Cubic Mesoporous Graphitic Carbon(IV) Nitride: An All-in-One Chemosensor for Selective Optical Sensing of Metal Ions

Development of Two-Dimensional Functional Nanomaterials for Biosensor Applications: Opportunities, Challenges, and Future Prospects

New possibilities for the development of biosensors that are ready to be implemented in the field have emerged thanks to the recent progress of functional nanomaterials and the careful engineering of nanostructures. Two-dimensional (2D) nanomaterials have exceptional physical, chemical, highly anisotropic, chemically active, and mechanical capabilities due to their ultra-thin structures. The diversity of the high surface area, layered topologies, and porosity found in 2D nanomaterials makes them amenable to being engineered with surface characteristics that make it possible for targeted identification. By integrating the distinctive features of several varieties of nanostructures and employing them as scaffolds for bimolecular assemblies, biosensing platforms with improved reliability, selectivity, and sensitivity for the identification of a plethora of analytes can be developed. In this review, we compile a number of approaches to using 2D nanomaterials for biomolecule detection. Subsequently, we summarize the advantages and disadvantages of using 2D nanomaterials in biosensing. Finally, both the opportunities and the challenges that exist within this potentially fruitful subject are discussed. This review will assist readers in understanding the synthesis of 2D nanomaterials, their alteration by enzymes and composite materials, and the implementation of 2D material-based biosensors for efficient bioanalysis and disease diagnosis.

Optical and quantitative detection of cobalt ion using graphitic carbon nitride-based chemosensor for hydrometallurgy of waste lithium-ion batteries

A hydrometallurgy is one of the most important techniques for recycling waste LIBs, where identifying the exact composition of the metal-leached solution is critical in controlling the metal extraction efficiency and the stoichiometry of the regenerated product. In this study, we report a simple and selective optical detection of high-concentrated Co²⁺ using a graphitic carbon nitride (g-CN)-based fluorescent chemosensor. g-CN is prepared by molten salt synthesis using dicyandiamide (DCDA) and LiI/KI. The mass ratio of LiI/KI to DCDA modifies the resulting g-CN (CNI) in terms of in-plane molecular distances of base sites including cyano functional groups (─CN) and fluorescent emission wavelength via nucleophilic substitution. The fluorescent sensing performance of CNIs is evaluated through photoluminescence (PL) emission spectroscopy in a broad Co²⁺ concentration range (10^-4-10⁰ M). The correlation between the surface exposure of hidden nitrogen pots (base sites) and PL intensity change is achieved where the linear relationship between the PL quenching and the logarithm of Co²⁺ concentration in the analyte solution is well established with the regression of 0.9959. This study will provide the design principle of the chemosensor suitable for the fast and accurate optical detection of Co²⁺ present in a broad concentration range for hydrometallurgy for the recycling of waste LIBs.

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C₃N₄) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C₃N₄ a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C₃N₄ unique features, synthesis methods, and g-C₃N₄-based nanomaterials. In addition, recent relevant studies on using g-C₃N₄ in biosensors in regard to improving treatment pathways are reviewed.

Gold@Carbon Nitride Yolk and Core-Shell Nanohybrids

Graphitic carbon nitride (g-C₃N₄) is a promising conjugated polymer with visible light responsiveness and numerous intriguing characteristics that make it highly beneficial for a myriad of potential applications. A novel design and universal approach for the fabrication of unique plasmonic g-C₃N₄ nanoscale hybrids, with well-controlled morphology, is presented. A single gold nanoprism is encapsulated within dense or hollow g-C₃N₄ spheres for the formation of Au@g-C₃N₄ core-shell and Au@g-C₃N₄ yolk-shell nanohybrids. Au nanoprisms were chosen duo to the strong (visible range) plasmon resonances and electromagnetic field hotspots formed at their sharp corners. The incorporation of Au nanoprisms into the g-C₃N₄ nanospheres results in a dramatic ∼threefold rise in the emission of plasmonic g-C₃N₄ yolk-shell nanohybrids and ∼3.6-fold enhancement of the photocurrent density obtained from the plasmonic g-C₃N₄ core-shell nanohybrids, when compared with the g-C₃N₄ hollow nanospheres. Hence, these hybrids can potentially benefit applications in the areas spanning from solar energy harvesting to biomedical imaging and theranostics.

