Modulating charge separation and transfer kinetics in carbon nanodots for photoredox catalysis

Artificial photosynthesis has gained increasing interest as a promising solution to the worldwide energy and environmental issues. A crucial requirement for realizing a sustainable system for artificial photosynthesis is to explore low cost, highly-efficient and stable photoactive materials. Carbon nanodots(CNDs) have attracted considerable attention owing to their low cost, tunable chemistry and unique light-harvesting capability. Previous review articles have highlighted the photocatalytic and photoelectrocatalytic applications of CNDs and CNDs-based composite photocatalysts. However, the control of the separation and transfer processes of photogenerated electron/hole pairs in CNDs has not been reviewed.This review summarizes the recent progress in the design of CNDs as new light-harvesting materials and highlights their applications in photocatalytic hydrogen production, CO2 photoreduction and environmental remediation. Strategies that have been employed to modulate the separation and transfer kinetics of photogenerated charge carriers in CNDs are discussed in detail. The challenges and new directions in this emerging area of research are also proposed.

Super-strong and Intrinsically Fluorescent Silkworm Silk from Carbon Nanodots Feeding

Fluorescent silk is fundamentally important for the development of future tissue engineering scaffolds.Despite great progress in the preparation of a variety of colored silks,fluorescent silk with enhanced mechanical properties has yet to be explored.In this study,we report on the fabrication of intrinsically super-strong fluorescent silk by feeding Bombyx mori silkworm carbon nanodots(CNDs).The CNDs were incorporated into silk fibroin,hindering the conformation transformation,confining crystallization,and inducing orientation of mesophase.The resultant silk exhibited super-strong mechanical properties with breaking strength of 521.9±82.7 MPa and breaking elongation of 19.2±4.3%,improvements of 55.1%and 53.6%,respectively,in comparison with regular silk.The CNDs-reinforced silk displayed intrinsic blue fluorescence when exposed to 405 nm laser and exhibited no cytotoxic effect on cells,suggesting that multi-functional silks would be potentially useful in bioimaging and other applications.

A Glucose-Responsive Enzymatic Electrode on Carbon Nanodots for Glucose Biosensor and Glucose/Air Biofuel Cell

In this study, an enzymatic electrode for glucose biosensing and bioanode of glucose/air biofuel cell has been fabricated by immobilizing poly (methylene green) (polyMG) for electrocatalytic NADH oxidation and NAD+-dependent glucose dehydrogenase (GDH) for oxidizing glucose on carbon nanodots (CNDs). The polyMG-CNDscomposites obtained by electro-polymerization of dye MG molecules adsorbed on CNDs display excellent electrocatalytic activity toward NADH electro-oxidation at a low overpotential of ca. -0.10 V (vs. Ag/AgCl) and the integrated enzymatic electrode shows fast response to glucose electrooxidation. Using the fabricated GDH-based enzymatic electrode, a glucose biosensor was constructed and exhibits a wide linear dynamic range from 0 to 8 mM, a low detection limit of 0.02 μM (S/N = 3), and fast response time (ca. 4 s) under the optimized conditions. The developed glucose biosensor was used to detect glucose content in human blood with satisfactory results. The fabricated GDH-based enzymatic electrode was also employed as bioanode to assembly a glucose/air biofuel cell with the laccase-CNDs/GC as the biocathode. The maximum power density delivered by the assembled glucose/air biofuel cell reaches 3.1 μW·cm-2 at a cell voltage of 0.22 V in real sample fruit juice. The present study demonstrates that potential applications of GDH-based CNDs electrode in analytical and biomedical measurements.

