Tannic acid (TA) is one of the active components in the Galla Chinensis and has various effects, including antioxidant and anti-inflammatory properties. However, research on its antiviral properties remains limited. Here, tannic acid carbon dots (TA-CDs) were prepared as potential antiviral drugs from polyphenol TA under different temperature conditions (180, 200, 220 and 240 °C). Compared to TA alone, TA-CDs exhibited lower cytotoxicity and a tenfold enhanced in antiviral activity. Additionally, the antiviral effects of TA-CDs varied with preparation temperatures, with the best effect observed at 200 °C (CDs-2), reaching a titer of 2.8 orders of magnitude in porcine reproductive and respiratory syndrome virus (PRRSV), mainly due to its relatively higher number of functional groups and smaller particle size. Mechanically, CDs-2 was shown to inhibit PRRSV by targeting the stages of inactivation, adsorption, invasion, replication, and down-regulating reactive oxygen species (ROS) levels. Moreover, CDs-2 exhibited a high inhibitory effect on porcine epidemic diarrhea virus (PEDV), reaching a titer of 7 orders of magnitude. This study reveals the importance of temperature in synthesis of traditional Chinese medicine-derived carbon dots (TCM-CDs) and confirms their potential as antiviral drugs, providing valuable information for development of TCM antiviral drugs.

This study details the synthesis and characterization of phosphorus-sulfur co-doped graphitic carbon nitride quantum dots (PSQ) and their integration into g-C3N4 (CN) to form PSQ/CN composites for the enhanced photocatalytic reduction of Cr(VI) and fluorescence detection. Incorporating PSQ into CN was found to significantly improve light absorption, narrow the band gap, and enhance charge separation efficiency. Notably, the composite material exhibits superior photocatalytic performance, especially in acidic environments. Photocatalytic assessments utilizing Cr(VI) demonstrated that the PSQ/ CN composite outperformed both undoped and singly doped materials, indicating its superior photocatalytic activity. Additionally, phosphorus-sulfur co-doping markedly increased the fluorescence quantum yield of PSQ. The fluorescence intensity exhibited a linear decrease with increasing Cr(VI) concentrations, enabling sensitive and selective detection of Cr(VI) with a detection limit as low as 1.69 μmol/L. Collectively, the PSQ/CN composite and PSQ highlight their potential for photocatalysis and fluorescence-based detection of Cr(VI), providing high sensitivity, selectivity, and synergistic interactions within the composite material.

Waste utilization is not only a way to protect the environment and realize green chemistry, but also a means to create novel materials. In this study, based on waste grape seeds as the biowaste-derived carbon dots (G-BCDs), a straightforward one-pot green method was employed for the rapid detection of folic acid (FA). Owing to the internal filter effect and the static mixing quenching mechanism, the sensing principle of G-BCDs was effectively quenched by FA. The results showed fluorescence at an emission wavelength of 415 nm upon excitation at 330 nm with a quantum yield of 1.5%. Particularly, the FA sensing assay obtained a broad linear range of 2–220 μM and the limit of detection was 0.48 μM. In addition, the fluorescence probe was successfully utilized for detecting FA in tablets, blood, and urine samples, yielding desirable results, which indicated promising applications in the fields of biological and pharmaceutical analysis.

Quantum dot nanocomposite-based luminescent materials have gained attention for solid-state lighting and optical displays. This study presents a one-step, eco-friendly hydrothermal process to synthesize nitrogen, potassium, and calcium-doped carbon quantum dots (N, K, Ca-doped CQDs) from the flower extract of Mesembryanthemum crystallinum L. (ice plant). The CQDs were characterized using HRTEM, EDX, SAED, XPS, XRD, NMR, FTIR, zeta potential, UV–Vis, and photoluminescence spectroscopy. HRTEM revealed an average particle size of 4.6 nm, with a range of 2 to 7 nm. The CQDs exhibited a quantum yield of 20%, excellent water solubility, photostability, and greenish fluorescence under UV (365 nm). The fluorescence spectra were analyzed using CIE (Commission Internationale de l’Eclairage) chromaticity coordinates to determine the emitted color. The fluorescence emission behavior was influenced by solvent polarity, locally excited (LE) states, intramolecular charge transfer (ICT) processes, and hydrogen bonding. The hydrogen bonds between N, K, Ca-doped CQDs and DI water likely enhanced the stability of the ICT state, resulting in a red shift in fluorescence. Additionally, we developed an eco-friendly wheat-starch-based bioplastic nanocomposite by embedding the CQDs. The effects of CQD concentration and pH sensitivity on luminescent properties were explored. Finally, we demonstrated a practical application by designing a conceptual nameplate-like calligraphy using the optimized CQDs@bioplastic nanocomposite film (CQD concentration: 240 mg/mL, pH: 2.7), highlighting its potential for luminescent film applications.

