Green preparation of palm powder-derived carbon dots co-doped with sulfur/chlorine and their application in visible-light photocatalysis

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.

"Five birds one stone" tri-modal monitoring driven lab-on-magnetic aptasensor for accurate pathogen detection and enhanced germicidal application

The effective combination of ultra-precise detection and on-demand sterilization stands out as one of the most valuable antifouling methods to combat pathogenic bacteria source and ensure the environment and food safety. Herein, an innovative "five birds one stone" aptasensor has been reported. It integrates magnetic separation, tri-modal precision detection, and efficient sterilization for monitoring of Staphylococcus aureus. Firstly, as a switch of the aptasensor, aptamer-modified potassium chloride-doped carbon dots (apt/KCl@CDs) could be adsorbed onto the surface of magnetic multi-walled carbon nanotube composites (M-MWCNTs) through π-π stacking, which could be replaced by the specific binding of the target bacteria to the aptamer. The mutual interference between the nanomaterials could be eliminated by this reverse magnetosorption strategy, enhancing the test sensitivity. In addition to the fluorescence properties, the peroxidase activity possessed by apt/KCl@CDs enables the conversion of the (3,3',5,5'-tetramethylbenzidine) TMB-H2O2 colorimetric system to a photothermal modal. Then, the ultra-precision detection in the assay was achieved by the fluorescence-colorimetric-photothermal tri-modal sensing from the formation of S. aureus-apt/KCl@CDs in the supernatant. Besides, the efficient sterilization could be ensured by adsorbing the apt/KCl@CDs on the surface of S. aureus, generating toxic •OH for direct attacking cells. This was the first report that was more beneficial for bacterial eradication. The detection limits of fluorescence, colorimetric and photothermal modals were 4.81 cfu/mL, 3.40 cfu/mL and 6.74 cfu/mL, respectively. The magnetic nanoplatform integrating tri-modal detection-sterilization meets the demand for highly sensitive and precise detection in different scenarios, providing immediate control for pathogens and broad application prospects.

The future of plant based green carbon dots as cancer Nanomedicine: From current progress to future Perspectives and beyond

BACKGROUND

The emergence of carbon dots (CDs) as anticancer agents had sparked a transformation in cancer research and treatment strategies. These fluorescent CDs, initially introduced in the early 2000 s, possess exceptional biocompatibility, tunable fluorescence, and surface modification capabilities, positioning them as promising tools in biomedical applications.

AIM OF REVIEW

The review encapsulates the transformative trajectory of green CDs as future anticancer nanomedicine, poised to redefine the strategies employed in the ongoing fight against cancer.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The versatility of CDs was rooted in their various synthesis approaches and sustainable strategies, enabling their adaptability for diverse therapeutic uses. In vitro studies had showcased CDs' selective cytotoxicity against cancer cells while sparing healthy counterparts, forming the basis for targeted therapeutic potential. This selectivity had been attributed to the reactive oxygen species (ROS) generation, which opened avenues for targeted interventions. The role of CDs in combination therapies, synergizing with chemotherapy, radiotherapy, and targeted approaches was then investigated to heighten their anticancer efficacy. Notably, in vivo studies highlight CDs' remarkable biocompatibility and minimal side effects, endorsing their translational promise. Integration with conventional cancer treatments such as chemotherapy, radiotherapy, and immunotherapy amplified the versatility and effectiveness of CDs. The exploration of CDs' applications in photo-induced treatments further solidified their significance, positioning them as photosensitizers (PS) in photodynamic therapy (PDT) and photothermal agents (PA) in photothermal therapy (PTT). In PDT, CDs triggered the generation of ROS upon light exposure, facilitating cancer cell elimination, while in PTT, they induced localized hyperthermia within cancer cells, enhancing therapeutic outcomes. In vitro and in vivo investigations validated CDs' efficacy in PDT and PTT, affirming their potential for integration into combination therapies. Looking ahead, the future of CDs in anticancer treatment encompasses bioavailability, biocompatibility, synergistic treatments, tumor targeting, artificial intelligence (AI) and robotics integration, personalized medicine, and clinical translation. This transformative odyssey of CDs as future anticancer agents is poised to redefine the paradigm of cancer treatment strategies.

