Graphitic Carbon Nitride Quantum Dots Research Articles

Unlocking multi-mode sensing potential: Phosphorus-doped graphitic carbon nitride quantum dots for Ag+, ciprofloxacin, and riboflavin analysis in environment and food matrices

The simultaneous detection of multiple analytes through a single fluorescence sensor is highly attractive. In this study, phosphorus-doped graphitic carbon nitride quantum dots (P-CNQDs) were developed, achieving multi-mode sensing through three distinct response mechanisms. The preparation involved using melamine as the carbon and nitrogen source and ammonium dihydrogen phosphate as the phosphorus source. Uniform and narrowly distributed P-CNQDs were successfully synthesized through chemical oxidation and hydrothermal methods, with an average size of 2.4 nm. These unique P-CNQDs exhibited fluorescence quenching through photo-induced electron transfer (PET) in response to Ag+. Additionally, the formation of hydrogen bonds and coordination interactions between P-CNQDs-Ag+ and ciprofloxacin (CIP) led to a pronounced fluorescence response to CIP by the chelation enhanced fluorescence (CHEF) mechanism. Furthermore, leveraging the principle of fluorescence resonance energy transfer (FRET), P-CNQDs-CIP served as a ratio fluorescence sensor for riboflavin (RF), enabling ultra-sensitive detection of RF. The combination of PET, CHEF, and FRET response mechanisms successfully facilitated multi-mode sensing for Ag+, CIP, and RF. The detection ranges were 0.05–100 μM, 0.002–2 μM, and 0.05–60 μM, with corresponding lowest detection limits of 17.1 nM, 1.1 nM, and 29.2 nM, respectively. This versatile sensor has been effectively applied to real samples, including the detection of river water and vitamin B2 tablets.

Internal light-driven efficient chemiluminescence of graphitic carbon nitride quantum dots for improved carboxin sensing

Developing a new chemiluminescence (CL) sensor platform to achieve the identification of pollutants in the water environment is a significant and currently hot topic for researchers. Building on the effective development of a CL internal light source, this paper designed a direct, simple, and rapid pesticide identification strategy. Specifically, graphite carbon nitride quantum dots (CNQDs) with excellent optical properties were synthesized using a solvent heat treatment strategy. Acting as an energy acceptor, CNQDs triggered CL emission in the presence of singlet oxygen (1O2). The newly developed CNQDs/1O2 CL sensor exhibited a specific response toward carboxin (CBX) with high sensitivity. Based on this discovery, we have developed a highly selective, ultra-sensitive, and fast CL sensing platform for detecting CBX in water environments. Through numerous experiments, we attributed the CL emission of the CNQDs/1O2 system to the specific chemiluminescent resonance energy transfer (CRET) process between CNQDs and 1O2. Interestingly, the CL light of the CNQDs/1O2 system could serve as an internal light source to excite CBX generating a large amount of 1O2 through photosensitization, which was crucial for further enhancing the CL efficiency of the CNQDs/1O2/CBX system and also enabled the CL sensing of CBX. This study is the first to successfully identify CBX in water using CL sensors, showcasing the potential of CL internal light sources in regulating CL efficiency and offering new perspectives on detecting pollutants in complex environments.

Axial O Atom‐Modulated Fe(III)‐N4 Sites for Enhanced Cascade Catalytic 1O2‐Induced Tumor Therapy

AbstractThe rational construction of efficient hypoxia‐tolerant nanocatalysts capable of generating singlet oxygen (1O2) without external stimuli is of great importance for tumor therapy. Herein, uniformly dispersed and favorable biosafety profile graphitic carbon nitride quantum dots immobilized with Fe‐N4 moieties modulated by axial O atom (denoted as O‐Fe‐N4) are developed for converting H2O2 into 1O2 via Russell reaction, without introducing external energy. Notably, O‐Fe‐N4 performs two interconnected catalytic properties: glutathione oxidase‐mimic activity to provide substrate for subsequent 1O2 generation, avoiding the blunting anticancer efficacy by glutathione. The O‐Fe‐N4 catalyst demonstrates a specific activity of 79.58 U mg−1 at pH 6.2, outperforming the most reported Fe‐N4 catalysts. Density functional theory calculations demonstrate that the axial O atom can effectively modulate the relative position and electron affinity between Fe and N, lowering the activation energy, strengthening the selectivity, and thus facilitating the Russell‐type reaction. The gratifying enzymatic activity stemming from the well‐defined Fe‐N/O structure can inhibit tumor proliferation by efficiently downregulating glutathione peroxidase 4 activity and inducing lipid peroxidation. Altogether, the O‐Fe‐N4 catalyst not only represents an efficient platform for self‐cascaded catalysis to address the limitations of 1O2‐involved cancer treatment but also provides a paradigm to enhance the performance of the Fe‐N4 catalyst.

