Carbogenic nanodots derived from organo-templated zeolites with modulated full-color luminescence

Electrochemistry of Thin Films and Nanostructured Materials

In the last few decades, the development and use of thin films and nanostructured materials to enhance physical and chemical properties of materials has been common practice in the field of materials science and engineering. The progress which has recently been made in tailoring the unique properties of thin films and nanostructured materials, such as a high surface area to volume ratio, surface charge, structure, anisotropic nature, and tunable functionalities, allow expanding the range of their possible applications from mechanical, structural, and protective coatings to electronics, energy storage systems, sensing, optoelectronics, catalysis, and biomedicine. Recent advances have also focused on the importance of electrochemistry in the fabrication and characterization of functional thin films and nanostructured materials, as well as various systems and devices based on these materials. Both cathodic and anodic processes are being extensively developed in order to elaborate new procedures and possibilities for the synthesis and characterization of thin films and nanostructured materials.

Detection of Gastric Cancer-Associated d-Amino Acids and Carcinoembryonic Antigen by Colorimetric and Immuno ECL Sensing Platform Based on the Catalysis of N/S-Doped Carbon Dots @ N-Rich Porous Carbon Nanoenzyme

Gastric cancer is a malignant tumor, and its early diagnosis remains challenging due to the lack of simple and sensitive detection methods and specific biomarkers. In this work, to improve the detection reliability, we developed a dual-mode detection strategy for the detection of two biomarkers associated with it. First, an N- and S-doped carbon dots-N-rich porous carbon nanoenzyme (N/S-CDs@NC) was prepared by a two-step pyrolysis of thiourea-penetrated zinc-based zeolite imidazole framework. It was then combined with the 3,3',5,5'-tetramethylbenzidine-H₂O₂ system for the colorimetric detection of d-amino acids (i.e., d-proline (d-Pro) and d-alanine (d-Ala)) in saliva, based on d-amino acid oxidase catalyzing d-amino acid oxidation to produce H₂O₂. In this way, the low detection limits (S/N = 3) of d-Pro and d-Ala were 0.14 and 0.35 μM, respectively. Furthermore, N/S-CDs@NC was combined with the luminol-H₂O₂ electrochemiluminescence (ECL) system and magnetic immune accumulation/separation strategy to detect the carcinoembryonic antigen (CEA) in serum. The porous N/S-CDs@NC could facilitate participant contact, promote the generation of hydroxyl radical (^•OH), and electrostatically attract ^•OH, thereby significantly amplifying the ECL signal of luminol and improving the signal stability. Thus, the detection mode showed considerable sensitivity and selectivity, with a low detection limit of 0.26 pg mL^-1. The strategy proposed in this work can also be used for the detection of other disease markers by substituting the recognition elements, thus having good application potential.

Facile Synthesis of Carbon Dots from Amido Black 10b for Sensing in Real Samples

Herein, a one-step hydrothermal synthesis method was adopted to fabricate carbon dots (CDs) from amido black 10b in a sodium hydroxide solution. The morphology and composition of the CDs were investigated by XRD, FTIR TEM, XPS, UV-vis, and fluorescence spectroscopy. The obtained CDs (AB-CDs) with an average diameter of 19.4 nm displayed a well-dispersed characteristic in aqueous solutions. The as-prepared CDs showed bright blue fluorescence and good photostability, with a high quantum yield of 24.1%. AB-CDs displayed a selective and noticeable turn-off response to Fe3+. Accordingly, the quantitative detection of Fe3+ was achieved in the range of 5-200 μmol L-1 with a detection limit of 1.84 μmol L-1. The fluorescence response mechanism of Fe3+ to AB-CDs was ascribed to static quenching due to the emergence of the ground-state complex. Moreover, ascorbic acid could restore the fluorescence of AB-CDs quenched by Fe3+ by reducing Fe3+ to Fe2+. The developed nanoprobe was used to detect ascorbic acid with a limit of detection of 7.26 μmol L-1 in the range of 20-300 μmol L-1. Furthermore, the developed sensing system was successfully applied for an Fe3+ assay in a lake water sample and ascorbic acid detection in a human urine sample. The AB-CD-based analytical system showed its latent practical value in the chemical analysis and bioanalytical fields.

