Lithium-ion batteries (LIBs) are widely used as essential power sources for electric vehicles and energy storage systems. Among various cathode materials, Li[Ni0.9Mn0.1]O2 (NM90) has gained significant attention for enhancing the performance of LIBs due to its high energy density and nontoxicity. However, increasing the nickel content introduces challenges, including structural instability and cation mixing. To address these issues, we propose a surface coating strategy using nitrogendoped carbon quantum dots (NCQDs). NCQDs provide high electrical conductivity and electrochemically active sites, so the NCQDs coating effectively enhanced both structural stability and electrical/ionic conductivity. The NCQDs were synthesized via a hydrothermal method, and NM90 were synthesized by co-precipitation. The fabricated NCQD/NM_5 electrode exhibited superior electrochemical properties, including a high initial capacity of 189.6 mAh/g, excellent rate performance, and an outstanding capacity retention of 81.5 % after 200 cycles in 1C. These superior results demonstrate that surface modification using the NCQDs strategy for Li[Ni0.9Mn0.1]O2 cathode materials will contribute to the further development of cycle stability and ultrafast performance in energy storage systems.

A simple and effective method was developed to prepare fluorescent carbon quantum dots (CQDs) for the detection of Fe3+ and Cu2+ in aqueous solution. The water-soluble CQDs with the diameter around 2–5 nm were synthesized using anthracite coal as the precursor. In addition, the as-prepared CQDs exhibits sensitive detection properties for Fe3+ and Cu2+ metal cations with a detection limit of 18.4 nM and 15.6 nM, respectively, indicating that the coal-derived CQDs sensor is superior for heavy metal recognition and environmental monitoring.

Complex structure constituting of several layers of heteroatom-doped N-CDs are used as a main sensing film along with aluminum electrodes in conductometric gas sensing system for sensitive and selective monitoring of CO2 and CO gases diluted with normal air, which are extensively prevalent in the atmosphere primarily due to the industrial revolution, locomotives, and numerous natural phenomena’s and the limit of detection (LOD) turned out to be 400 ppm and 30 ppm, respectively, with 20% relative humidity at 30 °C and pressure 1 (atm) which are good for healthy air quality checks. The sensor performance was satisfactory and bidirectional at ambient room temperature (30 °C) and pressure (1 atm) conditions but the relative humidity (50%) at 30 °C had a detrimental impact on the sensing responses, therefore intermittent heating at 80 °C for several minutes between the sensing responses was provided to the sensing chip or one should use gas filter membranes to block humidity, thereby maintaining its constant performance with great ease and accuracy. The cyclic voltammetry revealed well-defined oxidation and reduction peaks, with excellent stability and reversibility. In a nutshell, heteroatom-doped N-CDs’ nanocomposite material can revolutionize in a better environmental pollution monitoring by sensing gases in an extensively lesser response and recovery times.

Carbon quantum dots (CQDs) are novel nanocarbon materials and widely used nanoparticles. They have gradually gained popularity in various fields due to their abundance, inexpensive cost, small size, ease of engineering, and distinct properties. To determine the antibacterial activity of metal-doped CQDs (metal-CQDs) containing Fe, Zn, Mn, Ni, and Co, we chose Staphylococcus aureus as a representative Gram-positive strain and Escherichia coli as a representative Gram-negative bacterial strain. Paper disc diffusion tests were conducted for the qualitative results, and a cell growth curve was drawn for quantitative results. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and IC50 were measured from cell growth curves. As a result, all of the metal-CQDs showed toxicity against both Gram-positive and Gram-negative bacteria. Furthermore, Gram-negative bacteria was vulnerable to metal-CQDs than Gram-positive bacteria. The toxicity differed concerning the type of metal-CQDs; Mn-CQDs exhibited the highest efficacy. Hence, this study suggested that CQDs can be used as new nanoparticles for antibiotics.

Fluorescent Carbon Quantum Dots (FCQDs), a new generation of carbon nanomaterials, have attracted a lot of attention throughout the years. This paper applied a straightforward and environmentally beneficial way to create water-soluble FCQDs hydrothermally from coconut shells. The as-prepared FCQDs have desirable functional groups and exhibit strong blue-emitting fluorescence with a relative quantum yield of 0.6 and 0.7%. The optical bandgap of FCQDs is calculated using UV–Vis spectra to be between 3.9 and 4.4 eV. Optical studies show that FCQDs have good fluorescence properties when excited at 360 nm. Whereas the fluorescence decay lifetime using TCSPC are 1.6–0.99 ns. The synthesized FCQDs were found by HRTEM to have a spherical shape and a particle-size distribution of 2.8–5.4 nm. As-prepared FCQDs has a very low hemotoxicity of 0.5 to 1.3%, which indicates that they have acceptable biocompatibility and are not hazardous. According to the DPPH antioxidant data, FCQDs had a stronger antioxidant activity compared to earlier reports. These important characteristics enable its applications in biomedical, food packaging, fluorescence imaging, photocatalysis, and sensing. The enhanced antioxidant characteristics of the produced FCQDs make them appropriate for use in biomedical, bioimaging, chemical, and industrial applications. The as-synthesized FCQDs were used for the detection of ferric ions with good selectivity.