Microwave-assisted preparation of yellow fluorescent graphitic carbon nitride quantum dots for trace tetracycline-specific detection

Tetracycline (TC) is extensively utilized in livestock breeding, aquaculture, and medical industry. TC residues seriously harm food security, the environment, and human health. There is an urgent need to exploit a highly efficient and sensitive testing method to monitor TC residue levels in aquatic environments. In this study, graphitic carbon nitride quantum dots (g-CNQDs) were successfully synthesized by a one-step microwave-assisted method using citric acid and urea as precursors. The as-prepared g-CNQDs with size of 1.25–3.75 nm exhibited bright yellow fluorescence at 523 nm when excited at 397 nm. Interestingly, this characteristic fluorescence emission of g-CNQDs could be selectively and efficiently quenched by TC. Based on this phenomenon, for TC detection was successfully explored and applied in real water samples. Wide linear scope of 7–100 μM, low detection limit (LOD) of 0.48 μM, satisfactory recovery of 97.77%–103.4%, and good relative standard deviation (RSD) of 1.05–5.87% were obtained. Mechanism investigations revealed that the static quenching and the inner filter effect (IFE) were responsible for this fluorescence quenching between g-CNQDs and TC. This work not only provided a facile approach for g-CNQDs synthesis but also constructed a g-CNQDs-based fluorescent sensor platform for the highly sensitive and selective detection of TC in aquatic environments.

Development of graphitic carbon nitride quantum dots-based oxygen self-sufficient platforms for enhanced corneal crosslinking

Keratoconus, a disorder characterized by corneal thinning and weakening, results in vision loss. Corneal crosslinking (CXL) can halt the progression of keratoconus. The development of accelerated corneal crosslinking (A-CXL) protocols to shorten the treatment time has been hampered by the rapid depletion of stromal oxygen when higher UVA intensities are used, resulting in a reduced cross-linking effect. It is therefore imperative to develop better methods to increase the oxygen concentration within the corneal stroma during the A-CXL process. Photocatalytic oxygen-generating nanomaterials are promising candidates to solve the hypoxia problem during A-CXL. Biocompatible graphitic carbon nitride (g-C3N4) quantum dots (QDs)-based oxygen self-sufficient platforms including g-C3N4 QDs and riboflavin/g-C3N4 QDs composites (RF@g-C3N4 QDs) have been developed in this study. Both display excellent photocatalytic oxygen generation ability, high reactive oxygen species (ROS) yield, and excellent biosafety. More importantly, the A-CXL effect of the g-C3N4 QDs or RF@g-C3N4 QDs composite on male New Zealand white rabbits is better than that of the riboflavin 5’-phosphate sodium (RF) A-CXL protocol under the same conditions, indicating excellent strengthening of the cornea after A-CXL treatments. These lead us to suggest the potential application of g-C3N4 QDs in A-CXL for corneal ectasias and other corneal diseases.

