Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

Carbon Dots Derived from Non-Biomass Waste: Methods, Applications, and Future Perspectives

Carbon dots (CDs) are luminescent carbon nanoparticles with significant potential in analytical sensing, biomedicine, and energy regeneration due to their remarkable optical, physical, biological, and catalytic properties. In light of the enduring ecological impact of non-biomass waste that persists in the environment, efforts have been made toward converting non-biomass waste, such as ash, waste plastics, textiles, and papers into CDs. This review introduces non-biomass waste carbon sources and classifies them in accordance with the 2022 Australian National Waste Report. The synthesis approaches, including pre-treatment methods, and the properties of the CDs derived from non-biomass waste are comprehensively discussed. Subsequently, we summarize the diverse applications of CDs from non-biomass waste in sensing, information encryption, LEDs, solar cells, and plant growth promotion. In the final section, we delve into the future challenges and perspectives of CDs derived from non-biomass waste, shedding light on the exciting possibilities in this emerging area of research.

Environmentally sustainable synthesis of whey-based carbon dots for ferric ion detection in human serum and water samples: evaluating the greenness of the method

Carbon dots (CDs) are valued for their biocompatibility, easy fabrication, and distinct optical characteristics. The current study examines using whey to fabricate CDs using the hydrothermal method. When stimulated at 350 nm, the synthetic CDs emitted blue light at 423 nm and revealed a selective response to ferric ion (Fe3+) in actual samples with great sensitivity, making them a suitable probe for assessing Fe3+ ions. The produced carbon dots demonstrated great photostability, high sensitivity, and outstanding biocompatibility. The findings showed that Fe3+ ions could be quickly, sensitively, and extremely selectively detected in an aqueous solution of carbon dots, with a revealing limit of 0.409 μM in the linear range of 0-180 μM. Interestingly, this recognition boundary is far inferior to the WHO-recommended threshold of 0.77 μM. Two metric tools which were AGREE and the ComplexGAPI were also used to evaluate the method's greenness. The evaluation confirmed its superior environmental friendliness.

Development of carbon quantum dot-based lateral flow immunoassay for sensitive detection of aflatoxin M1 in milk

Currently, there is a great demand for simple, sensitive, and accurate sensors for aflatoxin M1 (AFM1) in dairy products. In the present research, a novel fluorescent immunosensor based on nitrogen-doped carbon quantum dots (CQDs) has been developed for AFM1 analysis. The N-doped CQDs were synthesized through the hydrothermal approach using citric acid and polyethyleneimine as precursors. The CQDs showed bright blue emission under ultraviolet light irradiation and a maximum emission was observed at 450 nm upon excitation at 350 nm. The anti-AFM1 antibody (Ab) was immobilized on the as-obtained amine-functionalized CQDs and the obtained CQDs/Ab probe was then directly used for developing the immunoassays for AFM1. The fluorescence of the CQDs/Ab solution was effectively quenched in the presence of increasing AFM1 concentrations. Under the optimized conditions, the fluorescent nanosensor exhibited high sensitivity towards AFM1 in the range of 0.2-0.8 ng/mL with low limit of detection i.e., 0.07 ng/mL in standard buffer. Furthermore, the CQDs/Ab immunosensor was developed as a lateral flow design for detecting the aflatoxin residues in milk. This strategy can be used for the development of low-cost, rapid, and highly sensitive sensor strips for the detection of AFM1 in dairy products.

Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Inheritance of physico-chemical properties and ROS generation by carbon quantum dots derived from pyrolytically carbonized bacterial sources

Bacteria are frequently used in industrial processes and nutrient supplementation to restore a healthy human microflora, but use of live bacteria is often troublesome. Here, we hypothesize that bacterially-derived carbon-quantum-dots obtained through pyrolytic carbonization inherit physico-chemical properties from probiotic and pathogenic source-bacteria. Carbon-quantum-dots carbonized at reaction-temperatures below 200 ​°C had negligible quantum-yields, while temperatures above 220 ​°C yielded poor water-suspendability. Fourier-transform infrared-spectroscopy demonstrated preservation of amide absorption bands in carbon-quantum-dots derived at intermediate temperatures. X-ray photoelectron-spectroscopy indicated that the at%N in carbon-quantum-dots increased with increasing amounts of protein in source-bacterial surfaces. Carbonization transformed hydrocarbon-like bacterial surface compounds into heterocyclic aromatic-carbon structures, evidenced by a broad infrared absorption band (920-900 ​cm⁻¹) and the presence of carbon in C–C functionalities of carbon-quantum-dots. The chemical composition of bacterially-derived carbon-quantum-dots could be explained by the degradation temperatures of main bacterial cell surface compounds. All carbon-quantum-dots generated reactive-oxygen-species, most notably those derived from probiotic lactobacilli, carrying a high amount of surface protein. Concluding, amide functionalities in carbon-quantum-dots are inherited from surface proteins of source-bacteria, controlling reactive-oxygen-species generation. This paves the way for applications of bacterially-derived carbon-quantum-dots in which reactive-oxygen-species generation is essential, instead of hard-to-use live bacteria, such as in food supplementation or probiotic-assisted antibiotic therapy.

