Direct carbonization of organic solvents toward graphene quantum dots

A Novel Green Synthesis Method for the Preparation of Highly Fluorescent Carbon Dots for Security Ink Applications

Environmentally benign biosynthesized carbon dots with diverse chemical and physical properties play an important role in today's scientific research. In the present study, a new approach utilizing dye extraction from betel leaf, followed by a rapid, additive-free dye-derived-hydrothermal process, to synthesize carbon dots with a high quantum yield. The synthesized carbon dots were characterized using UV-visible, Photoluminescence (PL), Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy. The UV-visible spectrum of the carbon dot exhibited two major peaks at 233 nm and 294 nm and a tail continuing into the value 342 nm corresponding to π→π* and n→π* transitions. The PL spectra for different excitation wavelengths exhibit a broad peak at 465 nm, attributed to the carbon dot's surface defect state. FTIR spectra confirmed the presence of various functional groups present in the sample. The formation of carbon dots with an average diameter of 3.4 nm was confirmed by transmission electron microscopy (TEM) images. Energy-dispersive X-ray (EDAX) analysis showed the presence of elements C and O in the prepared sample. The synthesized carbon dots with low toxicity, strong fluorescence, and excellent photostability demonstrate immense potential as biocompatible fluorescent ink in future security applications.

A review on synthesis, properties, and biomedical applications of graphene quantum dots (GQDs)

A new type of 0-dimensional carbon-based materials called graphene quantum dots (GQDs) is gaining significant attention as a non-toxic and eco-friendly nanomaterial. GQDs are nanomaterials composed of sp2hybridized carbon domains and functional groups, with their lateral size less than 10 nm. The unique and exceptional physical, chemical, and optical properties arising from the combination of graphene structure and quantum confinement effect due to their nano-size make GQDs more intriguing than other nanomaterials. Particularly, the low toxicity and high solubility derived from the carbon core and abundant edge functional groups offer significant advantages for the application of GQDs in the biomedical field. In this review, we summarize various synthetic methods for preparing GQDs and important factors influencing the physical, chemical, optical, and biological properties of GQDs. Furthermore, the recent application of GQDs in the biomedical field, including biosensor, bioimaging, drug delivery, and therapeutics are discussed. Through this, we provide a brief insight on the tremendous potential of GQDs in biomedical applications and the challenges that need to be overcome in the future.

Engineering functionalization and properties of graphene quantum dots (GQDs) with controllable synthesis for energy and display applications

Graphene quantum dots (GQDs), a new type of 0D nanomaterial, are composed of a graphene lattice with sp2 bonding carbon core and characterized by their abundant edges and wide surface area. This unique structure imparts excellent electrical properties and exceptional physicochemical adsorption capabilities to GQDs. Additionally, the reduction in dimensionality of graphene leads to an open band gap in GQDs, resulting in their unique optical properties. The functional groups and dopants in GQDs are key factors that allow the modulation of these characteristics. So, controlling the functionalization level of GQDs is crucial for understanding their characteristics and further application. This review provides an overview of the properties and structure of GQDs and summarizes recent developments in research that focus on their controllable synthesis, involving functional groups and doping. Additionally, we provide a comprehensive and focused explanation of how GQDs have been advantageously applied in recent years, particularly in the fields of energy storage devices and displays.

