Ultrathin graphitic carbon nitride nanosheet: a highly efficient fluorosensor for rapid, ultrasensitive detection of Cu(2+)

Purification of aqueous orange II solution through adsorption and visible-light-induced photodegradation using ZnO-modified g-C3N4 composites

Semiconductor-based remediation enables environmentally friendly methods of removing aqueous pollutants. Simply fabricated ZnO modified g-C3N4 composites were utilized as bifunctional adsorptive photocatalysts for orange II removal from aqueous solution through adsorption and photocatalysis processes. The adsorption isotherm data of the g-C3N4 (g-CN) and ZnO modified g-C3N4 (ZCN) composites on orange II solution were better fitted with the Langmuir isotherm compared to the Freundlich isotherm. The maximum adsorption capacity for ZCN-2.5 was slightly higher than that of bare g-CN. According to the adsorption thermodynamics investigation of ZCN-2.5 in orange II solution, the positive values of Gibb's free energy change (ΔG0) suggested a non-spontaneous adsorption process. Furthermore, the negative values of entropy change (ΔS) and enthalpy change (ΔH) indicated the decrement of randomness and exothermic nature during the adsorption process, respectively. The photocatalytic degradation kinetics of g-CN and ZCN composites indicated that the degradation process follows the pseudo-first-order reaction kinetic. The degradation rate of orange II with the ZCN-2.5 composite was 6.67 times higher than that obtained with bare g-CN. Possible adsorption and photocatalytic mechanisms have been proposed.

Ultrasensitive detection of Ag+and Ce3+ions using highly fluorescent carboxyl-functionalized carbon nitride nanoparticles

The fluorescence quenching of carboxyl-rich g-C3N4nanoparticles was found to be selective to Ag+and Ce3+with a limit of detection as low as 30 pM for Ag+ions. A solid-state thermal polycondensation reaction was used to produce g-C3N4nanoparticles with distinct green fluorescence and high water solubility. Dynamic light scattering indicated an average nanoparticle size of 95 nm. The photoluminescence absorption and emission maxima were centered at 405 nm and 540 nm respectively which resulted in a large Stokes shift. Among different metal ion species, the carboxyl-rich g-C3N4nanoparticles were selective to Ag+and Ce3+ions, as indicated by strong fluorescence quenching and a change in the fluorescence lifetime. The PL sensing of heavy metal ions followed modified Stern-Volmer kinetics, and CNNPs in the presence of Ag+/Ce3+resulted in a higher value ofKapp(8.9 × 104M-1) indicating a more efficient quenching process and stronger interaction between CNNP and mixed ions. Sensing was also demonstrated using commercial filter paper functionalized with g-C3N4nanoparticles, enabling practical on-site applications.

Smartphone-integrated ratiometric sensing strategy for on-line quantitation of tetracycline based on functionalized g-C3N4/Eu electrospun film

On-line quantitation of tetracycline (TC) is significant to ensure environmental health and food security. Hence, a novel smartphone-integrated ratiometric sensing platform for on-line quantitative analysis of TC was designed. A CitNa-functionalized g-C3N4/Eu3+ (g-C3N4/CitNa/Eu) composites with blue and red dual-emissive feature were fabricated as dual indicators for shielding background interference, enhancing anti-interference capability. The fluorescent response (F620/F450) ratio and TC concentration demonstrated good linear relationship ranged from 0.0 to 100.0 μM with a detection limit of 1.96 nM. Furthermore, the combination of g-C3N4/CitNa/Eu and polyacrylonitrile polymers forming electrospun film was achieved via electrospinning method. Smartphone-integrated ratiometric sensing platform was developed based on the fluorescent color of electrospun film from blue to light red with TC. This solid sensing platform achieved excellent sensitivity with a detection limit of 7.42 nM. Combining the solid ratiometric fluorescent film with smartphone reader provides a potential way for on-line quantitation of TC in food and other fields.

