Coupling of BiOCl Ultrathin Nanosheets with Carbon Quantum Dots for Enhanced Photocatalytic Performance

Over the past few decades,photocatalysis technology has received extensive attention because of its potential to mitigate or solve energy and environmental pollution problems.Designing novel materials with outstanding photocatalytic activities has become a research hotspot in this field.In this study,we prepared a series of photocatalysts in which BiOCl nanosheets were modified with carbon quantum dots(CQDs)to form CQDs/BiOCl composites by using a simple solvothermal method.The photocatalytic performance of the resulting CQDs/BiOCl composite photocatalysts was assessed by rhodamine B and tetracycline degradation under visible-light irradiation.Compared with bare BiOCl,the photocatalytic activity of the CQDs/BiOCl composites was significantly enhanced,and the 5 wt%CQDs/BiOCl composite exhibited the highest photocatalytic activity with a degradation efficiency of 94.5%after 30 min of irradiation.Moreover,photocatalytic N_(2)reduction performance was significantly improved after introducing CQDs.The 5 wt%CQDs/BiOCl composite displayed the highest photocatalytic N_(2)reduction performance to yield NH_3(346.25μmol/(g h)),which is significantly higher than those of 3 wt%CQDs/BiOCl(256.04μmol/(g h)),7 wt%CQDs/BiOCl(254.07μmol/(g h)),and bare BiOCl(240.19μmol/(g h)).Our systematic characterizations revealed that the key role of CQDs in improving photocatalytic performance is due to their increased light harvesting capacity,remarkable electron transfer ability,and higher photocatalytic activity sites.

Energy Transfer Dynamics between Carbon Quantum Dots and Molybdenum Disulfide Revealed by Transient Absorption Spectroscopy

Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-tion spectroscopies to study the energy transfer dynamics between CQDs and molybdenum disulfide(MoS_(2)).Transient absorption plots showed photoinduced absorption and stimulated emission features,which involved the intrinsic and defect states of CQDs.Adding MoS_(2)to CQDs solution,the lowest unoccupied molecular orbital of CQDs transferred energy to MoS_(2),which quenched the intrinsic emission at 390 nm.With addition of MoS_(2),CQD-MoS_(2)composites quenched defect emission at 490 nm and upward absorption,which originated from another energy transfer from the defect state.Two energy transfer paths between CQDs and MoS_(2)were efficiently manipulated by changing the concentration of MoS_(2),which laid a foundation for improving device performance.

Carbon quantum dots for advanced electrocatalysis

Zero-dimensional(0D)carbon quantum dots(CQDs),as a nanocarbon material in the carbon family,have garnered increasing attention in recent years due to their outstanding features of low cost,nontoxicity,large surface area,high electrical conductivity,and rich surface functional groups.By virtue of their rapid electron transfer and large surface area,CQDs also emerge as promising functional materials for the applications in energy-conversion sectors through electrocatalysis.Besides,the rich functional groups on the surface of CQDs offer abundant anchoring sites and active sites for the engineering of multicomponent and high-performance composite materials.More importantly,the heteroatom in the CQDs could effectively tailor the charge distribution to promote the electron transfer via internal interactions,which is crucial to the enhancement of electrocatalytic performance.Herein,an overview about recent progress in preparing CQDs-based composites and employing them as promising electrode materials to promote the catalytic activity and stability for electrocatalysis is provided.The introduced CQDs could enhance the conductivity,modify the morphology and crystal phase,optimize the electronic structure,and provide more active centers and defect sites of composites.After establishing a deep understanding of the relationship between CQDs and electrocatalytic performances,the issues and challenges for the development of CQDs-based composites are discussed.

Graphitic Carbon Quantum Dots Modified Nickel Cobalt Sulfide as Cathode Materials for Alkaline Aqueous Batteries

Carbon quantum dots(CQDs)as a new class of emerging materials have gradually drawn researchers’concern in recent years.In this work,the graphitic CQDs are prepared through a scalable approach,achieving a high yield with more than 50%.The obtained CQDs are further used as structure-directing and conductive agents to synthesize novel N,S-CQDs/NiCo2S4 composite cathode materials,manifesting the enhanced electrochemical properties resulted from the synergistic effect of highly conductive N,S-codoped CQDs offering fast electronic transport and unique micro-/nanostructured NiCo2S4 microspheres with Faradaic redox characteristic contributing large capacity.Moreover,the nitrogen-doped reduced graphene oxide(N-rGO)/Fe2O3 composite anode materials exhibit ultrahigh specific capacity as well as significantly improved rate property and cycle performance originating from the high-capacity prism-like Fe2O3 hexahedrons tightly wrapped by highly conductive N-rGO.A novel alkaline aqueous battery assembled by these materials displays a specific energy(50.2 Wh kg^−1),ultrahigh specific power(9.7 kW kg^−1)and excellent cycling performance with 91.5%of capacity retention at 3 A g^−1 for 5000 cycles.The present research offers a valuable guidance for the exploitation of advanced energy storage devices by the rational design and selection of battery/capacitive composite materials.

