Multicolor polymeric carbon dots: synthesis, separation and polyamide-supported molecular fluorescence

Carbon Dots: A Review with Focus on Sustainability

Carbon dots (CDs) are an emerging class of nanomaterials with attractive optical properties, which promise to enable a variety of applications. An important and timely question is whether CDs can become a functional and sustainable alternative to incumbent optical nanomaterials, notably inorganic quantum dots. Herein, the current CD literature is comprehensively reviewed as regards to their synthesis and function, with a focus on sustainability aspects. The study quantifies why it is attractive that CDs can be synthesized with biomass as the sole starting material and be free from toxic and precious metals and critical raw materials. It further describes and analyzes employed pretreatment, chemical-conversion, purification, and processing procedures, and highlights current issues with the usage of solvents, the energy and material efficiency, and the safety and waste management. It is specially shown that many reported synthesis and processing methods are concerningly wasteful with the utilization of non-sustainable solvents and energy. It is finally recommended that future studies should explicitly consider and discuss the environmental influence of the selected starting material, solvents, and generated byproducts, and that quantitative information on the required amounts of solvents, consumables, and energy should be provided to enable an evaluation of the presented methods in an upscaled sustainability context.

Mechanism study of Dual-Emission ratiometric fluorescent pH-Sensitive carbon quantum dots and its application on mornitoring enzymatic catalysis

Carbon dots (CQD) have received significant attention as a novel ratiometric fluorescent pH nanoprobe, owing to their favorable optical properties and excellent biocompatibility. Despite their appealing features, the precise mechanism behind the pH-sensitive photoluminescence of CQDs remains to be fully understood. This study endeavors to unravel the mechanism underlying the pH-responsive ratiometric fluorescence in dual-emission CQDs, synthesized through a one-step hydrothermal method using o-phenylenediamine and oxalic acid as precursors. The resultant CQDs exhibit inherent dual-emission at wavelengths of 383 nm and 566 nm, with the ratiometric fluorescence response tailored by the ratio of precursors, providing a robust tool for pH sensing across a range of 2 to 6. Detailed characterizations, including chemical, morphological, and optical analyses, alongside theoretical insights from time-dependent density functional theory (TD-DFT), elucidate the mechanism underlying the pH-dependent luminescence, attributed to the electron cloud transmission between amide and adjacent carboxyl groups on the CQD surface. The superior performance of these CQDs in real-time pH monitoring is demonstrated through their application in glucose oxidase-catalyzed reactions, showcasing their potential as efficient, reliable nanoprobes for biomedical research and diagnostic applications.

Rare-Earth-Metal-Free Solid-State Fluorescent Carbonized-Polymer Microspheres for Unclonable Anti-Counterfeit Whispering-Gallery Emissions from Red to Near-Infrared Wavelengths

Colloidal carbon dots (CDs) have garnered much attention as metal-free photoluminescent nanomaterials, yet creation of solid-state fluorescent (SSF) materials emitting in the deep red (DR) to near-infrared (NIR) range poses a significant challenge with practical implications. To address this challenge and to engineer photonic functionalities, a micro-resonator architecture is developed using carbonized polymer microspheres (CPMs), evolved from conventional colloidal nanodots. Gram-scale production of CPMs utilizes controlled microscopic phase separation facilitated by natural peptide cross-linking during hydrothermal processing. The resulting microstructure effectively suppresses aggregation-induced quenching (AIQ), enabling strong solid-state light emission. Both experimental and theoretical analysis support a role for extended π-conjugated polycyclic aromatic hydrocarbons (PAHs) trapped within these microstructures, which exhibit a progressive red shift in light absorption/emission toward the NIR range. Moreover, the highly spherical shape of CPMs endows them with innate photonic functionalities in combination with their intrinsic CD-based attributes. Harnessing their excitation wavelength-dependent photoluminescent (PL) property, a single CPM exhibits whispering-gallery modes (WGMs) that are emission-tunable from the DR to the NIR. This type of newly developed microresonator can serve as, for example, unclonable anti-counterfeiting labels. This innovative cross-cutting approach, combining photonics and chemistry, offers robust, bottom-up, built-in photonic functionality with diverse NIR applications.

Deuteration-Induced Energy Level Structure Reconstruction of Carbon Dots for Enhancing Photoluminescence

Constrained by a limited understanding of the structure and luminescence mechanisms of carbon dots (CDs), achieving precise enhancement of their photoluminescence (PL) performance without altering the emission wavelength and color remains a challenge. In this work, a deuterated CD is first achieved by simply replacing the reaction solvent from H2O to D2O. The substitution of D atoms for H atoms is not limited on the surface but also within the internal structure of CDs. Deuteration affects the formation of the π-conjugated network structure by altering the content of sp2 carbon and sp3 carbon, ultimately inducing a reconstruction for energy level structure of CDs. Both the intrinsic state and surface state emission, including quantum yield, emission intensity and lifetime, are significantly enhanced after deuteration. It benefits from the reduction in non-radiative transitions, since the lowered vibrational frequencies of D atoms and optimized local energy level distribution in CDs structure. The deuterated CDs are applied in the fabrication of white-light-emitting diodes to show their application potential. This work provides a highly versatile route for improving and controlling photoluminescence performance of CDs and has opportunities to guide the development of CDs for practical applications.

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.

Bioinspired Carbonized Polymer Microspheres for Full-Color Whispering Gallery Mode Emission for White Light Emission, Unclonable Anticounterfeiting, and Chemical Sensing Applications

Light-element-based fluorescent materials, colloidal graphene quantum dots, and carbon dots (CDs) have sparked an immense amount of scientific interest in the past decade. However, a significant challenge in practical applications has emerged concerning the development of solid-state fluorescence (SSF) materials. This study addresses this knowledge gap by exploring the unexplored photonic facets of C-based solid-state microphotonic emitters. The proposed synthesis approach focuses on carbonized polymer microspheres (CPMs) instead of conventional nanodots. These microspheres exhibit remarkable SSF spanning the entire visible spectrum from blue to red. The highly spherical shape of CPMs imparts built-in photonic properties in addition to its intrinsic CD-based attributes. Leveraging their excitation-dependent photoluminescence property, these microspheres exhibit amplified spontaneous emission, assisted by the whispering gallery mode resonance across the visible spectral region. Remarkably, unlike conventional semiconductor quantum dots or dye-doped microresonators, this single microstructure showcases adaptable resonant emission without structural/chemical modifications. This distinctive attribute enables a plethora of applications, including microcavity-assisted energy transfer for white light emission, highly sensitive chemical sensing, and secure encrypted anticounterfeiting measures. This interdisciplinary approach, integrating photonics and chemistry, provides a robust solution for light-element-based SSF with inherent photonic functionality and wide-ranging applications.

