Comprehensive Overview of Controlled Fabrication of Multifunctional Fluorescent Carbon Quantum Dots and Exploring Applications

In recent years, carbon dots (CDs) have garnered increasing attention due to their simple preparation methods, versatile performances, and wide-ranging applications. CDs can manifest various optical, physical, and chemical properties including quantum yield (QY), emission wavelength (Em), solid-state fluorescence (SSF), room-temperature phosphorescence (RTP), material-specific responsivity, pH sensitivity, anti-oxidation and oxidation, and biocompatibility. These properties can be effectively regulated through precise control of the CD preparation process, rendering them suitable for diverse applications. However, the lack of consideration given to the precise control of each feature of CDs during the preparation process poses a challenge in obtaining the requisite features for various applications. This paper is to analyze existing research and present novel concepts and ideas for creating CDs with different distinct features and applications. The synthesis methods of CDs are discussed in the first section, followed by a comprehensive overview of the important properties of CDs and the modification strategy. Subsequently, the application of CDs and their requisite properties are reviewed. Finally, the paper outlines the current challenges in controlling CDs properties and their applications, discusses potential solutions, and offers suggestions for future research.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Carbon Dots-Embedded Silica Tubes: An Excitation-Independent Yellow-Emitting Turn-On Probe for Simultaneous Detection and Removal of Inorganic Arsenic with In Vivo Tracking in Living Organisms

The environmental monitoring and remediation of highly toxic inorganic arsenic species in natural water are needed for the benefit of the ecosystem. Current studies on arsenic detection and removal often employ separate materials, which exhibit blue luminescence with fluorescence quenching, making them unsuitable for biological and environmental samples. In this study, carbon dot-embedded mesoporous silica tubes functionalized with melamine are synthesized to address these limitations and enable specific and turn-on probing of inorganic arsenic. The newly synthesized material demonstrates excitation-independent yellow luminescence and can effectively detect both As (III) and As (V) at low detection limits (11 × 10-9 m, 11.2 × 10-9 m), well below the prescribed threshold limits in drinking water. It also exhibits a high adsorption capacity (≈125, 159 mg g-1 ) with fast kinetics. The material's applicability in environmental samples is validated through the successful quantification of arsenic in real samples with satisfactory recoveries. Moreover, the material shows recyclability for reuse, as demonstrated by its arsenic adsorption and desorption for several cycles under basic conditions. Additionally, the material's capability for monitoring arsenic in a biological sample (Artemia salina) is demonstrated through fluorescence imaging. The encouraging outcomes underscore the material's potential use in monitoring and mitigating arsenic in aqueous systems.

Carbon dots-based fluorescent molecularly imprinted photonic crystal hydrogel strip: Portable and efficient strategy for selective detection of tetracycline in foods of animal origin

Rapid, portable, and sensitive detection of tetracycline (TC) is crucial for the environment and human health. In this study, we developed carbon dots (CDs)-based fluorescent molecularly imprinted photonic crystal hydrogel (FMIPH) strips for TC detection in animal-derived foods. CDs emit fluorescent signals, and molecularly imprinted polymers provide specific recognition sites for TC. Inverse opal photonic crystals afford stable 3D macroporous mass transfer channels that considerably reduce binding time between TC and the strips. The portable FMIPH strip exhibited a linear fluorescence response to TC in the concentration range of 0.1-50 μg mL-1, with a detection limit of 0.067 μg mL-1. Good recoveries of TC (93.86-112.59%) were observed in TC-spiked commercially available pork, eggs, and milk. A combination of FMIPH strips with a portable fluorescent reading device could achieve sensitive, on-site, and real-time detection of TC in animal-derived foods.