Rational design multi-color-emissive chemiluminescent carbon nanodots in a single solvothermal reaction

Recently,the chemiluminescence(CL)induced by carbon nanodots(CDs)has intrigued researchers’extensive interests in various applications due to its special light emission principle.However,the difficulty of synthesizing chemiluminescent CDs with full-spectrum emission severely hinders the further regulation of the CL emission mechanism.Herein,the multi-color-emissive chemiluminescent CDs are rational designed and further synthesized by regulating the sp2-hybrid core and sp3-hybrid surface from the citrate-ammonia molecular in a single solvothermal reaction.More experimental characterizations and density functional theory calculations reveal that the higher temperature can promote the crosslinking polymerization/carbonization of carbon core and the higher protonation of solvent can determine the core size of final CDs,resulting in the variant CL emission from molecular-,crosslinking-and core-states.Thus,the CL emission of the CDs can be further synthesized by tuning the luminescence chromophores in the formation process via regulating the temperature and solvent,enabling the applications of the CL CDs in illumination and information encryption.This study paves a new technology to understand the luminescence of CDs and affords an industry translational potential over traditional chemiluminescent molecular.

Supra-(carbon nanodots) with a strong visible to near-infrared absorption band and efficient photothermal conversion

A novel concept and approach to engineering carbon nanodots(CNDs)were explored to overcome the limited light absorption of CNDs in low-energy spectral regions.In this work,we constructed a novel type of supra-CND by the assembly of surface charge-confined CNDs through possible electrostatic interactions and hydrogen bonding.The resulting supra-CNDs are the first to feature a strong,well-defined absorption band in the visible to near-infrared(NIR)range and to exhibit effective NIR photothermal conversion performance with high photothermal conversion efficiency in excess of 50%.

Near-infrared carbon nanodots for effective identification and inactivation of Gram-positive bacteria

An unacceptable increase in antibacterial resistance has arisen due to the abuse of multiple classes of broad-spectrum antibiotics.Therefore,it is significant to develop new antibacterial agents,especially those that can accurately identify and kill specific bacteria.Herein,we demonstrate a kind of perilla-derived carbon nanodots(CNDs),integrating intrinsic advantages of luminescence and photodynamic,providing the opportunity to accurately identify and kill specific bacteria.The CNDs have an exotic-doped andπ-conjugated core,vitalizing them near-infrared(NIR)absorption and emission properties with photoluminescence quantum yield of 21.1%;hydrophobic chains onto the surface of the CNDs make them to selectively stain Gram-positive bacteria by insertion into their membranes.Due to the strong absorption in NIR region,reactive oxygen species are in situ generated by the CNDs onto bacterial membranes under 660 nm irradiation,and 99.99%inactivation efficiency against Gram-positive bacteria within 5 min can be achieved.In vivo results demonstrate that the CNDs with photodynamic antibacterial property can eliminate the inflammation of the area affected by methicillin-resistant Staphylococcus aureus(MRSA),and enabling the wound to be cured quickly.

Unravelling charge carrier dynamics in protonated g-C3N4 interfaced with carbon nanodots as co-catalysts toward enhanced photocatalytic CO2 reduction： A combined experimental and first-principles DFT study

In this work, we demonstrated the successful construction of metal-free zero- dimensional/two-dimensional carbon nanodot （CND）-hybridized protonatedg=C3N4 （pCN） （CND/pCN） heterojunction photocatalysts b; means of electrostatic attraction. We experimentally found that CNDs with an average diameter of 4.4 nm were uniformly distributed on the surface of pCN using electron microscopy analysis. The CND/pCN-3 sample with a CND content of 3 wt.% showed thehighest catalytic activity in the CO2 photoreduction process under visible and simulated solar light. This process results in the evolution of CH4 and CO. Thetotal amounts of CH4 and CO generated by the CND/pCN-3 photocatalyst after 10 h of visible-light activity were found to be 29.23 and 58.82 molgcatalyst-1, respectively. These values were 3.6 and 2.28 times higher, respectively, than thearn＊ounts generated when using pCN alone. The corresponding apparent quantum efficiency （AQE） was calculated to be 0.076%. Furthermore, the CND/pCN-3 sample demonstrated high stability and durability after four consecutive photoreaction cycles, with no significant decrease in the catalytic activity.

Recent Advances in Carbon Nanodots:Properties and Applications in Cancer Diagnosis and Treatment

Cancer is a serious threat to human health.Survival rates of cancer patients are highly dependent on the early diagnosis and treatment.Carbon nanodots(CDs),a rising star of carbon nanomaterial family,can be developed as a promising terrace for cell labeling,bioimaging,drug delivery,diagnosis,and therapy by virtue of many superior properties including unique photo-luminescence properties,low toxicity,excellent biocompatibility,and easy functionalization.In this mini review,we present the recent progress in fundamental properties of CDs,and highlight their bioapplications in cancer diagnosis and treatment.