Interfacial coupling of CuFe2O4 induced hotspots over self-assembled g-C3N4 nanosheets as an efficient photocatalytic bacterial disinfectant

Most bacterial disinfectants contain high levels of extremely toxic and environmental hazardous chemicals, which pose a significant threat to the ecosystem. Semiconductor photocatalysis exhibits attractive prospects as an emerging greener technology for waste water disinfection. However, the fast recombination of charge carriers limits its practical application. Herein, self-assembled polymeric feather-like g-C3N4 (GCN) nanosheets modified with ferromagnetic CuFe2O4 (CFO) nanospheres were successfully applied as a reusable visible light photocatalytic disinfectant. As expected, the g-C3N4/CuFe2O4 (GCF) nanohybrid displayed superior photocatalytic inactivation efficiency of 0.157log within 120 min towards Escherichia coli DH5α (E. coli) compared with pristine GCN and CFO. The characterization results revealed the synergistic heterostructure interfaces, high surface area, and the transformative self-assembly of GCN to feather-like structure providing a rich active site for improved charge separation efficiency, and wide spectral response, therefore the superior performance of GCF. The radical trapping assay proclaimed that both O2•- and •OH radical played major role in the photocatalytic inactivation among the other reactive oxygen species (ROS). Furthermore, the chemical oxygen demand (COD), protein estimation, and DNA estimation assay results validated the cell damage caused by the photocatalyst. Besides that, GCN showed applicability in real-time wastewater samples with improved efficiency than in the saline solution. The excellent magnetic characteristics facilitated the recycling of the catalyst with insignificant leaching, magnetic induction, and distinguished separation. The results of this work signify the well-designed GCF as a high-performance and reusable photocatalyst for real-world pathogenic bacterial disinfection operations.

Room-temperature phosphorescence and fluorescence nanocomposites as a ratiometric chemosensor for high-contrast and selective detection of 2,4,6-trinitrotoluene

Reports on using complementary colours for high-contrast ratiometric assays are limited to date. In this work, graphitized carbon nitride (g-C3N4) nanosheets and mercaptoethylamine (MEA) capped Mn-doped ZnS QDs were fabricated by liquid exfoliation of bulk g-C3N4, and by a coprecipitation and postmodification strategies, respectively. Mn-doped ZnS quantum dots were deposited onto g-C3N4 nanosheets through an electrostatic self-assembly to form new nanocomposites (denoted as Mn-ZnS QDs@g-C3N4). Mn-ZnS QDs@g-C3N4 can emit a pair of complementary colour light, namely, orange room-temperature phosphorescence (RTP) at 582 nm and blue fluorescence at 450 nm. After 2,4,6-trinitrotoluene (TNT) dosing into Mn-ZnS QDs@g-C3N4 aqueous solution, and pairing with MEA to generate TNT anions capable of quenching the emission of Mn-doped ZnS QDs, the fluorescence colours of the solution changed from orange to blue across white, exhibiting unusual high-contrast fluorescence images. The developed ratiometric chemosensor showed very good linearity in the range of 0-12 μM TNT with a limit of detection of 0.56 μM and an RSD of 6.4 % (n = 5). Also, the ratiometric probe had an excellent selectivity for TNT over other nitroaromatic compounds, which was applied in the ratiometric test paper to image TNT in water, and TNT sensing under phosphorescence mode to efficiently avoid background interference. A high-contrast dual-emission platform for selective ratiometric detection of TNT was therefore established.

Efficient photocatalytic reduction of p-nitrophenol under visible light irradiation based on Ag NPs loaded brown 2D g-C3N4 / g-C3N4 QDs nanocomposite

Recently, low-cost graphitic carbon nitride (g-C3N4) revealed high photocatalytic activities and provided solutions to environmental pollution. In this study, we synthesized brown mesoporous 2D g-C3N4 by calcination dicyandiamide with pluronic P123. This is followed by loading of Ag NPs on the prepared 2D g-C3N4 by photodeposition process. After that, a ternary composite 2% Ag/ 2D g-C3N4 / g-C3N4 QDs heterojunction photocatalyst has been successfully prepared. The prepared nanomaterials were comprehensively characterized by various analysis techniques such as XRD, UV-Vis., BET, XPS, SEM, TEM. This new system exhibited a large surface area with porous structure and a wide absorption of visible light. The results verified that Ag NPs decoration enhanced the charge separation of photo-generated carriers of g-C3N4 2D and g-C3N4 QDs, promote significant enhancement in the photocatalytic activity for reduction of p-nitrophenol with a rate constant (k) value of 0.49729 / min in 6 min. This rate is about two-fold higher than that observed for pure g-C3N4 2D and g-C3N4 QDs as well as shows an improvement compared to 2% Ag/ g-C3N4 2D and g-C3N4 2D/ g-C3N4 QDs. The results open the door to design highly efficient 2D/0D nanocomposite photocatalysts for a wide variety of environmental applications.