Preparation of Multicolour Solid Fluorescent Carbon Dots for Light-Emitting Diodes Using Phenylethylamine as a Co-Carbonization Agent

Carbon dots (CDs), as a new type of photoluminescent nanomaterial, have attracted extensive attention in various fields because of their unique luminescence properties. However, CDs will exhibit fluorescence quenching in the solid state or aggregate state, which limits their application. In this paper, a unique strategy is proposed to regulate solutions to achieve multicolour fluorescence of CDs in the solid state. We report the successful preparation of orange, green and blue solid fluorescent CDs using citric acid, urea and phenylethylamine as precursors and methanol, ethanol and water as solvents, respectively. The solid-state fluorescence of CDs may be caused by the linkage of the phenylethyl structure to the surface of CDs during formation, which effectively disperses the CDs and prevents π-π interactions between graphitized nuclei. Meanwhile, multicolour solid fluorescent CDs are realized by adjusting the solvent in the preparation process. Based on the excellent fluorescence properties of CDs, orange, green and blue light-emitting diodes (LEDs) are prepared. A white LED (WLED) can be obtained by mixing the three colours of solid fluorescent CDs, which shows the application potential of CDs in display lighting equipment.

Efficient eradication of antibiotic and dye by C-dots@zeolite nanocomposites: Performance evaluation, and degraded products analysis

Metronidazole (MET), a recalcitrant antibiotic from the nitro-imidazole family and commercially used Rhodamine B (RhB) dye, contributes a huge to water pollution, which needs to eliminate, preferably by photocatalytic degradation technique. The Cdots@zeolite (CDZ) nanocomposites with different weight ratios (1:1, 1:3, 1:5, 5:1, 1:7) were synthesized hydrothermally to degrade MET and RhB molecules. The CDZ composites were characterized by XRD, BET, EDS, and XPS technique which verifies the crystalline nature, incorporation of C-dots into zeolite frameworks with high surface area (∼187 m²/g). The morphology, d-spacing and lattice planes were analyzed by SEM images, HR-TEM and SAED analysis. The maximum degradation (∼79%) was achieved at an optimum catalyst dose of 0.2 g/L and pH 4 for MET and that of RhB was ∼90% at a catalyst dose of 0.4 g/L. The PZC (point of zero charge) value for CDZ composite was about pH 3.4, which justifies the maximum removal of MET at pH 4. The obtained rate constants 'k' were found to be 0.0081, 0.0041, and 0.0101 min^-1 in sun, UV, and visible light sources, respectively. The real industrial wastewater sample has been treated to give ∼68% of COD and ∼62% TOC removal. Moreover, the intermediates of plausible degradation pathways were identified by the m/z values obtained from GC-MS analysis.

Carbon Dots with an Emission in the Near Infrared Produced from Organic Dyes in Porous Silica Microsphere Templates

Carbon dots (CDs) with an emission in the near infrared spectral region are attractive due to their promising applications in bio-related areas, while their fabrication still remains a challenging task. Herein, we developed a template-assisted method using porous silica microspheres for the formation of CDs with optical transitions in the near infrared. Two organic dyes, Rhodamine 6G and IR1061 with emission in the yellow and near infrared spectral regions, respectively, were used as precursors for CDs. Correlation of morphology and chemical composition with optical properties of obtained CDs revealed the origin of their emission, which is related to the CDs' core optical transitions and dye-derivatives within CDs. By varying annealing temperature, different kinds of optical centers as derivatives of organic dyes are formed in the microsphere's pores. The template-assisted method allows us to synthesize CDs with an emission peaked at 1085 nm and photoluminescence quantum yield of 0.2%, which is the highest value reported so far for CDs emitting at wavelengths longer than 1050 nm.

Optical encoding of luminescent carbon nanodots in confined spaces

Stable emissive carbon nanodots were generated in zeolite crystals using near infrared photon irradiation gradually converting the occluded organic template, originally used to synthesize the zeolite crystals, into discrete luminescent species consisting of nano-sized carbogenic fluorophores, as ascertained using Raman microscopy, and steady-state and time-resolved spectroscopic techniques. Photoactivation in a confocal laser fluorescence microscope allows 3D resolved writing of luminescent carbon nanodot patterns inside zeolites providing a cost-effective and non-toxic alternative to previously reported metal-based nanoclusters confined in zeolites, and opens up opportunities in bio-labelling and sensing applications.

Red, orange, yellow and green luminescence by carbon dots: hydrogen-bond-induced solvation effects

The mechanism of the solvation-dependent multicolor luminescence of carbon dots (CDs) is not clear, despite the fact that multicolor luminescent CDs have important applications in many fields. In this article, we report solvated chromogenic CDs with productivity of up to 57%. The luminescence of the CD particles exhibits a regular redshift in N,N-dimethylformamide (DMF), ethanol, water, and acetic acid. The redshift of the CDs may be ascribed to the linking of the CD surfaces to the solvent through hydrogen bonds (HB). Different surface level states are formed by HB between the surfaces of the CDs and the solvent, and differences in dispersion states lead to different energy resonance transfer (ETR) efficiencies. The CDs/B₂O₃ composite exhibits excellent fluorescence thermal stability, and it has also been used to manufacture white-light-emitting devices with a high color rendering index of 87. Additionally, the excellent solvation effects of the CDs have application prospects in the detection of the water content in organic solvents. Finally, the CDs are used to realize cell imaging and positioning, which has significant application prospects in biological fields.