Photothermal therapy using graphene quantum dots

The rapid development of powerful anti-oncology medicines have been possible because of advances in nanomedicine. Photothermal therapy (PTT) is a type of treatment wherein nanomaterials absorb the laser energy and convert it into localized heat, thereby causing apoptosis and tumor eradication. PTT is more precise, less hazardous, and easy-to-control in comparison to other interventions such as chemotherapy, photodynamic therapy, and radiation therapy. Over the past decade, various nanomaterials for PTT applications have been reviewed; however, a comprehensive study of graphene quantum dots (GQDs) has been scantly reported. GQDs have received huge attention in healthcare technologies owing to their various excellent properties, such as high water solubility, chemical stability, good biocompatibility, and low toxicity. Motivated by the fascinating scientific discoveries and promising contributions of GQDs to the field of biomedicine, we present a comprehensive overview of recent progress in GQDs for PTT. This review summarizes the properties and synthesis strategies of GQDs including top-down and bottom-up approaches followed by their applications in PTT (alone and in combination with other treatment modalities such as chemotherapy, photodynamic therapy, immunotherapy, and radiotherapy). Furthermore, we also focus on the systematic study of in vitro and in vivo toxicities of GQDs triggered by PTT. Moreover, an overview of PTT along with the synergetic application used with GQDs for tumor eradication are discussed in detail. Finally, directions, possibilities, and limitations are described to encourage more research, which will lead to new treatments and better health care and bring people closer to the peak of human well-being.

Sustainable Preparation of Graphene Quantum Dots from Leaves of Date Palm Tree

The date palm (Phoenix dactylifera), a subtropical and tropical tree, included in the family Palmae (Arecaceae) is one of the oldest cultivated plants of mankind. Date palm is a major agricultural product in the semi-arid and arid areas of the world, particularly in Arab countries. These trees generate high quantities of agricultural waste in the form of dry leaves, seeds, etc. In this study, dried date palm leaves were used as green precursors for synthesizing graphene quantum dots (GQDs). This work reported the preparation of GQDs using two different sustainable methods. GQD-1 was developed using a simple, hydrothermal technique at 200 °C for 12 h in water, with no requirement of reducing or passivizing agents or organic solvents. GQD-2 was prepared using a hydrothermal technique at 200 °C for 12 h in water, with the usage of just distilled water and absolute ethanol. The compositional analysis of the leaf extract was performed, along with the morphological, compositional, and optical examination of the sustainably developed GQDs. The characterization results confirmed the successful formation of GQDs, with average sizes ranging from 3.5 to 8 nm. This study helps to obtain GQDs in an economical, eco-friendly, and biocompatible manner and can assist in large-scale production and in recycling date palm tree waste products from Middle East countries into value-added products.

Versatile Synthesis of Carbon Materials using Protic Ionic Liquids and Salts as Precursors

Carbon materials (CMs) hold immense potential for applications across a wide range of fields. However, current precursors often confront limitations such as low heteroatom content, poor solubility, or complicated preparation and post-treatment procedures. Our research has unveiled that protic ionic liquids and salts (PILs/PSs), generated from the neutralization of organic bases with protonic acids, can function as economical and versatile small-molecule carbon precursors. The resultant CMs display attractive features, including elevated carbon yield, heightened nitrogen content, improved graphitic structure, robust thermal stability against oxidation, and superior conductivity, even surpassing that of graphite. These properties can be elaborate modulated by varying the molecular structure of PILs/PSs. In this Personal Account, we summarize recent developments in PILs/PSs-derived CMs, with a particular focus on the correlations between precursor structure and the physicochemical properties of CMs. We aim to impart insights into the foreseeable controlled synthesis of advanced CMs.

Hydrophobic Carbon Dots Derived from Organic Pollutants and Applications in NIR Anticounterfeiting and Bioimaging

In an effort to fulfill the strategy of sustainable development, Rhodamine B, a common and toxic organic pollutant in the textile industry, was reported for the first time as a single precursor to develop a kind of novel hydrophobic nitrogen-doped carbon dot (HNCD) through a green and facile one-pot solvothermal method. The HNCDs with an average size of 3.6 nm possess left and right water contact angles of 109.56° and 110.34°, respectively. The HNCDs manifest excitation wavelength-tunable and upconverted fluorescence from the ultraviolet (UV) to the near-infrared (NIR) range. Furthermore, the PEGylation of HNCDs enables them to be used as an optical marker for cell and in vivo imaging. Notably, the HNCDs with solvent-dependent fluorescence can be used for invisible inks with a wide range of light responses from UV-vis-NIR spectra. This work not only provides an innovative way to recycle chemical waste but also expands the potential application of HNCDs in NIR security printing and bioimaging.