Chemical- and green-precursor-derived carbon dots for photocatalytic degradation of dyes

Rapid industrialization and untreated industrial effluents loaded with toxic and carcinogenic contaminants, especially dyes that discharge into environmental waters, have led to a rise in water pollution, with a substantial adverse impact on marine life and humankind. Photocatalytic techniques are one of the most successful methods that help in degradation and/or removal of such contaminants. In recent years, semiconductor quantum dots are being substituted by carbon dots (CDs) as photocatalysts, due to the ease of formation, cost-effectiveness, possible sustainability and scalability, much lower toxicity, and above all its high capacity to harvest sunlight (UV, visible, and near infrared) through electron transfer that enhances the lifetime of the photogenerated charge carriers. A better understanding between the properties of the CDs and their role in photocatalytic degradation of dyes and contaminants is required for the formation of controllable structures and adjustable outcomes. The focus of this review is on CDs and its composites as photocatalysts obtained from different sustainable green as well as chemical precursors. Apart from the synthesis, characterization, and properties of the CDs, the study also highlights the effect of different parameters on the photocatalytic properties of CDs and their composites for catalytic dye degradation mechanisms in detail. Besides the present research development in the field, potential challenges and future perspectives are also presented.

Caffeic acid-grafted chitosan/sodium alginate/nanoclay-based multifunctional 3D-printed hybrid scaffolds for local drug release therapy after breast cancer surgery

Breast cancer is one of the most common malignant tumors in women all over the world. Mastectomy is the most effective treatment, but there are serious problems such as high tumor recurrence rate and side effects of chemotherapy. Therefore, there is an urgent need for a therapeutic strategy that can effectively promote postoperative wound healing and inhibit local tumor recurrence. In this study, a 3D printing scaffold based on carbon dots-curcumin nano-drug release (CCNPs) was developed as a local drug delivery platform (named CCNACA using CCNPs, Sodium alginate, Nanoclay and Caffeic Acid grafted Chitosan as raw materials), which has the ability to visualize drug release. The 14-day drug release test in vitro showed that the tumor inhibition rate of CCNACA scaffolds on breast cancer cells (MCF-7) was 73.77 ± 1.68 %. And the CCNACA scaffolds had good long-term antibacterial (Escherichia coli and Staphylococcus aureus) activity. Animal experiments have shown that implanting CCNACA scaffolds into surgical defects can inhibit postoperative residual cancer cells, reduce inflammation, promote angiogenesis, and repair tissue defects caused by surgery. In summary, the local drug delivery system of this manuscript has great potential in wound healing and prevention of tumor recurrence after breast cancer surgery.

White light emission from helically stacked humin-mimic based H-aggregates in heteroatom free carbon dots

White light emission (WLE), particularly from heteroatom free carbon dots (CDs), is unusual. Besides, deciphering the origin of WLE from a H-aggregated molecular fluorophore in such kinds of CDs is a challenging task due to their non-fluorescent character resulting from a forbidden transition from a lower-energy excitonic state. Therefore, rigorous investigation on their elusive excited state photophysical properties along with their steady-state optical phenomena has to be carried out to shed light on the nature of distinct emissive states formed in the CDs. Herein, for the first time, we report WLE from imperfect H-aggregates of co-facially π-π stacked humin-like structures comprising furfural monomer units as a unique molecular fluorophore in CDs, as revealed from combined spectroscopic and microscopic studies, synthesized through hydrothermal treatment of the single precursor, dextrose. H-aggregates in CDs show a broad range of excitation-dependent emission spectra with color coordinates close to pure white light, i.e., CIE (0.35, 0.37) and a color temperature of 6000 K. Imperfect orientation between the transition dipole moments of adjacent monomer units in the H-aggregate's molecular arrangement is expected to cause ground state symmetry breaking, as confirmed by Circular Dichroism (CD) studies, which established helically stacked nature in molecular aggregates and produced significant oscillatory strength at lower energy excitonic states to enable fluorescence. TRES and TAS investigations have been performed to minimise the intricacies associated with excited state photophysics, which is regarded as an essential step in gaining a grasp on emissive states. Based on the observation of two isoemissive spots in the time-resolved area normalized emission spectra (TRANES), the existence of three oligomeric species in the excited state equilibrium of the pure/hybrid H-aggregates has been established. The exciton dynamics through electron relaxation from the higher to the lower excitonic states, charge transfer (CT) states, and surface trap mediated emission in excimer states of H-aggregates have also been endorsed as three distinct emissive states from femtosecond transient absorption spectroscopy (TAS) studies corroborating with their steady-state absorption and emission behavior. The results would demonstrate the usage of CDs as a cutting-edge fluorescent material for creating aggregate-induced white light emission.

Properties of Carbon Dots versus Small Molecules from "Bottom-up" Synthesis

A major challenge in the "bottom-up" solvothermal synthesis of carbon dots (CDs) is the removal of small-molecule byproducts, noncarbonized polyamides, or other impurities that confound the optical properties. In previously reported benzene diamine-based CDs, the observed fluorescence signal already has been shown to arise from free small molecules, not from nanosized carbonized dots. Here we have unambiguously identified the small-molecule species in the synthesis of CDs starting with several isomers of benzene diamine by directly matching their NMR, mass spectrometry, and optical data with commercially available small organic molecules. By combining dialysis and chromatography, we have sufficiently purified the CD reaction mixtures to measure the CD size by TEM and STM, elemental composition, optical absorption and emission, and single-particle blinking dynamics. The results can be rationalized by electronic structure calculations on small model CDs. Our results conclusively show that the purified benzene diamine-based CDs do not emit red fluorescence, so the quest for full-spectrum fluorescence from isomers of a single precursor molecule remains open.