Graphitic carbon nitride derived probes for the recognition of heavy metal pollutants of environmental concern in water bodies

Graphitic carbon nitride (g-CN) has a number of valuable features that have been recognized during the studies related to its photocatalytic activity enhancement derived by visible light. Because of these characteristics, g-CN can be used as a detecting signal transducer with different transmission modalities. The latest up-to-date detection capabilities of modified g-CN nanoarchitectures are covered in this study. The structural features and synthetic methodologies have been discussed in a number of reports. Herein, employment of the g-CN as a promising probing modality for the recognition of different toxic heavy metals is the promising feature of the present study.

Graphitic carbon nitride (g-C3N4)-assisted materials for the detection and remediation of hazardous gases and VOCs

Graphitic carbon nitride (g-C3N4)-based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C3N4 to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g-C3N4- photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C3N4 and C3N4 assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C3N4 with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C3N4/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C3N4/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C3N4 for enhanced photocatalytic application. In the later part, we have summarised the application of g-C3N4 and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C3N4 with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g-C3N4-based photocatalysts and sensors with practical applications.

Two-Dimensional Graphitic Carbon Nitride for Improving the Performance of Organic Solar Cells

Organic solar cells (OSCs) have attracted lots of attention owing to their low cost, lightweight, and flexibility properties. Nowadays, the performance of OSCs is continuously improving with the development of active layer materials. However, the traditional hole transport layer (HTL) material Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) presents insufficient conductivity and rapid degradation, which decreases the efficiency and stability of OSCs. To conquer the challenge, the two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanomaterials incorporated into the PEDOT:PSS as hybrid HTL are reported. The addition of g-C₃N₄ into PEDOT:PSS enables the thickness of the HTL to decrease for enhancing the transmittance of the film and increase the conductivity of PEDOT:PSS. Thus, the device exhibts improved charge transport and suppressed carrier recombination, leading to the increase in short-circuit current density and power conversion efficiency of the devices. This work demonstrates that the incorporation of 2D g-C₃N₄ into PEDOT:PSS for D18:Y6 and PM6:L8-BO-based OSCs can significantly improve the device efficiency to 17.48% and 18.47% with the enhancement of 7.04% and 8.46%, respectively.

A ratiometric fluorescence sensor based on gold silver nanoclusters and tungsten disulfide quantum dots with simple fabrication for the detection of copper ions in river water

Copper plays a key role in the human body; meanwhile, excess Cu²⁺ ions can result in various diseases. Nanoclusters (NCs) are often used to measure Cu²⁺ ions, but there are two difficulties. On the one hand, a single probe of NCs is easily affected by environmental factors. On the other hand, it is difficult to mask the interference of Pb²⁺ ions and Cd²⁺ ions in the process of detecting Cu²⁺ ions. As a new type of quantum dots (QDs), tungsten disulfide quantum dots (WS₂-QDs) have some advantages of simple synthesis and stable luminescence properties. Stable WS₂-QDs with blue fluorescence are used as a reference probe, while gold silver nanoclusters (AuAgNCs) with red fluorescence are used as a response probe. A ratiometric fluorescent sensor was constructed by mixing the two styles of fluorescent probes, which is abbreviated as NCs/QDs. This nano-sensor can be used to detect the concentration of Cu²⁺ ions, in which the fluorescence of QDs does not change significantly, while the fluorescence of NCs can be quenched by Cu²⁺ ions. The concentration of Cu²⁺ ions can be determined as low as 0.12 μM with a linear range from 0.3 to 3 μM. The common interference caused by Pb²⁺ and Cd²⁺ ions can be eliminated by the phosphate buffer solution (PBS). This sensor was used to detect the concentration of Cu²⁺ in river water with satisfactory results.

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.

A facile and green synthesis of Mn and P functionalized graphitic carbon nitride nanosheets for spintronics devices and enhanced photocatalytic performance under visible-light