Multifarious roles of carbon quantum dots in heterogeneous photocatalysis

As a new member of carbon material family, carbon quantum dots (CQDs) have attracted tremendous attentions for their potentials in the heterogeneous photocatalysis applications. Due to the unique microstructure and optical properties, the roles of CQDs played in the CQDs-based photocatalytic systems have been found to be diverse with the continuous researches in this regard. Herein, we provide a concise minireview to elaborate the multifarious roles of CQDs in photocatalysis, including photoelectron mediator and acceptor, photosensitizer, photocatalyst, reducing agent for metal salt, enhancing adsorption capacity and spectral converter. In addition, the perspectives on future research trends and challenges are proposed, which are anticipated to stimulate further research into this promising field on designing a variety of efficient CQDs-based photocatalysts for solar energy conversion. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

ZnIn_2S_4 flowerlike microspheres embedded with carbon quantum dots for efficient photocatalytic reduction of Cr(Ⅵ)

Development of efficient heterostructured photocatalysts that respond to visible light remains a considerable challenge.We herein show the synthesis of ZnIn2S4/carbon quantum dot hybrid photocatalysts with flowerlike microspheres via a facile solvothermal method.The ZnIn2S4/carbon quantum dot flowerlike microspheres display enhanced photocatalytic and photoelectrochemical activity compared with that of pure ZnIn2S4.With a content of only 0.5 wt%carbon quantum dots,93%of Cr(VI)is reduced under visible‐light irradiation at 40 min.As a co‐catalyst,the carbon quantum dots improve the light absorption and lengthen the lifetime of charge carriers,consequently enhancing the photocatalytic and photoelectrochemical activity.

Photocatalytic degradation of organic pollutants using green oil palm frond-derived carbon quantum dots/titanium dioxide as multifunctional photocatalysts under visible light radiation

The present work suggested the use of waste oil palm frond as an alternative precursor for nitrogendoped carbon quantum dots(NCQDs)and proposed a straightforward in-situ hydrothermal method for the preparation of NCQDs/TiO_(2)nanocomposites.The elemental composition,morphological,structural and optical characteristics of NCQDs/TiO_(2)nanocomposites have been comprehensively investigated.The successful grafting of NCQDs on TiO_(2)matrix was confirmed by the formation of Ti AOAC bond and the electronic coupling between theπ-states of NCQDs and the conduction band of TiO_(2).For the first time,the oil palm frond-derived NCQDs/TiO_(2)was adopted in the photodegradation of methylene blue(MB)under visible-light irradiation.As a result,the photocatalytic efficiency of NCQDs/TiO_(2)nanocomposites(86.16%)was 2.85 times higher than its counterpart TiO_(2)(30.18%).The enhanced performance of nanocomposites was attributed to the pivotal roles of NCQDs serving as electron mediator and visiblelight harvester.Besides,the optimal NCQDs loading was determined at 4 ml while the removal efficiency of NCQDs/TiO_(2)-4 was the highest at a catalyst dosage of 1 g.L^(-1)under alkaline condition.This research work is important as it proposed a new insight to the preparation of biomass-based NCQDs/TiO_(2)using a facile synthetic method,which offers a green and sustainable water remediation technology.

Synthesis of Fluorescent Carbon Quantum Dots and Their Application in the Plant Cell Imaging

Carbon quantum dots(CQDs) exhibit tremendous advantages for plant growth study due to its strong fluorescence and good biocompatibility. The fluorescent CQDs were synthesized by the onestep microwave method with the raw materials of citric acid(CA) and urea(UR), and expressed a unique green fluorescence with the optimal excitation wavelength of over 400 nm through adjusting the doping of N elements. It is demonstrated that CQDs can act as deliver media in plant and fluorescent probes for plant cell imaging through directly cultivated in the seedlings of melon and wheat, respectively. Based on the effects of the fluorescent CQDs on plants growth, we can further study the mechanisms of the ions transport in plants.