Carbon Dots for Electroluminescent Light-Emitting Diodes: Recent Progress and Future Prospects

Carbon dots (CDs), as emerging carbon nanomaterials, have been regarded as promising alternatives for electroluminescent light-emitting diodes (LEDs) owing to their distinct characteristics, such as low toxicity, tuneable photoluminescence, and good photostability. In the last few years, despite remarkable progress achieved in CD-based LEDs, their device performance is still inferior to that of well-developed organic, heavy-metal-based QDs, and perovskite LEDs. To better exploit LED applications and boost device performance, in this review, a comprehensive overview of currently explored CDs is presented, focusing on their key optical characteristics, which are closely related to the structural design of CDs from their carbon core to surface modifications, and to macroscopic structural engineering, including the embedding of CDs in the matrix or spatial arrangement of CDs. The design of CD-based LEDs for display and lighting applications based on the fluorescence, phosphorescence, and delayed fluorescence emission of CDs is also highlighted. Finally, it is concluded with a discussion regarding the key challenges and plausible prospects in this field. It is hoped that this review inspires more extensive research on CDs from a new perspective and promotes practical applications of CD-based LEDs in multiple directions of current and future research.

Lignocellulosic Biomass-Based Carbon Dots: Synthesis Processes, Properties, and Applications

Carbon dots (CDs), a new type of carbon-based fluorescent nanomaterial, have attracted widespread attention because of their numerous excellent properties. Lignocellulosic biomass is the most abundant renewable natural resource and possesses broad potential to manufacture different composite and smart materials. Numerous studies have explored the potential of using the components (such as cellulose, hemicellulose, and lignin) in lignocellulosic biomass to produce CDs. There are few papers systemically aiming in the review of the state-of-the-art works related to lignocellulosic biomass-derived CDs. In this review, the significant advances in synthesis processes, formation mechanisms, structural characteristics, optical properties, and applications of lignocellulosic biomass-based CDs such as cellulose-based CDs, hemicellulose-based CDs and lignin-based CDs in latest research are reviewed. In addition, future research directions on the improvement of the synthesis technology of CDs using lignocellulosic biomass as raw materials to enhance the properties of CDs are proposed. This review will serve as a road map for scientists engaged in research and exploring more applications of CDs in different science fields to achieve the highest material performance goals of CDs.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Using 19F NMR to Investigate Cationic Carbon Dot Association with Per- and Polyfluoroalkyl Substances (PFAS)

There is much concern about per- and polyfluoroalkyl substances (PFAS) based on their environmental persistence and toxicity, resulting in an urgent need for remediation technologies. This study focused on determining if nanoscale polymeric carbon dots are a viable sorbent material for PFAS and developing fluorine nuclear magnetic resonance spectroscopy (19F NMR) methods to probe interactions between carbon dots and PFAS at the molecular scale. Positively charged carbon dots (PEI-CDs) were synthesized using branched polyethyleneimine to target anionic PFAS by promoting electrostatic interactions. PEI-CDs were exposed to perfluorooctanoic acid (PFOA) to assess their potential as a PFAS sorbent material. After exposure to PFOA, the average size of the PEI-CDs increased (1.6 ± 0.5 to 7.8 ± 1.8 nm) and the surface charge decreased (+38.6 ± 1.1 to +26.4 ± 0.8 mV), both of which are consistent with contaminant sorption. 19F NMR methods were developed to gain further insight into PEI-CD affinity toward PFAS without any complex sample preparation. Changes in PFOA peak intensity and chemical shift were monitored at various PEI-CD concentrations to establish binding curves and determine the chemical exchange regime. 19F NMR spectral analysis indicates slow-intermediate chemical exchange between PFOA and CDs, demonstrating a high-affinity interaction. The α-fluorine had the greatest change in chemical shift and highest affinity, suggesting electrostatic interactions are the dominant sorption mechanism. PEI-CDs demonstrated affinity for a wide range of analytes when exposed to a mixture of 24-PFAS, with a slight preference toward perfluoroalkyl sulfonates. Overall, this study shows that PEI-CDs are an effective PFAS sorbent material and establishes 19F NMR as a suitable method to screen for novel sorbent materials and elucidate interaction mechanisms.

Elucidating the relationship between red fluorescence and structural dynamics of carbon dots dispersed in different solvents

The mechanism of intrinsic fluorescence of carbon dots (CDs), the latest nanomaterial from the carbon family, was supposedly deciphered through multiple theories. However, the much sought-after persistent red emission of CDs as a foreseeable consequence of experiments remains elusive prompting the question of whether tuning of the red emission of CDs is a predictable outcome or a serendipitous coincidence. Herein, we tried to decode the same by exploring Alizarin Red S (ARS)-based red emitting CDs in different solvents with wisely chosen analytical tools. The findings are aptly supported by molecular dynamics studies through an experimental intuition-driven model-building approach. Parallel interception of the CDs with powder X-ray diffraction (pXRD) and photophysical spectroscopic studies revealed an important relationship between the solvent and CDs. Tautomerism, a well-known phenomenon with chemical entities, was found to be operative for CDs that greatly influence the Stokes shift and ultimately the fluorescence outcome. Most importantly, pXRD studies established the turbostratism of the CDs where the well-ordered graphitic structure of CDs gets disrupted with solvent molecules. The extent of such disruption is a function of solvent and CD composition that plays a formidable role in obtaining red fluorescence. Thus, for the first time, we demonstrate that the red emission of CDs is related to its structural integrity and if taken care of could be sustained, a tremendously desirable outcome for relevant applications.

