Recent advancements and prospects in carbon-based nanomaterials derived from biomass for environmental remediation applications

The conversion of waste biomass into a value-added carbonaceous nanomaterial highlights the appealing power of biomass valorization. The advantages of using sustainable and cheap biomass precursors exhibit the tremendous opportunity for boosting energy production and their application in environmental remediation processes. This review emphasis the development and production of carbon-based nanomaterials derived from biomass, which possess favourable characteristics such as biocompatibility and photoluminescence. The advantages and limitations of various nanomaterials synthesised from different precursors were also discussed with insights into their physicochemical properties. The surface morphology of the porous nanomaterials is also explored along with their characteristic properties like regenerative nature, non-toxicity, ecofriendly nature, unique surface area, etc. The incorporation of various functional groups confers superiority of these materials, resulting in unique and advanced functional properties. Further, the use of these biomass derived nanomaterials was also explored in different applications like adsorption, photocatalysis and sensing of hazardous pollutants, etc. The challenges and outcomes obtained from different carbon-based nanomaterials are briefly outlined and discussed in this review.

Fluorescent Nanocarbons: From Synthesis and Structure to Cancer Imaging and Therapy

Nanocarbons are emerging at the forefront of nanoscience, with diverse carbon nanoforms emerging over the past two decades. Early cancer diagnosis and therapy, driven by advanced chemistry techniques, play a pivotal role in mitigating mortality rates associated with cancer. Nanocarbons, with an attractive combination of well-defined architectures, biocompatibility, and nanoscale dimension, offer an incredibly versatile platform for cancer imaging and therapy. This paper aims to review the underlying principles regarding the controllable synthesis, fluorescence origins, cellular toxicity, and surface functionalization routes of several classes of nanocarbons: carbon nanodots, nanodiamonds, carbon nanoonions, and carbon nanohorns. This review also highlights recent breakthroughs regarding the green synthesis of different nanocarbons from renewable sources. It also presents a comprehensive and unified overview of the latest cancer-related applications of nanocarbons and how they can be designed to interface with biological systems and work as cancer diagnostics and therapeutic tools. The commercial status for large-scale manufacturing of nanocarbons is also presented. Finally, it proposes future research opportunities aimed at engendering modifiable and high-performance nanocarbons for emerging applications across medical industries. This work is envisioned as a cornerstone to guide interdisciplinary teams in crafting fluorescent nanocarbons with tailored attributes that can revolutionize cancer diagnostics and therapy.

Biomass derived green carbon dots for sensing applications of effective detection of metallic contaminants in the environment

The rapid consumption of metals and unorganized disposal have led to unprecedented increases in heavy metal ion concentrations in the ecosystem, which disrupts environmental homeostasis and results in agricultural biodiversity loss. Mitigation and remediation plans for heavy metal pollution are largely dependent on the discovery of cost-effective, biocompatible, specific, and robust detectors because conventional methods involve sophisticated electronics and sample preparation procedures. Carbon dots (CDs) have gained significant importance in sensing applications related to environmental sustainability. Fluorescence sensor applications have been enhanced by their distinctive spectral properties and the potential for developing efficient photonic devices. With the recent development of biomass-functionalized carbon dots, a wide spectrum of multivalent and bivalent transition metal ions responsible for water quality degradation can be detected with high efficiency and minimal toxicity. This review explores the various methods of manufacturing carbon dots and the biochemical mechanisms involved in metal detection using green carbon dots for sensing applications involving Cu (II), Fe (III), Hg (II), and Cr (VI) ions in aqueous systems. A detailed discussion of practical challenges and future recommendations is presented to identify feasible design routes.

QD-based fluorescent nanosensors: Production methods, optoelectronic properties, and recent food applications

Food quality and safety are crucial public health concerns with global significance. In recent years, a series of fluorescence detection technologies have been widely used in the detection/monitoring of food quality and safety. Due to the advantages of wide detection range, high sensitivity, convenient and fast detection, and strong specificity, quantum dot (QD)-based fluorescent nanosensors have emerged as preferred candidates for food quality and safety analysis. In this comprehensive review, several common types of QD production methods are introduced, including colloidal synthesis, self-assembly, plasma synthesis, viral assembly, electrochemical assembly, and heavy-metal-free synthesis. The optoelectronic properties of QDs are described in detail at the electronic level, and the effect of food matrices on QDs was summarized. Recent advancements in the field of QD-based fluorescent nanosensors for trace level detection and monitoring of volatile components, heavy metal ions, food additives, pesticide residues, veterinary-drug residues, other chemical components, mycotoxins, foodborne pathogens, humidity, and temperature are also thoroughly summarized. Moreover, we discuss the limitations of the QD-based fluorescent nanosensors and present the challenges and future prospects for developing QD-based fluorescent nanosensors. As shown by numerous publications in the field, QD sensors have the advantages of strong anti-interference ability, convenient and quick operation, good linear response, and wide detection range. However, the reported assays are laboratory-focused and have not been industrialized and commercialized. Promising research needs to examine the potential applications of bionanotechnology in QD-based fluorescent nanosensors, and focus on the development of smart packaging films, labeled test strips, and portable kits-based sensors.