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Pyrolytic carbonization of bacteria between 200°C and 220°C yields water-suspendable CQDs.

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Bacterially-derived CQDs inherit amide functionalities from bacterial cell surface proteins.

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Hydrocarbon-like bacterial surface compounds give heterocyclic aromatic-carbon structures in bacterially-derived CQDs.

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Bacterially-derived CQDs possess graphitic nitrogen.

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Zeta potentials of CQDs relate with nitrogen occurrence in CQDs.

Carbon Quantum Dots Derived from Different Carbon Sources for Antibacterial Applications

Nanoparticles possess unique features due to their small size and can be composed of different surface chemistries. Carbon quantum dots possess several unique physico-chemical and antibacterial activities. This review provides an overview of different methods to prepare carbon quantum dots from different carbon sources in order to provide guidelines for choosing methods and carbon sources that yield carbon quantum dots with optimal antibacterial efficacy. Antibacterial activities of carbon quantum dots predominantly involve cell wall damage and disruption of the matrix of infectious biofilms through reactive oxygen species (ROS) generation to cause dispersal of infecting pathogens that enhance their susceptibility to antibiotics. Quaternized carbon quantum dots from organic carbon sources have been found to be equally efficacious for controlling wound infection and pneumonia in rodents as antibiotics. Carbon quantum dots derived through heating of natural carbon sources can inherit properties that resemble those of the carbon sources they are derived from. This makes antibiotics, medicinal herbs and plants or probiotic bacteria ideal sources for the synthesis of antibacterial carbon quantum dots. Importantly, carbon quantum dots have been suggested to yield a lower chance of inducing bacterial resistance than antibiotics, making carbon quantum dots attractive for large scale clinical use.

Facile synthesis and performance of pH/temperature dual-response hydrogel containing lignin-based carbon dots

This study demonstrated a facile method to synthesize lignin-based carbon dots (L-CDs) first. Results indicated that the L-CDs had a diameter of 2-5 nm and a graphene-like crystalline structure. It was found that under the optimal synthesis conditions, the fluorescence lifetime of L-CDs was about 12 ns. Within the range of pH 1-10, the fluorescence intensity of the L-CDs and pH value followed a linear relationship. With the contribution of L-CDs, pH/temperature dual responsive hydrogel was synthesized. The elastic modulus G' of hydrogel was much higher than viscous modulus G″. When the PVA content was larger than 10 wt%, the temperature sensitivity and water retention rate gradually decreased. The skeleton of hydrogels had a typical porous honeycomb structure, which made it possible to control its internal pore size by adjusting the content of PVA. There was a linear relationship between the fluorescence intensity of hydrogels and pH value in the range of pH 1-7. Therefore, the pH/temperature dual responsive hydrogel presented a new route for designing tissue engineering scaffolds and drug carriers.

Green Synthesis of Self-Passivated Fluorescent Carbon Dots Derived from Rice Bran for Degradation of Methylene Blue and Fluorescent Ink Applications

Recently, natural products are the powerful carbon source to synthesize carbon dots (CDs) with interesting physical and chemical properties. In this present work, we report a facile hydrothermal synthesis method for preparing fluorescent carbon dots using a biogenic precursor of rice bran without any surface passivation agent. The synthetic methodology was easy, simple, environmental friendly and convenient. Structural and optical properties of the RB-CDs have been studied by UV-visible, Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), Fluorescence spectra and X-ray photoelectron spectroscopy (XPS) techniques. The prepared RB-CDs exhibited green emission upon irradiation with UV light and the calculated fluorescence quantum yield (QY) was found to be 7.4%. The morphological features of the synthesized RB-CDs were characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), the average size of the RB-CDs was found to be 2.96 nm. The synthesized RB-CDs were beneficially applied as a catalyst for the catalytic degradation of methylene blue (MB) dye using NaBH₄ as the reducing agent in the ambient conditions. The degradation of MB dye under light illumination was 89.20% in 30 min. Further, the obtained highly fluorescent RB-CDs were efficiently utilized as a fluorescent ink for luminescent pattern printing (patterning agent) in the anti-counterfeiting applications.