Carbon dots (C-dots) are a developing subclass of nanomaterials which are characterized by a typical diameter of less than 10 nm. C-dots are a type of core–shell composites that feature a surface passivation with various functional groups, including amine, carboxyl, hydroxyl group, and a carbon core. Green C-dots, which have drawn a lot of interest from researchers due to their superior water solubility, excellent biocompatibility, and environmental-friendly behavior when compared to chemically generated C-dots, can be made from a variety of low-cost and renewable materials. Since green C-dots have heteroatoms on their surface in the form of carboxyl, amine, hydroxyl, or other functional groups, which can enhance their physicochemical characteristics, quantum yield (QY), and likelihood of visible light absorption, further surface passivation is not necessary. Green C-dots may find use in the areas of biosensing, catalysis, bioimaging, and gene and drug delivery. In this paper, the creation of C-dots was outlined, and its fluorescence process examined. This review represents the summary of synthesis, mechanism, properties, characterization, and applications of C-dots. This article aims at the green chemistry strategies for C-dot synthesis. Furthermore, a discussion on the applications of C-dots produced with green approaches is presented. The paper may help the researchers in the field to develop new C-dots with potential features to attract the attention of new applications.

A phenylboric acid functionalized carbon dot (2-FPBA-CD) for rapid fluorescent sensing of glucose in blood was synthesized by simply mixing N, S-doped carbon dots (CDs) with phenylboric acid at room temperature. At pH 7.4, the response of 2-FPBA-CD to glucose could reach equilibrium in a very short time (10 min), with a wide responsive linear range of 19.70 μM to 2.54 mM, which can be applied to the detection of glucose in serum. The mechanism studies showed that the layered carbon film of 2-FPBA-CD aggregated after adding glucose, thereby leading to the fluorescence quenching of 2-FPBA-CD.

InP quantum dots (QDs) have attracted researchers’ interest due to their applicability in quantum dot light-emitting displays (QLED) or biomarkers for detecting cancers or viruses. The surface or interface control of InP QD core/ shell has substantially increased quantum efficiency, with a quantum yield of 100% reached by introducing HF to inhibit oxide generation. In this study, we focused on the control of bandgap energy of quantum dots by changing the Zn/(In+Zn) ratio in the In(Zn)P core. Zinc incorporation can change the photoluminescent light colors of green, yellow, orange, and red. Diluting a solution of as-synthesized QDs by more than 100 times did not show any quenching effects by the Förster resonance energy transfer phenomenon between neighboring QDs.

This study is about the optical properties of InP-based quantum dot nanoparticles depending on their core/shell structure. The need to synthesize non-cadmium-based quantum dot nanoparticles with high quantum efficiency has become necessary due to the harmful effects of the element cadmium. We synthesized three types of quantum dot nanoparticles in 2000ml three-necked flasks by varying the synthesis temperature and time to have the same PL spectra according to the composition of the core and shell. The PL spectra, absolute quantum efficiency, and nanoparticle size were compared and analyzed according to the composition at red emission wavelengths of 614, 616, and 630 nm. InP/ZnSe/ZnS nanoparticles were synthesized with the highest PL-AQY of 94% at 614 μm, and Ga-doped InP/GaP/ZnSe/ZnS nanoparticles were synthesized with the highest PL-AQY of 97% at 616 μm. InZnP/ZnSe/ZnS nanoparticles with alloy cores were able to synthesize quantum dot nanoparticles with a peak PL-AQY of 98% at 630μm.

