Dynamic Room Temperature Phosphorescence of Silane-Functionalized Carbon Dots Confining within Silica for Anti-Counterfeiting Applications.

Room temperature phosphorescent (RTP) materials with long-lived, excitation-dependent, and time-dependent phosphorescence are highly desirable but very hard to achieve. Herein, this work reports a rational strategy of multiple wavelength excitation and time-dependent dynamic RTP color by confining silane-functionalized carbon dots (CDs) in a silica matrix (Si-CDs@SiO2). The Si-CDs@SiO2 possesses unique green-light-excitation and a change in phosphorescence color from yellow to green. A slow-decaying phosphorescence at 500 nm with a lifetime of 1.28 s and a fast-decaying phosphorescence at 580 nm with a lifetime of 0.90 s are observed under 365 nm of irradiation, which originated from multiple surface triplet states of the Si-CDs@SiO2. Given the unique dynamic RTP properties, the Si-CDs@SiO2 are demonstrated for applications in fingerprint recognition and multidimensional dynamic information encryption. These findings will open an avenue to explore dynamic phosphorescent materials and significantly broaden their applications.

Simultaneous High Ionic Conductivity and Lithium-Ion Transference Number in Single-Ion Conductor Network Polymer Enabling Fast-Charging Solid-State Lithium Battery.

Developing solid-state electrolyte with sufficient ionic conduction and flexible-intimate interface is vital to advance fast-charging solid-state lithium batteries. Solid polymer electrolyte yields the promise of interfacial compatibility, yet its critical bottleneck is how to simultaneously achieve high ionic conductivity and lithium-ion transference number. Herein, single-ion conducting network polymer electrolyte (SICNP) enabling fast charging is proposed to positively realize fast lithium-ion locomotion with both high ionic conductivity of 1.1 × 10-3 S cm-1 and lithium-ion transference number of 0.92 at room temperature. Experimental characterization and theoretical simulations demonstrate that the construction of polymer network structure for single-ion conductor not only facilitates fast hopping of lithium ions for boosting ionic kinetics, but also enables a high dissociation level of the negative charge for lithium-ion transference number close to unity. As a result, the solid-state lithium batteries constructed by coupling SICNP with lithium anodes and various cathodes (e.g., LiFePO4 , sulfur, and LiCoO2 ) display impressive high-rate cycling performance (e.g., 95% capacity retention at 5 C for 1000 cycles in LiFePO4 |SICNP|lithium cell) and fast-charging capability (e.g., being charged within 6 min and discharged over than 180 min in LiCoO2 |SICNP|lithium cell). Our study provides a prospective direction for solid-state electrolyte that meets the lithium-ion dynamics for practical fast-charging solid-state lithium batteries.

Preparation of nitrogen-doped carbon dots and their enhancement on lettuce yield and quality.

Nanotechnology is an effective way to stimulate the yield potential of crops. Various nano-fertilizers and nano-carriers are gradually being developed to bring about a technological revolution in the agricultural industry. As a biocompatible water-soluble nanomaterial, carbon dots (CDs) have attracted the attention of researchers for applications in agriculture. In this study, we prepared nitrogen-doped CDs (N-CDs) as a type of water-soluble carbon nanofertilizer by a one-pot hydrothermal method, and investigated its effects on lettuce biomass and quality. 100 and 200 mg L-1 of N-CDs substantially promoted lettuce biomass accumulation (41.70%), elevated lettuce nutrient content, as well as promoted the accumulation of major nutrients. Moreover, 100 mg L-1 N-CDs increased the chlorophyll a content by 12.68%, significantly increased the electron transport rate (ETR) by 38.61%, significantly increased the light energy conversion efficiency (Y(II)) by 31.24% and increased the Rubisco activity by 60.61%, which are important reasons for its increase in actual photosynthesis rate. N-CDs also have a positive effect on plant nitrogen metabolism by promoting the activity of glutamine synthetase. The significant benefits of N-CDs on lettuce make them have great potential for agricultural yield increase and quality improvement.

Inhibition of UV-B stress in lettuce through enzyme-like Scutellaria baicalensis carbon dots.