Stepwise preparation of Ti-doped functionalized carbon nitride nanoparticles and hybrid TiO2/graphitic-C3N4 for detection of free residual chlorine and visible-light photocatalysis

Ti-doped functionalized carbon nitride nanoparticles and hybrid TiO2/graphitic-C3N4 were prepared stepwise and applied to the detection of free residual chlorine and visible-light photocatalysis. The photocatalytic degradation rate of methylene blue by the latter could reach 24.5 times that without a catalyst.

Future Perspectives and Review on Organic Carbon Dots in Electronic Applications

Over the span of the past decade, carbon dots (CDs) synthesized from renewable organic resources (organic CDs) have gathered a considerable amount of attention for their photoluminescent properties. This review will focus on organic CDs synthesized using clean chemistry and conventional synthetic chemistry from organic sources and their fluorescence mechanisms, such as quantum confinement effect and surface/edge defects, before outlining their performance in electronic applications, including organic photovoltaic devices, organic light-emitting devices, biosensors, supercapacitors, and batteries. The various organic resources and methods of organic CDs synthesis are briefly covered. Many challenges remain before the adoption of CDs can become widespread; their characterization, structure, functionality, and exact photoluminescent mechanism all require additional research. This review aims to summarize the current research outcomes and highlight the area where further research is needed to fully use these materials.

Biomolecule-derived quantum dots for sustainable optoelectronics

The diverse chemical functionalities and wide availability of biomolecules make them essential and cost-effective resources for the fabrication of zero-dimensional quantum dots (QDs, also known as bio-dots) with extraordinary properties, such as high photoluminescence quantum yield, tunable emission, photo and chemical stability, excellent aqueous solubility, scalability, and biocompatibility. The additional advantages of scalability, tunable optical features and presence of heteroatoms make them suitable alternatives to conventional metal-based semiconductor QDs in the field of bioimaging, biosensing, drug delivery, solar cells, photocatalysis, and light-emitting devices. Furthermore, a recent focus of the scientific community has been on QD-based sustainable optoelectronics due to the primary concern of partially mitigating the current energy demand without affecting the environment. Hence, it is noteworthy to focus on the sustainable optoelectronic applications of biomolecule-derived QDs, which have tunable optical features, biocompatibility and the scope of scalability. This review addresses the recent advances in the synthesis, properties, and optoelectronic applications of biomolecule-derived QDs (especially, carbon- and graphene-based QDs (C-QDs and G-QDs, respectively)) and discloses their merits and disadvantages, challenges and future prospects in the field of sustainable optoelectronics. In brief, the current review focuses on two major issues: (i) the advantages of two families of carbon nanomaterials (i.e. C-QDs and G-QDs) derived from biomolecules of various categories, for instance (a) plant extracts including fruits, flowers, leaves, seeds, peels, and vegetables; (b) simple sugars and polysaccharides; (c) different amino acids and proteins; (d) nucleic acids, bacteria and fungi; and (e) biomasses and their waste and (ii) their applications as light-emitting diodes (LEDs), display systems, solar cells, photocatalysts and photo detectors. This review will not only bring a new paradigm towards the construction of advanced, sustainable and environment-friendly optoelectronic devices using natural resources and waste, but also provides critical insights to inspire researchers ranging from material chemists and chemical engineers to biotechnologists to search for exciting developments of this field and consequently make an advance step towards future bio-optoelectronics.