From 1D to 3D Graphitic Carbon Nitride (Melon): A Bottom-Up Route via Crystalline Microporous Templates

Herein, we present a novel bottom-up preparation route for heptazine-based polymers (melon), also known as graphitic carbon nitride. The growth characteristics of isolated 1D melon strings in microporous templates are presented and studied in detail. Removal of the microporous silicate template via etching is accompanied by the self-assembly of a 1D melon to stacked 3D structures. The advantages and limitations of the bottom-up approach are shown by using microporous templates with different pore sizes (ETS-10, ZSM-5, and zeolite Y). In accordance with the molecular size of the heptazine units (0.67 nm), a 1D melon can be deposited in ETS-10 with a pore width of about 0.78 nm, whereas its formation in the smaller 0.47 nm pores of ZSM-5 is sterically impeded. The self-assembly of isolated 1D melon to stacked 3D structures offers a novel experimental perspective to the controversial debate on the polymerization degree in 2D sheets of graphitic carbon nitride as micropore sizes below 1 nm confine the condensation degree of heptazine to isolated 1D strands at a molecular level. The growth characteristics and structural features were investigated by X-ray diffraction, N2 physisorption, scanning transmission electron microscopy/energy-dispersive X-ray analysis, 13C CP-NMR spectroscopy, and attenuated total reflection-infrared spectroscopy.

Photoelectrochemical monitoring of miRNA based on Au NPs@g-C3N4 coupled with exonuclease-involved target cycle amplification

Herein, a sensitive photoelectrochemical (PEC) biosensing platform was designed for quantitative monitoring of microRNA-141 (miRNA-141) based on Au nanoparticles@graphitic-like carbon nitride (Au NPs@g-C₃N₄) as the signal generator accompanying with T7 exonuclease (T7 Exo)-involved target cycle amplification process. Initially, the prepared Au NPs@g-C₃N₄ as the signal generator was coated on the electrode surface, which could produce a strong PEC signal due to the unique optical and electronic properties of g-C₃N₄ and the surface plasmonic resonance (SPR) enhanced effect of Au NPs. Meanwhile, the modified Au NPs@g-C₃N₄ was also considered as the fixed platform for immobilization of S1-S2 through Au-N bond. Thereafter, the T7 Exo-involved target cycle amplification process would be initiated in existence of miRNA-141 and T7 Exo, leading to abundant single chain S1 exposed on electrode surface. Ultimately, the S3-SiO₂ composite was introduced through DNA hybridization, thereby producing high steric hindrance to block external electrons supply and light harvesting, which would further cause a significantly quenched PEC signal. Experimental results revealed that the PEC signal was gradually inhibited with the raising miRNA-141 concentration in the range from 1 fM to 1 nM with a detection limit of 0.3 fM. The PEC biosensor we proposed here provides a valuable scheme in miRNA assay for early disease diagnosis and biological research.

Carbon Nitride Quantum Dot-Embedded Poly(vinyl alcohol) Transparent Thin Films for Greenish-Yellow Light-Emitting Diodes

Recently, freestanding polymer thin films encapsulated with nanostructures have attracted the significant attention of the scientific community due to their promising application in portable optoelectronic devices. In this research contribution, we have fabricated a freestanding polymer thin film of poly(vinyl alcohol) (PVA) encapsulated with carbon nitride quantum dots (CN-QDs) using the casting method, for the first time. The PVA polymer matrix provides mechanical support as well as dispersion of the CN-QDs preventing its solid-state quenching. From UV-visible spectra, it is revealed that optical transparency decreases with an increase in the concentration of CN-QDs within the PVA polymeric thin film. Such kind of decrease in optical transparency is one of the crucial factors for the optical concert of a nanomaterial. Interestingly, we have optimized the synthesis protocol to retain 40% transparency of the thin film by incorporating 10 wt % CN-QDs along with PVA without deteriorating its optical behavior. It is observed that when CN-QDs are embedded in the PVA matrix, emission becomes independent of excitation wavelength and is localized in the 510-530 nm region of the spectrum. Thus, the films exhibit excellent greenish-yellow emission when excited at 420 nm with the Commission Internationale de l'èclairage (CIE) coordinates (0.39, 0.46) and a correlated color temperature (CCT) of 4105 K. These excellent optoelectronic properties make them a promising candidate for practical phosphor applications. In a nutshell, this study demonstrates a promising way to exhibit the luminescence potential of freestanding polymer/CN-QD films in CN-QD-based solid-state lighting systems.