Fluorescent carbon dots synthesized by waste wind turbine blade for photocatalytic degradation

Developing novel waste recycling strategies has become a feasible solution to overcome environmental pollution. In this work, a method of using waste wind turbine blade (WTB) as a carbon source to synthesize blue fluorescent carbon dots (B-CDs) by hydrothermal treatment is proposed. B-CDs are spherical and have an average particle size of 5.2 nm. The surface is rich in C-O, C=O, -CH3 , and N-H bond functional groups, containing five elements: C, O, N, Si, and Ca. The optimal emission wavelength of B-CDs is 463 nm, corresponding to an excitation wavelength of 380 nm. Notably, a relatively high quantum yield of 29.9% and a utilization rate of 40% were obtained. In addition, B-CDs can serve as a photocatalyst to degrade methylene blue dye, with a degradation efficiency of 64% under 40-min irradiation conditions. The presence of holes has a significant influence on the degradation process.

Carbon dots as potential candidate for photocatalytic treatment of dye wastewater

Water is the utmost important element for the existence of life. In recent decades, water resources have become highly contaminated by a variety of pollutants, especially toxic dyes that are harmful to both living beings and environment. Hence, there is an urgent need to develop more effective methods than traditional wastewater treatment approaches for treatment of hazardous dyes. Herein, we have addressed the various aspects related to the effective and economically feasible method for photocatalytic degradation of these dyes employing carbon dots. The photocatalysts based on carbon dots including those mediated from biomass have many superiorities over conventional methods such as utilization of economically affordable, non-toxic, rapid reactions, and simple post-processing steps. The current study will also facilitate better insight into the understanding of photocatalytic treatment of dye-polluted wastewater for future wastewater treatment studies. Additionally, the possible mechanistic pathways of photocatalytic dye decontamination, several challenges, and future perspectives have also been summarized.

Biogenic synthesis of highly fluorescent carbon dots using Azadirachta indica leaves: An eco-friendly approach with enhanced photocatalytic degradation efficiency towards Malachite green

A simpler and efficient method has been developed for the green synthesis of highly fluorescent carbon dots (CDs) from Azadirachta Indica leaves. The surface morphology of developed CDs has shown the existence of spherical particles in the size range of 3-8 nm with superior biocompatibility and high quantum yield value i.e. 42.3%. The particles exhibited a highly fluorescent and crystalline nature along with a bandgap value of 4.02 eV. The prepared CDs served as a factorial design for the sensing and degradation of Malachite green among other dyes. The main perspective of the current finding is that the designed catalyst exhibits excellent sensing results towards Malachite green with a limit of detection i.e. 0.144 μM in the concentration range of 0-50 μM. Moreover, the UV triggered results of photocatalysis illustrated a good dye removal efficacy by developed CDs with an average of 90.73, 98.25, 52 and 6.13% degradation in Methylene blue (MB), Malachite green (MG), Rhodamine 6G (Rh 6G) and Methyl orange (MO) upon 70 min of irradiation with mercury lamp. Additionally, the proton NMR, FTIR and FESEM results of the recycled samples also confirm the complete degradation of MG dye with the application of N-CDs.