The advanced role of carbon quantum dots in nanomedical applications

Carbon quantum dots (CQDs) have emerged as a potential material in the diverse fields of biomedical applications due to their numerous advantageous properties including fluorescence, water solubility, biocompatibility, low toxicity, small size and ease of modification, inexpensive scale-up production, and versatile conjugation with other nanoparticles. Thus, CQDs became a preferable choice in various biomedical applications such as nanocarriers for drugs, therapeutic genes, photosensitizers, and antibacterial molecules. Further, their potentials have also been verified in multifunctional diagnostic platforms, cellular and bacterial bio-imaging, development of theranostics nanomedicine, etc. This review provides a concise insight into the progress and evolution in the field of CQD research with respect to methods/materials available in bio-imaging, theranostics, cancer/gene therapy, diagnostics, etc. Further, our discussion is extended to explore the role of CQDs in nanomedicine which is considered to be the future of biomedicine. This study will thus help biomedical researchers in tapping the potential of CQDs to overcome various existing technological challenges.

Amorphous Carbon Dots and their Remarkable Ability to Detect 2,4,6-Trinitrophenol

Apparently mundane, amorphous nanostructures of carbon have optical properties which are as exotic as their crystalline counterparts. In this work we demonstrate a simple and inexpensive mechano-chemical method to prepare bulk quantities of self-passivated, amorphous carbon dots. Like the graphene quantum dots, the water soluble, amorphous carbon dots too, exhibit excitation-dependent photoluminescence with very high quantum yield (~40%). The origin and nature of luminescence in these high entropy nanostructures are well understood in terms of the abundant surface traps. The photoluminescence property of these carbon dots is exploited to detect trace amounts of the nitro-aromatic explosive - 2,4,6-trinitrophenol (TNP). The benign nanostructures can selectively detect TNP over a wide range of concentrations (0.5 to 200 µM) simply by visual inspection, with a detection limit of 0.2 µM, and consequently outperform nearly all reported TNP sensor materials.

Mechanochemical synthesis of fluorescent carbon dots from cellulose powders

A novel mechanochemical method was firstly developed to synthesize carbon nanodots (CNDs) or carbon nano-onions (CNOs) through high-pressure homogenization of cellulose powders as naturally abundant resource depending on the treatment times. While CNDs (less than 5 nm in size) showed spherical and amorphous morphology, CNOs (10-50 nm in size) presented polyhedral shape, and onion-like outer lattice structure, graphene-like interlattice spacing of 0.36 nm. CNOs showed blue emissions, moderate dispersibility in aqueous media, and high cell viability, which enables efficient fluorescence imaging of cellular media.

Electrochemically prepared oxygen and sulfur co-doped graphitic carbon nitride quantum dots for fluorescence determination of copper and silver ions and biothiols

Although great advances have been achieved in synthesis of fluorescent graphitic carbon nitride quantum dots (g-C₃N₄-dots), it is still challenging to develop g-C₃N₄-dots with high fluorescence quantum yield (FLQY) and multiple sensing functionalities. Herein, the oxygen and sulfur co-doped graphitic carbon nitride quantum dots (OS-g-C₃N₄-dots) with high FLQY of 33.9% were firstly synthesized by a simple electrochemical "tailoring" process. It was found that OS-g-C₃N₄-dots could specifically bind copper ions (Cu²⁺) and silver ions (Ag⁺), accompanied with a dramatic "turn-off" fluorescence response. With the help of different masking agents, OS-g-C₃N₄-dots are able to selectively detect Cu²⁺ and Ag⁺. Furthermore, the generated OS-g-C₃N₄-dots/Ag⁺ displayed a "turn-on" fluorescent response specific to biothiols (HCy, Cys and GSH). Therefore, the multiple functional sensing platforms based on "ON-OFF-ON" fluorescence response of OS-g-C₃N₄-dots for the detection of Cu²⁺, Ag⁺ and biothiols were constructed. Under the optimal conditions, the detection limits of Cu²⁺, Ag⁺, HCy, Cys and GSH were as low as 7.0 × 10^-10 M, 2.0 × 10^-9 M, 1.0 × 10^-8 M, 1.0 × 10^-8 M and 8.4 × 10^-9 M, respectively. Moreover, the prepared platforms could be successfully applied to the determination of Cu²⁺, Ag⁺ and biothiols in practical samples and exhibited excellent sensitivity and selectivity.