Synthesis and post-synthesis strategies for polychromatic carbon dots toward unique and tunable multicolor photoluminescence and associated emission mechanism

Carbon dots (CDs) with unique and tunable multicolor photoluminescence (PL) emission has attracted tremendous attention in the past few years due to their potential multifaceted application, specially in the biomedical and optoelectronic fields. There has been extensive deliberation and efforts to engineer the synthesis or post synthesis approach to obtain multicolor-emissive CDs and tune their optical properties toward longer wavelength. This review mainly focuses on the advancement of strategies for synthesis and post-synthesis techniques of CDs toward tunable multicolor emission. Based on the above discussion to achieve desired goals, several synthesis strategies (selection of proper benzenoid precursor, acid/base treatment of biomass, optimization of reaction conditions, optimization of the reagents, solvent engineering, acid strength regulation, reaction temperature regulation, chemical doping) and various post synthesis strategies (column chromatographic separation or purification, solvatochromism, pH variation, surface functionalization, concentration variation) have been reviewed. Although numerous research articles have been published on the synthesis of multicolor CDs for multifaceted application, there is still a lack of a concise review article focusing on systematic synthesis/post synthesis strategies with PL mechanism elucidation. Thus, we focused on providing a comprehensive overview of the state-of-the-art advances on the strategies for the preparation of polychromatic CDs with tunable emission and elucidating their emission mechanism.

Synthetic strategies, properties and sensing application of multicolor carbon dots: recent advances and future challenges

Recently, carbon dots (CDs) as newly developed carbon-based nanomaterials due to advantages such as excellent photostability and easy surface functionalization have generated wide application prospects in fields such as biological imaging and chemical sensing. The multicolor emission carbon dots (M-CDs) were acquired through the selection of different carbon source precursors, change of synthesis conditions and synthesis environment. Therefore, the aim of this review is to summarize the latest research progress in polychromatic CDs from the perspectives of synthesis strategies, luminescent mechanisms, luminescent properties and applications. This review focuses on how to prepare MCDs by changing raw materials and synthesis conditions such as reaction temperature, synthesis time, synthesis pH, and synthesis solvent. This review also presents the optical properties of MCDs, concentration effects, solvent effects, pH effects, elemental doping, and surface passivation on them, as well as their creative applications in the field of sensing applications. It is anticipated that this review will serve as a guide for the development of multifunctional M-CDs and inspire future research on controllable design and preparation of M-CDs.

Optical Properties of Carbon Dots Synthesized by the Hydrothermal Method

In this study, the optical and structural properties of carbon dots (CDs) synthesized using a hydrothermal method were investigated. CDs were prepared from various precursors such as citric acid (CA), glucose, and birch bark soot. The SEM and AFM results show that the CDs are disc-shaped nanoparticles with dimensions of ~7 nm × 2 nm for CDs from CA, ~11 nm × 4 nm for CDs from glucose, and ~16 nm × 6 nm for CDs from soot. The TEM images of CDs from CA showed stripes with a distance of 0.34 nm between them. We assumed that the CDs synthesized from CA and glucose consisted of graphene nanoplates located perpendicular to the disc plane. The synthesized CDs contain oxygen (hydroxyl, carboxyl, carbonyl) and nitrogen (amino, nitro) functional groups. CDs have strong absorption in the ultraviolet region in the range of 200-300 nm. All CDs synthesized from different precursors displayed bright luminescence in the blue-green region of the spectrum (420-565 nm). We found that the luminescence of CDs depended on the synthesis time and type of precursors. The results show that the radiative transitions of electrons occur from two levels with energies ~3.0 eV and ~2.6 eV, which are due to the presence of functional groups.

Structural and Photoluminescence Characterization of Oxyfluorides for Phosphor Applications

ConspectusRare-earth-containing phosphors were crucial to the advances made to compact fluorescent lamps (CFLs), which assisted in protecting a widely used halophosphate phosphor from degrading after exposure to a high ultraviolet flux. The CFL phosphors are often coated twice by depositing a light coat of rare-earth-containing phosphors over the inexpensive halophosphate phosphor, which generates white light with high efficacy and a good color rendering index and possesses a balance between phosphor cost and performance. Costs of phosphors can be mitigated by requiring lower rare-earth ion concentrations or by completely eliminating rare-earth ions, which was one of the main goals of investigating the oxyfluorides Sr₃AlO₄F and Ba₂SrGaO₄F as potential phosphors. Changes in the Sr₃AlO₄F and Ba₂SrGaO₄F structures were studied using high-resolution neutron diffraction annealing these materials in 5%H₂/95%Ar and 4%H₂/96% Ar, respectively. Annealing in these atmospheres causes self-activated photoluminescence (PL) to occur under 254 nm light, which makes them ideal materials for rare-earth-free CFL phosphors. Additionally, these hosts possess two distinct sites for isovalent or aliovalent substitution of Sr denoted as the A(1) and A(2) sites. Ga³⁺ can be substituted for Al³⁺ at the M site, which is known to have an impact on the self-activated PL emission color. The structural distortions noted included closer packing in the FSr₆ octahedrons and AlO₄ tetrahedrons in the Sr₃AlO₄F structure as compared to in air-annealed samples, which show no PL emission. Temperature-dependent studies reveal that both the air- and reductively annealed samples have identical thermal expansion within this temperature range (3-350 K). High-resolution neutron diffraction at room temperature confirmed the tetragonal structure (I4/mcm) for Ba₂SrGaO₄F, a novel material in the Sr₃AlO₄F family of materials, has been synthesized via a solid-state method. Analysis of the refined Ba₂SrGaO₄F structure at room temperature revealed expansion in the lattice parameters and its polyhedral subunits between the reductively annealed and air-annealed samples, which are correlated with the PL emission. Previous studies related to the application of these host structure types revealed that they have potential as commercial solid-state lighting phosphors due to their ability to resist thermal quenching as well as accommodate various levels of substitutions that will assist with color tunability.

Carbon dots: Types, preparation, and their boosted antibacterial activity by photoactivation. Current status and future perspectives

Carbon dots (CDs) correspond to carbon-based materials (CBM) with sizes usually below 10 nm. These nanomaterials exhibit attractive properties such us low toxicity, good stability, and high conductivity, which have promoted their thorough study over the past two decades. The current review describes four types of CDs: carbon quantum dots (CQDs), graphene quantum dots (GQDs), carbon nanodots (CNDs), and carbonized polymers dots (CPDs), together with the state of the art of the main routes for their preparation, either by "top-down" or "bottom-up" approaches. Moreover, among the various usages of CDs within biomedicine, we have focused on their application as a novel class of broad-spectrum antibacterial agents, concretely, owing their photoactivation capability that triggers an enhanced antibacterial property. Our work presents the recent advances in this field addressing CDs, their composites and hybrids, applied as photosensitizers (PS), and photothermal agents (PA) within antibacterial strategies such as photodynamic therapy (PDT), photothermal therapy (PTT), and synchronic PDT/PTT. Furthermore, we discuss the prospects for the possible future development of large-scale preparation of CDs, and the potential for these nanomaterials to be employed in applications to combat other pathogens harmful to human health. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Activating One/Two-Photon Excited Red Fluorescence on Carbon Dots: Emerging n→π Photon Transition Induced by Amino Protonation