Carbon Dot-NaCl Crystals for White-Light Generation and Fabry-Perot Lasing

Phosphor materials with broad spectral range and an average emission lifetime (20 μs) have been achieved from carbon dots (CDs)-NaCl crystals. A one-pot synthesis pathway has been developed for CDs-NaCl crystals formation at room temperature. Precursor for CDs materials was screened at room temperature by oxidation methodology from different simple sugar molecules. CDs (size less than 10 nm) prepared from the fructose sugar exhibit most intense emission. Utilizing ripe banana peel (contains ∼27% of fructose) as a precursor for the carbon dot formation, white-light emission with a CIE index of (0.29, 0.34) has been achieved from the single source with CDs-NaCl crystals upon excitation at 430 nm. The crystals also function as Fabry-Perot (F-P) mode resonator for lasing, with a laser threshold value of 0.9 mW and a resonating Q-factor of 207. These results outline a new approach for realizing F-P lasing and white light emission from a non-toxic green source with a quick, facile and low-cost synthesis procedure.

Multimodal Imaging of Autofluorescent Sites Reveals Varied Chemical Speciation in SSZ-13 Crystals

A multimodal imaging study of chabazite is used to show the distribution of and discriminate between different emissive deposits arising as a result of the detemplation process. Confocal imaging, 3D fluorescence lifetime imaging, 3D multispectral fluorescence imaging, and Raman mapping are used to show three different types of emissive behaviours each characterised by different spatial distributions, trends in lifetime, spectral signals, and Raman signatures. A notable difference is seen in the morphology of agglomerated surface deposits and larger subsurface deposits, which experience lifetime augmentation due to spatial confinement. The distribution of organic residue throughout the crystal volume is comparable to XRF mapping that shows Si enrichment on the outer edges and higher Al content through the centre, demonstrating that a fluorescence-based technique can also be used to indirectly comment on the compositional chemistry of the inorganic framework.

A zeolite-based ship-in-a-bottle route to ultrasmall carbon dots for live cell labeling and bioimaging

Fluorescent carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have excellent biocompatibility and low toxicity, useful for cell labeling and bioimaging. However, it is challenging to reproducibly create CQDs that are uniform and small in size with controlled toxicity and fluorescence properties, and this status quo hinders the practical application of CQDs, especially in vivo. In this report, CQDs with a uniform size of ∼1.53 ± 0.42 nm are synthesized via in situ pyrolysis of organics confined in the smallest-pore zeolite SAPO-20 with a micropore aperture of 0.28 nm. The ultrasmall fluorescent CQDs show a bright green fluorescence with a quantum yield (QY) of 16%, higher than that of most of the bare CQDs without any functionalization and maximum emission at 523 nm under the irradiation of xenon-light at an excitation wavelength of 470 nm. X-ray photoelectron spectroscopy (XPS) characterization confirms the presence of rich carboxyl and hydroxyl groups on the CQD surface containing N- and O-based functional groups. The synthesized CQDs with high QY and low cytotoxicity have been successfully used for cellular imaging with excellent biocompatibility.

Revival of Zeolite-Templated Nanocarbon Materials: Recent Advances in Energy Storage and Conversion

Nanocarbon materials represent one of the hottest topics in physics, chemistry, and materials science. Preparation of nanocarbon materials by zeolite templates has been developing for more than 20 years. In recent years, novel structures and properties of zeolite-templated nanocarbons have been evolving and new applications are emerging in the realm of energy storage and conversion. Here, recent progress of zeolite-templated nanocarbons in advanced synthetic techniques, emerging properties, and novel applications is summarized: i) thanks to the diversity of zeolites, the structures of the corresponding nanocarbons are multitudinous; ii) by various synthetic techniques, novel properties of zeolite-templated nanocarbons can be achieved, such as hierarchical porosity, heteroatom doping, and nanoparticle loading capacity; iii) the applications of zeolite-templated nanocarbons are also evolving from traditional gas/vapor adsorption to advanced energy storage techniques including Li-ion batteries, Li-S batteries, fuel cells, metal-O2 batteries, etc. Finally, a perspective is provided to forecast the future development of zeolite-templated nanocarbon materials.