Oxidative stress in plants caused by UV-B stress has always been a great challenge to the yield of agricultural products. Carbon dots (CDs) with enzyme-like activity have been developed, and inhibiting oxidative stress in animals has been achieved, but little is known about abiotic stress resistance in plants, especially UV-B stress. In this study, CDs were synthesized from Scutellaria baicalensis via a hydrothermal method. The ability of CDs to scavenge reactive oxygen species (ROS) in vivo and in vitro and to enhance antioxidant resistance in vivo was evaluated. The results show that CDs promoted the nutrient assimilation ability of lettuce seedlings and protected the plants from UV-B stress by increasing the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX). Moreover, the antioxidant metabolism of plants can be activated by CDs and the expression levels of aquaporin (AQP) genes PIP1 and PIP2 are also up-regulated. These results facilitate the design and fabrication of CDs to meet the challenge of abiotic stress in food production.

Glycine assists in efficient synthesis of herbal carbon dots with enhanced yield and performance.

As a special type of biomass, herbal medicine often contains a variety of biologically active substances, and taking it as a carbon source, it is expected to produce various types of biologically functional carbon dots (CDs). However, there are few reports in this field, especially in achieving enhanced performance of CDs by improving the utilization efficiency of active substances in medicinal materials. In this work, by adding glycine as an auxiliary agent in the preparation of CDs from herbal medicine (Exocarpium Citri Grandis), the carboxyl and amino groups of the adjuvant provided more reactive sites, which greatly improved the yield of CDs (about 6 times). More importantly, the antioxidant and biological activities of herbal CDs were also improved. By controlling the functional groups of adjuvants, the effects of carboxyl and amino groups in adjuvants on the synthesis of herbal CDs were compared. The results reveal that both carboxyl and amino groups can react with the substances in the carbon source, and the influence of amino groups was greater. After adding glycine, the size of the CDs became larger, resulting from the more abundant functional groups on the carbon skeleton, which was the main reason for the improved performance of the CDs. Finally, the biological activity experiment demonstrated that CDs derived from Exocarpium Citri Grandis and glycine could greatly enhance the vitality of cells and activate immune cells, which are expected to be applied in the field of cell reproduction and biological immunity. The method proposed in this work provides a potential strategy for high-yield preparation of CDs from biomass.

Immunoregulatory Activity of Herbal Tea-Derived Carbon Dots.

The activation of immune cells by immunoregulatory active substances can improve the body immunity. Carbon dots (CDs) with immunoregulatory activity are rarely reported. In this study, transmission electron microscopy results demonstrate the existence of CDs in herbal tea, while Fourier transform infrared and X-ray photoelectron spectroscopy results suggest the participation of polyphenol in herbal tea CD (H-CD) formation. The photoluminescence spectrum has shown that H-CDs have fluorescence emission at 565 nm and exhibit an excitation-dependent property. The toxicity and immunostimulatory activity of H-CDs on mouse macrophage RAW264.7 suggested that H-CDs had no toxicity to RAW264.7 cells. Meanwhile, compared with herbal tea, H-CDs have more obvious effect of promoting the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase. In addition, the secretion of nitric oxide (NO) was promoted by H-CDs. This work suggests that H-CDs have stronger immunoregulatory function than that of original herbal tea, which provides a direction for the application of phenolic hydroxyl-modified CDs in the biomedical field.

Salvia miltiorrhiza Derived Carbon Dots and Their Heat Stress Tolerance of Italian Lettuce by Promoting Growth and Enhancing Antioxidant Enzyme Activity.

With global warming, plants often suffer damage from high temperatures during the growth process, which inhibits their growth. In this work, carbon dots (CDs), synthesized by Salvia miltiorrhiza (S. miltiorrhiza) with a one-step hydrothermal method, were selected as heat-resistant enhancement agents for plants. Inspired by this background, this work studied Italian lettuce grown at 25, 35, and 45 °C and treated with CD and deionized water control (sprayed on leaves). The results showed that the biomass, chlorophyll content, net photosynthetic rate, activities of SOD (superoxide dismutase), POD (peroxidase), CAT (catalase), soluble sugar, and soluble protein contents of lettuce treated by CDs were increased while the contents of malondialdehyde (MDA) and proline (Pro) were decreased at 35 and 45 °C. The application of CDs at 35 and 45 °C could maintain the growth of plants by reducing oxidative damage and lipid peroxidation especially at the temperature of 35 °C, the growth status of lettuce treated by CDs was no different from that of lettuce grown naturally at the optimal temperature of 25 °C, or even better than the latter. This finding verified that the CDs could significantly improve the high-temperature tolerance of lettuce, thus alleviating the heat stress of plants.