Carbon nanodots:A metal-free,easy-to-synthesize,and benign emitter for light-emitting electrochemical cells

Light-emitting electrochemical cells(LECs)can be fabricated with cost-efficient printing and coating methods,but a current drawback is that the LEC emitter is commonly either a rare-metal complex or an expensive-to-synthesize conjugated polymer.Here,we address this issue through the pioneering employment of metal-free and facile-to-synthesize carbon nanodots(CNDs)as the emitter in functional LEC devices.Circular-shaped(average diameter=4.4 nm)and hydrophilic CNDs,which exhibit narrow cyan photoluminescence(peak=485 nm,full width at half maximum=30 nm)with a high quantum yield of 77%in dilute ethanol solution,were synthesized with a catalyst-free,one-step solvothermal process using low-cost and benign phloroglucinol as the sole starting material.The propensity of the planar CNDs to form emission-quenching aggregates in the solid state was inhibited by the inclusion of a compatible 2,7-bis(diphenylphosphoryl)-9,9’-spirobifluorene host compound,and we demonstrate that such pristine host-guest CND-LECs turn on to a peak luminance of 118 cd·m^(−2)within 5 s during constant current-density driving at 77 mA·cm^(−2).

Microwave-assisted synthesis of colorimetric and fluorometric dual-functional hybrid carbon nanodots for Fe^(3+) detection and bioimaging

Carbon nanodots(CDs) based fluorescent nanoprobes have recently drawn much attention in chemo-/bio-sensing and bioimaging.However,it is still challenging to integrate the colorimetric and fluorometric dual readouts into a single CD.Herein,novel hybrid CDs(HCDs) are prepared by a simple microwave-assisted reaction of citric acid(CA),branched polyethyleneimine(BPEI) and potassium thiocyanate(KSCN).As-prepared HCDs show extraordinary properties,including excitation-dependent emission,satisfactory fluorescence quantum yield(46.8%),excellent biocompatibility and optical stability.Significantly,the fluorescence intensity at 450 nm exhibits linear correlation over the Fe^(3+)concentration from 1 mmol/L to 150 mmol/L with a detection limit(LOD) of 52 nmol/L.Meanwhile,the solution color changes from colorless to orange,and the absorbance at 460 nm increased linearly with Fe^(3+)concentration ranging from 0.02 mmol/L to 5 mmol/L(LOD:3.4 mmol/L).All the evidence illustrates that the HCDs can be conditioned for specific Fe^(3+)sensing with colorimetric and fluorometric dual readouts,which has also been verified with paper-based microchips.The possible mechanism is attributed to the specific interactions between surface functional groups on the HCDs and Fe^(3+).Additionally,the HCDs are successfully applied in sensing Fe^(3+)in wastewater and living cells,demonstrating its potential applications in future environment monitoring and disease diagnosis.

Self-exothermic reaction driven large-scale synthesis ofphosphorescent carbon nanodots

Phosphorescent carbon nanodots(CNDs)have various attractive properties and potential applications,but it remains a formidable challenge to achieve large-scale phosphorescent CNDs limited by current methods.Herein,a large-scale synthesis method for phosphorescent CNDs has been demonstrated via precursors’self-exothermic reaction at room temperature.The as-prepared CNDs show fluorescence and phosphorescence property,which are comparable with that synthesized by solvothermal and microwave method.Experimental and computational studies indicate that exotic atom doped sp^(2) hybridized carbon core works as an emissive center,which facilities the intersystem crossing from singlet state to triplet state.The CNDs show phosphorescence with tunable lifetimes from 193 ms to 1.13 s at different temperatures.The demonstration of large-scale synthesis of phosphorescent CNDs at room temperature opens up a new window for room temperature fabrication phosphorescent CNDs.