Convenient and highly sensitive detection of Cu2+ using chitosan solid film with g-C3N4 nanosheets

A solid fluorescence sensor composed of g-C3N4 nanosheets and chitosan solid film was fabricated by electrostatic interaction. The g-C3N4 nanosheet/chitosan solid film showed selectivity and sensitivity to Cu2+ which was higher than that of other metal ions in common use. Cu2+ ions were found to efficiently bind and quench the fluorescence of the g-C3N4 nanosheet/chitosan solid film. The absorption band of the g-C3N4 nanosheet/chitosan solid film was at 240 nm in the presence of Cu2+, and the maximum emission peak was at 380 nm. Copper ion concentrations were between 0 and 3.1 × 10−5 mol/L at pH 7, the detection limit is 5 nM, compared with previous reports, it was much lower than before. Good linear relationships existed between the metal ion concentration and fluorescence intensity of g-C3N4 nanosheets in the quenching and recovering processes. This is the first study to report on the detection of Cu2+ by utilizing g-C3N4 nanosheet/chitosan composite film. The as-prepared films were conveniently prepared, easy to operate, and recyclable, as well as sensitive and selective to detect Cu2+ in water. All these features indicate the sensor’s potential application in disease diagnosis.

Amperometric sensor based on ZIF/g-C3N4/RGO heterojunction nanocomposite for hydrazine detection

A dense  zeolitic imidazolate framework (ZIF) nanosheet is for the first time molded by reduced graphite oxide (RGO) and graphitic carbon nitride (g-C₃N₄) to fabricate an original 2D/2D/2D heterojunction (ZIF/g-C₃N₄/RGO nanohybrid), which is pipetted onto carbon cloth electrode (CCE) (ZIF/g-C₃N₄/RGO/CCE) as an electrochemical sensor. Profiting from the renowned synergistic and coupling effects, the resulting nanohybrid endows excellent electrocatalytic activity towards hydrazine. Amperometric detection reveals that the hybrid sensor possesses a low detection limit of 32 nM (S/N = 3) in a monitoring range of 0.0001 to 1.0386 mM, along with a high sensitivity 93.71 μA mM^-1 cm^-2. Importantly, the minimum detection concentration of hydrazine in the actual sample is lower than the maximum allowable limit of the World Health Organization (WHO) and has high reproducibility (RSD = 4.82%). As expected, the high sensing capability  of ZIF/g-C₃N₄/RGO combines the advantages of abundant surface-active sites and high conductivity along with 2D interfaces between ZIF, g-C₃N₄, and RGO nanosheets. This study provides a promising to expand 2D-based ternary nanojunction as a bridge for promoting sensing performance.Graphical abstract.

Facile Microwave-Assisted Synthesis of Functionalized Carbon Nitride Quantum Dots as Fluorescence Probe for Fast and Highly Selective Detection of 2,4,6-Trinitrophenol

Functionalized carbon nitride quantum dots (CNQDs) are fabricated by moderate carbonization of L-tartaric acid and urea in oil acid media by a facile microwave-assisted solvothermal method. The obtained CNQDs are monodispersed with a narrow size distribution (average size of 3.5 nm), and exhibit excellent selectivity and sensitivity of fluorescence quenching for 2,4,6-trinitrophenol (TNP) with a quenching efficiency coefficient Ksv of 4.75 × 104 M-1. This sensing system exhibits a fast response time within 1 min and a wide linear response range from 0.1 to 15 μM. The limit of detection is as low as 87 nM, which is comparable or lower than the other probes. The application of the developed probe to the detection of TNP in spiked water samples yields satisfactory results. The mechanism of fluorescence quenching is also discussed. Graphical Abstract An optical sensor based on functionalized carbon nitride quantum dots (CNQDs) were fabricated from L-tartaric acid and urea by a facile one-pot microwave-assisted solvothermal method, and were effectively utilized to the detection of 2,4,6-trinitrophenol (TNP) based on fluorescence (FL) quenching.