Construction of Carbon Dots with Color-Tunable Aggregation-Induced Emission by Nitrogen-Induced Intramolecular Charge Transfer.

As one of the most promising fluorescent nanomaterials, the fluorescence of carbon dots (CDs) in solution is extensively studied. Nevertheless, the synthesis of multicolor solid-state fluorescence (SSF) CDs is rarely reported. Herein, CDs with multicolor aggregation-induced emission are prepared using amine molecules, all of them exhibiting dual fluorescence emission at 480 nm (Em-1) and 580-620 nm (Em-2), which is related to the SS bonds of dithiosalicylic acid and the conjugated structure attached to CO/CN bonds, respectively. As a strong electron-withdrawing group, the increase of CN content makes dual-fluorescent groups on the surface of CDs produce push and pull electrons, which determines intramolecular charge transfer (ICT) between the double emission. With the increase in CN content from 35.6% to 58.4%, the ICT efficiency increases from 8.71% to 45.94%, changing the fluorescence of CDs from green to red. The increase of ICT efficiency causes fluorescence quantum yield enhancement by nearly five times and redshift of the fluorescence peak. Finally, based on the multicolor luminescence properties induced by the aggregation of CDs, pattern encryption and white-LED devices are realized. Based on the fat solubility and strong ultraviolet absorption characteristics of CDs, fingerprint detection and leaf anti-UV hazards are applied.

A mild method to prepare nitrogen-rich interlaced porous carbon nanosheets for high-performance supercapacitors.

In this work, a non-toxic and mild strategy was presented to efficiently fabricate porous and nitrogen-doped carbon nanosheets. Silkworm cocoon (SCs) acted as carbon source and original nitrogen source. Sodium carbonate (Na2CO3) could facilitate the SCs to expose silk protein and played a catalytic role in the subsequent activation of calcium chloride (CaCl2). Calcium chloride served as pore-making agent. The as-obtained carbon materials with protuberant porous nanosheets exhibit high specific surface area of 731 m2 g-1, rich native nitrogen-doped of 7.91 atomic %, wide pore size distribution from 0.5 to 65 nm, and thus possessing high areal specific capacitances of 34 µF cm-2 as well as excellent retention rate of 97% after 20 000 cycles at a current density of 20 A g-1 in 6 M KOH electrolyte. The assembled carbon nanosheet-based supercapacitor displays a maximum energy density of 21.06 Wh kg-1 at the power density of 225 W kg-1 in 1 M Na2SO4 electrolyte. Experimental results show that a mild and non-toxic treatment of biomass can be an effective and extensible method for preparing optimal porous carbon for electrochemical energy storage.

Homogeneous triple-phase interfaces enabling one-pot route to metal compound/carbon composites.

Metal compounds (e.g., metal phosphides/sulfides/selenides) coupled with carbon materials have recently drawn great attraction for boosting the electrochemical performances because of their appealing synergistic effect and valuable structural stability. Despite many examples for their synthesis exist, there is still a need for a simplistic and comprehensive approach to such metal compound/carbon (MC/C) composites. Herein, an effective, facile, yet versatile strategy to produce various types of MC/C composites is presented. Key to this strategy is construction of a homogeneous triple-phase interface, which is realized by utilization of a hybrid assembly integrated with carbon, metal and sulfide (or selenide, phosphide) precursors through coupling metal cations with anion groups of a functional polymer. Such an intimately binding carbon-metal-sulfide (or selenide, phosphide) interface structure enables the successful in situ generation of MC nanoparticles uniformly encapsulated into the carbon matrix just after a one-step carbonization treatment. The present synthetic strategy provides remarkable adjustability, predictability and generality to facilely fabricate a series of MC/C composites, offering sufficient freedom to explore their unique energy storage/conversation properties. As a proof of concept, the as-prepared SnS/C composite exhibits superior lithium ion and potassium ion storage capabilities when used as anode materials for alkali-metal ion batteries. The present work provides impressive insights into the design principles for MC/C composites that are the potential materials in targeted application fields, and opens up an efficacious avenue for their facile synthesis as well.