Production and Patterning of Fluorescent Quantum Dots by Cryogenic Electron-Beam Writing

Graphene quantum dots (GQDs) have emerged as a promising type of functional material with distinguished properties. Although tremendous effort was devoted to the preparation of GQDs, their applications are still limited due to a lack of methods for processing GQDs from synthesis to patterning smoothly. Here, we demonstrate that aromatic molecules, e.g., anisole, can be directly converted into GQD-containing nanostructures by cryogenic electron-beam writing. Such an electron-beam irradiation product exhibits evenly red fluorescence emission under laser excitation at 473 nm, and its photoluminescence intensity can be easily tuned with the electron-beam exposure dose. Experimental characterizations on the chemical composition of the product reveal that anisole undergoes a carbonization and further graphitization process during e-beam irradiation. With conformal coating of anisole, our approach can create arbitrary fluorescent patterns on both planar and curved surfaces for concealing information or anticounterfeiting applications. This study provides a one-step method for production and patterning of GQDs, facilitating their applications in highly integrated and compact optoelectronic devices.

Graphene Quantum Dot-Added Thin-Film Composite Membrane with Advanced Nanofibrous Support for Forward Osmosis

Forward osmosis (FO) technology for desalination has been extensively studied due to its immense benefits over conventionally used reverse osmosis. However, there are some challenges in this process such as a high reverse solute flux (RSF), low water flux, and poor chlorine resistance that must be properly addressed. These challenges in the FO process can be resolved through proper membrane design. This study describes the fabrication of thin-film composite (TFC) membranes with polyethersulfone solution blown-spun (SBS) nanofiber support and an incorporated selective layer of graphene quantum dots (GQDs). This is the first study to sustainably develop GQDs from banyan tree leaves for water treatment and to examine the chlorine resistance of a TFC FO membrane with SBS nanofiber support. Successful GQD formation was confirmed with different characterizations. The performance of the GQD-TFC-FO membrane was studied in terms of flux, long-term stability, and chlorine resistance. It was observed that the membrane with 0.05 wt.% of B-GQDs exhibited increased surface smoothness, hydrophilicity, water flux, salt rejection, and chlorine resistance, along with a low RSF and reduced solute flux compared with that of neat TFC membranes. The improvement can be attributed to the presence of GQDs in the polyamide layer and the utilization of SBS nanofibrous support in the TFC membrane. A simulation study was also carried out to validate the experimental data. The developed membrane has great potential in desalination and water treatment applications.

Graphene Quantum Dots: Novel Properties and Their Applications for Energy Storage Devices

Batteries and supercapacitors are the next-generation alternative energy resources that can fulfil the requirement of energy demand worldwide. In regard to the development of efficient energy storage devices, various materials have been tested as electrode materials. Graphene quantum dots (GQDs), a new class of carbon-based nanomaterial, have driven a great research interest due to their unique fundamental properties. High conductivity, abundant specific surface area, and sufficient solubility, in combination with quantum confinement and edge effect, have made them appropriate for a broad range of applications such as optical, catalysis, energy storage and conversion. This review article will present the latest research on the utilization of GQDs and their composites to modify the electrodes used in energy storage devices. Several major challenges have been discussed and, finally, future perspectives have been provided for the better implementation of GQDs in the energy storage research.

Metal ion sensing with graphene quantum dots: detection of harmful contaminants and biorelevant species

Graphene quantum dots (GQDs) are attractive materials for use as highly selective and sensitive chemical sensors, owing to their simple preparation and affordability. GQDs have been successfully deployed as sensors for toxic metal ions, which is a significant issue due to the ever-increasing environmental contamination from agricultural and industrial activities. Despite the success of GQDs in this area, the mechanisms which underpin GQD-metal ion specificity are rarely explored. This lack of information can result in difficulties when attempting to replicate published procedures and can limit the judicious design of new highly selective GQD sensors. Furthermore, there is a dearth of GQD examples which selectively detect biologically relevant alkali and alkaline earth metals. This review will present the current state of GQDs as metal ion sensors for harmful contaminants, highlighting and discussing the discrepancies that exist in the proposed mechanisms regarding metal ion selectivity. The emerging field of GQD sensors for biorelevant metal ion species will also be reviewed, with a perspective to the future of this highly versatile material.