Two-dimensional materials in biomedical, biosensing and sensing applications

Two-dimensional (2D) materials are at the forefront of materials research. Here we overview their applications beyond graphene, such as transition metal dichalcogenides, monoelemental Xenes (including phosphorene and bismuthene), carbon nitrides, boron nitrides along with transition metal carbides and nitrides (MXenes). We discuss their usage in various biomedical and environmental monitoring applications, from biosensors to therapeutic treatment agents, their toxicity and their utility in chemical sensing. We highlight how a specific chemical, physical and optical property of 2D materials can influence the performance of bio/sensing, improve drug delivery and photo/thermal therapy as well as affect their toxicity. Such properties are determined by crystal phases electrical conductivity, degree of exfoliation, surface functionalization, strong photoluminescence, strong optical absorption in the near-infrared range and high photothermal conversion efficiency. This review conveys the great future of all the families of 2D materials, especially with the expanding 2D materials' landscape as new materials emerge such as germanene and silicene.

Carbon nitride-based nanocaptor: An intelligent nanosystem with metal ions chelating effect for enhanced magnetic targeting phototherapy of Alzheimer's disease

Metal ions imbalance, a well-established pathologic feature of alzheimer's disease (AD), ultimately results in the deposition of amyloid-β peptide (Aβ) proteins and Aβ-induced neurotoxicity. Herein, to overcome these hurdles, an intelligent Aβ nanocaptor with the capacity to chelate metal ions and targeted therapy is developed by anchoring carbon nitride (C₃N₄) nanodots to Fe₃O₄@mesoporous silica nanospheres, and decorated with benzothiazole aniline (BTA) (designated as B-FeCN). The C₃N₄ nanodots could effectively capture superfluous Cu²⁺ to suppress the formation of Cu²⁺-Aβ complex thereby eliminating Aβ aggregation. Simultaneously, the nanocaptor enables local low-temperature hyperthermia to promote the dissolution of preformed fiber precipitates, therefore, maximizing the therapeutic benefits. Owing to its favorable photothermal effect, the blood-brain barrier (BBB) permeability of the nanocaptor is noticeably ameliorated upon laser illumination, which conquers the limitations associated with traditional anti-AD drugs, as evidenced by in vivo and in vitro studies. Besides, leveraging on the magnetic properties of Fe₃O₄ core, the nanocaptor is magnetized to access to the targeted Aβ regions under extrinsic magnetic field. BTA conjugation, which specifically binds to the β₂ position of the Aβ fibers, executes specific targeting at Aβ plaques, and synchronously endows the BTA-modified nanocaptor with fluorescent imaging property for sensitively detecting Aβ aggregates. In view of these superiorities, nanocaptors combine metallostasis restoration and Aβ targeted therapy can surmount the interference of copper ions, enhance BBB permeability and protect cells against Aβ-induced neurotoxicity, which provides new avenues for developing neuroprotective nanosystems for the treatment of alzheimer's disease.

Strategies for development of nanoporous materials with 2D building units

It has already been realized that two-dimensional (2D) materials carry a great potential in energy conversion and storage, gas storage, chemical sensing, and many other applications closely related to human life. These applications benefit from a key feature of 2D materials, namely the large specific surface area, which however can be diminished significantly due to the tendency of these materials to restack. In this review, we revisit the strategies - including soft and hard templating - that have been developed for generating nanoporosity in 3D materials and demonstrate their adaptation for 2D materials using carbon nitride and graphene materials as examples. Owing to the 2D nature of the building units, a new type of nanopore can be generated by perforating the basal planes. These in-plane nanopores are essential in many emerging applications of 2D materials such as semipermeable membranes; hence, their creation methods, including post-synthesis activation, ion bombardment, electron beam drilling, and nanolithography, are worthy of a critical review. Lastly, techniques for preventing the restacking by fabricating 2D-0D, 2D-1D, and 2D-2D layer-by-layer composite structures are discussed. The goal is to promote the use of these methods for creating nanoporosity in more 2D materials.