Enhanced visible light photocatalytic degradation of styrene by g-C3N4 quantum dots/P25 nanocomposites

The enhancement of the visible light response of P25 is of significant importance for the photocatalytic degradation of volatile organic compounds (VOCs). Graphitic carbon nitride quantum dots (CNQD) are nano-sized counterparts of g-C3N4, exhibiting excellent optical properties. Using a simplified hydrothermal one-step approach, CNQD-loaded P25 (CNQD/P25) was obtained in this work. Under visible light, CNQD/P25 achieved styrene degradation rate of 95 % within 240 minutes, surpassing the 60 % degradation rate of pure P25 under identical conditions. This indicates that the presence of CNQDs greatly enhances the photocatalytic performance of P25 in the visible light region. Further investigations revealed that CNQD/P25 exhibited noticeable enhancement in the ultraviolet-visible absorption spectrum, demonstrating increased visible light absorption. CNQD/P25 demonstrated higher photocurrent response, lower photoresistance, and weaker fluorescence response compared to P25 at similar conditions. Therefore, the presence of CNQDs can enhance visible light absorption of P25, increases the number of photo-generated electrons, optimizes charge separation efficiency, and simultaneously reduces the recombination rate of electrons and holes.

Graphitic carbon nitride quantum dots seeding in MnTiO3 spheres: A novel visible light responsive photocatalyst with high interface charge transfer for antibiotic degradation

As a promising heterojunction photocatalyst, MnTiO3 was incorporated with graphitic carbon nitride quantum dots (CNQDs) by performing a simple thermal method. The optimal sample MnTiO3@CNQDs(III) could degrade 93.1% of tetracycline, which was about 5.56 times than that of the pristine perovskite. This could be due to high light absorption ability, an appropriate band structure, enhanced separation rate of the photoinduced carrier species and the nitrogen-rich oxygen species content of CNQDs structure. The photocatalytic efficiency remained 78.9% in the seven cycle tests, indicating a considerable stable behavior. The main active substances were superoxide and holes as well as hydroxyl radicals slightly mediated the reaction. At neutral condition, the photocatalyst showed its best activity. After 60 min, the removal efficiency reached 100% by adding PMS while in the presence of H2O2 the highest removal obtained for 90 min. Different wastewater environments held a slight impact on photocatalytic efficiency to reveal a good applicability in real-world environments. Thus, the study presented a novel heterostructured semiconductor that includes the synergistic effect between CNQDs and MnTiO3, contributing to high photocatalytic activity.

Smart fluorescent PVA/CS/AV/g-C3N4QDs hydrogel nanocomposites: synthesis and study of UV absorbance, rheological and self-healing properties

Response to exterior stimulants, such as light and pH and also self-healing behavior are the major specifications of smart nanocomposites. This project aims to synthesise various weight percentages of smart fluorescent hydrogel nanocomposites using natural and bio-friendly materials including polyvinyl alcohol (PVA), corn starch (CS), aloe vera (AV) and g-C3N4QDs (PSA/CN). Graphitic carbon nitride quantum dots (g-C3N4QDs or CN) were synthesised by way of pyrolysis of the urea and citric acid (CA) blend with 18:1 weight proportion employing microwave-supported procedure. Next, synthesis and properties of the prepared nanocomposites were verified by means of microscopic and electroscopic methods. The strong absorption peaks registered at 230, 290 and 390 nm confirmed UV absorption ability of the synthesised PSA/CN nanocomposites. In response to 390 nm exciting wavelength, these nanocomposites emitted green fluorescence (FL) at 505–510 nm. Adding CN (0.25 wt% and 0.5 wt%) to the hydrogel matrix bred a growth in thermal stability of the resultant nanocomposites. Loading diverse weight percentages of CN into hydrogel matrix led the rheological features of the hydrogel nanocomposites to improve. Studies on pH-responsive and rheological analyses approved self-healing behavior of the PSA/CN nanocomposites against damages.

Graphitic Carbon Nitride Quantum Dots (g-C3N4 QDs): From Chemistry to Applications.