Alcohol Solvent Effect on Fluorescence Properties in the Solvothermal Synthesis of Carbon Quantum Dots

Highly monodisperse carbon quantum dots(CQDs)were synthesized by a solvothermal method using L-ascorbic acid as carbon source and different simple alcohols(methanol,ethanol,ethylene glycol,and isopropanol)as reaction solvents at 180℃for 4 hours.The performance of CQDs was characterized by transmission electron microscope(TEM),Fourier infrared spectrometer(FTIR),UV-visible spectrophotometer,and fluorescence spectrophotometer.The results show that the prepared CQDs are wavelength-dependent,and have good hydrophilicity and similar surface compositions.However,there are more carbon and oxygen-containing functional groups on the surface of CQDs prepared with ethanol(CQDs-ET),and the type and number of functional groups will directly affect the fluorescence emission of CQDs.Also,it is found that the luminescence mechanisms of CQDs prepared by this solvothermal method are mainly based on the defect state of the oxygen group surface.And alcohol solvents do not directly participate in the formation of carbon nuclei during the reaction process,but it will affect the number and type of surface groups.Therefore,the influence of surface groups on the CQDs performance is greater than that of carbon nuclei in this experiment.

Carbon quantum dot preparation and application to detecting active ingredients in traditional Chinese medicine

Carbon quantum dots(CQDs)are fluorescent carbon nanomaterials that have been applied to biology,medicine,and optoelectronics,owing to their significant advantages such as simple synthesis methods,low cost,and widely available sources of raw synthesis materials.This review summarizes CQD preparation methods,which include hydrothermal and microwave-assisted synthesis methods,as well as separation methods such as centrifugation,dialysis,and filtration.Additionally,we review the application of CQDs in the detection of active ingredients,primarily phenolic compounds,in traditional Chinese medicine.We also discuss the quenching mechanism of CQD fluorescence using the active ingredients of traditional Chinese medicine.Limitations such as insufficient test selectivity,weak fluorescence intensity,and an unclear quantitative relationship between preparation methods and properties should be resolved for the efficient use of CQDs to detect active ingredients in Chinese medicine.

Synthesis of Humin-based Carbon Quantum Dots and Luminescent Properties

The unique properties of carbon quantum dots （CQDs） make them promising materials in many ？elds. Herein, we present a facile method for the preparation of photo-luminescent CQDs using humins as the carbon precursor for the purpose of providing a high value-added solution for this “biomass conversion process waste”. The structure of the CQDs was analyzed, and the effects of reaction temperature and time on the CQDs’ ？uorescence were investigated. The results showed that humins were effectively carbonized during the reaction. The ？uorescence intensity of humin-based CQDs initially increased with reaction temperature and time, and subsequently decreased beyond 200℃ and 4 h. Polyaromatic structures and hydrophilic groups such as O-H, C-O, -COOH and C==O groups exist in the CQDs. The humin-based CQDs have the dimension of 3~7 nm with an average size of about 5.5 nm. The highest emission intensity of blue/cyan ？uorescence light at 440 nm is achieved on the excitation with UV light at the wavelength of 330 nm.

Enhanced visible-light-driven photocatalytic activities of 0D/1D heterojunction carbon quantum dot modified CdS nanowires

Zero‐dimensional carbon dots(0D C‐dots)and one‐dimensional sulfide cadmium nanowires(1D CdS NWs)were prepared by microwave and solvothermal methods,respectively.A series of heterogeneous photocatalysts that consisted of 1D CdS NWs that were modified with 0D C‐dots(C‐dots/CdS NWs)were synthesized using chemical deposition methods.The mass fraction of C‐dots to CdS NWs in these photocatalysts was varied.The photocatalysts were characterized using X‐ray diffraction,scanning electron microscopy,transmission electron microscopy,X‐ray photoelectron spectroscopy,and ultraviolet‐visible spectroscopy.Their photocatalytic performance for the spitting of water and the degradation of rhodamine B(RhB)under visible light irradiation were investigated.The photocatalytic performance of the C‐dots/CdS NWs was enhanced when compared with that of the pure CdS NWs,with the 0.4%C‐dots/CdS NWs exhibiting the highest photocatalytic activity for the splitting of water and the degradation of RhB.The enhanced photocatalytic activity was attributed to a higher carrier density because of the heterojunction between the C‐dots and CdS NWs.This heterojunction improved the electronic transmission capacity and promoted efficient separation of photogenerated electrons and holes.