Heavy metal ions pollution has become of worldwide critical concern, thus, it is particularly important to monitor it in the environment and food for ensuring human health. In this study, p-phenylenediamine and 2-mercaptothiazoline were used to prepare nitrogen (N) and sulfur (S) co-doped carbon dots (N/SCDs) for fluorescent and colorimetric detection of Cu2+. The fabricated N/SCDs with bright green fluorescence showed excellent optical characteristics and favorable water solubility. In an aqueous system, a significant fluorescence quenching of N/SCDs at 512 nm is obtained in the presence of Cu2+. It also caused a significant colorimetric response with the color of prepared N/SCDs solution changed from colorless to yellow. Under optimal conditions, the analytical results showed that the linear range spanning from 5 to 400 μM, with a detection limit of 0.215 μM in fluorescence and 0.225 μM in colorimetric detection. In addition, N/SCDs displayed high selectivity toward Cu2+. No obvious interference was observed over other metal ions. Furthermore, we have also used N/SCDs to monitor Cu2+ in tap and lake water. The recovery of Cu2+ ranged between 89.6% and 113.1%. Exhibiting remarkable sensitivity and selectivity, the designed sensor offers a promising detection method for Cu2+ detection in the real sample.

The detailed understanding of fluorescence emission processes is still unclear. This study demonstrates Aegle marmelos derived luminescent heteroatoms (N, Ca, K) doped carbon quantum dots (CQDs) using an economically and ecologically sustainable synthesis process without the necessity for any doping precursors due to its phytochemical, vitamin and mineral content. Carboxyl functionalization was done by adding lemon juice to the fruit extract. The morphological, physiochemical, compositional, crystallinity, and surface functional groups having heteroatom doped CQDs were analysed by HRTEM, EDX, XPS, XRD, FTIR etc. Besides, CQDs exhibited pH and solvent-dependent tuneable fluorescence characteristics. In fact, beyond pH 7.77, a protonation-deprotonation-driven red-shift was observed together with a decrease in the contribution of prominent peaks. Meanwhile, the features of solvatochromic fluorescence were examined in a range of aprotic and protic solvents with low and high polarity. Based on the studied Kamlet–Taft parameters and the obtained spectroscopic characterizations, a suitable fluorescence emission mechanism is provided. The observed solvatochromic fluorescence is thought to be caused by a combination of dipole moment polarisation, intramolecular charge transfer processes with or without H-bond stabilisation via the interaction of heteroatoms doped CQDs with solvent mediated by electron donation and acceptance from various surface functional groups such as hydroxyl, carboxyl with solvent molecules. Hence, this study is believed to promote the development of eco-tuneable fluorescent heteroatom doped CQDs and provide further insights into the fundamental fluorescence mechanisms, which include the relationship between morphology, surface properties and plausible quantum effects between CQDs and solvents.

4-Nitrophenol (4NP) is a vital intermediate in organic industries, and its exploitation creates serious environmental issues. We propose a fluorescence quenching-based strategy with nitrogen and sulfur co-doped carbon dots (NS-CDs) for highly sensitive 4NP detection with excellent selectivity. The NS-CDs are produced through the hydrothermal process, in which citric acid serves as a carbon source and cysteamine hydrochloride as a source of N and S. The effect of doping was also studied by synthesizing undoped CDs and examining their properties. As-developed NS-CDs exhibit a bright cyan blue color with maximum emission centered at 465 nm. The fluorescence of NS-CDs is significantly quenched in an approximately linear fashion with increasing 4NP concentration (7.5–97.5 μM). The inner filter effect (IFE) and static quenching (SQ) between NS-CDs and 4NP are responsible for such fluorescence reduction. The fluorimetry technique enables the quantification of 4NP with a limit of detection (LOD) of about 0.028 μM. Moreover, the fluorescence quenching is tested for several other chemical compounds but they generate false quenching signals; only 4NP leads to fluorescence quenching of NS-CDs, demonstrating excellent selectivity. The “turn-off” fluorescence properties and visually apparent color change of the fluorescent probe reveal the excellent performance for 4NP sensing. The NS-CDs’ capability of quantifying 4NP in real water samples (tap water and drinking water) produces an excellent recovery rate ranging between 96.24 and 98.36%.

Development of carbon-based biocompatible and flexible nanosensors is essential in different practical applications. Humidity sensor is crucial in different fields among them. Herein, a unique metal-free nanosensor comprised of 2D-graphitic carbon nitride (CN) decorated with 0D-carbon dots (C-dots) was fabricated to monitor humidity in human breath. Simple polymerization and carbonization techniques were used to synthesize nitrogen enriched heterostructure (CN@C-dots). The synthesized heterostructure showed excellent physicochemical properties including high surface area, hydrophilic functionalities and more active sites that were responsible for enhanced humidity sensing. The fabricated nanosensor indicated excellent resistivity against humidity due to diffused proton hoping through inhibition of ion transfer from multiple water layers. The interaction mechanism was explained through simple hydrogen bonding and defective site chemisorbed oxygen participation in physisorbed humidity molecules.