Robust solvatochromic carbon quantum dots for selective detection of water and Sn4+ and specific lipid imaging

Developing carbon quantum dots (CQDs) with the solvatochromic effect and exploring multifunctional applications remains challenging. Herein, robust solvatochromic carbon quantum dots (RS-CQDs) with emission shift up to ∼62 nm from yellow to red was fabricated by the hydrothermal method. The RS-CQDs was used to detect water and Sn⁴⁺ in the linear ranges and limits of detection of 2.0-97.6% and 0.14% and 6.24-53.18 μM and 66.3 nM, respectively, and was further applied to determine Sn⁴⁺ in practical water samples with satisfactory results. In addition, RS-CQDs exhibited bright red emission in oil media with a 9.7-fold increase in fluorescence relative to aqueous media, making them a wash-free probe for specifically staining lipids. Compared to the commercial lipid marker BODIPY 493/503, the RS-CQDs-based probe has significant advantages, such as longer emission, larger Stokes shift, and better photostability, ensuring that RS-CQDs-based marker can implement real-time and wash-free monitoring and imaging of lipids in living cells, liver tissues, zebrafish embryos, and zebrafish larvae. This study provides a novel research direction for the development of metal-doped CQDs by demonstrating RS-CQDs as the viability of fluorescence probes for water and Sn⁴⁺ detection and the efficiency of RS-CQDs as a fluorescent marker for lipid imaging.

Effect of Hydrothermal Conditions on Kenaf-Based Carbon Quantum Dots Properties and Photocatalytic Degradation

The development of biomass-based CQD is highly attentive to enhancing photocatalytic performance, especially in secondary or ternary heterogeneous photocatalysts by allowing for smooth electron-hole separation and migration. In this study, kenaf-based carbon quantum dots (CQD) were prepared. The main objective of the current work was to investigate temperature, precursor mass and time in hydrothermal synthesis treatment to improve the CQD properties and methylene blue photocatalytic degradation. Optimization of kenaf-based CQD for inclusion in hydrothermal treatment was analyzed. The as-prepared CQDs have been characterized in detail by Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscope (HRTEM), photoluminescence (PL) and ultraviolet–visible (UV–Vis) spectroscopy. It was found that C200-0.5-24 exhibits a higher photocatalytic activity of the methylene blue dye and optimized hydrothermal conditions of 200 °C, 0.5 g and 24 h. Therefore, novel kenaf-based CQD was synthesized for the first time and was successfully optimized in the as-mentioned conditions. During the hydrothermal treatment, precursor mass controls the size and the distribution of CQD nanoparticles formed. The C200-0.5-24 showed a clearly defined and well-distributed CQD with an optimized nanoparticle size of 8.1 ± 2.2 nm. Indeed, the C200-0.5-24 shows the removal rate of 90% of MB being removed within 120 min.

Applications of Fluorescent Carbon Dots as Photocatalysts: A Review

Carbon dots (CDs) have attracted considerable interest from the scientific community due to their exceptional properties, such as high photoluminescence, broadband absorption, low toxicity, water solubility and (photo)chemical stability. As a result, they have been applied in several fields, such as sensing, bioimaging, artificial lighting and catalysis. In particular, CDs may act as sole photocatalysts or as part of photocatalytic nanocomposites. This study aims to provide a comprehensive review on the use of CDs as sole photocatalysts in the areas of hydrogen production via water splitting, photodegradation of organic pollutants and photoreduction and metal removal from wastewaters. Furthermore, key limitations preventing a wider use of CDs as photocatalysts are pointed out. It is our hope that this review will serve as a basis on which researchers may find useful information to develop sustainable methodologies for the synthesis and use of photocatalytic CDs.

Recent Progress of Carbon Dots for Air Pollutants Detection and Photocatalytic Removal: Synthesis, Modifications, and Applications

Rapid industrialization has inevitably led to serious air pollution problems, thus it is urgent to develop detection and treatment technologies for qualitative and quantitative analysis and efficient removal of harmful pollutants. Notably, the employment of functional nanomaterials, in sensing and photocatalytic technologies, is promising to achieve efficient in situ detection and removal of gaseous pollutants. Among them, carbon dots (CDs) have shown significant potential due to their superior properties, such as controllable structures, easy surface modification, adjustable energy band, and excellent electron-transfer capacities. Moreover, their environmentally friendly preparation and efficient capture of solar energy provide a green option for sustainably addressing environmental problems. Here, recent advances in the rational design of CDs-based sensors and photocatalysts are highlighted. An overview of their applications in air pollutants detection and photocatalytic removal is presented, especially the diverse sensing and photocatalytic mechanisms of CDs are discussed. Finally, the challenges and perspectives are also provided, emphasizing the importance of synthetic mechanism investigation and rational design of structures.