Mechanofluorochromic carbon dots under grinding stimulation

The exploration of new hotspot nanomaterials to acquire mechanofluorochromic (MFC) properties has drawn substantial interest. However, previously reported MFC nanomaterials have required external pressures on the level of gigapascals, and observing distinct reversible MFC phenomena in nanomaterials under low-pressure conditions is still a challenge. Herein, a kind of reversible MFC-carbon dots (CDs) under low pressure has been reported for the first time. The MFC-CDs exhibited an apparent solid-state fluorescence color change, with emission shifting from green to blue via anisotropic grinding, owing to the alteration of hydrogen bonds and stacking structure among the CDs. Notably, these MFC-CDs exhibited a reversible fluorescence resulting from their being treated with acid vapors. This reversibility was indicated from X-ray diffraction analysis to be due to recovery of the crystalline state. The results highlighted the relationship between reversible MFC properties and structure, and showed the utility of these MFC-CDs as security films for further applications.

In Situ H2O Meter by Visualization in Hydrogels

The solvent content strongly affects the viscoelastic properties and network structure of hydrogels. Because of the gels' structural susceptibility and autofluorescence background, there is still no visual method to evaluate the water content in micropores. Herein, a colorimetric molecular probe (DHBYD) was synthesized for in situ visualization of water content in the micropores of hydrogels. The rapid and reversible colorimetric responses of DHBYD to solvents were obtained, which resulted a full linearity range (0 to 100%) for detecting water content in real time. Demonstrated by theoretical calculations, the sensing was attributed to changes in intramolecular charge transfer via deprotonation of phenol group. A cubic polynomial, on correlation of RGB values with water content, was established for real detection of water content in hydrogels. It reveals a new pathway for simple, in situ, and full-range evaluation of solvent content in micropores of hydrogels without any complicated procedures or expensive instruments. This would achieve fast and in situ monitoring of hydrogels to improve gel properties for better applications. It can be extended to evaluate the solvent content in other fields such as synthesis and industrial applications.

Carbon Nanolights in Piezopolymers are Self-Organizing Toward Color Tunable Luminous Hybrids for Kinetic Energy Harvesting

Herein, an all-solid-state sequential self-organization and self-assembly process is reported for the in situ construction of a color tunable luminous inorganic/polymer hybrid with high direct piezoresponse. The primary inorganic self-organization in solid polymer and the subsequent polymer self-assembly are achieved at high pressure with the first utilization of piezo-copolymer (PVDF-TrFE) as the host matrix of guest carbon quantum dots (CQDs). This process induces the spontaneous formation of a highly ordered, microscale, polygonal, and hierarchically structured CQDs/PVDF-TrFE hybrid with multicolor photoluminescence, consisting of very thermodynamic stable polar crystalline nanowire arrays. The electrical polarization-free CQDs/PVDF-TrFE hybrids can efficiently harvest the environmental available kinetic mechanical energy with a new large-scale group-cooperation mechanism. The open-circuit voltage and short-circuit current outputs reach up to 29.6 V cm^-2 and 550 nA cm^-2 , respectively. The CQDs/PVDF-TrFE-based hybrid nanogenerator demonstrates drastically improved durable and reliable features during the real-time demonstration of powering commercial light emitting diodes. No attenuation/fluctuation of the electrical signals is observed for ≈10 000 continuous working cycles. This study may offer a new design concept for progressively but spontaneously constructing novel multiple self-adaptive complex inorganic/polymer hybrids that promise applications in the next generation of self-powered autonomous optoelectronic devices.

Mechanisms behind excitation- and concentration-dependent multicolor photoluminescence in graphene quantum dots

Despite numerous efforts, the mechanism behind multicolor photoluminescence (PL) in graphene quantum dots (GQDs) is still controversial. A deep insight into the origin of the multicolor emissions in GQDs is quite necessary for modulating their luminescence to facilitate the better use of this fluorescent material. Herein, GQDs with amino, carboxyl, and ammonium carboxylate groups were synthesized. The as-prepared GQDs exhibited intriguing excitation- and concentration-dependent multicolor PL characteristics. By regulating the excitation wavelength or concentration of GQDs, specific luminescence colors including blue, cyan, green, yellow, and even orange can be obtained. Systematic structural and optical studies indicated that the graphene basal plane and different functional groups dominantly exhibited nN 2P-σ*, π-π*, nO 2p-π* (-COOH), nO 2p-π* (-COO-) and nN 2p-π* electronic transitions, which appeared as multi-fluorescent centers that gave rise to the excitation-dependent multicolor PL. The occurrence of different types of electronic transitions and their color emissions were proved by pH-dependent PL measurements. In addition, systematic optical and morphology analyses revealed that GQDs could self-assemble into J-type aggregates with different morphologies and sizes as the concentration increased, and the observed concentration-dependent multicolor PL can be ascribed to aggregation-mediated energy level reconstruction in GQDs. Our findings further suggest that the competition among various fluorescent centers and self-aggregation processes dominated the luminescent properties of GQDs. This work will contribute to understand the origins of excitation- and concentration-dependent multicolor emissions in GQDs, which is also highly instructive for broadening the application fields of GQDs.