Eco-Friendly and Sustainable Pathways to Photoluminescent Carbon Quantum Dots (CQDs)

Carbon quantum dots (CQDs), a new family of photoluminescent 0D NPs, have recently received a lot of attention. They have enormous future potential due to their unique properties, which include low toxicity, high conductivity, and biocompatibility and accordingly can be used as a feasible replacement for conventional materials deployed in various optoelectronic, biomedical, and energy applications. The most recent trends and advancements in the synthesizing and setup of photoluminescent CQDs using environmentally friendly methods are thoroughly discussed in this review. The eco-friendly synthetic processes are emphasized, with a focus on biomass-derived precursors. Modification possibilities for creating newer physicochemical properties among different CQDs are also presented, along with a brief conceptual overview. The extensive amount of writings on them found in the literature explains their exceptional competence in a variety of fields, making these nanomaterials promising alternatives for real-world applications. Furthermore, the benefits, drawbacks, and opportunities for CQDs are discussed, with an emphasis on their future prospects in this emerging research field.

Sustainable Preparation of Graphene Quantum Dots for Metal Ion Sensing Application

Over the past several years, graphene quantum dots (GQDs) have been extensively studied in water treatment and sensing applications because of their exceptional structure-related properties, intrinsic inert carbon property, eco-friendly nature, etc. This work reported on the preparation of GQDs from the ethanolic extracts of eucalyptus tree leaves by a hydrothermal treatment technique. Different heat treatment times and temperatures were used during the hydrothermal treatment technique. The optical, morphological, and compositional analyses of the green-synthesized GQDs were carried out. It can be noted that the product yield of GQDs showed the maximum yield at a reaction temperature of 300 °C. Further, it was noted that at a treatment period of 480 min, the greatest product yield of about 44.34% was attained. The quantum yields of prepared GQDs obtained after 480 min of treatment at 300 °C (named as GQD/300) were noted to be 0.069. Moreover, the D/G ratio of GQD/300 was noted to be 0.532 and this suggested that the GQD/300 developed has a nano-crystalline graphite structure. The TEM images demonstrated the development of GQD/300 with sizes between 2.0 to 5.0 nm. Furthermore, it was noted that the GQD/300 can detect Fe³⁺ in a very selective manner, and hence the developed GQD/300 was successfully used for the metal ion sensing application.

Development of Highly Luminescent Water-Insoluble Carbon Dots by Using Calix[4]pyrrole as the Carbon Precursor and Their Potential Application in Organic Solar Cells

Carbon dots (CDs) are carbon-based fluorescent nanomaterials that are of interest in different research areas due to their low cost production and low toxicity. Considering their unique photophysical properties, hydrophobic/amphiphilic CDs are powerful alternatives to metal-based quantum dots in LED and photovoltaic cell designs. On the other hand, CDs possess a considerably high amount of surface defects that give rise to two significant drawbacks: (1) causing decrease in quantum yield (QY), a crucial drawback that limits their utilization in LEDs, and (2) affecting the efficiency of charge transfer, a significant factor that limits the use of CDs in photovoltaic cells. In this study, we synthesized highly luminescent, water-insoluble, slightly amphiphilic CDs by using a macrocyclic compound, calix[4]pyrrole, for the first time in the literature. Calix[4]pyrrole-derived CDs (CP-DOTs) were highly luminescent with a QY of over 60% and size of around 4-10 nm with graphitic structure. The high quantum yield of CP-DOTs indicated that they had less amount of surface defects. Furthermore, CP-DOTs were used as an additive in the active layer of organic solar cells (OSC). The photovoltaic parameters of OSCs improved upon addition of CDs. Our results indicated that calix[4]pyrrole is an excellent carbon precursor to synthesize highly luminescent and water-insoluble carbon dots, and CDs derived from calix[4]pyrrole are excellent candidates to improve optoelectronic devices.