Charge separation effect in the nanocomposites of Co3O4-QDs: visible light photocatalytic dye degradation in aqueous solutions

Photo-treatment of water is a promising environmentally friendly process that provides clean water and makes wastewater reusable in industry. Thus, efforts toward finding highly efficient photocatalysts have gained a huge attention to remove the organic contaminants in water. Quantum dots (QDs) are extensively utilized for photocatalytic remediation regarding their prominent optical, electrical, and chemical properties. Herein, we report the highly efficient and environmentally friendly synthesis of Co₃O₄-QDs-based graphene quantum dots (GQDs) and infinite coordination polymer comprising Zn nodes (Zn-ICP) nanocomposites as active and robust photocatalysts for photo-assisted water treatment. The pristine Co₃O₄-QDs, GQDs, and Zn-ICP showed lower activity under visible light. However, after functionalization of GQDs and Zn-ICP with Co₃O₄-QDs, the activity increased, and more photocatalytic efficiency was achieved. For instance, Zn-ICP, GQDs, Co₃O₄-QDs, Co₃O₄-QDs/Zn-ICP, and Co₃O₄-QDs/GQD degraded 21, 19, 52, 73, and 83% of rhodamine B (RhB) and 34, 46, 50, 73, and 76% of methylene blue (MB) after 60 min. The high photocatalytic efficiency was ascribed to the conjugation of Co₃O₄-QDs with GQDs and Zn-ICP which causes efficient absorption of visible light. The existence of Co₃O₄-QDs was found to be essential not only for effective charge separation but also widening the region of light absorption followed by increase in photocatalytic performances. Charge separation in photocatalytic reactions, energy levels of nanocomposites, and mechanism of the photocatalytic process were investigated by photoluminescence spectra (PL), Mott-Schottky, electrochemical impedance (EIS), and diffuse reflectance UV-Vis spectroscopy (DRS).

Halogen-Doped Carbon Dots: Synthesis, Application, and Prospects

Carbon dots (CDs) have many advantages, such as tunable photoluminescence, large two-photon absorption cross-sections, easy functionalization, low toxicity, chemical inertness, good dispersion, and biocompatibility. Halogen doping further improves the optical and physicochemical properties of CDs, extending their applications in fluorescence sensors, biomedicine, photocatalysis, anti-counterfeiting encryption, and light-emitting diodes. This review briefly describes the preparation of CDs via the “top-down” and “bottom-up” approaches and discusses the preparation methods and applications of halogen (fluorine, chlorine, bromine, and iodine)-doped CDs. The main challenges of CDs in the future are the elucidation of the luminescence mechanism, fine doping with elements (proportion, position, etc.), and their incorporation in practical devices.

Facile Synthesis of Multi-Emission Nitrogen/Boron Co-Doped Carbon Dots from Lignin for Anti-Counterfeiting Printing

The transformation of lignin with natural aromatic structure into value-added carbon dots (CDs) achieves a win-win situation for low-cost production of novel nanomaterials and reasonable disposal of biomass waste. However, it remains challenging to produce multi-emission CDs from biomass for advanced applications. Herein, a green and facile approach to preparing multi-emission CDs from alkali lignin via N and B co-doping is developed. The obtained N and B co-doped CDs (NB-CDs) show multi-emission fluorescence centers at 346, 428 and 514 nm under different excitations. As the doping amount of N and B increases, the fluorescence emission band gradually shifts to 428 and 514 nm, while that at 346 nm decreases. The fluorescence mechanism is explored through the research of the structure, composition and optical performance of NB-CDs in combination with density functional theory (DFT) calculations. It demonstrates that the effect of doping with B-containing functional groups on the fluorescence emission behavior is multivariate, which may be the crucial contribution to the unique multi-emission fluorescence of CDs. The multi-emission NB-CDs with prominent stability are applied for multilevel anti-counterfeiting printing. It provides a promising direction for the sustainable and advanced application of biomass-derived CDs, and the theoretical results highlight a new insight into the deep understanding of the multi-emission fluorescence mechanism.