Boosting zinc ion energy storage capability of inert MnO cathode by defect engineering.

Aqueous zinc ion battery constitutes a safe, stable and promising next-generation energy storage device, but suffers the lack of suitable host compounds for zinc ion storage. Development of a facile way to emerging cathode materials is strongly requested toward superior electrochemical activities and practical applications. Herein, defect engineering, i.e., simultaneous introduction of nitrogen dopant and oxygen vacancy into commercial and low-cost MnO, is proposed as a positive strategy to activate the originally inert phase for kinetically propelling its zinc ion storage capability. Both experimental characterization and theoretical calculations demonstrate that the nitrogen dopant significantly improves the electric conductivity of electrochemical inert MnO. Simultaneously, the oxygen vacancy creates sufficient large inserted channels and available activated adsorption sites for zinc ions storage. These synergistic structural advantages obviously ameliorate the electrochemical performance of inert MnO. Therefore, even without any conductive agent additive, the as-prepared material shows high specific capacity, superb rate capability, prolonged cycling stability and attractive energy density, which are dramatically superior to those of the pristine MnO as well as many other host cathode materials. This work presents fresh insights on the role of defect engineering in the enhancement of the intrinsic electrochemical reactivity of inert cathode, and an effective strategy for scalable fabrication of high-performance cathode for zinc ion battery.

Surface chemical functionality of carbon dots: influence on the structure and energy storage performance of the layered double hydroxide.

As a kind of zero-dimensional material, carbon dots (CDs) have become a kind of promising novel material due to their incomparable unique physical and chemical properties. Despite the optical properties of CDs being widely studied, their surface chemical functions are rarely reported. Here we propose an interesting insight into the important role of surface chemical properties of CDs in adjusting the structure of the layered double hydroxide (LDH) and its energy storage performance. It was demonstrated that CDs with positive charge (p-CDs) not only reduce the size of the flower-like LDH through affecting the growth of LDH sheets, but also act as a structure stabilizer. After calcination, the layered double oxide (LDO) maintained the morphology of the LDH and prevented the stacking of layers. And the superiority of the composite in lithium-ion batteries (LIBs) was demonstrated. When used as an anode of LIBs, composites possess outstanding specific capacity, cycle stability and rate performance. It presents the discharge capacity of 1182 mA h g-1 and capacity retention of 94% at the current density of 100 mA g-1 after 100 cycles. Our work demonstrates the important chemical functions of CDs and expands their future applications.

Nitrogen and Sulfur Co-doped Carbon Dots Enhance Drought Resistance in Tomato and Mung Beans.

Drought stress is widespread worldwide, which severely restricts world food production. The antioxidant property of carbon dots (CDs) is promising for inflammation and disease treatment. However, little is known about the functions of CDs in the abiotic stress of plants, especially in drought-resistant fields. In this study, CDs were synthesized using cysteine and glucose by the hydrothermal method. The in vitro antioxidant capacity of CDs and the reactive oxygen species (ROS) scavenging capacity were evaluated. We speculate on the antioxidant mechanism of CDs by comparing size distribution, fluorescence spectra, elements, and surface functional groups of CDs before and after oxidation. Besides, we evaluated the effects of CDs on seed germination and seedling physiology under drought stress. Also, the responses of antioxidant CDs to long-term drought stress and subsequent recovery metabolism in tomato plants were evaluated. The results show that CDs accelerated the germination rate and the germination drought resistance index by promoting the water absorption of seeds. CDs enhanced the drought resistance of seedlings by improving the activity of peroxidase (POD) and superoxide dismutase (SOD). Moreover, CDs can activate the antioxidant metabolism activity and upregulate the expression of aquaporin (AQP) genes SlPIP2;7, SlPIP2;12, and SlPIP1;7. All of these results render tomato plants distinguished resilience once rewatering after drought stress. These results facilitate us to design and fabricate CDs to meet the challenge of abiotic stress in food production.