Energy Transfer and Electron Transfer in Composite System of Carbon Quantum Dots/Rhodamine B Molecules

In this work, we investigated the energy transfer (EnT) and electron transfer (ET) processes as well as their relationship in the carbon quantum dots/rhodamine B (CQDs/RhB) including o-CQDs/Rh B and m-CQDs/RhB systems by using photoluminescence spectroscopy in combination with steady-state and transient absorption spectroscopy. We found that the ET process is negligible in the o-CQDs/RhB system with an EnT efficiency as high as 73.2%,while it becomes pronounced in the m-CQDs/RhB system whose EnT efficiency is lower than 33.5%. Such an interplay of En T and ET processes revealed in the prototypical composite system consisting of carbon quantum dots and dye molecules would provide helpful insights for applications of relevance to exciton quenching.

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots(NSCQDs)nanoparticles on the surface of sheet cobalt-based metal-organic framework(Co-MOF)and graphitic carbon nitride(g-C_(3)N_(4),CN).The structure and properties of the obtained catalysts were systematically analyzed.NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region.The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254μmol/(g·h)at pH=9.At the same time,NSCQDs synergy Co-MOF/CN composites have good stability.After four cycles of hydrogen production,the performance remains relatively stable.The tran sient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts.The semiconductor type(n-type semico nductor)of the single-phase catalyst was determined by the Mott-Schottky test,and the band structure was analyzed.The conductive and valence bands of CN are-0.99 and 1.72 eV,respectively,and the conduction and valence bands of Co-MOF are-1.85 and 1.33 eV,respectively.Th e mechanism of the photocatalytic reaction can be inferred,that is,Z-type heterojunction is formed between CN an d Co-MOF,and NSCQDs was used as cocatalyst.

The resistance switching performance of the memristor improved effectively by inserting carbon quantum dots(CQDs)for digital information processing

As an emerging information device that adapts to development of the big data era,memristor has attracted much attention due to its advantage in processing massive data.However,the nucleation and growth of conductive filaments often exhibit randomness and instability,which undoubtedly leads to a wide and discrete range of switching parameters,damaging the electrical performance of device.In this work,a strategy of inserting carbon quantum dots(CQDs)into graphene oxide(GO)resistance layer is utilized to improve the stability of the switching parameters and the reliability of the device is improved.Compared with GO-based devices,GO/CQDs/GO-based devices exhibit a more stable resistance switching curve,low power,lower and more concentrated threshold voltage parameters with lower variation coefficient,faster switching speed,and more stable retention and endurance.The cause-inducing performance improvement may be attributed to the local electric field generated by CQDs in resistance switching that effectively guides the formation and rupture of conductive filaments,which optimizes the effective migration distance of Ag^(+),thereby improving the uniformity of resistance switching.Additionally,a convolutional neural network model is constructed to identify the CIFAR-10 data set,showing the high recognition accuracy of online and offline learning.The cross-kernel structure is used to further implement convolutional image processing through multiplication and accumulation operations.This work provides a solution to improve the performance of memristors,which can contribute to developing digital information processing.

Red-emissive carbon quantum dots minimize phototoxicity for rapid and long-term lipid droplet monitoring

Long-term fluorescence monitoring of subcellular organelles is crucial for cellular physiology and pathology studies.Lipid droplets(LDs)are increasingly recognized for their involvement in various biological processes,to influence disease development through diverse behaviors However,existing LD probes face challenges in achieving high targeting and long-term monitoring due to poor photostability and long-term phototoxicity.Carbon quantum dots(CQDs)have gained prominence due to their exceptional fluorescence properties,but their prevalent blue excitation wavelength presents difficulties for long-term imaging.Herein,we synthesized red-emissive carbon quantum dot(R-CQDs)with superior photobleaching resistance and red-emission,thus enabling harmlessly fluorescence monitoring of cells longer than3 h.In addition,R-CQD exhibits suitable amphiphilicity and remarkable solvatochromic effect,allowing rapid targeting to LDs for immediate imaging without cumbersome washing steps.Hence,R-CQD shows high performance for extended observation of dynamic LD behavior in various biological processes,which is confirmed by documenting the course of LDs during starvation as well as lipotoxicity.Compared to commercial probes,R-CQD extends live cell imaging time by at least 9-fold,facilitating the study of LD behavioral characteristics under diverse physiological or pathological conditions.This work provides a reliable fluorescence tool for tracking intercellular microenvironment dynamically thus to understand the divers biological or disease mechanism.