Manganese and phosphorus co-doped, graphitic carbon nitride (g-C₃N₄) nanosheet (Mn/P-g-C₃N₄) is prepared by facile and green calcination process of melamine (C₃H₆N₆), manganese chloride tetrahydrate (MnCl₂·4H₂O), and ammonium dihydrogen phosphate ((NH₄)H₂PO₄). The Mn/P co-doping significantly enhances magnetic values compared to pristine-g-C₃N₄, phosphorus-doped g-C₃N₄ (P-g-C₃N₄), and manganese-doped g-C₃N₄ (Mn-g-C₃N₄). We find that Mn/P-g-C₃N₄ is a half-metallic ferromagnetic material having a magnetic moment and Curie temperature of 4.51 μ_B and ∼ 800 K, respectively. The ultraviolet-visible (UV-vis) absorption spectrum of Mn/P-g-C₃N₄ reveals superior absorption in broader wavelength compared to pristine-g-C₃N₄, P-g-C₃N₄, and Mn-g-C₃N₄. The methyl orange degradation efficiency of Mn/P-g-C₃N₄ photocatalyst is 94 %, which is three times more than that of pristine-g-C₃N₄ (29 %) and more significant than the P-g-C₃N₄ (46 %) and Mn-g-C₃N₄ (58 %). Furthermore, density functional theory (DFT) calculation explains the origin of high magnetic behavior, the boosted photocatalytic efficiency of Mn/P-g-C₃N₄, and the essential material properties like structure, bandgap, the density of states (DOS), and atomic level interaction. This work may be helpful for reasonably designing ferromagnetic material for spintronics devices and boosting visible-light (VL) photocatalytic performance for environmental remediation.

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.

Colorimetric Cu2+ Detection of (1E,2E)-1,2-Bis((1H-pyrrol-2-yl)methylene)hydrazine Using a Custom-Built Colorimeter

The compound (1E,2E)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (1) was investigated for its chemosensor application. The colorimetric response of 1 with various ions was investigated, and the selective optical change upon mixing with Cu²⁺ was found. The Cu²⁺ binding stoichiometry of 1 derived from Job's plot and the in silico study give us the tentative structural detail of the binding mode of 1 and Cu²⁺ being 1:1. The binding constant between 1 and Cu²⁺ from the Benesi-Hildebrand plot was 1.49 × 10⁴ M^-1. The limit of detection of 1 in Cu²⁺ detection was 0.64 μM (0.040 ppm), which is much lower than the WHO and US EPA maximum allowable Cu²⁺ level in drinking water (2 and 1.3 ppm, respectively). The custom-built colorimeter demonstrates a good linear relationship between Cu²⁺ concentration and electrical resistance (Ω) upon 1-Cu²⁺ ion binding.

Eu(III) Functionalized Crystalline Polyimide Hydrogel Film as a Multifunctional Platform for Consecutive Sensing of Spermine and Copper Ions

In this study, a novel Eu(III) functionalized crystalline polyimide hydrogel film (Eu-1) is fabricated by incorporating highly stable polyimide (PI) into a sodium alginate (SA) matrix, followed by cross-linking reaction with Eu³⁺ ions. Based on different fluorescence responses, Eu-1 is used for the consecutive detection of spermine (Spm) and copper ions (Cu²⁺). Eu-1 can be employed as a sensor for polyamine, especially for Spm with significant fluorescence enhancement based on the "turn on" mode. The fluorescent sensor Eu-1@Spm constructed by the Eu-1 and Spm can be further used as a "turn off" sensor to quantitatively monitor Cu²⁺. The good selectivity combined with the low detection limit of the sensor meets the requirements for monitoring Cu²⁺. The possible luminescence response mechanisms to Spm and Cu²⁺ have been studied through experimental data and theoretical calculations. In addition, a back-propagation neural network (BPNN) model based on an Eu-1@Spm sensor is constructed, which can accurately distinguish Cu²⁺ concentrations by deep machine learning (ML). This work not only puts forward a facile method to prepare a novel Eu-functionalized PI-based hybrid film but also demonstrates the potential of PI-based film materials for fluorescence detection.

Multicolor colorimetric assay for copper ion detection based on the etching of gold nanorods

An effective, selective, and multicolor colorimetric assay for Cu²⁺ detection based on the regulation of peroxidase-like nanozyme-mediated etching of gold nanorods (Au NRs) is proposed. Cu²⁺-creatinine complex is selected as the nanozyme that exhibits excellent peroxidase-like activity even in the case of low concentration of Cu²⁺, which can catalyze 3,3,5,5-tetramethylbenzidine (TMB) to produce oxidized TMB (TMB⁺) in the presence of hydrogen peroxide, and TMB⁺ is oxidized to generate TMB²⁺ after adding H⁺, and the TMB²⁺ can etch Au NRs. The determination of Cu²⁺ is achieved based on the blue shift of the longitudinal localized surface plasmon resonance peak of Au NRs. Under the optimal conditions, the developed colorimetric assay exhibits high sensitivity for the detection of Cu²⁺ (limit of detection is 0.034 μM) with a wide linear range of 0.05-4.0 μM (R² = 0.987). The solution shows a rainbow-like color in response to the increase of Cu²⁺ concentration, which can realize the semi-quantitative detection of Cu²⁺ by naked eyes. In addition, the developed method exhibits excellent selectivity for Cu²⁺-detection. The established method was used for the determination of Cu²⁺ in lake water, soil, and normal human serum with satisfactory recovery of spiked samples.