Gram-Scale Synthesis and Kinetic Study of Bright Carbon Dots from Citric Acid and Citrus japonica via a Microwave-Assisted Method

Tracking dynamic cellular processes necessitates fluorescent materials that are photostable, biocompatible, water-soluble, nanosized, and nontoxic. In this study, highly fluorescent carbon dots (CDs) were produced from cheap and readily available sources, citric acid (CA) and Philippine citrus (Citrus japonica Thunb.) or calamansi juice (CJ) via a microwave-assisted method. A number of synthetic conditions were investigated systematically to optimize the preparation of CDs from CA and CJ. The formation mechanism, surface chemistry, and photoluminescence of CA-based CDs (CA-CDs) and CJ-based CDs (CJ-CDs) were evaluated after each stage of pyrolysis in detail using different characterization techniques, such as dynamic light scattering, diffusion-ordered spectroscopy, atomic force microscopy, ζ potential, X-ray diffraction, Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, and absorption/emission spectroscopy. Gram-scale pyrolysis of CA with ethylenediamine (EDA) and CJ with EDA were carried out to provide CA-CDs (CA-18) within 18 min total pyrolysis time at 97% yield and CJ-CDs (CJ-14) within 14 min total pyrolysis time at 7% yield. Aqueous suspensions of CA-18 and CJ-14 CDs gave comparable bright blue luminescence at 462 nm. CA-CDs were shown to be nontoxic for mung beans up to 2 mg/mL, whereas CJ-CDs with higher surface negative charges inhibited growth above 0.5 mg/mL. This study demonstrates that bright CA- and CJ-CDs can be produced in gram-scale quantities using inexpensive methods. The size, amount, and extent of EDA incorporation are important in contributing to the formation of highly emissive particles.

Simple Microwave-Assisted Synthesis of Amphiphilic Carbon Quantum Dots from A3/B2 Polyamidation Monomer Set

Highly fluorescent and amphiphilic carbon quantum dots (CQDs) were prepared by microwave-assisted pyrolysis of citric acid and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), which functioned as an A₃ and B₂ polyamidation type monomer set. Gram quantities of fluorescent CQDs were easily obtained within 5 min of microwave heating using a household microwave oven. Because of the dual role of TTDDA, both as a constituting monomer and as a surface passivation agent, TTDDA-based CQDs showed a high fluorescence quantum yield of 29% and amphiphilic solubility in various polar and nonpolar solvents. These properties enable the wide application of TTDDA-based CQDs as nontoxic bioimaging agents, nanofillers for polymer composites, and down-converting layers for enhancing the efficiency of Si solar cells.

Carbon dots: materials, synthesis, properties and approaches to long-wavelength and multicolor emission

Herein, we summarize recent research developments and progress of carbon dots (CDs), which have been attracting considerable attention as a new type of photoluminescent material. Raw materials, from single carbonaceous compounds to colorful natural substances, for the synthesis of CDs are discussed. A range of diverse synthetic methodologies to achieve better photoluminescence performance and more advanced functions are summarized, and these are basically divided into two classes: top-down and bottom-up. The inspiring properties, mainly including composites, optical properties and cytotoxicity, are listed. In particular, the luminescence mechanism and surface functionalization of the CDs are briefly discussed. Moreover, on the basis of the above, the long-wavelength and multicolor emission properties of CDs and ways to achieve these goals including surface state and size controlled by synthesis strategies, proper precursors, chemical doping and modification, solvatochromic effects and energy transfer are reviewed in detail.

New insights and perspectives into biological materials for flexible electronics

Materials based on biological materials are becoming increasingly competitive and are likely to be critical components in flexible electronic devices.

Sustainable carbon-dots: recent advances in green carbon dots for sensing and bioimaging

This review article highlights recent progress in use of green precursors for synthesis of carbon-dots and their applications in fluorescence-based sensing and bioimaging.

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366nm and 423nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303nm and 430nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0μmolL(-1), with a limit of detection (3σ/k) of 79.6nmolL(-1). Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

Carbogenically coated silica nanoparticles and their forensic applications

The color-tunable C-SiO₂ are ideal powders for fingerprint enhancement, and they can also generate self-assembled nanotags suitable for object authentication.

Paper carbon dot based fluorescence sensor for distinction of organic and inorganic sulphur in analytes

In this work a paper carbon dot (PCDs) based fluorescence sensor was developed which can distinguish between the organic and inorganic sulphur in analytes.