Bio-inspired honeycomb-like graphitic carbon nitride for enhanced visible light photocatalytic CO2 reduction activity

Graphitic carbon nitride (g-C₃N₄) is paying attention lately owing to its interesting characteristics and substantial application in improving environmental and energy concerns. Nevertheless, the photocatalytic activity of g-C₃N₄ is constrained by the inertness of the surface and particle aggregation during photocatalytic activity. Herein, we report the preparation of g-C₃N₄ with honeycomb-like morphology (HC-C₃N₄) via thermal condensation of prepared SiO₂ templates and dicyandiamide. The etching out of the SiO₂ templates by NH₄HF₂ created hollow or macropores in the C₃N₄ matrix resulting in its structural changes. Similar, to the bulk C₃N₄, the HC-C₃N₄ exhibited higher photocatalytic CO₂ reduction in hydrocarbons. This improved photocatalytic achievement is associated with higher specific surface area, excellent visible light absorption capability, higher electron donor density, easy mass diffusion of materials for surface reaction, and effective segregation of photogenerated charge carriers. Furthermore, the HC-C₃N₄ honeycomb structure was deposited with Ni(OH)₂ clusters which showed remarkable CO₂ reduction activity of 1.48 μmolh^-1 g^-1 of CH₄ and 0.73 μmolh^-1 g^-1 of CH₃OH generation which is 3.5 and 4.3 times higher CO₂ reduction activity compared with bulk C₃N₄ clustered with Ni(OH)₂ particles. This comprehensive study demonstrated that HC-C₃N₄ nanostructured polymeric semiconductor is envisaged to have great potential in the application of a variety of fields such as photocatalysis, sensor technology, and nanotechnology.

Nanostructured Carbon Nitrides for CO2 Capture and Conversion

Carbon nitride (CN), a 2D material composed of only carbon (C) and nitrogen (N), which are linked by strong covalent bonds, has been used as a metal-devoid and visible-light-active photocatalyst owing to its magnificent optoelectronic and physicochemical properties including suitable bandgap, adjustable energy-band positions, tailor-made surface functionalities, low cost, metal-free nature, and high thermal, chemical, and mechanical stabilities. CN-based materials possess a lot of advantages over conventional metal-based inorganic photocatalysts including ease of synthesis and processing, versatile functionalization or doping, flexibility for surface engineering, low cost, sustainability, and recyclability without any leaching of toxic metals from photocorrosion. Carbon nitrides and their hybrid materials have emerged as attractive candidates for CO₂ capture and its reduction into clean and green low-carbon fuels and valuable chemical feedstock by using sustainable and intermittent renewable energy sources of sunlight and electricity through the heterogeneous photo(electro)catalysis. Here, the latest research results in this field are summarized, including implementation of novel functionalized nanostructured CNs and their hybrid heterostructures in meeting the stringent requirements to raise the efficiency of the CO₂ reduction process by using state-of-the-art photocatalysis, electrocatalysis, photoelectrocatalysis, and feedstock reactions. The research in this field is primarily focused on advancement in the synthesis of nanostructured and functionalized CN-based hybrid heterostructured materials. More importantly, the recent past has seen a surge in studies focusing significantly on exploring the mechanism of their application perspectives, which include the behavior of the materials for the absorption of light, charge separation, and pathways for the transport of CO₂ during the reduction process.

Multistage Polymerization Design for g-C3N4 Nanosheets with Enhanced Photocatalytic Activity by Modifying the Polymerization Process of Melamine