Since their emergence in 2014, graphitic carbon nitride quantum dots (g-C3N4 QDs) have attracted much interest from the scientific community due to their distinctive physicochemical features, including structural, morphological, electrochemical, and optoelectronic properties. Owing to their desirable characteristics, such as non-zero band gap, ability to be chemically functionalized or doped, possessing tunable properties, outstanding dispersibility in different media, and biocompatibility, g-C3N4 QDs have shown promise for photocatalysis, energy devices, sensing, bioimaging, solar cells, optoelectronics, among other applications. As these fields are rapidly evolving, it is very strenuous to pinpoint the emerging challenges of the g-C3N4 QDs development and application during the last decade, mainly due to the lack of critical reviews of the innovations in the g-C3N4 QDs synthesis pathways and domains of application. Herein, an extensive survey is conducted on the g-C3N4 QDs synthesis, characterization, and applications. Scenarios for the future development of g-C3N4 QDs and their potential applications are highlighted and discussed in detail. The provided critical section suggests a myriad of opportunities for g-C3N4 QDs, especially for their synthesis and functionalization, where a combination of eco-friendly/single step synthesis and chemical modification may be used to prepare g-C3N4 QDs with, for example, enhanced photoluminescence and production yields.

Photochemical fluorination of graphitic carbon nitride quantum dots: Fluorescent properties, and their mechanisms

Fluorinated graphitic carbon nitride quantum dots (F-GCNQDs) with adjustable photoluminescence (PL) were prepared by a facile photochemical method using graphitic carbon nitride quantum dots (GCNQDs) powder as the precursor and XeF2 as the dopant source. It is observed that the emission peaks of the F-GCNQDs exhibit a maximal red-shift of about 8.8 nm compared to that of the GCNQDs. Density functional theory (DFT) calculations reveal that such red-shifts can be understood by the enhancement of electron-ion core interactions upon the addition of F to C, where the presence of strongly electronegative F atoms leads to a drop in the highest unoccupied energy level.

A graphitic C3N4 nanocomposite-based fluorescence platform for label-free analysis of trace mercury ions.

In this study, a nanocomposite consisting of graphitic carbon nitride nanosheets loaded with graphitic carbon nitride quantum dots (CNQDs/CNNNs) was synthesized via a one-step pyrolysis method. This nanocomposite exhibited excellent thermal stability, photobleaching and salt resistance. Then a new fluorescence sensing platform based on CNQDs/CNNNs was constructed, which showed high sensitivity and selectivity towards trace mercury ions (Hg2+). By using X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectra and density functional theory, the fluorescence response mechanism was elucidated where Hg2+ could interact with CNQDs/CNNNs, causing a structural change in the nanocomposite, further affecting its bandgap structure, and finally leading to fluorescence quenching. The linear range for detecting Hg2+ was found to be 0.025-4.0 μmol L-1, with a detection limit of 7.82 nmol L-1. This strategy provided the advantages of a rapid response and a broad detection range, making it suitable for quantitative detection of Hg2+ in environmental water.

Calibration of varying MoS2 amount with dual fabrication GCN/CQDs for supercapacitor’s electrode and strengthening of the energy parameters

A heptazine form of graphitic carbon nitride (h-g-CN) and Carbon Quantum Dots (CQDs), each was obtained through thermal polymerization procedure and furthered their nano-ranged duo-composite as g-CN/CQDs through hydrothermal method. The influence of different amounts of MoS2insertions was studied on this duo after making its trio recipe (g-CN/CQDs/MoS2) as a super-capacitive working electrode for energy storing capability. After the ample characterization of the composites, these were tested for electrochemical applications.During the optimized study in a three-electrode system, it was found that CQDs and g-C3N4in 1:2 (fixed) by varying MoS2(30 %) shows the specific capacitance as 445.4F/g at 2 mV/s in 1 M H2SO4with cyclic stability of 89.3 % even after 10,000 cycles. Theenergy density and power density were observed as 37.5 Wh/kg and 404.19 W/kg respectively, at1 A/g.In a two-electrode system with specific capacitance of GCN/CQDs/30 % MoS2as 122.5F/g at 0.1 A/g.

Synthesis of multicolour luminescent graphitic carbon nitride quantum dots through controlled graphitization and surface states

Carbon nitride quantum dots are important metal free semiconductors due to their controlled optoelectronics and low toxicity. Here the sulphur heteroatom doping of these nanomaterials is achieved by the low cost hydrothermal process leading to a multicolour photoluminescence. A simple change in water/dimethyl sulfoxide ratio as a solvent helps to achieve a wide tunability in photoluminescence, almost from blue, green, yellow to red with a high quantum yield. This change has been accounted for the particle size, bond conjugation, and heteroatom doping of carbon nitride nanoparticles. Due to multicolour emission, benignity and low cost these materials can be the promising candidates for various optoelectronic applications.