Evolution and Synthesis of Carbon Dots: From Carbon Dots to Carbonized Polymer Dots

Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.

Excitons in Carbonic Nanostructures

Unexpectedly bright photoluminescence emission can be observed in materials incorporating inorganic carbon when their size is reduced from macro–micro to nano. At present, there is no consensus in its understanding, and many suggested explanations are not consistent with the broad range of experimental data. In this Review, I discuss the possible role of collective excitations (excitons) generated by resonance electronic interactions among the chromophore elements within these nanoparticles. The Förster-type resonance energy transfer (FRET) mechanism of energy migration within nanoparticles operates when the composing fluorophores are the localized electronic systems interacting at a distance. Meanwhile, the resonance interactions among closely located fluorophores may lead to delocalization of the excited states over many molecules resulting in Frenkel excitons. The H-aggregate-type quantum coherence originating from strong coupling among the transition dipoles of adjacent chromophores in a co-facial stacking arrangement and exciton transport to emissive traps are the basis of the presented model. It can explain most of the hitherto known experimental observations and must stimulate the progress towards their versatile applications.

Silicoaluminophosphate (SAPO)-Templated Activated Carbons

Microporous activated carbon was prepared by depositing and pyrolyzing propylene within the microporous voids of SAPO-37 and subsequently removing the template by a treatment with HCl and NaOH. The carbon had a high surface area and large micropore and ultramicropore volumes. The yield, crystallinity, morphology, and adsorption properties compared well with those of a structurally related zeolite-Y-templated carbon. No HF was needed to remove the SAPO-37 template in contrast to the zeolite Y template, which could be of industrial importance.

Red Room-Temperature Phosphorescence of CDs@Zeolite Composites Triggered by Heteroatoms in Zeolite Frameworks

Carbon dots (CDs) with red-emitting room-temperature phosphorescence (RTP) are rarely reported because of the increasing nonradiative decay of the excited states and the decreasing energy gap between the excited states and ground states. Herein, we demonstrate a facile strategy for modulating the RTP properties of CDs in terms of donor-acceptor energy transfer (EnT) in the CDs-in-zeolite system. Upon tuning of the heteroatoms (Zn²⁺, Mn²⁺) doped in the aluminophosphate zeolite frameworks, CDs@zeolite composites with green and red phosphorescence have been prepared via in situ hydrothermal synthesis. In such composites, the zeolite matrix provides an efficient confinement role in stabilizing the triplet states of CDs. Significantly, the Mn-doped zeolite could act as an energy acceptor allowing EnT from excitons of CDs to the dopant in the host matrix, generating the intriguing red RTP behavior. This work provides an effective strategy for developing CD-based composite materials with special RTP emissions as well as new fields for applications.

Microwave-assisted fabrication of multicolor photoluminescent carbon dots as a ratiometric fluorescence sensor for iron ions

Multicolor CDs were prepared by a microwave-assisted method and used as a ratiometric fluorescence sensor for the detection of iron ions.

Ionothermal synthesis of a photoelectroactive titanophosphite with a three-dimensional open-framework

A new titanophosphite open-framework exhibits photovoltaic properties and photocatalytic activity as an n-type semiconductor.

Full-color emissive carbon-dots targeting cell walls of onion for in situ imaging of heavy metal pollution

Full-colour emissive carbon-dots were prepared and applied in targeting onion CWs for in situ imaging of heavy metal pollution.

Lignite-derived carbon quantum dot/TiO2 heterostructure nanocomposites: photoinduced charge transfer properties and enhanced visible light photocatalytic activity

A facile and green route to cleanly utilize lignite coal as a carbon source for preparing CQDs/TiO₂ catalysts.

Solvent-controlled synthesis of multicolor photoluminescent carbon dots for bioimaging

Multicolor fluorescent carbon dots (CDs) have potential applications in multichannel detection and multicolor imaging. In this study, multicolor fluorescent CDs were synthesized by changing the solvent type and adjusting the reactant ratio. The four prepared CDs emitted bright and stable blue (B-), green (G-), yellow (Y-), and red (R-) fluorescence under a single UV light (λ_ex = 365 nm). The photoluminescence (PL) emission wavelengths changed from 445 nm for B-CDs to 620 nm for R-CDs, and therefore covered the entire visible spectrum. The absolute quantum yields for the B-, G-, Y-, and R-CDs were 27.3%, 31.1%, 22.9%, and 8.8%, respectively. Characterization of the CDs showed that the differences among the optical features of the four prepared CDs arise from the differences among the surface states and nitrogen-derived structures in the carbon core. The four prepared CDs all showed low toxicity and steady PL, and therefore have potential applications in both in vitro and in vivo imaging.

The synthesis and bioimaging of multicolor carbon dots from citric acid and urea.