Selective Fe(ii)-fluorescence sensor with validated two-consecutive working range using N,S,I-GQDs associated with garlic extract as an auxiliary green chelating agent

The goal of this work was to use the pyrolysis process to synthesize graphene quantum dots doped with garlic extract (as N,S-GQDs) and simultaneously co-doped with iodine (as I-GQDs). XPS, HR-TEM, FE-SEM/EDX, FT-IR, fluorescence, and UV-visible absorption spectroscopy were used to characterize the N,S,I-GQDs and analyze their morphological images. The quantum yield of N,S,I-GQDs was found to be 45%, greater than that of undoped GQDs (31%). When stimulated at 363 nm, the N,S,I-GQDs display a strong fluorescence intensity at a maximum wavelength of 454 nm. Using N,S,I-GQDs as a fluorescence quenching sensor for screening tests with various metal ions, it was discovered that they are extremely selective towards Fe2+ over Fe3+ and other ions. Thus, solution pH, concentration of N,S,I-GQDs, quantity of garlic extract, EDTA and AgNO3 concentration as masking agents, reaction duration under ultrasonic aid, and tolerable limit of Fe3+ presence in the target analyte were all optimized for Fe2+ detection. A highly sensitive detection of Fe2+ was obtained using a linear curve with y = 141.34x + 5.5855, R 2 = 0.9961, LOD = 0.11 mg L-1, and LOQ = 0.35 mg L-1. The method precision, given as RSDs, was determined to be satisfactory at 1.04% for intra-day analysis and 3.22% for inter-day analysis, respectively. As a result, the selective determination of trace amounts of Fe2+ in real water samples using such labile multi-element doped GQDs in conjunction with garlic extract as a green chelating agent to maintain its enhanced sensitivity was successfully applied with good recoveries ranging from 89.16 to 121.45%.

Morphology Effect of One-Dimensional MnO2 Nanostructures on Heteroatom-Doped Carbon Dot-Based Biosensors for Selective Detection of Glutathione

Structural versatility of MnO₂ nanostructures plays a significant role in biosensing applications. So, we have prepared simple and selective "turn-off-on" sensing probes for the detection of glutathione (GSH), based on nitrogen, sulfur codoped carbon dots (N, S-Cdots) and different morphologies of one-dimensional (1-D) MnO₂ nanostructures. N, S-Cdots with a high fluorescence quantum yield (73.42%) were prepared by a green approach through high-temperature pyrolysis in just 5 min. The different morphologies of 1-D MnO₂ nanostructures (nanowires with varying aspect ratios and nanorods) were synthesized through a hydrothermal method by varying the reaction period (8, 10, and 12 h). MnO₂ nanowires prepared at 8 h showed a high specific surface area (34 m² g^-1) with a large aspect ratio. They showed significant fluorescence quenching, Stern-Volmer constants, and binding constants in the presence of N, S-Cdots. Further, ultraviolet-visible absorption, zeta potential, and time decay studies showed that the quenching mechanism of the developed sensing system was the inner filter effect, which was further confirmed by using the Parker equation. The N, S-Cdots-MnO₂ nanowire (with a high aspect ratio) sensing system showed the best limit of detection, i.e., 28.5 μM for GSH. This fast, simple, eco-friendly, and cost-effective sensing system can be further used for real-time biosensing and bioimaging application.

Hydrophilic graphene quantum dots as turn-off fluorescent nanoprobes for toxic heavy metal ions detection in aqueous media

Efforts are being made to develop fast, cost-effective and sensitive sensor to detect water contamination by toxic heavy metal ions. The oxygenated functional groups decorated graphene quantum dots (GQDs) effectively enhances the aqueous solubility and considered as a more desirable and simple sensing material with high sensitivity. Here, photoluminescence (PL) property of GQDs has been employed to devise an optical nanosensor for the detection of toxic heavy metal ions in aqueous media. Hydrothermal method was employed to synthesize highly fluorescent and water soluble GQDs. The fluorescence intensity reduces with the increase in toxic heavy metal ions concentration. The observed PL was analyzed by the Stern-Volmer equation to study the fluorescent quenching mechanism of the system. Nonlinear behavior of Stern-Volmer plot suggests that the reduction in the fluorescent intensity is due to the combination of dynamic and static processes. The fluorescence quenching results showed that, the as synthesized GQDs are an efficient fluorescent probe for heavy metal ions viz. Hg²⁺, Cd²⁺ and Pb²⁺ with the detection limit of 1.171 μM, 2.455 μM and 2.011 μM respectively. This study shows the viability of GQDs as promising material for sensing the heavy metal ions in aqueous solution.

Graphene quantum dots as nanosensor for rapid and label-free dual detection of Cu2+ and tiopronin by means of fluorescence “on–off–on” switching: mechanism and molecular logic gate

(A) Schematic diagram of the interaction and dual detection of Cu2+ and MPG by means of fluorescence “on–off–on” switching. (B) Molecular logic gate and truth table constructed based on Cu2+ and MPG as inputs and emission signal as output.