Sustainable Life Cycles of Natural-Precursor-Derived Nanocarbons

Sustainable societal and economic development relies on novel nanotechnologies that offer maximum efficiency at minimal environmental cost. Yet, it is very challenging to apply green chemistry approaches across the entire life cycle of nanotech products, from design and nanomaterial synthesis to utilization and disposal. Recently, novel, efficient methods based on nonequilibrium reactive plasma chemistries that minimize the process steps and dramatically reduce the use of expensive and hazardous reagents have been applied to low-cost natural and waste sources to produce value-added nanomaterials with a wide range of applications. This review discusses the distinctive effects of nonequilibrium reactive chemistries and how these effects can aid and advance the integration of sustainable chemistry into each stage of nanotech product life. Examples of the use of enabling plasma-based technologies in sustainable production and degradation of nanotech products are discussed-from selection of precursors derived from natural resources and their conversion into functional building units, to methods for green synthesis of useful naturally degradable carbon-based nanomaterials, to device operation and eventual disintegration into naturally degradable yet potentially reusable byproducts.

Production of quasi-2D graphene nanosheets through the solvent exfoliation of pitch-based carbon fiber

Stable dispersion of quasi-2D graphene sheets with a concentration up to 1.27 mg mL(-1) was prepared by sonication-assisted solvent exfoliation of pitch-based carbon fiber in N-methyl pyrrolidone with the mass yield of 2.32%. Prepared quasi-2D graphene sheets have multi-layered 2D plate-like morphology with rich inclusions of graphitic carbons, a low number of structural defects, and high dispersion stability in aprotic polar solvents, and facilitate the utilization of quasi-2D graphene sheets prepared from pitch-based carbon fiber for various electronic and structural applications. Thin films of quasi-2D graphene sheets prepared by vacuum filtration of the dispersion of quasi-2D graphene sheets demonstrated electrical conductivity up to 1.14 × 10(4) Ω/□ even without thermal treatment, which shows that pitch-based carbon fiber might be useful as the source of graphene-related nanomaterials. Because pitch-based carbon fiber could be prepared from petroleum pitch, a very cheap structural material for the pavement of asphalt roads, our approach might be promising for the mass production of quasi-2D graphene nanomaterials.

Synthesis of nitrogen-doped carbon nanostructures from polyurethane sponge for bioimaging and catalysis

A facile and environmentally friendly method was developed for the fabrication of N-doped carbon nanomaterials by hydrothermal treatment using polyurethane (PU) sponge as a carbon source. We have demonstrated that the hydrothermal decomposition of PU sponge involves top-down hydrolysis and bottom-up polymerization processes for the synthesis of N-doped carbon dots (N-CDs). Fluorescence spectroscopy and cytotoxicity studies indicated that these highly-soluble N-CDs show excellent photoluminescence properties and low cytotoxicity, and can be used as good probes for cellular imaging. Additionally, the N-doped hollow carbon nanostructures can be designed using a simple template method. The prepared N-doped double-shelled hollow carbon nanotubes exhibited excellent ORR electrocatalytic activity and superior durability. Indeed, our method described here can provide an efficient way to synthesize N-doped carbon-based materials for a broad range of applications.

One pot selective synthesis of water and organic soluble carbon dots with green fluorescence emission

This work reports a simple and energy-saving strategy for selective synthesis of water-soluble and organic-soluble carbon dots at room temperature.

A simple one-step hydrothermal route towards water solubilization of carbon quantum dots from soya-nuggets for imaging applications

A high yield simple synthetic approach for water soluble photoluminescent carbon quantum dots via a single step, hydrothermal process, was described. Photoluminescent multi-colored emissions were used to label E. coli cells.

Preparation of biocompatible and antibacterial carbon quantum dots derived from resorcinol and formaldehyde spheres

Green or yellow emitting carbon quantum dots (CQDs) were prepared through the combination of bottom-up and top-down approaches from resorcinol and formaldehyde.

Covalent conjugation of carbon dots with Rhodamine B and assessment of their photophysical properties

Applying the Förster formalism we studied the potential of urethane-like linkage at the surface of CDs to form donor–acceptor FRET pair in CD–Rhodamine conjugates.

Direct synthesis of highly stable nitrogen rich carbon dots toward white light emission

Here we report a single step, rapid synthetic strategy for white light emitting nitrogen rich carbon dots (NCDs) under a range of excitation wavelengths by carbonizing ethylenediamine using P₂O₅ and water.

Purification, organophilicity and transparent fluorescent bulk material fabrication derived from hydrophilic carbon dots

High-efficiency oil/water interfacial self-assembly strategy has been used for the first time to purify hydrophilic CDs prepared by hydrothermal method.