Composites of carbon quantum dots (CQDs) are important materials to utilize the optical properties of CQDs in diverse applications including photoluminescence-based sensing and LED phosphors. Combining pre-prepared CQDs with a polymeric matrix usually causes changes in the optical properties of CQDs due to unavoidable aggregation. Recently, the preparation of composites based on in-situ formed CQDs has been debated to overcome the aggregation limits of the conventional mixing methods. Herein, we have demonstrated the synthesis of homogeneous CQDs composites by simple thermal annealing blends of aluminum hydroxide (AlOH), citric acid (CA), and urea (URA). Transmission electron microscopy (TEM), X-ray diffraction, and Raman spectroscopy studies revealed the formation of individual CQDs with a diameter of about 2–9 nm dispersed homogeneously over the AlOH matrix. The composites have a broad excitation band centered at about 360 nm and exhibit excitation-dependent photoluminescence which was similar to that of hydrothermally synthesized CQDs from CA and URA. The photoluminescent intensity of the composite was stable to UV irradiation and responded selectively to Cu(II) ion demonstrating its potential application in Cu(II) sensing.

Carbon dots (CDs) are a novel type of fluorescent nanoparticles with a particle size smaller than 10 nm. They possess several advantageous properties, including excellent biocompatibility, light stability, water solubility, and low toxicity. CDs have been widely researched in recent years. As a treasure of ancient Chinese science, traditional Chinese medicine (TCM) is rich in various active ingredients and has a variety of pharmacodynamic effects, which have been used for thousands of years. TCM-CDs prepared with TCM as carbon source can create some special functions and then may play a greater medicinal value. The purpose of this review was to engage in an in-depth conversation about the use of TCM-CDs in medical therapy and bioimaging. Firstly, this study provides a comprehensive exploration of different synthesis methods for TCM-CDs, comparing their respective advantages and disadvantages. Subsequently, the intrinsic pharmacological activity of TCMCDs, encompassing antibacterial, hypoglycemic, hemostatic, anticancer, and anti-inflammatory effects, is mainly discussed, alongside their underlying mechanisms of action. Additionally, investigations into in vitro imaging of diverse cell types and the distribution and uptake of TCM-CDs under in vivo imaging guidance are presented. Finally, the significance of TCM-CD research, key challenges and issues within this field, and future directions for development are summarized and outlined.

Graphene quantum dots (GQDs) are zero-dimensional carbonous materials with exceptional physical and chemical properties such as a tuneable band gap, good conductivity, quantum confinement, and edge effect. The introduction of GQDs in various layers of solar cells (SCs) such as hole transport layer (HTL), electron transport materials (ETM), cathode interlayer (CIL), photoanode materials (PAM), counter electrode (CE), and transparent conducting electrode (TCE) could improve the solar energy (SE) harvesting, separation and transportation of electrons and hole, thus ultimately enhance the overall performance and stability of SCs. The incorporation of GQDs in various layers such as HTL, ETM, CIL, PAM, CE, and TCE achieved photo conversion efficiencies (PCEs) of 18.63, 21.1, 12.81, 9.41, 8.1, and 3.66%, respectively. Furthermore, GQDs improved stabilities such as resistance to degradation for HTL (up to 77%), ETM (80%), resistance to UV light for ETM (94%), resistance to temperature in ETM (90%), and bending stabilities after 1000 cycles for HTL (88%) and for TCE (90%). There are reviews focused on the utilization of different carbon-structured materials such as graphene, carbon nanotubes (CNT), fullerenes, and carbon dots in SCs applications. More specifically, the utilization of GQDs for SCs is limited and yet to be explored in greater detail. This review mainly focuses on the recent advancement of various techniques of production of GQDs synthesis, utilization of GQDs in various layers like HTL, ETM, CIL, PAM, CE, and TCE for the enhancement of PCE, and the stability of SCs. As a result, we believe that an exclusive study on GQDs-sensitized solar cells (GQDSSCs) could provide an in-depth analysis of the recent progress, achievements, and challenges.