Due to the complicated nature of carbon dots (CDs), fluorescence mechanism of red fluorescent CDs is still unrevealed and features highly controversial. Reliable and effective strategies for manipulating the red fluorescence of CDs are urgently needed. Herein, CDs with one-photon excited (622 nm, QYs ≈ 17%) and two-photon (629 nm) excited red fluorescence are prepared by acidifying o-phenylenediamine-based reaction sediments. Systematic analysis reveals that the protonation of amino groups increases the particle surface potential, disperse the bulk sediments into nano-scale CDs. In the meanwhile, amino protonation of pyridinic nitrogen (-N=) structure inserts numerous n orbital energy levels between the π → π* transition, narrows the gap distance for photon transition, and induces red fluorescence emission on CDs. Present research reveals an effective pathway to activate CDs reaction sediments and trigger red emission, thus may open a new avenue for developing CDs with ideal optical properties and promising application prospects.

High performance carbon dots based prodrug Platform: Image-Guided photodynamic and chemotherapy with On-Demand drug release upon laser irradiation

The design of therapeutic nanoplatforms based on fluorescent carbon dots (CDs) has become a viable strategy because of their aqueous solubility, biocompatibility, and ease of further functionalization. By doping various heteroatoms into pristine CDs structures, we synthesized N-, Cl-, and S-doped CDs (NClS/CDs), as well as Se-, N-, and Cl-doped CDs (NClSe/CDs) with superior optoelectronic properties using rapid and straightforward microwave heating. The quantum efficiencies of these NClS/CDs and NClSe/CDs were enhanced to 30.7 % and 42.9 %, respectively, compared to those of undoped CDs (0.66 %). Owing to their better light absorption properties, NClS/CDs efficiently produced reactive oxygen species (ROS) under 532 nm laser irradiation for photodynamic therapy (PDT). Considering the ROS generation and surface carrier abilities of NClS/CDs, we designed the loading of camptothecin (CPT) drug via a thioketal linker (TL), resulting in h/CDs@CPT nanovesicles (NVs) with a drug-loading efficiency of 46.5 %. Under laser irradiation in an acidic environment, ROS-triggered CPT release was observed, with 50.2 % of CPT released following the breakdown of the ROS-sensitive TL. In vitro cellular studies revealed that h/CDs@CPT NVs possessed minimal cytotoxicity toward HeLa and 4 T1 cancer cells, despite the high clinical efficacy of PDT and ROS-induced chemotherapeutic response under laser treatment. Confocal microscopy of HeLa and 4 T1 cells revealed that h/CDs@CPT NVs produced red-emissive photographs for potential cancer cell detection. Therefore, our study presents an image-guided PDT and chemotherapeutic platform based on h/CDs@CPT NVs, which will be an attractive candidate for future cancer treatment.

S-Doped carbonized polymer dots inhibit early myocardial fibrosis by regulating mitochondrial function

Myocardial fibrosis (MF) is a critical pathological lesion in the progression of various acute and chronic cardiovascular diseases. However, there is still a lack of clinically effective drugs and treatments for MF therapies. Herein, for the first time, we developed fluorescent sulfur-doped carbonized polymer dots (S-CPDs) as new nano-antioxidants to reduce the cardiomyocyte damage caused by reactive oxygen species (ROS) in the early stage of fibrotic lesions. In vitro results suggested that the pre-protection of S-CPDs significantly increased the survival rate of H9c2 cells under severe oxidative stress, inhibited the isoproterenol (ISO)-induced hypertrophy of myocardial cells through improving the content of mitochondria related proteins and adenosine triphosphate (ATP) in cells. Moreover, S-CPD administration could effectively decrease cardiac hypertrophy and promote heart function in MF rat models. The rapid internalization, high biocompatibility and fluorescence imaging potential of S-CPDs revealed their promising application prospects in the diagnoses and treatments of cardiovascular diseases.

A comprehensive model of nitrogen-free ordered carbon quantum dots

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.

Chemically induced crosslinked enhanced emission of carbon polymer dots discerning healthy and cancer cells through pH-dependent tunable photoluminescence

Chemically induced crosslinked enhanced emission (CEE) of urea and citric acid-derived carbon polymer dot (CPD) nanoparticles is established here with a rare zero linker approach, i.e. without the use of any separate crosslinkers. Such chemical CEE like any chemical reaction was achieved through amide bond formation using carbodiimide chemistry, pointing towards the feasibility of developing a general methodology for their formation through engineering the nanoparticle surface functionality. Exhaustive characterization was done to pinpoint the structure, morphology, and photophysics of the CPDs and concurrently eliminate the possibility of the involvement and interference by molecular fluorophores for the unique optical tuning of the CPDs. The structure-photophysics relation was further restated through theoretical studies involving density functional theory (DFT) that correlated significantly well with the experimental findings. Most interestingly, the CPDs revealed pH responsiveness due to the formation or hydrolysis of amide bonds with acid or base, respectively, which was manifested through a spectacular change in fluorescence emission visible to the naked eye through UV illumination. This distinct pH-dependent photoluminescence properties of CPDs opens up an enormous opportunity for interesting applications, including discriminating normal and cancerous cells, which we demonstrate herein as a proof of concept through in vitro imaging.

Fluorescent Carbon Dots for Super-Resolution Microscopy

Conventional fluorescence microscopy is limited by the optical diffraction of light, which results in a spatial resolution of about half of the light's wavelength, approximately to 250-300 nm. The spatial resolution restricts the utilization of microscopes for studying subcellular structures. In order to improve the resolution and to shatter the diffraction limit, two general approaches were developed: a spatially patterned excitation method and a single-molecule localization strategy. The success of super-resolution imaging relies on bright and easily accessible fluorescent probes with special properties. Carbon dots, due to their unique properties, have been used for super-resolution imaging. Considering the importance and fast development of this field, this work focuses on the recent progress and applications of fluorescent carbon dots as probes for super-resolution imaging. The properties of carbon dots for super-resolution microscopy (SRM) are analyzed and discussed. The conclusions and outlook on this topic are also presented.