A Topotactic Synthetic Methodology for the Synthesis of Nanosized MFI Zeolites with Hierarchical Structures

Much effort has been invested in the designed synthesis of zeolites with nanosized and hierarchical structures in recent decades, on account of increasing demands in practical applications, especially catalysis. Herein, a new topotactic synthetic strategy is demonstrated to synthesize nanosized and hierarchical zeolites in a one-step procedure. By using silica spheres as the adjustable amorphous precursors and tetrapropylammonium hydroxide as a structure-directing agent, effortless control of both size and porosity can be achieved in this system with no extra templates. With a simple hydrothermal process, hierarchical zeolite spheres can be modified with acid cites (Al species incorporated in the framework). Benefitting from its mesoporosity, palladium nanoparticles are incorporated into the nanosized hierarchical zeolite, which makes the materials suitable for use in a cascade catalysis reaction of benzimidazole derivatives, including independent acid catalysis and hydrogenation sites. The nanocomposites show exceptional activity and stability in catalysis and recycling reaction. This strategy can be developed into other versatile and practicable scaffolds for advanced zeolite catalytic nanoreactor systems.

Formation and origin of multicenter photoluminescence in zeolite-based carbogenic nanodots

Carbogenic nanodots (CNDs) are inspiring intensive research efforts owing to their excellent optical properties; however, their chemical structures and photoluminescent origins are still under study. Herein, CNDs with interesting multicenter photoluminescence (PL) have been successfully prepared by pyrolysis of organo-templated zeolites. The simultaneously observed excitation-dependent blue and excitation-independent green PL emissions as well as an uncommon ultraviolet-excited cyan emission are quite different from those of the known multicenter emissive CNDs. To get a thorough understanding of the formation of these CNDs and their PL origins, structural characterizations coupled with femtosecond transient absorption and fluorescence lifetime spectra analyses have been employed to study such PL behavior. The results show that the as-prepared CNDs consist of three main batches with different polarities, and they are composed of a combination of six small fluorophores with diverse ratios. The multicenter PL is obtained due to competition between the conjugated domain fluorophores and the surface-occupied functional group fluorophores. This study provides a comprehensive insight into the origin of multicenter photoluminescence in zeolite-based CNDs.

Zeolite-templated carbons - three-dimensional microporous graphene frameworks

Zeolite-templated carbons (ZTCs) are ordered microporous carbons synthesized by using zeolite as a sacrificial template. Unlike well-known ordered mesoporous carbons obtained by using mesoporous silica templates, ZTCs consist of curved and single-layer graphene frameworks, thereby affording uniform micropore size (ca. 1.2 nm), developed microporosity (∼1.7 cm3 g-1), very high surface area (∼4000 m2 g-1), good compatibility with chemical modification, and remarkable softness/elasticity. Thus, ZTCs have been used in many applications such as hydrogen storage, methane storage, CO2 capture, liquid-phase adsorption, catalysts, electrochemical capacitors, batteries, and fuel cells. Herein, the relevant research studies are summarized, and the properties as well as the performances of ZTCs are compared with those of other materials including metal-organic frameworks, to elucidate the intrinsic advantages of ZTCs and their future development.

Supramolecular Cross-Link-Regulated Emission and Related Applications in Polymer Carbon Dots

Involvement of clear photoluminescence (PL) mechanism in specific chemical structure is at the forefront of carbon dots (CDs). Supramolecular interaction exists in plenty of materials, offering an inherent way to administrate the optical and photophysical properties, especially in terms of newly developed polymer carbon dots (PCDs). However, supramolecular-interaction-derived PL regulation is always ignored in the shadow of many kinds of PL factors, and we still have a limited understanding on the distinct chemical structure and mechanism of supramolecular effect in PCDs. Herein, several distinct photoluminescent phenomena of PCDs under aqueous and solid state are reviewed in terms of supramolecular cross-linking, with highly emphasizing the importance of supramolecular cross-link-enhanced emission (SCEE) effects, and the regulated function of supramolecular interaction's intensity and types between PCDs for special PL behaviors of PCDs. In addition, we categorize the photoluminescent phenomena in PCDs into the following aspects: supramolecular cross-link-enhanced dilute-solution-state emission, concentration-controlled multicolor emission, supramolecular regulation for quenching-resistant solid-state fluorescence, as well as supramolecular cross-link-assisted room-temperature- phosphorescence (RTP) under solid states. Furthermore, the applications of PCDs in light-emitting diodes (LED), solar cells, and anticounterfeiting and data encryption, etc., are presented, based on the distinct supramolecular cross-link-regulated photoluminescent phenomena, especially the solid-state emission. Finally, a brief outlook is given, highlighting the currently existing problems and development direction of supramolecular cross-link-regulated emission in PCDs.