Unprecedented Two‑Step Chemiluminescence of Polyamine‑Functionalized Carbon Nanodots Induced by Fenton‑Like System

We reported an unprecedented chemiluminescence(CL)behavior of polyamine-functionalized carbon dots induced by Fe^(3+)–H_(2)O_(2) Fenton-like system.The firststep CL intensity increased with the increasing of the concentration of H_(2)O_(2) and Fe^(3+),when the Fe^(3+)concentration came to 10^(−3) M,the unprecedented two-step CL behavior appeared.The CL intensity of BPEI-CDs induced by Fenton-like system was about 10 times stronger than that of naked CDs.The possible two-step CL mechanism was speculated based on the photoluminescence spectra,CL emission spectra,and the effects of radical scavengers on the CL intensity.Radiative recombination of the injected holes by strong oxidant perferrate formed through Fe^(3+)–H_(2)O_(2) reaction and the;OH generated from successive Fenton reaction with the thermally excited electrons was proposed,which further facilitate full understanding about the optical properties of carbon dots.

Multicolor biomass based carbon nanodots for bacterial imaging

Biomass-based carbon nanodots(CNDs) are becoming promising fluorescent materials due to their superior optical properties and excellent biocompatibility. However, most fluorescent CNDs are prepared under high temperatures with artificial chemicals as precursors. In this work, multicolor biomass-based CNDs have been prepared by employing natural biomass as precursors through an ultrasonic-assisted method at room temperature. The multicolor biomass-based CNDs can be prepared within 10 min, and cavitation produced by ultrasound in solution contributes to the polymerization of biomolecules into nanodots. The emission of the CNDs covers from blue to red region, with emission peaks centered at 410 nm, 520 nm and 670 nm, and the corresponding photoluminescence quantum yields of the CNDs are 11%, 12% and28%, respectively. Furthermore, bacterial imaging by using the biomass-based CNDs as fluorescent imaging agent has been demonstrated. This work provides a convenient ultrasonic-assisted way for fabrication multicolor and eco-friendly biomass CNDs, demonstrating their application in bacterial imaging.

Carbon nanodots enhanced performance of Cs_(0.15)FA_(0.85)PbI_(3) perovskite solar cells

A high-quality hybrid Cs_(0.15)FA_(0.85)PbI_(3) thin film is deposited through doping of carbon nanodots(CNDs)into perovskite precursor solution.The corresponding inverted planar perovskite solar cells(PSCs)of ITO/PTAA/Cs_(0.15)FA_(0.85)PbI_(3)/PC_(61)BM/BCP/Ag exhibit an improvement in efficiency from 17.36%to 20.06%,which could be attributed to the passivation of the defects at the crystallized perovskite thin film and enhanced perovskite phase uniformity.The results of electron trap density indicate that the addition of CNDs significantly reduces the defects density at the perovskite thin film and the recombination of charge carriers in transport process is minimized.These results demonstrate that low-cost CNDs are effective additives for passivating defects,further reducing charge carrier recombination and improving device efficiency.

Carbon nanodots:a new precursor to achieve reactive nanoporous HOPG surfaces

In the present work we develop an electrochemical assisted method to form nanopores on the surface of highly oriented pyrolytic graphite(HOPG),which was accomplished by a simple electrochemical route and a scalable nanomaterial,carbon nanodots,without applying high voltages,high temperatures or toxic reagents.HOPG electrodes are in a solution of N-enrich carbon nanodots in acidic media and the potential scans applied on HOPG lead to the formation of a spatially inhomogeneous porous surface.The diameter of the resulting nanopores can be tuned by controlling the number of electrochemical reduction cycles.The resulting nanoporous surfaces are characterized by atomic force microscopy,Raman spectroscopy,scanning electrochemical microscopy,electrochemical impedance spectroscopy and electrochemistry.These nanoporous HOPG showed high capacitance.Hence the potential of these surfaces to the development of energy storage devices is demonstrated.