Using durian shell as a carbon source and triethanolamine as a nitrogen dopant, nitrogen-doped carbon dots (N-CDs) were prepared via the hydrothermal method. First, by exploring different reaction times, reaction temperatures, and carbon source/dopant ratios to synthesize nitrogen-doped carbon dots, it is concluded that the best process conditions are 200 ℃, reaction time being 15h, and the dopant addition amount being 2mL. Structure and characteristics of the synthesized CDs were analyzed using X-ray photoelectron spectroscopy, Fourier-transform infrared, fluorescence (FL), ultraviolet–visible absorption, and Raman spectra. The N-CDs showed blue FL with a quantum efficiency of 4.28%. The FL characteristics of the N-CDs were utilized for ion detection, which demonstrated that MnO− 4 and Cr 2 O2− 7 ions caused distinct FL quenching through static quenching, while other ions had no significant quenching effect. The detection limits for MnO− 4 and Cr 2 O2− 7 were 37.5 and 46.2 nM, respectively. The N-CDs were subsequently employed to detect these ions in actual water samples, producing satisfactory results. Therefore, the preparation of N-CDs using durian shell as raw material and its application in practical detection work have good application feedback, which not only provides a new way for the reuse of fruit and vegetable wastes but also provides a new detection means for environmental monitoring pollutants.

This study incorporates the formation of carbon quantum dots (CQDs) via a hydrothermal approach, recording the first-time use of castor leaves as a natural precursor. The used precursor offers various benefits including novelty, abundance, elemental composition, and biocompatibility. CQDs were further characterized with multiple techniques including high-resolution transmission electron microscope (HR-TEM), X-ray photoelectron microscopy (XPS), X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR), Raman spectroscopy, UV–visible spectroscopy, Zeta analysis, and optical spectroscopy. They are fundamentally composed of carbon (71.37%), nitrogen (3.91%), and oxygen (24.73%) and are nearly spherical, and uniformly distributed with an average diameter of 2.7 nm. They possess numerous interesting characteristics like broad excitation/emission bands, excitation-sensitive emission, marvelous photostability, reactivity, thermo-sensitivity, etc. A temperature sensor (thermal sensitivity of 0.58% C− 1) with repeatability and reversibility of results is also demonstrated. Additionally, they were found selective and sensitive to ions in aqueous solutions. So, they are also utilized as a fluorescent probe for metal ion ( Fe3+) sensing. The lowest limit of detection (LOD) value for the current metal ion sensor is 19.1 μM/L.

Due to the sturdy photoluminescence and absorption, CQDs emerged as a suitable candidate for optical sensing probe. The present study deals with the synthesis of blue-fluorescent Carbon Quantum Dot (TAA-CQD) using tannic acid and glycine as novel precursors. The TAA-CQD were synthesised hydrothermally with the high production yield and QY to be 86.12 and 21%, respectively, and an average particle size of 1.9 nm. The TAA-CQD aqueous solution displays excitation-dependent fluorescence emission in the excited range from 420 to 650 nm. The CIE co-ordinates in a highly blue region at (0.14, 0.19) confirmed the synthesised TAA-CQD were blue in fluorescent. Fluorescence of TAA-CQD was stable under all pH range, resisted the high ionic strengths condition and stable over 8 months. Furthermore, the fluorescent TAA-CQD was capable in detecting a tetracycline-classed antibiotic Doxycycline (DXY) along with remarkable selectivity and sensitivity. The measures limit of detection (LOD) was very low 2.42 mM in comparison to other methods. Moreover, the applicability of the proposed work has been fruitfully employed on the pharmaceutical waste. Thus, our designed TAA-CQD based fluorescence sensing system hold great promise for the advanced sensing materials in the detection of DXY and we believe that our approach will be promising and viable in a clinical applications.