Facile preparation of aqueous-soluble fluorescent polyethylene glycol functionalized carbon dots from palm waste by one-pot hydrothermal carbonization for colon cancer nanotheranostics

Carbon dots (CDs) are categorized as an emerging class of zero-dimension nanomaterials having high biocompatibility, photoluminescence, tunable surface, and hydrophilic property. CDs, therefore, are currently of interest for bio-imaging and nano-medicine applications. In this work, polyethylene glycol functionalized CDs (CD-PEG) were prepared from oil palm empty fruit bunch by a one-pot hydrothermal technique. PEG was chosen as a passivating agent for the enhancement of functionality and photoluminescence properties of CDs. To prepare the CDs-PEG, the effects of temperature, time, and concentration of PEG were investigated on the properties of CDs. The as-prepared CDs-PEG were characterized by several techniques including dynamic light scattering, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy and Thermogravimetric analysis. The as-prepared CDs under hydrothermal condition at 220 °C for 6 h had spherical morphology with an average diameter of 4.47 nm. Upon modification, CDs-PEG were photo-responsive with excellent photoluminescence property. The CDs-PEG was subsequently used as a drug carrier for doxorubicin [DOX] delivery to CaCo-2, colon cancer cells in vitro. DOX was successfully loaded onto CDs-PEG surface confirmed by FT-IR and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometer (MALDI-TOF/MS) patterns. The selective treatment of CDs-PEG-DOX against the colorectal cancer cells, , relative to normal human fibroblast cells was succesfully demonstrated.

Metal ions mediated carbon dots nanoprobe for fluorescent turn-on sensing of N-acetyl-L-cysteine

Carbon dots (CDs) was facilely synthesized from aspartic acid through a pyrolysis method in this work. Based on their favorable fluorescence property, CDs was utilized to design a metal ions-mediated fluorescent probe for N-acetyl-L-cysteine (NAC) detection. The fluorescence intensity of CDs was firstly quenched by manganese ion (Mn²⁺ ) through static quenching effect and subsequently restored by NAC via the combination with Mn²⁺ owing to the coordination effect. Therefore, the fluorescent turn-on sensing of NAC was actuated based on the fluorescence quenching stimulated by Mn²⁺ and recovery induced by coordination. The fluorescence recovery efficiencies showed a proportional range to the concentration of NAC in the range of 0.04-5 mmol L^-1 and the detection limit was 0.03 mmol L^-1 . Further, this metal ions-mediated fluorescent nanoprobe was applied to human urine sample detection and the standard recovery rates were located in the range of 97.62-102.34 %. It was the first time that Mn²⁺ was used to construct fluorescent nanoprobe for NAC. Compared to other heavy metal ions, Mn²⁺ with good biosecurity prevented the risk of application, which made the nanoprobe green and bio-practical. The facile synthesis of CDs and novel metal ions-mediated sensing mode made it a promising method for pharmaceutical analysis.

Recent Progress on Carbon Quantum Dots Based Photocatalysis

As a novel carbon allotrope, carbon quantum dots (CQDs) have been investigated in various fields, including photocatalysis, bioimaging, optoelectronics, energy and photovoltaic devices, biosensing, and drug delivery owing to their unique optical and electronic properties. In particular, CQDs' excellent sunlight harvesting ability, tunable photoluminescence (PL), up-conversion photoluminescence (UCPL), and efficient photo-excited electron transfer have enabled their applications in photocatalysis. This work focuses on the recent progress on CQDs-related materials' synthesis, properties, and applications in photocatalysis.