Improved comprehensive performance of CsPbI_(2) Br perovskite solar cells by modifying the photoactive layers with carbon nanodots

Introducing additives into perovskite layers is an effective method to enhance the power conversion efficiency(PCE)and operation stability of perovskite solar cells(PSCs).Herein,we reported an addition of carbon nanodots(CNDs)into the CsPbI_(2) Br photoactive layer to boost performance of the related PSCs.It is found that the trap density can be notably suppressed,and the crystallinity can be enhanced after introducing CNDs with an optimal quantity.The PSC with 1.0 wt%addition of CNDs delivers a notable improved average PCE of 13.77%(the highest PCE:14.69%)from that of 12.14%for the control device without CND addition.Moreover,the CND-added CsPbI 2 Br PSCs exhibit superior stability,i.e.,~86% retention of the initial PCE after 160 h aging in air with the humidity of 20%-30%,to the control device.

Selective toxicity of hydroxyl-rich carbon nanodots for cancer research

The toxicity of nanoparticles in a biological system is an integration of effects arising from surface functionali~ particle size, ionic dissolution, etc. This complexity suggests that generalization of a material＇s toxicity may be inappropriate. Moreover, from a medicinal point of view, toxicity can be used for treatment of malignant cells, such as cancer. In this stud~ highly biocompatible carbon nanodots （gCDs） were synthesized by reacting citric acid and urea in glycerol, which resulted in abundant hydroxyl functional groups on the particle surface. gCDs show excitation-dependent photoluminescence but with bright green to yellow emission. Importantly, a series of toxicity assessments showed that as-synthesized gCDs possessed exceptional biocompatibilities to various biological entities including 18 bacteria species, Petunia axillaris seedlings, and Artemia franciscana nauplii. Furthermore, the particles were shown to have low to no toxic effects on human embryonic kidney （HEK-293）, breast （MCF-7）, and oral squamous （CAL-27） carcinoma cell lines. Of particular interest, the gCDs displayed antiproliferative activities against ovarian choriocarcinoma cells （JAr/Jeg-3 cell lines）, which may be further explored for cancer drug discovery.

Synthesis of Carbon dots from Biomass Chenpi for the Detection of Hg^(2+)

Biomass-derived carbon dots(C-dots)are considered a very important carbon material in metal ion detection of their small environmental impact,simple preparation process,and relatively low cost.A green approach for synthesizing biomass-derived C-dots from Chenpi using a hydrothermal method without further processing is proposed in the present study.The as-synthesized C-dots show excellent fluorescence properties,superior resistance to UV irradiation photobleaching,and high photostability in salt-containing solutions.The C-dots were used in the form of label-free fluorescent probes for sensitively detecting Hg^(2+)selectively.The outcome relationship behaved linearly and was established based on a given range between 10–300 nM concentration,with a detection limit of 7.0 nM.This green strategy obtains a high C-dot quantum yield of 10.8%and satisfactory results in detecting Hg^(2+)in actual water samples.

The photoluminescence mechanism in carbon dots （graphene quantum dots, carbon nanodots, and polymer dots）： Current state and future perspective

目前，光致发光(PL ) 的实际机制荧光灯碳点(CD ) 仍然是在研究人员之中的开的争论。因为 CD 的变化，为这些种碳材料总结 PL 机制是高度重要的；那么做能指导有效合成线路和新奇应用程序的开发。这评论将集中于 CD 的 PL 机制。三种类型荧光灯 CD 被包含：graphene 量点(GQD ) ，碳 nanodots (CND ) ，和聚合物点(PD ) 。四合理 PL 机制被证实了：被碳核心决定的量监禁效果或结合的 -domains, ；表面状态，它由碳脊梁和连接的化学的组的杂交坚定；分子状态，它完全坚定由荧光灯分子在 CD 的表面或内部上连接了；并且提高交叉连接的排放(C ) 效果。为 CD 给一篇彻底的摘要，范畴和合成线路，以及化学 / 物理的性质，简短预先被介绍。

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(NCDs)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(Fe^(3+))through a fluorescence static quenching process in a wide linear range of 0.005–60 mmol/L.The detection limit was as low as 1.43 nmol/L,allowing the analysis of Fe^(3+)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 Fe^(3+)sensing further verified this novel N-CDs may open more opportunities in biosensor,bioimaging and biological assay.