An optical and visual multi-mode sensing platform base on nitrogen, sulfur, boron co-doped carbon dots for rapid and simple determination of ferric ions in water

Abnormal iron ions levels may lead to some diseases and serious environmental pollution. Herein, optical and visual detection strategies of Fe3+ in water based on co-doped carbon dots (CDs) were established in the present study. Firstly, a one-pot synthetic strategy for the preparation of the N, S, B co-doped CDs with a home microwave oven was developed. Secondly, the optical properties, chemical structures, and morphology of CDs were further characterized by fluorescence spectroscopy, Uv-vis absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscope. Finally, the results indicated that the fluorescence of the co-doped CDs was quenched by ferric ions via the static mechanism and the aggregation of CDs, accompanied by the increased red color. The multi-mode sensing strategies of Fe3+ with fluorescence photometer, UV-visible spectrophotometer, portable colorimeter and smartphone had the advantages of good selectivity, excellent stability and high sensitivity. Fluorophotometry based on co-doped CDs was a powerful probe platform for measuring lower concentrations of Fe3+ due to its higher sensitivity, better linear relationship, lower limit of detection (0.27 μM) and limit of quantitation (0.91 μM). In addition, the visual detection methods with a portable colorimeter and smartphone had been proven to be very suitable for rapid and simple sensing of higher concentrations of Fe3+. Moreover, the co-doped CDs utilized for Fe3+ probes in tap water and boiler water obtained satisfactory results. Consequently, the efficient, versatile optical and visual multi-mode sensing platform could be extended to apply such a visual analysis of ferric ions in the biological, chemical and other fields.

Nitrogen-doped carbon dots with bright fluorescence for highly sensitive detection of Fe3+ in environmental waters

In this study, we synthesized stable nitrogen-doped carbon dots by a simple and economical one-step hydrothermal method using l-cysteine and anhydrous ethylenediamine as precursors. The prepared carbon dots have bright and stable blue light emission near 383 nm and can be used as fluorescent probes to detect the concentration of Fe³⁺ in environmental waters. It was demonstrated that due to intermolecular electrostatic interaction, a non-fluorescent complex N-CDs/Fe³⁺ is formed by coordination of Fe³⁺ with amino and carboxyl functional groups on the surface of carbon dots. Therefore, in combination with internal filtration effect, the fluorescence of carbon dots can be quenched in the presence of Fe³⁺, and the degree of quenching is linearly related to the concentration of Fe³⁺. The limit of detection in deionized water was as low as 0.069 μM with R² of 0.998 and a linear range of 0.3 to 20 μM. In addition, satisfactory recoveries were achieved for the determination of Fe³⁺ in environmental water samples. The method is reliable, with highly sensitivity and selectivity, and has potential for practical applications in environmental metal analysis.

Recyclable waste Dry-cell batteries derived carbon dots (CDs) for detection of Two-fold metal ions and degradation of BTB dye

In modern era, electronic wastes are one of the major threats around us, most of them are reused with less efficiency instead of re-usage, and conversion into valuable products is highly recommended. In this work, we report an innovative approach for the synthesis of highly photoluminescent CDs from waste dry-cell batteries through one-step hydrothermal treatment for the detection and degradation of environmental pollutants. The as-prepared CDs were studied by X-ray photoelectron spectroscopy (XPS), HR-TEM studies, X-ray diffractometer (XRD), Raman spectrometer, FTIR spectroscopy, UV-visible spectrophotometer, and spectrofluorometric measurements. The calculated quantum yield for synthesized CDs was around 13 %. The CDs have uniform particle size distribution, strong photoluminescent behavior, and possess high stability against various environmental conditions. Also, CDs display the selective and sensitive detection of Cr⁶⁺ and Co²⁺ and ions with a detection limit of around 0.11 µM and 0.10 µM respectively. The possible mechanism of CDs was also examined. Moreover, the photocatalytic activity of CDs with Bromothymol Blue (BTB) dye was studied. The degradation efficiency of BTB dye can be achieved at around 84 % over 180 min under the irradiation of direct sunlight in presence of H₂O₂. To date, it's the first time we have recycled waste dry-cell batteries into CDs as an effective probe for the detection and decomposition of environmental pollution. Furthermore, this work provides not only an easier route to make good quality and improved photoluminescent CDs from waste material like used batteries and also paves way for the reconversion of global treating waste. Finally, the outstanding detection capability with multiple properties of as-prepared CDs provides various environmental applications like the detection of pollutants and carcinogenic polluted water treatment.