Calcium-chloride-assisted approach towards green and sustainable synthesis of hierarchical porous carbon microspheres for high-performance supercapacitive energy storage.

Spherical carbon materials exhibit great competence as electrode materials for electrochemical energy storage, owing to the high packing density, low surface to volume ratio, and excellent structure stability. How to utilize renewable biomass precursor by green and efficient strategy to fabricate porous carbon microspheres remains a great challenge. Herein, we report a KOH-free and sustainable strategy to fabricate porous carbon microspheres derived from cassava starch with high specific surface area, high yield, and hierarchical structure, in which potassium oxalate monohydrate (K2C2O4·H2O) and calcium chloride (CaCl2) are employed as novel activator. The green CaCl2 activator is crucial to regulate the graphitization degree, specific surface area, and porosity of the carbon microspheres for improving the electrochemical performance. The as-prepared carbon microspheres exhibit high specific surface area (1668 m2 g-1), wide pore size distribution (0.5-60 nm), high carbon content (95%), and exfoliated surface layer. The hierarchical porous carbon microspheres show high specific and areal capacitance (17.1 µF cm-2), superior rate performance, and impressive cycling stability. Moreover, the carbon microspheres based symmetric supercapacitor exhibits high capacitance and excellent cycling performance (100% after 20 000 cycles at a current density of 5 A g-1). This green and novel approach holds great promise to realize low-cost, high-efficient and scalable of renewable cassava starch-derived carbon materials for advanced supercapacitive energy storage applications.

Facile construction of uniform ultramicropores in porous carbon for advanced sodium-ion battery.

Facile fabrication of anode materials with low cost, good rate capability and high capacity is a critical factor towards developing sodium-ion battery for practical applications. Herein, a N, O co-doped porous carbon with uniform ultramicropores (NOPC-UM), is synthesized by an in-situ ultramicro templating strategy, and demonstrated as a high-performance sodium-ion storage material. Key to this strategy is employment of an inherent KCl as untramicro template, which leads to formation of uniform size of ultramicropores and heteroatoms (i.e., N and O) doping after high-temperature pyrolysis. The as-constructed NOPC-UM delivers a large capacity of 305 mAh g-1, accompanying with a 93% specific capacity below 1.00 V, and superior cycling stability about 100% after 4000 cycles. These attractive electrochemical performances endow NOPC-UM with impressive potential use as anode materials of sodium-ion battery.

The changing structure by component: Biomass-based porous carbon for high-performance supercapacitors.

In this work, a simple and efficient method is introduced to prepare biomass-based porous carbon with excellent performance by changing the content of component (e.g., cellulose, hemicellulose, lignin, and extractives) of the raw materials. When the content of the components change, the corresponding carbon skeleton will be separated, resulting in a structure that is conducive to activation conditions. Using bagasse with fiber tubular structure as carbon precursor, the synthetic hierarchical porous carbon (BHPC-4) possesses a high specific surface area (SSA) of 3135 m2 g-1 more than the control sample (2484 m2 g-1). Benefitting from the improvement of the structure, the BHPC-4 electrode exhibits an appealing capacitance of 410.5F g-1 at 0.5 A g-1 and long-term cycling stability of 100% capacitance retention after 10,000 cycles in the 6.0 M KOH system. Furthermore, a delightful energy density of 25.6 Wh kg-1 at a 226 W kg-1 can be achieved in 1.8 V Na2SO4 aqueous symmetrical supercapacitors. This method has universal significance in preparing high-porosity and high-performance biomass-based carbon materials for various energy storage/conversion.

Propelling electrochemical kinetics of transition metal oxide for high-rate lithium-ion battery through in situ deoxidation.

To engineer advanced anodes for high-rate lithium-ion battery, rational structural design with insightful understanding of rapid reaction kinetics is important and still highly desirable. In this work, a high-temperature in situ deoxidation strategy is used to propel electrochemical kinetics of NiO through incorporating an intrinsic Ni component. Both theoretical calculation and experimental study demonstrate that the Ni-NiO heterojunction significantly enhances the electronic conductivity and ion diffusion properties. Accordingly, the lithium-ion battery modified with the heterostructured Ni-NiO shows remarkably improved charge transfer efficiency and rate performance, substantially outperforming many reported NiO-based anodes. This work opens up the exploration of heterostructured metal compounds as kinetic regulators for high-rate lithium-ion battery and also enlightens the understanding of defect chemistry in propelling electrochemical reactions.