Graphene-like g-C₃N₄ nanosheets (NSs) have been successfully synthesized with a modified polymerization process of melamine by cocondensation with volatile salts. Volatile ammonium salts such as urea-NH₄Cl/(NH₄)₂SO₄/(NH₄)₃PO₄ were added with melamine to modulate the thermodynamic process during polymerization and optimize the structure formation in situ. The surface area, surface structure, and surface charge state of the obtained g-C₃N₄ NSs could be controlled by simply adjusting the mass ratio of the melamine/volatile ammonium salt. As a consequence, the g-C₃N₄ NSs exhibited much higher activity than bulk g-C₃N₄ for the photocatalytic degradation of target pollutants (rhodamine B, methylene blue, and methyl orange), and it also exhibited greater hydrogen evolution under visible light irradiation with an optimal melamine/volatile ammonium salt ratio. The as-prepared g-C₃N₄ NSs with melamine-urea-NH₄Cl showed the highest visible light photocatalytic H₂ production activity of 1853.8 μmol·h^-1·g^-1, which is 9.4 times higher than that of bulk g-C₃N₄ from melamine. The present study reveals that the synergistic effect of the enhanced surface area, surface structure, and surface charge state is the key for the enhancement of photocatalytic degradation and hydrogen evolution, which could be controlled by the proposed strategy. The result is a good explanation for the hypothesis that adding properly selected monomers can truly regulate the polymerization process of melamine, which is beneficial for obtaining g-C₃N₄ NSs without molecular self-assembly. Considering the inexpensive feedstocks used, a simple synthetic controlling method provides an opportunity for the rational design and synthesis, making it decidedly appealing for large-scale production of highly photocatalytic, visible-sensitizable, metal-free g-C₃N₄ photocatalysts.

Environmental remediation of heavy metal ions by novel-nanomaterials: A review

Recently, novel-nanomaterials with excellent sorption capacities, mild stability, and environmental-friendly performance, have enabled massive developments in capturing heavy metal ions. This review firstly introduces the preparation and modification of novel-nanomaterials (e.g., MOFs, nZVI, MXenes, and g-C₃N₄). Then, the heavy metal ions' sorption properties and the impact of environmental conditions have been discussed. Subsequently, the sorption mechanisms are verified through batch experiments, spectral analysis, surface complexation models, and theoretical calculations. Finally, the applications prospects of novel-nanomaterials in removing heavy metal ion polluted water have also been discussed, which provide perspective for future in-depth research and practical applications.

Selective liquid phase oxidation of ethyl benzene to acetophenone by palladium nanoparticles immobilized on a g-C3N4–rGO composite as a recyclable catalyst

A hybrid structure g-C₃N₄–rGO with honeycomb units was prepared for immobilizing Pd nanoparticles by a simple wet impregnation method.

Accurate K-edge X-ray photoelectron and absorption spectra of g-C3N4 nanosheets by first-principles simulations and reinterpretations

Accurate N1s and C1s XPS spectra of g-C₃N₄ were obtained by a combined cluster-periodic approach and we make new assignments.

In situ sulfur-doped graphitic carbon nitride nanosheets with enhanced electrogenerated chemiluminescence used for sensitive and selective sensing of l-cysteine

In this study, in situ sulfur-doped carbon nitride nanosheets (S-g-C₃N₄ NSs) are used for the sensitive and selective sensing of l-cysteine (l-Cys) based on the competitive coordination chemistry of Cu²⁺ between l-Cys and S-g-C₃N₄ NSs.

Emerging trends in sensors based on carbon nitride materials

A new class of functional materials, carbon nitrides, has recently attracted the attention of researchers.

Au-TiO2-Loaded Cubic g-C3N4 Nanohybrids for Photocatalytic and Volatile Organic Amine Sensing Applications

A green and efficient approach for efficient nanohybrid photocatalysts in extending the light response to the visible spectrum is a hot research topic in sustainable energy technologies. In this work, novel Au-TiO₂@m-CN nanocomposite was synthesized using hard template of cubic ordered mesoporous KIT-6 via the nanocasting process. The as-prepared Au-TiO₂@m-CN nanohybrids exhibit enhanced photocatalytic activities with improved stability and reusability using methyl orange dye. The enhanced photocatalytic performance is a result of the conjugated effect of catalytic active Au and TiO₂ nanoparticles supported on highly efficient visible light sensitizer, graphitic carbon nitride (m-CN or g-C₃N₄), and ordered mesoporous morphology. Besides, the sensing performance of Au-TiO₂@m-CN nanohybrids was also tested for the detection of amine gases, wherein a significant response was reported for triethylamine at low operating temperatures. This study reveals a simple and scalable methodology to design and develop next generation of layered mesoporous materials for multifunctional applications.