Triple-emission nitrogen and boron co-doped carbon quantum dots from lignin: Highly fluorescent sensing platform for detection of hexavalent chromium ions

Considering that hexavalent chromium ions (Cr⁶⁺) with high toxicity poses a huge threat to human health and the ecological environment, constructing a rapid and accurate sensing platform is of great significance in detecting the toxic substance. The novel nitrogen and boron co-doped carbon quantum dots (N, B-CQDs) from lignin are synthesized as fluorescent sensors for the detection of Cr⁶⁺. The synthetic processes involve the acid hydrolysis step followed by the hydrothermal treatment step. Lignin is firstly depolymerized by cleaving ether bonds in the acidolysis, and N, B-CQDs are consequently formed by the aromatic re-fusion of lignin nanoparticles in the hydrothermal process. The lignin-derived N, B-CQDs show triple emission of purple, blue and green fluorescence under the excitation of 300, 330, and 490 nm, respectively. The triple-emission N, B-CQDs are applied for the triple-channel detection of Cr⁶⁺, which exhibit highly sensitive and selective fluorescence quenching for Cr⁶⁺ with good linearity (R² ≤ 0.996) and very low limit of detection as 0.054, 0.049, and 0.077 μM under the excitation of 300, 330 and 490 nm, respectively. The utilization of renewable lignin as CQDs-based fluorescent sensors opens a new avenue for the rapid and accurate detection of Cr⁶⁺ through a multichannel sensing platform.

Facile synthesis of a luminescent carbon material from yogurt for the efficient photocatalytic degradation of methylene blue

The present study is focused on yogurt as a simple, inexpensive, abundant, and green source for the preparation of luminescent carbon material for enhancing the photodegradation of methylene blue (MB). It introduces an ecological and sustainable approach for the large-scale production of carbon material using the direct thermal annealing of yogurt in a muffle furnace. The size of the as-prepared carbon material is about 200–300 nm, with average particle size distribution of 355 nm. The material exhibits clear luminescence under illumination with ultraviolet light. The synthesized carbon material shows an outstanding degradation functionality of MB under the irradiation of ultraviolet (UV) light in aqueous media. Various dye degradation parameters such as initial dye concentration, catalyst dose, pH of dye solution, and scavenger effects have been investigated. The optimum MB concentration was found to be 2.3 × 10⁻⁵ M with a degradation efficiency of 94.8%. The degradation was highly enhanced at pH 11 with a degradation efficiency of 98.11%. The degradation of MB under highly alkaline conditions was mainly governed by the high amount of hydroxyl radicals. Furthermore, the scavenger study confirmed that the hydroxyl radicals were mainly involved in the degradation process. The degradation kinetics of MB followed first order kinetics with large values of rate constant. The reusability was also studied to ensure the stability of the as-prepared carbon material during the degradation of MB. The preparation of carbon materials with efficient photosensitivity for the degradation of organic dyes from yogurt shows a green and innovative methodology. Therefore, it can be of great interest for future studies related to energy and environmental applications.

Left hand side: structural and optical aspects of the as-prepared carbon material from yogurt. Right hand side: the absorbance spectra of methylene blue degradation using the as-prepared carbon material from yogurt.

Boron doped Fluorescent Carbon Nano Dots for reduction of ionic dyes and as Encryption and decryption QR code labels

This work discusses the synthesis of fluorescent undoped and boron-doped carbon nanodots (BDCNDs) by a simple hydrothermal approach using Tribulus terretris as carbon precursor and boric acid as boron source....