See the Unseen: Red-Emissive Carbon Dots for Visualizing the Nucleolar Structures in Two Model Animals and In Vivo Drug Toxicity

Nucleolus, which participates in many crucial cellular activities, is an ideal target for evaluating the state of a cell or an organism. Here, bright red-emissive carbon dots (termed CPCDs) with excitation-independent/polarity-dependent fluorescence emission are synthesized by a one-step hydrothermal reaction between congo red and p-phenylenediamine. The CPCDs can achieve wash-free, real-time, long-term, and high-quality nucleolus imaging in live cells, as well as in vivo imaging of two common model animals-zebrafish and Caenorhabditis elegans (C. elegans). Strikingly, CPCDs realize the nucleolus imaging of organs/flowing blood cells in zebrafish at a cellular level for the first time, and the superb nucleolus imaging of C. elegans suggests that the germ cells in the spermatheca probably have no intact nuclei. These previously unachieved imaging results of the cells/tissues/organs may guide the zebrafish-related studies and benefit the research of C. elegans development. More importantly, a novel strategy based on CPCDs for in vivo toxicity evaluation of materials/drugs (e.g., Ag⁺ ), which can visualize the otherwise unseen injuries in zebrafish, is developed. In conclusion, the CPCDs represent a robust tool for visualizing the structures and dynamic behaviors of live zebrafish and C. elegans, and may find important applications in cell biology and toxicology.

Boosting efficiency of luminescent solar concentrators using ultra-bright carbon dots with large Stokes shift

Luminescent solar concentrators (LSCs) are able to collect sunlight from a large-area to generate electric power with a low cost, showing great potential in building-integrated photovoltaics. However, the low efficiency of large-area LSCs caused by the reabsorption losses is a critical issue that hampers their practical applications. In this work, we synthesized novel yellow emissive carbon dots (CDs) with a large Stokes shift of 193 nm, which exhibit nearly zero reabsorption. The quantum yield (QY) of the yellow emitting CDs is up to 61%. The yellow emitting CDs can be employed to fabricate high-performance large-area LSCs due to successful suppression of the reabsorption losses. The as-prepared LSCs are able to absorb 14% of the sunlight as the absorption of the CDs matches well with the sun's spectrum. The large-area LSC (10 × 10 cm²) with a laminated structure based on the yellow emitting CDs achieves an optical conversion efficiency (η_opt) of 4.56% and power conversion efficiency (η_PCE) of 4.1% under natural sunlight (45 mW cm^-2), which are significantly higher than other previously reported works with similar sizes. Furthermore, the prepared high-performance LSCs show good stability. This method of synthesizing novel CDs for high-efficiency LSCs provides a useful platform for future study and practical application of LSCs.

Machine Learning-Assisted Carbon Dot Synthesis: Prediction of Emission Color and Wavelength

Carbon dots (CDs) have attracted great attention in a range of applications due to their bright photoluminescence, high photostability, and good biocompatibility. However, it is challenging to design CDs with specific emission properties because the syntheses involve many parameters, and it is not clear how each parameter influences the CD properties. To help bridge this gap, machine learning, specifically an artificial neural network, is employed in this work to characterize the impact of synthesis parameters on and make predictions for the emission color and wavelength for CDs. The machine reveals that the choice of reaction method, purification method, and solvent relate more closely to CD emission characteristics than the reaction temperature or time, which are frequently tuned in experiments. After considering multiple models, the best performing machine learning classification model achieved an accuracy of 94% in predicting relative to actual color. In addition, hybrid (two-stage) models incorporating both color classification and an artificial neural network k-ensemble model for wavelength prediction through regression performed significantly better than either a standard artificial neural network or a single-stage artificial neural network k-ensemble regression model. The accuracy of the model predictions was evaluated against CD emission wavelengths measured from experiments, and the minimum mean average error is 25.8 nm. Overall, the models developed in this work can effectively predict the photoluminescence emission of CDs and help design CDs with targeted optical properties.

Facile Access to Fabricate Carbon Dots and Perspective of Large-Scale Applications

Carbon dots (CDs), fluorescent carbon nanoparticles with particle sizes < 10 nm, are constantly being developed for potential large-scale applications. Recently, methods allow CD synthesis to be carried out on large-scale preparation in a controlled fashion are potentially important for multiple disciplines, including bottom-up strategy, top-down method. In this review, the recent progresses in the research of the methods for large-scale production of CDs and their functionalization are summarized. Especially, the methods of CD synthesis, such as large-scale preparation, hydrothermal/solvothermal, microwave-assisted, magnetic hyperthermia microfluidic and other methods, along with functionalization of CDs, are summarized in detail. By promising applications of CDs, there are three aspects have been already reported, such as enhancing mechanical properties, flame retardancy, and energy storage. Also, future development of CDs is prospected.

Synthesis Processes, Photoluminescence Mechanism, and the Toxicity of Amorphous or Polymeric Carbon Dots