Coal-Based Carbon Nanomaterials: En Route to Clean Coal Conversion toward Net Zero CO2

As the world is committed to reach carbon peak by 2030 and net zero by 2050, the use of coal as an energy source is facing unprecedented challenges. According to the International Energy Agency (IEA), global annual coal demand is estimated to drop from more than 5640 million tonnes of coal equivalent (Mtce) in 2021 to 540 Mtce in 2050 under the net zero emission scenario, mostly being replaced by renewable energy such as solar and wind. Therefore, the coal industry is vigorously seeking alternative applications to keep it thriving, and nanotechnology can be one of the contributors. Herein, the challenges to coal-based carbon nanomaterials syntheses are outlined, along with a path toward commercialization. Coal-based carbon nanomaterials can be promising contributors to the concept of clean coal conversion, initiating its migration from an energy source to a high-value-added carbon source.

Multiple heteroatom dopant carbon dots as a novel photoluminescent probe for the sensitive detection of Cu2+ and Fe3+ ions in living cells and environmental sample analysis

Heavy metal ion pollution harms human health and the environment and continues to worsen. Here, we report the synthesis of boron (B), phosphorous (P), nitrogen (N), and sulfur (S) co-doped carbon dots (BP/NS-CDs) by a one-step facile hydrothermal process. The optimum synthetic parameters are of 180 °C temperature, 12 h reaction time and 15% of PBA mass. The as-synthesized BP/NS-CDs exhibits excellent water solubility, strong green photoluminescence (PL) at 510 nm, and a high quantum yield of 22.4%. Moreover, BP/NS-CDs presented high monodispersity (7.2 ± 0.45 nm), excitation-dependent emission, PL stability over large pH, and high ionic strength. FTIR, XRD, and XPS are used to confirm the successful B and P doping of BP/NS-CDs. BP/NS-CD photoluminescent probes are selectively quenched by Cu²⁺ and Fe³⁺ ions but showed no response to the presence of other metal cations. The PL emission of BP/NS-CDs exhibited a good linear correlation with Cu²⁺ and Fe³⁺ concentrations with detection limits of 0.18 μM and 0.27 μM for Cu²⁺ and Fe³⁺, respectively. Furthermore, the HCT116 survival cells kept at 99.4 ± 1.3% and cell imaging capability, when the BP/NS-CDs concentration is up to 300 μg/mL by MTT assay. The proposed sensor is potential applications for the detection of Cu²⁺ and Fe³⁺ ions in environmental water samples.

Enhanced UV Protection, Heavy Metal Detection, and Antibacterial Properties of Biomass-Derived Carbon Dots Coated on Protective Fabrics

Carbon dots (CDs) were simply prepared from charcoal by hydrothermal processing at 180 °C for 15 h without any chemicals. The as-prepared CDs with an average diameter of 5 ± 6 nm exhibited a predominant absorption peak at 290 nm, corresponding to the n to π* transition of the oxygen functional groups (C═O) and the free amine functional groups (-NH₂). The resulting CDs were then incorporated into cotton and polyester by facile ultrasonication for 1 h. The obtained CD-coated fabrics were first evaluated for their UV-blocking capability and then for their antibacterial properties against two model pathogens: Gram-negative E. coli and Gram-positive S. aureus. Both cotton and polyester showed no UV protection at 280 or 380 nm; conversely, cotton or polyester decorated with CDs exhibited a UV blocking ratio of 82-98%. The CD-coated fabrics showed 100% antibacterial activities against E. coli and S. aureus, whereas the pristine fabrics showed no effect. The CDs/fabrics could adsorb Hg²⁺ and Fe³⁺, resulting in a drastic fluorescence quenching. As such, this distinct feature was exploited for the removal and detection of these two ions with the limits of detection of 55and 72 μM, respectively.