Concentration-induced multi-colored emissions in carbon dots: origination from triple fluorescent centers

Color-tunable carbon dots have been synthesized via a one pot hydrothermal synthesis and re-dispersed in dimethylformamide solution after purification. Structural and optical property characterizations indicate that the concentration-dependent photoluminescent properties can be ascribed to the existence of multi-emissive centers in the carbon dots from core states, edge states and surface states. Therefore, a multi-center fluorescent mechanism for the carbon dots has been proposed according to the preservation effect and inductive effect of the solvent. The emission wavelength of the carbon dots with different concentrations can be tuned from 585 to 514 nm under the fixed excitation of 420 nm blue light, and a warm white light-emitting diode with a CIE color coordinate at (0.42, 0.35) is fabricated on a InGaN blue chip emitting 420 nm blue light.

Carbon nanodots in ZIF-8: synthesis, tunable luminescence and temperature sensing

A new hybrid material CNDs@ZIF-8 with tunable luminescence and temperature-responsive photoluminescence has been synthesized by a low temperature-calcination method. An approximate white light has been achieved by combining the blue emission of ZIF-8 framework and the high yellow emission of CNDs.

A new two-dimensional layered germanate with in situ embedded carbon dots for optical temperature sensing

A carbon dots@germanate composite has been synthesized by embedding carbon dots into a double-layered germanate in situ, which exhibits excitation-dependent and temperature-responsive photoluminescence.

Self-assembly facilitated and visible light-driven generation of carbon dots

Molecular self-assembly may facilitate visible light generation of carbon dots.

Carbon Nanodots as Dual-Mode Nanosensors for Selective Detection of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is an important product of oxidase-based enzymatic reactions, such as glucose/glucose oxidase (GOD) reaction. Therefore, the probing of generated H2O2 for achieving the detection of various carbohydrates and their oxidases is very significative. Herein, we report one kind of dual-emission carbon nanodots (CDs) that can serve as novel dual-mode nanosensors with both fluorometric and colorimetric output for the selective detection of H2O2. The dual-model nanosensors are established only by the undecorated dual-emission CDs, where significant fluorometric and colorimetric changes are observed with the addition of different concentrations of H2O2 in the CD solution, which benefit to the achievement of the naked-eye detection for H2O2. The mechanism of the nanosensors can be attributed to the fact that the external chemical stimuli like hydroxyl radicals from H2O2 bring about the change of surface properties and the aggregation of CDs, which dominate the emission and absorption of CDs. The constructed dual-mode nanosensors exhibit good biocompatibility and high selectivity toward H2O2 with a linear detection range spanning from 0.05 to 0.5 M and allow the detection of H2O2 as low as 14 mM.

Full-Color Emission Polymer Carbon Dots with Quench-Resistant Solid-State Fluorescence

Polymer carbon dots (PCDs) represent a new class of carbon dots (CDs) possessing sub-fluorophores and unique polymer-like structures. However, like small molecule dyes and traditional CDs, PCDs often suffer from self-quenching effect in solid state, limiting their potential applications. Moreover, it is hard to prepare PCDs that have the same chemical structure, exhibiting full-color emission under one fixed excitation wavelength by only modulating the concentration of the PCDs. Herein, self-quenching-resistant solid-state fluorescent polymer carbon dots (SSFPCDs) are prepared, which exhibit strong red SSF without any other additional solid matrices, while having a large production yield (≈89%) and a considerable quantum yield of 8.50%. When dispersed in water or solid matrices in gradient concentrations, they can exhibit yellow, green, and blue fluorescence, realizing the first SSFPCDs with the same chemical structure emitting in full-color range by changing the ratio of SSFPCDs to the solid matrices.

Molecular design of upconversion nanoparticles for gene delivery

Due to their large anti-Stokes shifts, sharp emission spectra and long excited-state lifetimes, upconversion nanoparticles (UCNPs) have attracted an increasing amount of research interests, and have shown great potential for enhancing the practical utility of gene therapy, whose versatility has been limited by existing gene delivery technologies that are basically mono-functional in nature. Despite this, up to now in-depth analysis of the development of UCNPs for gene delivery has been scant in the literature, even though there has been an upsurge of reviews on the chemistry of UCNPs and their applications in bioimaging and drug delivery. To fill this gap, this review aims to present the latest advances in the development and applications of UCNPs as gene carriers. Prior to describing the prominent works published in the field, a critical view on the properties, chemistry and molecular design of UCNPs for gene delivery is provided. With a synopsis of the recent advances in UCNP-mediated gene delivery, challenges and opportunities could be illuminated for clinical translation of works in this nascent field of research.