Tetracycline Removal Under Solar Illumination Over Ag3 VO4 /mpg-C3 N4 Heterojunction Photocatalysts

Ag₃ VO₄ /mpg-C₃ N₄ (mesoporous graphitic carbon nitride) heterojunction photocatalysts were prepared by anchoring tiny Ag₃ VO₄ particles on the nanosheet of mpg-C₃ N₄ . The prepared Ag₃ VO₄ /mpg-C₃ N₄ heterojunctions were used to remove tetracycline (TC), a kind of antibiotics widely released into the aquatic environment under solar irradiation. Compared with pure mpg-C₃ N₄ and Ag₃ VO₄ , Ag₃ VO₄ /mpg-C₃ N₄ displayed much higher photocatalytic activity (83.2% removal rate within 90 min under visible-light irradiation). Importantly, no apparent deactivation was observed for Ag₃ VO₄ /mpg-C₃ N₄ -40 after five cycles, inferring a good reusability. As confirmed by photocurrent measurement and photoluminescence spectra, the excellent photocatalytic property of Ag₃ VO₄ /mpg-C₃ N₄ was credit to the electron-hole separation enhancement at the formed heterojunction of two semiconductors. In addition, a possible mechanism and intermediate products for the Ag₃ VO₄ /mpg-C₃ N₄ photocatalysts toward the photodegradation of TC in aqueous solution under artificial sunlight radiation were proposed based on the scavengers trapping test, ESR spectra and a high-performance liquid chromatography (HPLC) coupled with mass spectrometer (MS) analysis. This investigation provides a low cost, green and easily practical approach to remove the antibiotics in the aquatic environment.

A label-free aptamer-based cytosensor for specific cervical cancer HeLa cell recognition through a g-C3N4-AgI/ITO photoelectrode

Facile and efficient detection of cancer cells in the early phases of the disease is one of the main challenges in cancer diagnostics. It has been found that photoactive materials and bio-recognition elements are two key factors in the development of promising photoelectrochemical (PEC) biosensors for cancer cell detection, which can play significant roles for realizing early cancer diagnostics with high sensitivity and selectivity. In this study, we designed a novel label-free PEC aptamer-based cytosensor for the specific detection of cancer cells such as HeLa cells by using water-dispersible g-C₃N₄-AgI nanocomposites as visible light-sensitive materials and anti-CEM/PTK7 aptamer as the bio-recognition element. It was observed that when a suitable amount of AgI nanoparticles was doped in two-dimensional graphite-like carbon nitride nano-sheets (g-C₃N₄ NSs), the visible light photocurrent response could be significantly improved. The PEC response of the as-prepared biosensor based on the g-C₃N₄-AgI/ITO photoelectrode was linearly proportional to the relevant cancer cells such as HeLa cells at concentrations ranging from 10 to 10⁶ cells per mL with a limit of detection of 5 cells per mL. In addition, the g-C₃N₄-AgI/ITO photoelectrode and the fabricated cytosensor exhibited long-term stability, good reproducibility, excellent selectivity, and high sensitivity, demonstrating the successful conjugation of g-C₃N₄-AgI NSs with the aptamer and target cancer cells in the high performance PEC cytosensor.

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties

Poly(triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C₃N₄, especially in photocatalysis. As most of the carbon nitrides, PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH-dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH-dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI, which we investigated in dye degradation experiments.

A sensitive fluorescent sensing strategy for nanomolar levels of metformin using graphitic carbon nitride nanosheets as nanofluoroprobe

A simple and green fluorescence detection system on the basis of the quenching effect of Cu(II) ions on the graphitic carbon nitride nanosheets (g-C₃N₄ NS) fluorescence and recording the changes of restored fluorescence intensity upon the addition of metformin (MET) was developed for the first time. The g-C₃N₄ NS were produced using high-temperature polymerization of melamine followed by ultrasonication-assisted liquid exfoliation. The method exhibited excellent sensitivity and accuracy toward MET with the detection as low as 3 nM and linear calibration curve in the range of 0.01-20 μM. In addition, this assay was successfully applied to the determination of MET concentration in human serum samples. It is robust and is suitable for fast, sensitive and cost effective measurement of MET in biological materials.