This work involves the development of a novel waste-derived carbon dots (CDs) conjugated with silver (Ag) nanohybrid system-based Fluorescence Resonance Energy Transfer (FRET) sensor for the detection of melamine. CDs and Ag nanoparticles served as energy donors and energy acceptors, respectively. CDs were synthesized from orange peel waste through a combined hydrothermal and ultra-sonication route. The synthesized CDs had hydroxyl, amino, and carboxyl groups on their surface, explaining that waste-derived CDs can act as reducing and stabilizing agents and showed strong absorption and fluorescence emission at 305 and 460 nm, respectively. The bandgap, linear refractive index, conduction band, and valance band potential of CDs were observed to be 2.86, 1.849, 1.14, and 4.002 eV, respectively. No significant difference was observed in the fluorescence properties at different pH (acid and alkaline) and ionic concentrations. Given their fluorescent nature, the synthesized CDs were used for the detection of melamine. The fluorescence of CDs was found to be quenched by Ag+ due to the FRET energy transfer between CDs to Ag. Notably, the zeta potential of Ag@CDs was changed from − 28.7 mV to − 30.6 mV after the incorporation of Ag+. Ag@CDs showed excellent selectivity and sensitivity toward the sensing of melamine in the aqueous solutions with the limit of detection ~ 0.85 μM. Increasing the melamine level also raises the FL intensity of Ag@CDs. The substrate was effectively used in the detection of melamine in milk as a real application and the recovery percentage was found to be 98.03%. Moreover, other adulterants such as urea and formaldehyde can be detected selectively by Ag@CDs. Overall, the synthesized Ag@CDs can be used as an efficient material for sensing applications involving such food adulterants.

The widespread and extensive use of glyphosate in agriculture has raised concerns about its potential impact on the quality and safety of agricultural products. Conventional detection methods require long analysis times, making them impractical for the rapid detection of large quantities of samples. Therefore, developing a fast and simple detection system for glyphosate pesticide residues is urgent. In this study, the development of a facile fluorescence probe synthesized using a simple one-pot hydrothermal method for the determination of glyphosate is an important step toward addressing the need for a fast and simple detection system. The present sensor was created using bovine serum albumin (BSA) as a precursor, and the sensor operates by producing an “off–on” fluorescent signal. The bovine albumin-derived BSA-CDs emitted light yellow fluorescence, but this fluorescence was quenched (or suppressed) by the presence of Cu2+ ions. However, the fluorescence can be restored by the presence of glyphosate, which interacts with the Cu2+ ions to form a complex and release the BSACDs from suppression. The functional groups in glyphosate can capture Cu2+ and break the BSA-CDs/Cu2+ combinatorial system. The BSA-CDs/Cu2+ fluorescence quenching system had good selectivity for glyphosate. The detection limit of the BSA-CD/Cu2+ fluorescence sensor was 0.05 μg/mL. This developed method was utilized to successfully detect glyphosate in Chinese wheat. The average recoveries ranged from 98.9 to 100.7%, with a relative standard deviation < 3.0%, showing good prospects for practical applicability.

Sulfur and nitrogen co-doped carbon dots (NSCDs) were quickly synthesized by the microwave-assisted method from triammonium citrate and thiourea. NSCDs showed a quantum yield of 11.5% with excitation and emission bands at 355 and 432 nm, respectively. Also, a fluorescence quenching was observed in the presence of Pb(II) ions, and the as-synthesized CDs were used as a sensitive probe for detecting Pb(II) in water and food samples. The results showed the optimal conditions for Pb(II) determination were CDs concentration of 0.02 mg mL− 1 at pH 6.0–7.0 and an incubation time of 20 min. The relative fluorescence intensity of NSCDs was proportional to Pb(II) concentrations in the range of 0.029–2.40 and 2.40–14.4 μmol L− 1 with a correlation coefficient (R2) of 0.998 and 0.955, respectively, and a detection limit of 9.2 × 10– 3 μmol L− 1. Responses were highly repeatable, with a standard deviation below 3.5%. The suggested method demonstrates the potential of a green, fast, and low-cost approach for Pb(II) determination in water, tea, and rice samples with satisfying results.

A novel kind of self-assembled graphene quantum dots-Co3O4 (GQDs-Co3O4) nanocomposite was successfully manufactured through a hydrothermal approach and used as an extremely effectual oxygen evolution reaction (OER) electrocatalyst. The characterization of morphology with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that Co3O4 nanosheets combined with graphene quantum dots (GQDs) had a new type of hexagonal lamellar selfassembly structure. The GQDs-Co3O4 electrocatalyst showed enhanced electrochemical catalytic properties in an alkaline solution. The start potential of the OER was 0.543 V (vs SCE) in 1 M KOH solution, and 0.577 V (vs SCE) in 0.1 M KOH solution correspondingly. The current density of 10 mA cm− 2 had been attained at the overpotential of 321 mV in 1 M KOH solution and 450 mV in 0.1 M KOH solution. Furthermore, the current density can reach 171 mA cm− 2 in 1 M KOH solution and 21.4 mA cm− 2 in 0.1 M KOH solution at 0.8 V. Moreover, the GQDs-Co3O4 nanocomposite also maintained an ideal constancy in an alkaline solution with only a small deterioration of the activity (7%) compared with the original value after repeating potential cycling for 1000 cycles.