High-Performance Circulating Tumor DNA Liquid Biopsy Based on Graphitic Carbon Nitride Nanosheet for Monitoring Gastric Cancer-Related Gene Mutations

Early diagnosis and timely monitoring of cancer progression are the most effective ways to improve the cure rate of cancer patients. And it is essential to create convenient, sensitive, accurate, as well as noninvasive or minimally invasive tests for better respecting patients’ wishes and optimizing diagnosis. The fluorescent biosensor discovered in our study on the basis of graphitic carbon nitride nanosheet (CNNS) could be used to detect the gastric cancer-associated circulating tumor DNA (ctDNA) in human blood by highly specific binding to fluorescein-labeled single-stranded DNA detection probes. The ssDNA detection probe was adsorbed on the surface of CNNS through weak Π–Π stacking, thereby obtaining efficient fluorescence quenching. With the presence of the target DNA, the ssDNA probe showed weak affinity for CNNS and restored fluorescence by base complementary pairing with target ssDNA through strong hydrogen bonds. The results show that the nanometer detection is a convenient, low-cost and high-efficiency technology, which is promising in biological detection and analysis.

Photomemristive sensing via charge storage in 2D carbon nitrides

Photomemristive sensors have the potential to innovate current photo-electrochemical sensors by incorporating new sensing capabilities including non-invasive, wireless and time-delayed (memory) readout. Here we report the charge storing 2D carbon nitride potassium poly(heptazine imide), K-PHI, as a direct photomemristive sensing platform by capitalizing on K-PHI's visible light bandgap, large oxidation potential, and intrinsic optoionic charge storage properties. Utilizing the light-induced charge storage function of K-PHI nanosheets, we demonstrate memory sensing via charge accumulation and present potentiometric, impedimetric and coulometric readouts to write/erase this information from the material, with no additional reagents required. Additionally, wireless colorimetric and fluorometric detection of the charging state of K-PHI nanoparticles is demonstrated, enabling the material's use as particle-based autonomous sensing probe in situ. The various readout options of K-PHI's response enable us to adapt the sensitivities and dynamic ranges without modifying the sensing platform, which is demonstrated using glucose as a model analyte over a wide range of concentrations (50 μM to 50 mM). Since K-PHI is earth abundant, biocompatible, chemically robust and responsive to visible light, we anticipate that the photomemristive sensing platform presented herein opens up memristive and neuromorphic functions.

Current advances on g-C3N4-based fluorescence detection for environmental contaminants

The development of highly-sensitive fluorescence detection systems for environmental contaminants has become high priority research in the past years. Special attention has been paid to graphitic carbon nitride (g-C₃N₄)-based nanomaterials, whose unique and superior optical property makes them promising and attractive candidates for this purpose. It is necessary to enhance the current understanding of the various classes of g-C₃N₄-based fluorescence detection systems and their mechanisms, as well as find suitable approaches to improve detection performance for environmental monitoring, protection, and management. In this review, the recent progresses on g-C₃N₄-based fluorescence detections for environmental contaminants, mainly including their basic principles, mechanisms, applications, modification strategies, and conclusions, are summarized. A particular emphasis is placed on the design and development of modification strategies for g-C₃N₄ with the objective of improving detection performance. High photoluminescence quantum yield, tunable fluorescence emission characteristics, and strong adsorption capacity of g-C₃N₄ could ensure the ultrasensitivity and selectivity of fluorescence detection of environmental contaminants. Concluding perspectives on the challenges and opportunities to design highly efficient g-C₃N₄-based fluorescence detection system are intensively put forward as well.

Fabrication of g-C3N4/Bi2WO6 as a direct Z-scheme excellent photocatalyst

To improve the photocatalytic efficiency of Bi2WO6, two types of g-C3N4 nanomaterial, g-C3N4 quantum dots and nanosheets, were incorporated with Bi2WO6 to construct two kinds of g-C3N4/Bi2WO6 photocatalysts with excellent photocatalytic activity.

Performance of graphitic carbon nitride nanosheets derived from liquid and thermal exfoliations towards the electrochemical reduction of nitrobenzene

The electrocatalytic activity of graphitic carbon nitride nanosheets prepared via thermal and solvent exfoliation is compared towards nitrobenzene reduction.