Fluorescence is the emission of light following photon absorption. This optical phenomenon has many applications in daily life, such as in LED lamps, forensics, and bioimaging. Traditionally, small-molecule fluorophores were most common, but the types of molecules and particles with compelling fluorescence properties have expanded. For example, green fluorescent protein (GFP) was isolated from jellyfish and won the Nobel prize in 2008 due to its significant utility as a fluorescent biomarker. Using the intrinsic fluorescence of GFP, many previously invisible biological processes and substances can now be observed and studied. Other fluorescent materials have also been developed, greatly expanding the potential applications. Semiconductor quantum dots (QDs), which have bright fluorescence and a narrow bandwidth, are a popular choice for display technologies. However, QDs are made of heavy metal elements such as Cd and Se, which pose potential safety concerns to the environment and human health. Thus, new fluorescent organic materials are being developed to mitigate the toxicological concerns while maintaining the QD advantages.One type of new material attracting great attention as an environmentally friendly substitute for semiconductor QDs is carbon dots (CDs). CDs have been developed with strong fluorescence, good photostability, and low toxicity using a variety of precursors, and some synthesis processes have good potential for scale-up. However, since they are made of a variety of materials and through different methods, the structure and properties of CDs can differ from preparation to preparation. There are three major types of CDs: graphene quantum dots (GQDs), carbon quantum dots (CQDs), and amorphous or polymeric carbon dots (PCDs). This Account focuses on PCDs and their unique properties by comparing it with other types of CDs. The synthesis processes, fluorescence properties, fluorescence mechanisms, and toxicity are discussed below with an emphasis on the distinct attributes of PCDs.PCDs can be synthesized from small molecules or polymers. They have an amorphous or cross-linked polymer structure with bright fluorescence. This fluorescence is possibly due to cross-link-enhanced emission or clusteroluminescence that arises from the through-space interactions of heteroatomic-rich functional groups. Other fluorescence mechanisms of CDs, including distinct contributions from the carbon core and surface states, may also contribute. The toxicological profiles of CDs are influenced by the chemical composition, surface functionalization, and light illumination. CDs are generally thought to be of low toxicity, and this can be further improved by removing toxic byproducts, functionalizing the surface, and reducing light exposure to minimize the generation of reactive oxygen species.

The Emerging Development of Multicolor Carbon Dots

As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and reaction environment, which directly or indirectly determines the multicolor emission characteristics of CDs. Therefore, this review is the first systematic classification and summary of multiple regulation methods of synthetic MCDs and reviews the recent research progress in the synthesis of MCDs from a variety of precursor materials such as aromatic molecules, small organic molecules, and natural biomass, focusing on how different regulation methods produce corresponding MCDs. This review also introduces the innovative applications of MCDs in the fields of biological imaging, light-emitting diodes (LEDs), sensing, and anti-counterfeiting due to their excellent PL properties. It is hoped that by selecting appropriate adjustment methods, this review can inspire and guide the future research on the design of tailored MCDs, and provide corresponding help for the development of multifunctional MCDs.

Unconventional aliphatic fluorophores discovered as the luminescence origin in citric acid-urea carbon dots

Carbon dots (CDs) are emerging as the material of choice in a range of applications due to their excellent photoluminescence properties, ease of preparation from inexpensive precursors, and low toxicity. However, the precise nature of the mechanism for the fluorescence is still under debate, and several molecular fluorophores have been reported. In this work, a new blue fluorophore, 5-oxopyrrolidine-3-carboxylic acid, was discovered in carbon dots synthesized from the most commonly used precursors: citric acid and urea. The molecular product alone has demonstrated interesting aggregation-enhanced emission (AEE), making it unique compared to other fluorophores known to be generated in CDs. We propose that this molecular fluorophore is associated with a polymer backbone within the CDs, and its fluorescence behavior is largely dependent on intermolecular interactions with the polymers or other fluorophores. Thus, a new class of non-traditional fluorophores is now relevant to the consideration of the CD fluorescence mechanism, providing both an additional challenge to the community in resolving the mechanism and an opportunity for a greater range of CD design schemes and applications.

A nanosized photothermal responsive core-shell carbonized polymer dots based on poly(N-isopropylacrylamide) for light-triggered drug release

Core-shell nanocomposites are one of the most important achievements in the fast-growing field of nanotechnology. The combination of multi-responsive nano-shell with luminescent and photothermal core has led to promising applications in various fields such as optics, electronics and medicine. In this work, a nanosized core-shell system composed by carbonized dots core and poly(N-isopropylacrylamide) shell was developed and the photothermal triggered release of doxorubicin was demonstrated. The system was fully characterized by H¹-NMR, DLS, Z-potential, AFM, optical absorption and fluorescence measurements. A photothermal conversion efficiency (η) value of about 67.9% and a doxorubicin photo-release rate value of about 1.0% min^-1 were measured. Molecular dynamic (MD) simulations data were in agreement with experimental results, at 310 K the coil-to-globule transition and a consequent desorption of doxorubicin from the polymer were observed. Both the radius of gyration and the fluctuation of the distance doxorubicin-PNIPAM pointed that the temperature above the LCST and the acid pH facilitated the polymer transition. Moreover, MD simulations and experimental data suggested an influence on the lower critical solution temperature (LCST) exerted by the number of polymer chains anchored to the carbon core.

Rational Synthesis of Solid-State Ultraviolet B Emitting Carbon Dots via Acetic Acid-Promoted Fractions of sp3 Bonding Strategy

Carbon dots (CDs) have received tremendous attention for their excellent photoluminescence (PL) properties. However, it remains a great challenge to obtain CDs with ultraviolet (UV, 200-400 nm) emission in solid state, which requires strict control of the CDs structure and overcoming the aggregation-caused quenching (ACQ). Herein, a new sp³ compartmentalization strategy is developed to meet these requirements, by employing acetic acid to promote fractions of sp³ bonding during the synthesis of CDs. It markedly decreases the size of sp² conjugating units in the CDs, and shifts PL emission to the ultraviolet B (UVB) region (λ_max  = 308 nm). Moreover, sp² domains are well spatially compartmentalized by sp³ domains and the ACQ effect is minimized, enabling the high quantum yield in solid state (20.2%, λ_ex  = 265 nm) with a narrow bandwidth of 24 nm and environmental robustness. The solid-state UVB emissive CDs are highly desired for application in photonic devices. Hence, a demo of UVB light-emitting diodes is fabricated for plant lighting, leading to a 29% increase of ascorbic acid content in the basil. Overall, a rational and efficient way to construct solid UVB-CDs phosphors for wide applications is provided.

An innovative way to modulate the photoluminescence of carbonized polymer dots

Cross-linking enhances the photoluminescence quantum yield of carbonized polymer dots, in which confined-domain promotes the energy level overlap, redshifts emission wavelength, and facilitates phosphorescence generation.