Photophysical properties of nitrogen-doped carbon quantum dots synthesized by graphite

Here,nitrogen-doped carbon quantum dots(N-CQDs)were successfully synthesized by the solvothermal method using graphite as the carbon source and N,N-dimethylformamide as the nitrogen source.We characterized the structure and chemical constitution of N-CQDs using X-ray diffraction,Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.We investigated the pump-and temperature-dependent photoluminescence(PL)properties and the dynamic exciton recombination processes of N-CQDs,using both steady-state and time-resolved PL techniques.The spectral results show that the PL emission peak located at 518 nm at room temperature,mainly originates from the n-π∗transition on the surface of N-CQDs.The pump fluence and PL integral intensity were analyzed to demonstrate the existence of single-photon excitation under the 405 nm laser excitation.As the temperature increases,the non-radiative transition gradually increases,which decreases the PL intensity,the full width at half maxima first narrows and then widens and the PL lifetime gradually decreases.Furthermore,we combined the N-CQDs with chip to prepare light-emitting diode(LED).The resulting chromaticity coordinate was obtained to be(0.29,0.40).This study offers a comprehensive understanding of the luminescence mechanism in N-doped CQDs and introduces a novel approach for the quickly fabrication of full-color display LEDs.

Preparation of a Novel Green Fluorescent Carbon Quantum Dots and Application in Fe^(3+)-Specific Detection in Biological System

Trace ferric ion(Fe^(3+))detection has attracted increasing attention as an essential and indispensable role in many physiological and pathological research.The green-emitting carbon quantum dots(Green-CQDs)were obtained through a green and facile one-step hydrothermal method for the specific recognition and trace detection of Fe^(3+)in this paper.The optimal excitation and emission wavelengths of the CQDs were 395 nm and 490 nm,respectively.The stokes shift was up to 95 nm,which can effectively reduce the background fluorescence interference.In addition,it also exhibited good water solubility,stability,and high biocompatibility.The fluorescence intensity of Green-CQDs was linearly related to the concentration of Fe^(3+)(range of 0-80μmol/L),and the detection limit was as low as 59 nmol/L.These good properties were favorable and successful for Fe^(3+)detection in tap water,human serum samples and living cells.In addition,a fluorescence visual test paper(FP@CQDs)was prepared utilizing filter paper as carrier,which can quickly identify Fe^(3+)in real time,and is suitable for the visualization analysis of Fe^(3+)in environment.As an efficient nanoprobe,the Green-CQDs held great promise and bright prospects in practical application in prevention and early clinical diagnosis of Fe^(3+)-associated diseases.

Incorporation of Fluorescent Carbon Quantum Dots into Metal-Organic Frameworks with Peroxidase-Mimicking Activity for High-Performance Ratiometric Fluorescent Biosensing

A new ratiometric fluorescent sensor based on the bifunctional carbon quantum dots(CQDs)@metal-organic framework(MOF)nanocomposite possessing peroxidase-mimicking catalytic and luminescent characteristics was developed for hydrogen peroxide(H_(2)O_(2))and cholesterol detection.The incorporation of fluorescent CQDs into the cavities of MIL-101(Fe)MOF with peroxidase-like activities endows the nanocomposite with bifunctional properties.The CQDs@MOF can oxidize o-phenylene-diamine to 2,3-diaminophenolazine by H_(2)O_(2)with yellow fluorescence(556 nm).Meantime,the intrinsic fluorescence signal(455 nm)of CQDs@MOF is inhibited due to the inner filter effect.Therefore,the ratio of the fluorescent intensity is employed as the signal output to construct the H_(2)O_(2)ratiometric biosensor.In addition,the cholesterol can be determined by the ratiometric sensor with high sensitivity.In addition,the total cholesterol in human serum is determined with high accuracy using our ratiometric biosensor.This ratiometric fluorescent platform based on the bifunctional CQDs@MOF provides new insights in the field of bio-sensing.

Ceftriaxone sodium degradation by carbon quantum dots(CQDs)-decorated C-doped a-Bi_(2)O_(3) nanorods

A novel carbon quantum dots decorated C-doped a-Bi_(2)O_(3)photocatalyst(CBO/CQDs)was synthesized by solvothermal method.The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies.The ceftriaxone sodium degradation rate constant(k)of CBO/CQDs was 11.4 and 3.2 times that of pure a-Bi2O3 and C-doped a-Bi_(2)O_(3),respectively.The interstitial carbon doping generated localized states above the valence band,which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes;the loading of CQDs improved the charge carrier separation and extended the visible light response;the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers.The·O2-and ht were identified as the dominant reactive species in ceftriaxone sodium degradation,and the key role of·O2-was further investigated by NBT transformation experiments.The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack,and intermediates analysis was conducted to explore the possible degradation pathways.The toxicity evaluation revealed that some degradation intermediates possessed high toxicity,thus the contaminants require sufficient mineralization to ensure safe discharge.The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of a-Bi2O3,which provides references for future studies.