magnetic field. Benefiting from the optimized performance, the composites loaded with 20 wt% CoS can maintain a mercury removal efficiency close to 90% for a long time, which is more than 4 times that of pure g-C 3 N 4 . In addition, the adsorption characteristics of CoS/g-C 3 N 4 on Hg 0 were analyzed by various kinetic models, and the maximum mercury adsorption capacity at 120℃ was calculated to be 15.22 mg/g. The XPS and Hg-TPD analysis showed that the adsorbed mercury mainly existed in the form of HgS on the surface of the adsorbent. The CoS/g-C 3 N 4 composite designed in this study can be used as a good adsorbent to replace traditional activated carbon for elemental mercury removal in coal-fired power plants due to its excellent mercury removal performance and recyclability.

Polymeric carbon nitride-based materials: Rising stars in bioimaging

Polymeric carbon nitrides (CN), due to their unique physicochemical properties, versatile surface functionalization, ultra-high surface area, and good biocompatibility, have attracted considerable interest in diverse biomedical applications, such as biosensors, drug delivery, bioimaging, and theranostics. In this review, the recent advances in bioimaging of CN-based nanomaterials are summarized according to the imaging modalities, including optical (fluorescence and Raman) imaging, magnetic resonance imaging (MRI), photoacoustic imaging (PAI), computed tomography (CT), and multimodal imaging. The pros and cons of CN bioimaging are comprehensively analyzed and compared with those in previous reports. In the end, the prospects and challenges of their future bioimaging applications are outlooked.

Advances in Carbon Nitride-Based Materials and Their Electrocatalytic Applications

Advances in Carbon Nitride-Based Materials and Their Electrocatalytic Applications

Boosting the Quantum Yield of Oxygen-Doped g-C3N4 via a Metal-Azolate Framework-Enhanced Electron-Donating Strategy for Highly Sensitive Sulfadimethoxine Tracing.

Two of the most persistent challenges for the sensing applications of luminescent carbon nitride-based materials are poor quantum yields and aggregation-induced luminescence quenching in aqueous environments. Herein, a highly emissive oxygen-doped carbon nitride composite (OCNP@M7) was synthesized, with a metal-azolate framework (MAF-7) serving as a luminous booster. Both experimental studies and theoretical calculations suggest that the MAF-enhanced electron-donating effect dramatically promoted the electron density on the π-structure of oxygen-doped carbon nitride. In addition, the structural rigidity of MAF-7 effectively inhibits both aggregation and nonradiative energy dissipation. Consequently, OCNP@M7 exhibits strong and stable blue emission under UV light irradiation and an absolute quantum yield up to 95.2%, which is, as far as we know, the highest value among fluorescent carbon nitride materials in solution ever reported. OCNP@M7 could further function as a high-efficiency fluorescent probe for the sensitive detection of sulfadimethoxine residues in complex environments. It is anticipated that this strategy can be extended to fabricate various carbon nitride-based antibiotic monitoring systems with tailor-made functions.

Enhanced photoelectrochemical aptasensing triggered by nitrogen deficiency and cyano group simultaneously engineered 2D carbon nitride for sensitively monitoring atrazine

Determination of atrazine (ATZ) residues in aquatic environment has important theoretical and practical significance for protecting the ecological environment and ensuring human health. A photoelectrochemical (PEC) aptasensing based on nitrogen deficiency and cyano group simultaneously engineered two-dimensional (2D) carbon nitride (named as DCN) has been proposed for sensitively detecting ATZ. The introduction of nitrogen deficiency can narrow band gap of DCN, leading to positive position of intermediate electronic state, and improving the absorption of visible light. The intermediate electronic state can function as an electron trap to promote the separation and migration of photogenerated carriers. Cyano groups can trap photoinduced electrons and suppress charge recombination. Gas produced by thermal decomposition has a tailoring effect, endowing DCN with 2D ultra-thin structure, which shortens transmission path of carriers. The synergistic effect of the above enhances PEC performance of DCN. The PEC aptasensing exhibited a wide linear range of 1.0 × 10−4 to 1.0 × 103 pM and a low detection limit of 3.33 × 10−5 pM with excellent selectivity, stability, and satisfactory accuracy during detecting real samples. The proposed design of carbon nitride-based materials may provide a better understanding of the relationship between kind of photoactive materials and PEC performance.

Improving hydrogen production for carbon-nitride-based materials: crystallinity, cyanimide groups and alkali metals in solution working synergistically

The recent findings on the fundamental understanding of the activity of carbon nitride-based materials in the hydrogen evolution reaction (HER) allow to design rationally the photocatalytic systems with improved activities.