Chitosan and κ-carrageenan-derived nitrogen and sulfur co-doped carbon dots "on-off-on" fluorescent probe for sequential detection of Fe3+ and ascorbic acid

This study develops a high sensitive and selective "on-off-on" fluorescent probe for sequential detection of iron ion (Fe³⁺) and ascorbic acid (AA) based on nitrogen and sulfur co-doped carbon dots (N, S-CDs), which were synthesized by using chitosan and κ-carrageenan as raw materials through one-step hydrothermal protocol. The synthesized N,S-CDs possess particularly high quantum yield (QY = 59.31%), excellent stability and excitation dependent behavior, showing great potential for practical applications. Furthermore, N,S-CDs provided high selectivity and strong anti-interference to Fe³⁺ due to its fluorescence quenching performance, revealing a wide linear concentration range from 1 to 100 μM for the detection of Fe³⁺ ion with an extremely low limit of detection of 57 nM, and presented reliable and accurate results in actual sample detection of Fe³⁺. The overall fluorescence quenching mechanism of N,S-CDs with Fe³⁺ was due to the formation of N,S-CDs/Fe³⁺ initiated to the aggregation and electron transfer of N,S-CDs, resulting in the static quenching of fluorescence. More interestingly, AA could reduce Fe³⁺ to Fe²⁺ and efficaciously recover the quenched fluorescence of N,S-CDs/Fe³⁺. N,S-CDs/Fe³⁺ as "turn-on" fluorescent probe was further applied for detecting AA in a linear range of 0.5-90 μM with a detection limit of 38 nM.

The development of biomass-derived carbon-based photocatalysts for the visible-light-driven photodegradation of pollutants: a comprehensive review

Biomass-derived carbonaceous materials have recently attracted extensive interest on account of their exceptional physicochemical properties which make them promising candidates for various critical applications. Several achieved advances have been reported in the recent literature, mainly focusing on the areas of energy storage and conversion. There is no review dedicated specifically to the potential applications of biomass-derived carbon-based photocatalytic materials for environmental remediation using the visible spectral region. The excellent characteristics of carbon materials, such as good electronic conductivity, unique nanocrystal structures, inherent hydrophobicity, and the tunable surface characteristics, are fully compatible with diverse catalytic reactions including organic transformations and photocatalysis processes. Importantly, biomass-carbon-based materials are considered to be green and viable alternative photocatalysts due to their environmentally friendly and naturally abundant nature. This work aims to provide a comprehensive review of recent advances relating to the synthesis of biomass-derived carbon-based photocatalysts, focusing on their potential for the photodegradation of various pollutants. First, potential natural biomass sources, various synthetic routes, and the properties of carbon materials are systematically discussed. Recent advances in the production of biomass-carbon-based photocatalysts (including material design, mechanisms, and photocatalytic performance) are highlighted. Regarding ideas for the development of new biomass-derived photocatalysts, we outline research gaps that are worthy of further research in the future.

This review highlights recent advances relating to the synthesis of biomass-derived carbon-based photocatalysts in light of their potential use in the photodegradation of various pollutants.

Gel-like carbon dots: A high-performance future photocatalyst

To protect water resources, halt waterborne diseases, and prevent future water crises, photocatalytic degradation of water pollutants arouse worldwide interest. However, considering the low degradation efficiency and risk of secondary pollution displayed by most metal-based photocatalysts, highly efficient and environmentally friendly photocatalysts with appropriate band gap, such as carbon dots (CDs), are in urgent demand. In this study, the photocatalytic activity of gel-like CDs (G-CDs) was studied using diverse water pollution models for photocatalytic degradation. The degradation rate constants demonstrated a remarkably enhanced photocatalytic activity of G-CDs compared with most known CD species and comparability to graphitic carbon nitride (g-C₃N₄). In addition, the rate constant was further improved by 1.4 times through the embedment of g-C₃N₄ in G-CDs to obtain CD-C₃N₄. Significantly, the rate constant was also higher than that of g-C₃N₄ alone, revealing a synergistic effect. Moreover, the use of diverse radical scavengers suggested that the main contributors to the photocatalytic degradation with G-CDs alone were superoxide radicals (O₂^-) and holes that were, however, substituted by O₂^- and hydroxyl radicals (OH) due to the addition of g-C₃N₄. Furthermore, the photocatalytic stabilities of G-CDs and CD-C₃N₄ turned out to be excellent after four cycles of dye degradation were performed continuously. Eventually, the nontoxicity and environmental friendliness of G-CDs and CD-C₃N₄ were displayed with sea urchin cytotoxicity tests. Hence, through various characterizations, photocatalytic degradation and cytotoxicity tests, G-CDs proved to be an environmentally friendly and highly efficient future photocatalyst.