A Novel "Off-On" Fluorescent Probe Based on Carbon Nitride Nanoribbons for the Detection of Citrate Anion and Live Cell Imaging

A novel fluorescent “off-on” probe based on carbon nitride (C₃N₄) nanoribbons was developed for citrate anion (C₆H₅O₇³⁻) detection. The fluorescence of C₃N₄ nanoribbons can be quenched by Cu²⁺ and then recovered by the addition of C₆H₅O₇³⁻, because the chelation between C₆H₅O₇³⁻ and Cu²⁺ blocks the electron transfer between Cu²⁺ and C₃N₄ nanoribbons. The turn-on fluorescent sensor using this fluorescent “off-on” probe can detect C₆H₅O₇³⁻ rapidly and selectively, showing a wide detection linear range (1~400 μM) and a low detection limit (0.78 μM) in aqueous solutions. Importantly, this C₃N₄ nanoribbon-based “off-on” probe exhibits good biocompatibility and can be used as fluorescent visualizer for exogenous C₆H₅O₇³⁻ in HeLa cells.

Boronic acid functionalized g-C3N4 nanosheets for ultrasensitive and selective sensing of glycoprotein in the physiological environment

As important biomarkers, glycoprotein sensing is frequently facilitated by boronic acid binding with its cis-diols. However, boronic acid based sensors suffer from drawbacks of alkali restriction and/or sensitivity limitation. Herein, we report boronic acid decorated g-C₃N₄ nanosheets (B-g-CN) with a Wulff-type boronic acid feature, which selectively bind glycoprotein under physiological conditions. Meanwhile, the binding causes significant enhancement of the B-g-CN nanosheet fluorescence, providing the basis for glycoprotein sensing. With IgG as a model, a detection limit (LOD) of 2.2 nM (3σ/s, n = 11) was obtained within a linear range of 6.7-67 nM. The LOD was further improved to 52 pM subject to enrichment of the nanosheets, which well enables IgG assay in human urine samples. Moreover, it was successful in imaging endogenous and exogenous glycoproteins in living cells.

Graphitic carbon nitride nanosheets as a fluorescent probe for chromium speciation

A fluorometric method was developed for simultaneous determination of Cr(VI) and Cr(III) ions using graphitic carbon nitride nanosheets (g-C₃N₄ NS) as a nanosized fluorescent indicator probe. The g-C₃N₄ NS were prepared using high-temperature carbonization of melamine followed by ultrasonication-assisted liquid exfoliation. The g-C₃N₄ NS display fluorescence with excitation/emission peaks located at 320 and 450 nm. The chromium speciation is based on the quenching of g-C₃N₄ NS fluorescence. The total concentration of chromium is determined after oxidation of Cr(III) to Cr(VI). The Cr(III) content was then calculated by subtracting the concentration of Cr(VI) from that of total chromium. The effects of pH value, probe amount, and contact time are optimized. Under optimum conditions, calibration plots are linear in the range in the 0.01 to 100 μM chromium concentration range. The limit of detection is 3 nM for for Cr(VI). The intra- and inter-day relative standard deviations (RSD) of the assay are 3.6-7.5% and 4.1-8.5%, respectively. The indicator probe was applied to the determination of chromium species in spiked water and food samples, and recoveries were satisfactory (93.9-107.0%). Graphical abstract Graphitic carbon nitride nanosheets are synthesized by melamine carbonization and employed for Cr speciation in water and food real samples. Total Cr(VI) and Cr(VI) are assessed based on the quenching of the fluorescence of nanosheets by Cr(VI).

Electrodeposition of carbon nitride nanosheets on the graphenized pencil lead as an effective sorbent

This study introduces a green, cheap, easy to prepare and powerful solid phase microextraction (SPME) sorbent for analytical monitoring applications.

Barbituric acid-modified graphitic carbon nitride nanosheets for ratiometric fluorescent detection of Cu2+

A ratiometric and visual fluorescent sensor for Cu²⁺ ions based on barbituric acid-modified graphitic carbon nitride nanosheets was designed.

Graphitic-phase carbon nitride-based electrochemiluminescence sensing analyses: recent advances and perspectives

This review describes the current trends in synthesis methods, signaling strategies, and sensing applications of g-C₃N₄-based ECL emitters.

Molecular engineering of polymeric carbon nitride: advancing applications from photocatalysis to biosensing and more

Different designs and constructions of molecular structures of carbon nitride for emerging applications, such as biosensing, are discussed.