Facile and large-scale synthesis of green-emitting carbon nanodots from aspartame and the applications for ferric ions sensing and cell imaging

A facile, economical and green strategy to prepare green-fluorescent nitrogen-doped carbon nanodots (N-CDs) with a quantum yield (QY) of approximately 31.91% has been built up, while aspartame was employed as the carbon-nitrogen source for the first time. The prepared N-CDs exhibited ultrahigh brightness, favorable strong photostability and negligible cytotoxicity. The outstanding optical properties are mainly derived from the their robost composition and steric distribution of the doped nitrogen atoms, which have been characterized detailedly. The obtained N-CDs showed highly selective and sensitive response toward ferric ions (Fe³⁺) through a fluorescence static quenching process in a wide linear range of 0.005-60µmol/L. The detection limit was as low as 1.43nmol/L, allowing the analysis of Fe³⁺ in a very simple method. The excitation-dependent luminescent behavior of the obtained N-CDs guaranteed the multicolor emissive property when they were used in cell imaging. And the application for intracellular Fe³⁺ sensing further verified this novel N-CDs may open more opportunities in biosensor, bioimaging and biological assay.

Full-colour carbon dots: integration of multiple emission centres into single particles

The single particle emission behaviours of our previously reported excitation-dependent full-colour carbon dots (F-C dots) have been analyzed by a single-particle fluorescence imaging technique. The co-localization of the F-C dots excited with different wavelengths shows that single F-C dots can also be excited with multiple energies. The co-localization of the F-C dots that emit at different colour regions under the same excitation wavelength or different excitation wavelengths shows that single F-C dots have a broad emission band from blue to red, but the emission intensities in different colour regions vary from one particle to another. So this study concretely proves that the full colour emissions are single particle behaviours; they are different from the other type of excitation dependent full-colour emission carbon dots whose full-colour behaviour originates from the large heterogeneity in both particle size and the structures of the ensemble. Then the origination of the full-colour emission at the single dot level was further studied by comparing the emission properties of the F-C dots and the small molecular byproducts, and it is found that the emissions of the dozens of molecular byproducts can also cover the full visible regions. And the emission positions of F-C dots are very similar to those of the byproducts at the same excitations, but they show different lifetimes. So a mechanism for the full colour emissions of F-C dots is proposed to originate from the hybridization of multiple small emissive molecules on the emissive carbon cores. This single particle level understanding of full-colour emission properties will pave the way towards the development of single dot imaging or tracking.

Chiral nanoprobes for targeting and long-term imaging of the Golgi apparatus

The targeting and long-term imaging of the Golgi apparatus have been realized vial-cysteine functionalized nanoprobes.

The Golgi apparatus is an essential subcellular organelle. Targeting and monitoring the Golgi change at the single-cell level over a long time scale are critical but are challenges that have not yet been tackled. Inspired by the precise Golgi positioning ability of galactosyltransferase and protein kinase D, due to their cysteine residues, we developed a method for long-term Golgi imaging. Fluorescent molecules, carbon quantum dots (CQDs) and silica nanoparticles could target the Golgi when they are modified with l-cysteine. l-Cysteine-rich chiral carbon quantum dots (LC-CQDs), which have the benefits of a high Golgi specificity from l-cysteine and excellent photostability and biocompatibility from the CQDs, are proven to be highly suitable for long-term in situ imaging of the Golgi. Investigation of the mechanism showed that free thiol groups and the l-type stereo configuration of LC-CQDs are essential for specific targeting of the Golgi. With the aid of the as-prepared LC-CQDs, the dynamic changes of the Golgi in the early stage of viral infection were visualized. The Golgi targeting and imaging strategy used in this work is beneficial for Golgi-targeted drug delivery and early diagnosis and therapy of Golgi diseases.

Carbon dots in zeolites: A new class of thermally activated delayed fluorescence materials with ultralong lifetimes

Thermally activated delayed fluorescence (TADF) materials are inspiring intensive research in optoelectronic applications. To date, most of the TADF materials are limited to metal-organic complexes and organic molecules with lifetimes of several microseconds/milliseconds that are sensitive to oxygen. We report a facial and general "dots-in-zeolites" strategy to in situ confine carbon dots (CDs) in zeolitic matrices during hydrothermal/solvothermal crystallization to generate high-efficient TADF materials with ultralong lifetimes. The resultant CDs@zeolite composites exhibit high quantum yields up to 52.14% and ultralong lifetimes up to 350 ms at ambient temperature and atmosphere. This intriguing TADF phenomenon is due to the fact that nanoconfined space of zeolites can efficiently stabilize the triplet states of CDs, thus enabling the reverse intersystem crossing process for TADF. Meanwhile, zeolite frameworks can also hinder oxygen quenching to present TADF behavior at air atmosphere. This design concept introduces a new perspective to develop materials with unique TADF performance and various novel delayed fluorescence-based applications.