Quantum dot assisted precise and sensitive fluorescence-based formaldehyde detection in food samples

Formaldehyde has an extremely reactive carbonyl group, commonly used as an antibacterial agent to sterilize and prevent food to spoil. This article describes an efficient and rapid detection method of formaldehyde from an aqueous solution by synthesizing 3-Aminopropyltriethoxysilane (APTES) quantum dots (Nano A) which react with formaldehyde to generate a Schiff base reaction. The photoinduced electron transfer produced by the quantum dots themselves results in fluorescence quenching to detect formaldehyde. The detection limit can reach 10^-9 M, and it can further be used to detect formaldehyde content in foods, such as baby vegetables, mushrooms, and vermicelli among other daily foods.

A Hydrothermal Method to Generate Carbon Quantum Dots from Waste Bones and Their Detection of Laundry Powder

Surfactants are one of the major pollutants in laundry powder, which have an impact on the environment and human health. Carbon quantum dots (CQDs) are spherical zero-dimensional fluorescent nanoparticles with great potential for fluorescent probing, electrochemical biosensing and ion sensing. Herein, a bottom-up approach was developed for the synthesis of CQDs from biomass to detect laundry detergent and laundry powder. Waste chicken bones were used as carbon precursors after being dried, crushed and reacted with pure water at 180 °C for 4 h to generate CQDs, which exhibited a monodisperse quasi-spherical structure with an average particle size of 3.2 ± 0.2 nm. Functional groups, including -OH, C=O, C=C and C-O, were identified on the surface of the prepared CQDs. The optimal fluorescence excitation wavelength of the yellow-brown CQDs was 380 nm, with a corresponding emission peak at 465 nm. CQDs did not significantly increase cell death in multiple cell lines at concentrations of 200 µg·mL⁻¹. Fluorescence enhancement of CQDs was observed after addition of sodium dodecyl benzene sulphonate, a major anionic surfactant in laundry powder. A linear relationship between fluorescence enhancement CQDs and the concentration of laundry powder was established. Thus, a hydrothermal method was developed to generate CQDs from waste biomass that may be used as a fluorescent probe to detect laundry powder.

Spectrally tunable humic acid-based carbon dots: a simple platform for metronidazole and ornidazole sensing in multiple real samples

Humic acid-based carbon dots (HACDs) have excellent properties and are widely used in environmental detection, bioimaging, and optoelectronic materials. Herein, we investigated the structure-activity relationship between the morphology and optical properties of HACDs, and reported on a novel strategy for metronidazole (MNZ) and ornidazole (ONZ) sensing in multiple real samples. It was found that the average particle size decreased from 3.28 to 2.44 nm, optimal emission wavelength was blue-shifted from 500 to 440 nm, and the quantum yield (QY) improved from 5 to 23% with the temperature increasing from 110 to 400 °C. Under the oxidation of hydrogen peroxide (H₂O₂) and potassium permanganate (KMnO₄), the UV-vis spectra of HACD aqueous solution showed time-dependent behavior, and the fluorescence emission of HACDs achieved spectrally tunable multi-color luminescence in the temporal dimension. The surface of HACDs contained a large number of hydroxyl (-OH) and carboxyl (-COOH) fluorophores, resulting in excellent pH sensing. Meanwhile, the synthesized HACDs revealed sensitive response to MNZ and ONZ with the limit of detection (LOD) of 60 nM and 50 nM in aqueous solutions, which had also been successfully applied in various actual samples such as lake water, honey, eggs, and milk with satisfactory results because of the inner filter effect (IFE). Our research is advantageous to enhance the potential applications of HACDs in advanced analytical systems.