Hydrothermal synthesis and ionic sensing properties of graphitic carbon nitride quantum dots

BackgroundThis work adopts an efficient method including thermal calcination, surface hydroxylation, and hydrothermal cutting to synthesize graphitic C3N4 quantum dots (CNQDs) for detecting metal ions in aqueous solutions. MethodsFunctionalized CNQDs, ranged from 2 to 6 nm in particle size, were of layered crystalline and contain a large amount of surface functionalities such as carbonyl, carboxylic, and amino groups. The CNQD suspension exhibited a maximal fluorescence intensity at 420 nm with high quantum yield of 13.6% under UV irradiation. Significant findingsThe CNQD suspension demonstrated superior sensitivity and selectivity toward iron ions with ppm-level detection limit in liquid phase. The Stern-Volmer analysis revealed that CNQD suspension was appropriate for the detection of Fe3+ and Fe2+ ions with LOD of 6.5 and 7.7 ppm, respectively. The fluorescence quenching mechanism of CNQD suspension mainly originates from a strong interaction between the ions and the surface functionalities followed by the photoinduced energy transfer effect, thus inducing the fluorescence extraction. Moreover, the CNQD suspension also offers a satisfactory biocompatibility toward 3T3 cell after 24 h. Accordingly, the robust design of CNQDs developed in this work paves the way for developing highly sensitive and selective probes for detecting target species in aqueous solutions.

Bisphenol A Imprinted Electrochemical Sensor Based on Graphene Quantum Dots with Boron Functionalized g-C3N4 in Food Samples.

A molecular imprinted electrochemical sensor based on boron-functionalized graphitic carbon nitride (B-g-C3N4) and graphene quantum dots (GQDs) was presented for selective determination of bisphenol A (BPA). In particular, by combining the selectivity and high stability properties, which are the most important advantages of molecular imprinted polymers, and the highly sensitive properties of GQDs/B-g-C3N4 nanocomposite, a highly selective and sensitive analytical method was developed for BPA analysis. Firstly, GQDs/B-g-C3N4 nanocomposite was characterized by using microscopic, spectroscopic, and electrochemical techniques. This novel molecular imprinted electrochemical sensor for BPA detection demonstrated a linearity of 1.0 × 10-11-1.0 × 10-9 M and a low detection limit (LOD, 3.0 × 10-12 M). BPA-imprinted polymer on GQDs/B-g-C3N4 nanocomposite also showed good stability, repeatability and selectivity in food samples.

Nanocarbon in Sodium‐ion Batteries – A Review. Part 1: Zero‐dimensional Carbon Dots

AbstractIn the recent past, sodium‐ion batteries (SIBs) have assumed to be an alternative to lithium‐ion batteries (LIBs) as sodium is abundantly available in nature. It is low cost with its storage mechanism almost similar to LIBs. The ionic radius of Na is three‐fold larger than that of Li and offers a low standard electrochemical potential than Li. The built‐in SIBs are better than LIBs. However, in terms of energy density, specific capacity, and rate capability, there is a lack of suitable anode materials for SIBs. Interestingly, carbon‐based quantum dots are a new class of zero‐dimensional (0D) material with ultra‐small size having unique physicochemical properties. The utility of carbon quantum dots (CQDs), graphene quantum dots (GQDs) and graphitic carbon nitride quantum dots (g‐C3N4 QDs) has drawn attention to the scientists and industrialists for the development of SIBs due to their quantum size and structural diversities, physicochemical properties, amenability for doping with heteroatoms and good electrical conductivity. This article reviews the role of various carbon quantum dots commonly used as anodes in SIBs.