A Facile Preparation of Multicolor Carbon Dots

Carbon dots (CDs) have raised broad interest because of their great potential in the fluorescence related fields, such as photocatalysis and bioimaging. CDs exhibit different optical properties when dissolved in various solvents. However, the effects of solvents during the process of preparation on the fluorescence emission of CDs are still unclear. In this work, CDs were prepared by a simple one-pot solvothermal route. Typical critic acid and thiourea were used as precursors. Through changing the volume ratio of water to N,N-dimethylformamide (DMF), we have obtained color tunable CDs, with the emission wavelength from 450 to 640 nm. TEM images, Raman and XPS spectra indicate that the particle size of CDs and the content of surface functional groups (C-N/C-S and C≡N bonds) increase with the increasing ratio of DMF to water, which results in the optimal emission wavelength red-shifted. The prepared multicolor CDs may have prospects in the lighting applications.

Carbon dots with aggregation induced quenching effect and solvatochromism for the detection of H2O in organic solvents

In this work, a type of carbon dots (CDs) which can be well dispersed in organic solvents but precipitated in neutral aqueous solution was synthesized by using one-step hydrothermal heating treatment of o-phenylenediamine in H₂SO₄ solution. Although the emissions of the CDs in different organic solvents are excitation independent, solvatochromism is observed for the CDs since the emission wavelength is red shifted with an increase in the polarity of solvents. The optical properties suggest that the emission of the CDs is controlled by molecular state. According to aggregation induced quenching effect and solvatochromism caused by an increase in the solvent polarity with the content of H₂O increasing, detection methods of H₂O in the organic solvents were developed by using the CDs as a probe. The spiked H₂O in acetone and methanol could be recovered in the range of 98.2% to 101.7%, which indicates that the as-proposed method has a high potential for the determination of H₂O in organic solvents.

A multifunctional chemical toolbox to engineer carbon dots for biomedical and energy applications

Photoluminescent carbon nanoparticles, or carbon dots, are an emerging class of materials that has recently attracted considerable attention for biomedical and energy applications. They are defined by characteristic sizes of <10 nm, a carbon-based core and the possibility to add various functional groups at their surface for targeted applications. These nanomaterials possess many interesting physicochemical and optical properties, which include tunable light emission, dispersibility and low toxicity. In this Review, we categorize how chemical tools impact the properties of carbon dots. We look for pre- and postsynthetic approaches for the preparation of carbon dots and their derivatives or composites. We then showcase examples to correlate structure, composition and function and use them to discuss the future development of this class of nanomaterials.

Revealing the synergetic interaction between amino and carbonyl functional groups and their effect on the electronic and optical properties of carbon dots

Nitrogen and oxygen-based functionalized carbon dots (CDs) surfaces have attracted significant attention due to their ability to tailor the optical and electronic properties of CDs.

Probing the emission dynamics in nitrogen doped carbon dots by reversible capping with mercury (II) through surface chemistry

In this study, the mechanistic insight and emission dynamics have been explored of size dependent nitrogen doped carbon quantum dots (namely 3A,3B & 3C) with toxic metal Hg2+ ions via...

Carbon Nanodots for All-in-One Photocatalytic Hydrogen Generation

Carbon nanodots (CNDs) were photochemically altered to produce dihydrogen under light irradiation. Within the complex structure of CNDs, photo-oxidation takes place at citrazinic acid molecular fluorophore sites. Important is the fact that the resulting CND materials have a dual function. On one hand, they absorb light, and on the other hand, they photo- and electrocatalytically produce dihydrogen from water and seawater, without any external photosensitizer or cocatalyst. Record HER activities of 15.15 and 19.70 mmol(H₂) g(catalyst)^-1 h^-1 were obtained after 1 h of 75 mW/cm² Xe lamp illumination, from water and seawater, respectively. This impressive performance outweighs the remaining structural uncertainties. A full-fledged physicochemical investigation based on an arsenal of steady-state and time-resolved spectroscopic characterizations together with microscopy enabled a comprehensive look into the reaction mechanism. For an efficient dihydrogen formation, a precatalytic activation by means of reduction with a sacrificial electron donor is imperative.

Aggregation-Induced Emissive Carbon Dots Gels for Octopus-Inspired Shape/Color Synergistically Adjustable Actuators

Some living organisms such as the octopus have fantastic abilities to simultaneously swim away and alter body color/morphology for disguise and self-protection, especially when there is a threat perception. However, it is still quite challenging to construct artificial soft actuators with octopus-like synergistic shape/color change and directional locomotion behaviors, but such systems could enhance the functions of soft robotics dramatically. Herein, we proposed to utilize unique hydrophobic carbon dots (CDs) with rotatable surficial groups to construct the aggregation-induced emission (AIE) active glycol CDs polymer gel, which could be further employed to be interfacially bonded to an elastomer to produce anisotropic bilayer soft actuator. When putting the actuator on a water surface, glycol spontaneously diffused out from the gel layer to allow water intake, resulting in a color change from a blue dispersion fluorescence to red AIE and a shape deformation, as well as a large surface tension gradient that can promote its autonomous locomotion. Based on these findings, artificial soft swimming robots with octopus-like synergistic shape/color change and directional swimming motion were demonstrated. This study provides an elegant strategy to develop advanced multi-functional bio-inspired intelligent soft robotics.

Carbon Dots: Classification, Properties, Synthesis, Characterization, and Applications in Health Care-An Updated Review (2018-2021)

Carbon dots (CDs) are usually smaller than 10 nm in size, and are meticulously formulated and recently introduced nanomaterials, among the other types of carbon-based nanomaterials. They have gained significant attention and an incredible interest in the field of nanotechnology and biomedical science, which is merely due to their considerable and exclusive attributes; including their enhanced electron transferability, photobleaching and photo-blinking effects, high photoluminescent quantum yield, fluorescence property, resistance to photo-decomposition, increased electrocatalytic activity, good aqueous solubility, excellent biocompatibility, long-term chemical stability, cost-effectiveness, negligible toxicity, and acquaintance of large effective surface area-to-volume ratio. CDs can be readily functionalized owing to the abundant functional groups on their surfaces, and they also exhibit remarkable sensing features such as specific, selective, and multiplex detectability. In addition, the physico-chemical characteristics of CDs can be easily tunable based on their intended usage or application. In this comprehensive review article, we mainly discuss the classification of CDs, their ideal properties, their general synthesis approaches, and primary characterization techniques. More importantly, we update the readers about the recent trends of CDs in health care applications (viz., their substantial and prominent role in the area of electrochemical and optical biosensing, bioimaging, drug/gene delivery, as well as in photodynamic/photothermal therapy).