Green Approaches to Carbon Nanostructure-Based Biomaterials

The family of carbon nanostructures comprises several members, such as fullerenes, nano-onions, nanodots, nanodiamonds, nanohorns, nanotubes, and graphene-based materials. Their unique electronic properties have attracted great interest for their highly innovative potential in nanomedicine. However, their hydrophobic nature often requires organic solvents for their dispersibility and processing. In this review, we describe the green approaches that have been developed to produce and functionalize carbon nanomaterials for biomedical applications, with a special focus on the very latest reports.

You Don't Learn That in School: An Updated Practical Guide to Carbon Quantum Dots

Carbon quantum dots (CQDs) have started to emerge as candidates for application in cell imaging, biosensing, and targeted drug delivery, amongst other research fields, due to their unique properties. Those applications are possible as the CQDs exhibit tunable fluorescence, biocompatibility, and a versatile surface. This review aims to summarize the recent development in the field of CQDs research, namely the latest synthesis progress concerning materials/methods, surface modifications, characterization methods, and purification techniques. Furthermore, this work will systematically explore the several applications CQDs have been subjected to, such as bioimaging, fluorescence sensing, and cancer/gene therapy. Finally, we will briefly discuss in the concluding section the present and future challenges, as well as future perspectives and views regarding the emerging paradigm that is the CQDs research field.

Facile synthesis of nitrogen-doped carbon dots from pork liver and its sensing of 6-thioguanine based on the inner filter effect

Nitrogen-doped carbon dots were facilely synthesized from pork liver and the fluorescence quenching determination of 6-thioguanine in human serum based on the inner filter effect was achieved with the limit of detection as low as 0.75 μM.

Green synthesis of fluorescent N,S-carbon dots from bamboo leaf and the interaction with nitrophenol compounds

A simple and green approach for the synthesis of photoluminescent N,S-carbon dots (N,S-CDs) has been proposed using a single natural source precursor (bamboo leaf) as raw materials. The as-synthesized N,S-CDs exhibited a highly stable, excitation wavelength-dependent emission, excellent photobleaching, alkali, and salt tolerance. Here, the mechanism of N,S-CDs luminescence was studied via the UV-vis absorption spectrum and photoluminescence spectroscopy. Based on the quenching properties of nitrophenol compounds on the fluorescence of N,S-CDs, the interaction between N,S-CDs and nitrophenol compounds was investigated on detail in aqueous solution. More importantly, the study on photophysical properties of the N,S-CDs may provide the basis for the development of the N,S-CDs for the fluorescent probe of nitrophenol compounds.

Recent advancements in the applications of carbon nanodots: exploring the rising star of nanotechnology

Nanoparticles possess fascinating properties and applications, and there has been increasing critical consideration of their use. Because carbon is a component with immaterial cytotoxicity and extensive biocompatibility with different components, carbon nanomaterials have a wide scope of potential uses. Carbon nanodots are a type of carbon nanoparticle that is increasingly being researched because of their astounding properties such as extraordinary luminescence, simplicity of amalgamation and surface functionalization, and biocompatibility. Because of these properties, carbon nanodots can be used as material sensors, as indicators in fluorescent tests, and as nanomaterials for biomedical applications. In this review, we report on the ongoing and noteworthy utilization of carbon quantum dots such as bioimaging tests and photocatalytic applications. In addition, the extension and future components of these materials, which can be investigated for new potential applications, are discussed.