A photoelectrochemical sensor of g-C3N4 QDs with synergistical sensitization by rGO and hemicucurbit[12]uril for detection of chloramphenicol

A novel photoelectrochemical sensor was constructed by ternary layer-by-layer composites of reduced graphene oxide (rGO), graphitic carbon nitride quantum dots (g-C3N4 QDs), and hemicucurbit[12]uril (HemiQ[12]), on the Indium-Tin Oxide (ITO) piece in sequence. Electrochemical Impedance Spectroscopy (EIS) was employed to confirm the successful assembly of the sandwich electrode, and the functionalization of each layer was explored by comparing of the currents with stepwise coating of the materials to achieve the synergistic enhancement of photoelectrochemical intensity. The application of proposed electrode was achieved by ultrasensitive sensing for chloramphenicol (CAP), which provided a limit of detection low to 0.089 nM, with high selectivity, good reproducibility and stability. The acceptable recoveries for the determination of CAP in real samples of honey and milk illustrated the feasibility of the established analytical method.

Graphitic carbon nitride quantum dots as novel and efficient friction-reduction and anti-wear additives for water-based lubrication

Undeniably, advances in water-based nano-additives play a considerable role in energy conservation and pollution reduction accompanied by the resurgence of water-based lubricants. Graphitic carbon nitride quantum dots (g-CNQDs) have attracted remarkable attention in water-based lubricant additives owing to their strong designability, favorable mechanical property, and unique self-lubricating effect. Therefore, a series of different-sized g-CNQDs with good water dispersibility were expediently synthesized via a hydrothermal strategy and directly used as water-based lubricant additives. Tribological tests indicated that the tribological behaviors of the g-CNQDs-based additives displayed an obvious phenomenon of performance-dependent physical dimensions. With the introduction of g-CNQDs-based additives (1.0 wt%) into the water-based lubrication system, which friction-reduction, anti-wear, and load-supporting performances can be maximally increased by 45.5%, 94.0%, and 233.3%, respectively. Meanwhile, the long-term operating performance of the lubrication system can be promoted under high-load conditions. The formed tribo-film caused by tribo-chemical reaction integrated with the nano-lubrication effect of g-CNQDs collectively contributed to their good tribological performances.

L-Glutathione modified graphitic carbon nitride quantum dots: An ultrasensitive fluorescent sensor for detection of Pb2+ in water

A facile, sensitive, and selective fluorescence detection method for Pb2+ ions is designed using L-Glutathione (GSH) modified graphitic carbon nitride quantum dots (GSH@g-C3N4 QDs). A carbodiimide-activated coupling reaction is used to bind GSH onto g-C3N4 QDs. When excited at 340 nm, the as-obtained passivated quantum dots exhibit strong blue emissions at 420 nm. With a relative quantum yield of 27%, the system demonstrates exceptional stability against ionic strength and photobleaching. Additionally, it is discovered that the fluorescence emission of the sensor is selectively quenched in the presence of Pb2+ ions. The limit of detection (LOD) for Pb2+ is measured to be 0.025 µM in a linear range of 0.01 µM-0.1 µM. The average lifetime calculations from the lifetime decay experiment along with UV–vis. absorption studies suggest that the quenching pattern follows a static quenching mechanism. Finally, the system is used in real water samples to detect Pb2+ with a substantial recovery percentage greater than 90%.

Green fluorescent unsaturated polyester/graphitic carbon nitride quantum dots nanocomposites: Preparation and study of UV-resistance, mechanical and viscoelastic properties

The present study has been conducted to investigate the protective effect of graphitic carbon nitride quantum dots (CNQDs) against high energetic and harmful ultraviolet (UV) rays in addition to strengthening impact of CNQDs over mechanical and viscoelastic properties of unsaturated polyester (UP). To achieve this purpose, CNQDs were synthesized using citric acid and extra urea via microwave-assisted method. Afterwards, several percentages of CNQDs (0.25, 0.5 and 0.75 wt%) were added to UP and after curing process, UP/CNQDs nanocomposites were obtained with different percentages. By certain microscopic and spectroscopic tests, correctness of CNQDs formation and various features of UP/CNQDs nanocomposites were examined. Adding CNQDs to the matrix of polyester resin allowed creation of nanocomposites with fluorescence emission ability, also blockage of UV rays by the strengthened samples. Strengthening UP by CNQDs resulted in growth of thermal stability, improvement of tensile strength, 10%–15% increase in flexibility, and progress in viscoelastic characteristics including storage modulus, Tg and cross-linking density.