Hollow Cuprous Oxide@Nitrogen-Doped Carbon Nanocapsules for Cascade Chemodynamic Therapy

Cuprous-based nanozymes have demonstrated great potential for cascade chemodynamic therapy (CDT) due to their higher catalytic efficiency and simple reaction conditions. Here, hollow cuprous oxide@nitrogen-doped carbon (HCONC) dual-shell structures are designed as nanozymes for CDT oncotherapy. This HCONC with a size distribution of 130 nm is synthesized by a one-step hydrothermal method using cupric nitrate and dimethyl formamide as precursors. The thin-layer carbon (1.88 nm) of HCONC enhances the water-stability and reduces the systemic toxicity of cuprous oxide nanocrystals. The dissolved Cu⁺ of HCONC in acid solution induces a Fenton-like reaction and exhibits a fast reaction rate for catalyzing H₂ O₂ into highly toxic hydroxyl radicals (·OH). Meanwhile, the formed Cu⁺ consumes oversaturated glutathione (GSH) to avoid its destruction of ROS at the intracellular level. In general, both cellular and animal experiments show that HCONC demonstrates excellent antitumor ability without causing significant systemic toxicity, which may present tremendous potential for clinical cancer therapy.

Facile Fabrication of Highly Fluorescent N-Doped Carbon Quantum Dots Using an Ultrasonic-Assisted Hydrothermal Method: Optical Properties and Cell Imaging

Fluorescent N-doped carbon nanodots (CNDs) are a type of environmentally friendly nanomaterial that is promising for application in cell imaging and optoelectronics. In this paper, a natural amino acid (l-glutamic acid) was used as a precursor, and two different morphological and structured N-doped carbon quantum dots (CQDs) were synthesized via a one-step ultrasonic-assisted hydrothermal method at 230 and 250 °C. Various microscopy and spectroscopy techniques were employed to characterize the morphology, structure, optical properties, and stability of the CQDs. The results showed that N-CQDs-1 are new CNDs composed of amorphous carbon with a large amount of pyroglutamic acid, and N-CQDs-2 are composed of pure amorphous carbon. The CQDs exhibit excellent optical properties, such as 40.5% quantum yield, strong photobleaching resistance, and superior photostability. Combining the fluorescence lifetimes and radiative and non-radiative decay constants, the photoluminescence mechanism of the CQDs was qualitatively explained. The two CQDs were used for BV2 cell imaging and showed good results, implying the ultrasonic-assisted hydrothermal approach as a facile method to obtain structure- and morphology-controllable N-doped CQDs with prospect for application in cell imaging.

In situ immobilization of silver nanocrystals in carbon nanoparticles for intracellular fluorescence imaging and hydroxyl radicals detection

Silver nanoparticles (Ag NPs) have attracted extensive research interest in bioimaging and biosensing due to their unique surface plasmon resonance. However, the potential aggregation and security anxiety of Ag NPs hinder their further application in biomedical field due to their high surface energy and the possible ionization. Here, binary heterogeneous nanocomplexes constructed from silver nanoparticles and carbon nanomaterials (termed as C-Ag NPs) were reported. The C-Ag NPs with multiple yolk structure were synthesized via a one-step solvothermal route using toluene as carbon precursor and dispersant. The hydrophilic functional groups on the carbon layer endowed the C-Ag NPs excellent chemical stability and water-dispersity. Results showed that C-Ag NPs demonstrated excellent safety profile and excellent biocompatibility, which could be used as an intracellular imaging agent. Moreover, the C-Ag NPs responded specifically to hydroxyl radicals and were expected to serve as a flexible sensor to efficiently detect diseases related to the expression of hydroxyl radicals in the future.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.