This paper is devoted to synthesizing a new type of CDs (carbon dots) with excellent NIR (near-infrared) emission in a biological water environment synthesized from small molecules. Citric acid was adopted as the precursor and treated by one-pot hydrothermal process in DMF solution with the assistance of a microwave. Urea (MH) and ammonium fluoride (MF) were adopted as nitrogen sources to synthesize two types of CDs, respectively. These conditions contributed to generate nanostructured carbon with a higher content of Pyrrolic-N, enrich the functional groups, and exfoliate the ordered layerstacking structure, which finally contributed to the higher NIR absorption band at 808 nm. The physicochemical properties and photothermal conversion ability were fully evaluated by UV–Vis-NIR (ultraviolet–visible light-NIR) absorption and photothermal experiments. MF possessed stronger absorption property and temperature-rising effect in the NIR region than MH, but both exhibited desirable photothermal stability. Next, the in vitro and in vivo experiments demonstrated that both MF and MH exhibited no significant toxicity for cells. NIR irradiation on CDs solution displayed an excellent killing effect on HeLa (breast cancer) and MCF7 (cervical cancer) cells but strongly depended on the concentration of CDs. MH had a weaker killing effect on MCF7 cells compared with MF in the same concentration. But HeLa cells suffered death from lower concentration of MH under NIR irradiation. Both MH and MF exhibited excellent therapy effects and no obvious tissue damage for these major organs of nude mice and BALB/C mice. Above all, both MF and MH with excellent photothermal effect under NIR irradiation had desirable NIR-triggered therapeutic effect on MCF7 and HeLa cells, while they also exhibited good biocompatibility without NIR irradiation.

Ibuprofen (IBU), a common pharmaceutical and personal care product (PPCP), is a pervasive water pollutant with adverse ecological and human health effects after transformation and accumulation. In this study, we synthesized Fe, N-doped carbon quantum dots (Fe, N-CQDs) using pig blood and FeCl3 as a precursor via a one-step hydrothermal method. TEM, XRD, XPS, and UV–Vis were used to characterize the physical and chemical properties of Fe, N-CQDs. We investigated the feasibility of Fe, N-CQDs in activating peroxymonosulfate (PMS) for IBU degradation under visible light. The experimental results revealed that Fe in Fe, N-CQDs predominantly formed a stable complex through Fe–N and Fe-OH, with a high degree of graphitization and a sp2- hybridized graphitic phase conjugate structure. The Fe, N-CQDs/Light/PMS system exhibited strong activity, degrading over 87% of IBU, maintaining a wide pH range (3–10) adaptability. Notably, Fe, N-CQDs acted as visible-light catalysts, promoting Fe3+/ Fe2+ cycling and PMS activation, generating both free radicals ( SO4 •–, ·OH) and non-radicals (1O2, h+) to effectively degrade IBU. This study presents an innovative approach for the sustainable utilization of pig blood as a biomass precursor to synthesize Fe- and N-doped carbon materials. This study provides a new approach for the sustainable and value-added utilization of natural wastes and biomass precursors of Fe- and N-doped carbon materials, which can be used to treat pollutants in water while treating discarded pig blood.

We report the simple one-step hydrothermal green synthesis of carbon dots (CDs) without any chemical reagents using mangosteen pulp (CDs1), peel (CDs2), and leaf (CDs3) extract as a green carbon source. In the aqueous medium, these CDs had a size of 8–15 nm with an energy gap of about 4 eV. The CDs emitted a bright green color under ultraviolet (UV) irritation with an average fluorescence quantum yield of the CDs of 1.6%. Moreover, the CDs contained various functional groups, such as C = C, C–C, C–O–C, C–O, C = O, C–H, and O–H, which were beneficial for enhancing their fluorescence property. Furthermore, the CDs were applied in the stain fluorescent imaging of myosatellite chicken stem cells and Vero cells. The CDs2 and CDs3 induced a strong fluorescence emission intensity of the strain cells, whereas CDs1 acted as the highest potential enhancer in cell proliferation as confirmed by its cellular viability which was the around four times that of the control. Therefore, the CDs were highly biocompatible and acted as enhancers in cell proliferation in myosatellite chicken stem cells and Vero cells. Thus, simple, cost-effective, scalable, and green synthetic approach-based CDs show promise for the development of selective organelle labeling and optical sensing probes.

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.

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.