A new “on–off–on” g-C3N4 nanosheets fluorescent sensor for 5-Br-PADAP and Co2+ under acidic conditions

A novel “on–off–on” g-C3N4 nanosheet fluorescent sensor based on IFE could detect 5-Br-PADAP and Co2+ under acidic conditions.

Nanostructural synergism as MnNC channels in manganese (IV) oxide and fluffy g-C3N4 layered composite with exceptional catalytic capabilities

The avenues of catalysis and material science are always accepted and it is hoped that a state-of-the-art catalyst with exceptional intrinsic redox characteristics would be produced. This study focused on developing a multi-featured catalyst of high economical and commercial standards to meet the multi-directional applications of environmental and energy demands. Manganese (IV) oxide nanosheets made of fluffy-sheet-like g-C₃N₄ material were successfully synthesized by pyrolysis method. The electron-rich g-C₃N₄ network and semiconducting metallic oxides of MnO₂ nanosheets generated high electron density interfaces within the intra-composite structure. The input of active interfaces along with strong metal-to-support interactions achieved between two parallel nanosheets in MnO₂/g-C₃N₄ catalyst intrinsically boosted up its electrochemical and optical characteristics for it to be used in multi-catalytic fields. Successful trails of catalysts' performance have been made in three major catalytic fields with enhanced activities such as heterogeneous catalysis (reduction of nitrobenzene with rate constant of "K = 0.734 min^-1" and hydrogenation of styrene with "100% conversion" efficiency, including negligible change in five consecutive cycles), photocatalysis (degradation of methylene blue dye model within 20 min with negligible change in five consecutive cycles) and electrocatalysis (oxygen reduction reactions having comparable "diffusion-limited-current density" behaviour with that of the commercial Pt/C catalyst). The enhanced performance of catalysts in transforming chemicals, degrading organic pollutant species and producing sustainable energy resources from air oxygen can mitigate the challenges faced in environmental and energy crises, respectively.

Enzyme Method-Based Microfluidic Chip for the Rapid Detection of Copper Ions

Metal ions in high concentrations can pollute the marine environment. Human activities and industrial pollution are the causes of Cu²⁺ contamination. Here, we report our discovery of an enzyme method-based microfluidic that can be used to rapidly detect Cu²⁺ in seawater. In this method, Cu²⁺ is reduced to Cu⁺ to inhibit horseradish peroxidase (HRP) activity, which then results in the color distortion of the reaction solution. The chip provides both naked eye and spectrophotometer modalities. Cu²⁺ concentrations have an ideal linear relationship, with absorbance values ranging from 3.91 nM to 256 μM. The proposed enzyme method-based microfluidic chip detects Cu²⁺ with a limit of detection (LOD) of 0.87 nM. Other common metal ions do not affect the operation of the chip. The successful detection of Cu²⁺ was achieved using three real seawater samples, verifying the ability of the chip in practical applications. Furthermore, the chip realizes the functions of two AND gates in series and has potential practical implementations in biochemical detection and biological computing.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

Metal-Nanoparticles-Loaded Ultrathin g-C3N4 Nanosheets at Liquid-Liquid Interfaces for Enhanced Biphasic Catalysis

Exploiting new interface-active solid catalysts is crucial to construct efficient Pickering emulsion systems for biphasic catalysis. In this work, ultrathin g-C₃N₄ nanosheets (g-C₃N₄-NSs) were developed as a new solid emulsifier to directly position catalytic sites at oil-water interfaces for improving the reaction efficiency of a biphasic reaction. Exemplified by a metal-involved biphasic reaction of nitroarenes reduction, the developed Pd/g-C₃N₄-NSs catalyst with Pd nanoparticles loaded on the surface of g-C₃N₄-NSs exhibited excellent activity with a catalytic efficiency of 1220 h^-1. Such activity was 4.2 and 17.9 times higher than those of Pd/g-C₃N₄-bulk and the ordinary Pd/C₈-SiO₂ catalyst, respectively. Also, in the biphasic oxidation reaction of alcohols, Pd/g-C₃N₄-NSs achieved a 2.3-fold activity enhancement. It was found by analyzing the solidified emulsion droplets that the Pd/g-C₃N₄-NSs catalyst was parallelly assembled at the oil-water interfaces. Because of the ultrathin thickness of g-C₃N₄-NSs, such a unique interfacial assembly behavior allowed precise positioning of Pd nanoparticles at the oil-water interfaces. As a result, the oil-soluble reactant could directly react with the water-soluble reactant at the oil-water interface hosting the Pd nanoparticles. Our elaborately designed reaction interface was believed to substantially avoid the diffusion barrier between oil-soluble and water-soluble reactants and then to significantly enhance the reactivity of biphasic reactions. This work highlights the importance of the interfacial location of catalytic sites in biphasic catalysis.

Systematic Study on Morphological, Electrochemical Impedance, and Electrocatalytic Activity of Graphitic Carbon Nitride Modified on a Glassy Carbon Substrate from Sequential Exfoliation in Water

Several researchers have synthesized graphitic carbon nitride (GCN) from various precursors and attached it to electrode substrates after exfoliation under different conditions and have reported inconsistent data on electrochemical impedance, electroactive surface areas, and electrocatalytic activity. Thus, the present study aims to study the same systematically in addition to morphology after modifying GCN on the GC substrate from different exfoliation times in water assisted by sonication. The GCN was prepared from urea by bulk condensation pyrolysis and then attached to the GC substrate by drop casting to study its morphology, electrochemical impedance, and electrocatalytic activity with respect to exfoliation. The SEM image of a GCN-modified GC plate after 15 and 30 min of exfoliation shows bulky structure whereas thin sheets of GCN were noticed after 120 min of exfoliation. On the other hand, broken sheets were observed when GCN was coated from beyond 120 min of exfoliation. The electrochemical impedance studies show that the charge transfer resistance (R_CT) of GCN modified from 15 and 30 min of exfoliation was higher than that for the bare GC electrode. However, it started to decrease while increasing the exfoliation time, and 1.8 kΩ was obtained after 120 min of exfoliation. The R_CT value was again increased to 3.2 and 5.0 kΩ for GCN coated after 150 and 180 min of exfoliation, respectively. The electroactive surface area (EASA) of GCN modified by 15 and 30 min of exfoliation was less than that of the bare GC electrode, whereas it was 3.8-fold higher for GCN coated from 120 min of exfoliation. The electrocatalytic activity of the GC electrodes modified with GCN was then tested by studying ascorbic acid (AA) and dopamine (DA) oxidation and reduction of hydrogen peroxide (HP). Among the different exfoliation times, GCN modified from 120 min of exfoliation displayed the highest electrocatalytic activity toward AA, DA, and HP. This was attributed to its higher EASA and lower charge-transfer resistance.

The integrated production of ultrathing-C3N4and membrane assisted by edible syrup for the sustained photocatalytic treatment of Cr(VI) and tetracycline

The exfoliation of bulk raw graphitic carbon nitride (g-C₃N₄) by edible glucose syrup to produce ultrathing-C₃N₄nanosheets in concentrations of up to 0.2 mg ml^-1was achieved. Detailed characterization through TEM, AFM, FT-IR, XRD, Raman and TGA confirmed the formation of ultrathin structure and improved properties. Compared to rawg-C₃N₄, the prepared thing-C₃N₄layers exhibited a 18-fold enhancement in Cr(VI) reduction and a 3-fold enhancement in tetracycline hydrochloride degradation, which is ascribed to their larger specific surface area and more exposed active sites. The layeredg-C₃N₄membrane was constructed via direct vacuum filtration. The layer-stackedg-C₃N₄nanosheet membrane exhibited an excellent and sustained photocatalytic performance as the prepared thing-C₃N₄layers could maintain a layered lamella after stacking in filtration process. The recyclable synthesis of ultrathing-C₃N₄layers and layer-stackedg-C₃N₄membrane by our method provides a sustainable strategy to pollution treatment by 2D materials.

A simple enzyme-catalyzed reaction induced "switch" type fluorescence biosensor based on carbon nitride nanosheets for the assay of alkaline phosphatase activity

An enzyme-catalyzed fluorescence "switch" type sensor was constructed for the determination of alkaline phosphatase (ALP) activity by combining the fluorescence quenching effect of Ag+ on ultrathin g-C3N4 nanosheets (CNNSs) with the simple redox reaction of AA and Ag+. Briefly, Ag+ exhibits a significant quenching effect on the fluorescence of CNNSs. Thus the fluorescence signal of the CNNS-Ag+ system is extremely weak even in the presence of l-ascorbic acid-2-phosphate (AAP) ("off" state). When ALP coexists in the system, the enzyme can specifically catalyze the hydrolysis of AAP to form ascorbic acid (AA), which reduces Ag+ to Ag0. In this case, the fluorescence signal of the system is recovered ("on" state). Based on this principle, a signal-enhanced CNNS fluorescence sensor was developed to determine the activity of alkaline phosphatase. The experimental results show that the detection range of alkaline phosphatase is 0.5-20 U L-1, and the detection limit is 0.05 U L-1 (S/N = 3). Meanwhile, this method was used to assay ALP in serum samples.

Two-dimensional FeP@C nanosheets as a robust oxidase mimic for fluorescence detection of cysteine and Cu2

In the past few years, the development of novel nanozymes with excellent performance has attracted increasing attention in biosensing. However, most of those nanozymes were found to possess peroxidase activity with the prerequisite of the presence of H2O2. In contrast, oxidase mimics can catalyze the oxidation of substrates without H2O2, delivering a higher signal-to-noise ratio than that of peroxidase mimics in practical applications. Herein, for the first time, two-dimensional (2D) nanosheets composed of iron phosphide embedded in a carbon matrix (FeP@C nanosheets) were found to demonstrate a robust oxidase-like property, different from those previously reported peroxidase mimics based on transition metal phosphides (TMPs). Based on this intriguing observation, the fluorescent substrate Amplex Red (AR) of peroxidase can be effectively oxidized by FeP@C nanosheets in the absence of H2O2. Benefiting from the oxidase-like enzymatic activity of the FeP@C nanosheets, a novel fluorescence sensing platform was developed for the detection of cysteine (Cys) and Cu2+. The outstanding performance of the 2D FeP@C nanosheets endows the proposed platform with superior sensitivity and selectivity compared to many previously reported approaches. Besides, the inherent features of simplicity, being label free, and low cost also allow this methodology to stand out among many other strategies, revealing its huge potential in practical analysis and detection applications.

Electrochemical detection of microRNA-21 based on a Au nanoparticle functionalized g-C3N4 nanosheet nanohybrid as a sensing platform and a hybridization chain reaction amplification strategy

Here, a sensitive sandwich-type electrochemical biosensor for microRNA-21 detection was reported. It was based on the use of a Au NP functionalized graphite-like carbon nitride nanosheet (g-C₃N₄ NS) nanohybrid (Au NPs-g-C₃N₄ NS) as a sensing platform and DNA concatemers containing methylene blue (MB) as a signal probe. The signal probe was prepared by using two different single strand DNAs with a complementary sequence (one of them labeled with MB at the 3' end) to form long concatemers via continuous hybridization chain reaction (HCR); thus numerous MB signal molecules were loaded on long concatemers. The biosensor was fabricated following the next step: a thiolated hairpin probe (HP) was first immobilized on the surface of the glassy carbon electrode (GCE) modified with a Au NPs-g-C₃N₄ NS nanohybrid. After it was blocked with MCH, the modified electrode was sequentially hybridized with microRNA-21 and a signal probe, respectively. As a result, a sandwich structure of HP-microRNA-signal probe covered the surface of the modified electrode. Differential pulse voltammetry (DPV) was employed to measure the sensing signal in phosphate buffered solution (0.10 M PBS, pH 7.4). The experimental conditions were optimized such as the hybridization time and the amount of g-C₃N₄ NS. The proposed biosensor exhibited a wide linear response range (1.0 fM to 500 nM) and a low limit of detection (0.33 fM; at S/N = 3) under the optimal conditions. Meanwhile, the biosensor could discriminate single base mismatched microRNA-21, indicating that the biosensor possessed high selectivity.

An "on-off-super on" photoelectrochemical sensor based on quenching by Cu-induced surface exciton trapping and signal amplification of copper sulfide/porous carbon nitride heterojunction

In this work, we report an "on-off-super on" photoelectrochemical sensor for probing hydrogen sulfide due to its toxicity in water environment by using porous carbon nitride as photoelectric transducers. Synthesized by an alkaline-assisted hydrothermal method, the porous carbon nitride photoanode exhibited a remarkable photocurrent on the initial "on" state. Cu²⁺ immobilized on the surfaces of porous carbon nitride could significantly decrease the charge transfer efficiency and quench the photoelectrochemical signal in the "off" state. In addition, the introduction of S^2- ions could eliminate the influence of Cu-induced surface exciton trapping and amplify the photoelectrochemical signal due to the formation of carbon nitride/copper sulfide heterojunction, thus leading to the achievement of the ''super on'' state and subsequently detection of hydrogen sulfide. More importantly, this photoelectrochemical sensor shows the excellent performance for probing hydrogen sulfide in terms of stability, selectivity, sensitivity and fabrication cost. Enabled by a unique "on-off-super on" strategy, it could serve as a reference for developing the new class of photoelectrochemical sensor.