Ultralong lifetime and efficient room temperature phosphorescent carbon dots through multi-confinement structure design.

Room temperature phosphorescence materials have inspired extensive attention owing to their great potential in optical applications. However, it is hard to achieve a room temperature phosphorescence material with simultaneous long lifetime and high phosphorescence quantum efficiency. Herein, multi-confined carbon dots were designed and fabricated, enabling room temperature phosphorescence material with simultaneous ultralong lifetime, high phosphorescence quantum efficiency, and excellent stability. The multi-confinement by a highly rigid network, stable covalent bonding, and 3D spatial restriction efficiently rigidified the triplet excited states of carbon dots from non-radiative deactivation. The as-designed multi-confined carbon dots exhibit ultralong lifetime of 5.72 s, phosphorescence quantum efficiency of 26.36%, and exceptional stability against strong oxidants, acids and bases, as well as polar solvents. This work provides design principles and a universal strategy to construct metal-free room temperature phosphorescence materials with ultralong lifetime, high phosphorescence quantum efficiency, and high stability for promising applications, especially under harsh conditions.

Non-tubular-biomass-derived nitrogen-doped carbon microtubes for ultrahigh-area-capacity lithium-ion batteries.

The ever-increasing electric vehicles and portable electronics make lithium-ion barreries (LIBs) toward high energy density, resulting in long driving range and standby times. Generally, excellent electrochemical performance can be obtained in thin electrode materials with low mass loadings (<1 mg cm-2), but it is difficult to be achieved in commercial electrodes with high mass loadings (>10 mg cm-2). In this work, we report a facile method for fabricating nitrogen doped carbon microtubes (N-CMTs) consisted of crumped carbon nanosheets for high-performance LIBs with ultrahigh mass loading, where non-tubular biomass waste (i.e., peanut dregs) is employed as the precursor. Benefiting from the hollow tubular conductive network, high graphitization, and hierarchical structure, the as-synthesized N-CMTs exhibit ultrahigh area capacity of 6.27 mAh cm-2 at a current density of 1.5 mA cm-2 with a high mass loading of 15 mg cm-2 and superior cycling stability for LIBs. Our approach provides an effective strategy for the preparation of nitrogen-doped carbon microtubes to develope high energy LIBs with high mass loading electrodes.

Carbon Dots as a Protective Agent Alleviating Abiotic Stress on Rice (Oryza sativa L.) through Promoting Nutrition Assimilation and the Defense System.

Abiotic stress severely threatens agriculture. Herein, we studied the effect of heteroatom-free carbon dots (CDs) on the alleviation of abiotic stresses in rice for the first time. During in vitro coincubation, suspended rice cells were exposed to 2,4-dichlorophenoxyacetate sodium (2,4-D-Na, 30 µg mL-1), 2,4-dichlorophenoxyacetic acid (2,4-D, 5 µg mL-1), NaCl (0.15 mol·L-1), and high light (2000 Lux), both with and without CDs (100 µg mL-1). After a week, CDs significantly reduced the inhibition rate of 2,4-D-Na on the rice cell biomass from 48.16 to 27.44% and increased the biomass of rice cells exposed to 2,4-D, NaCl, and high light, by 4.12, 1.10, and 4.01 times that of the control (pure nutrient medium), respectively. Furthermore, the growth of CD-germinated rice seedlings was not obviously affected by 2,4-D-Na, 2,4-D, and NaCl. Further results showed that the CDs demonstrated an intrinsic free-radical scavenging property and could increase the peroxidase activity and the contents of phenolics and flavonoids in rice by 125.81, 39.60, and 47.63%, respectively. Furthermore, CDs improved the nutrient assimilation of rice cells under 2,4-D stress by 14.69%. With higher antioxidant capacity and sufficient nutrients, the CD-treated rice showed excellent resistance to abiotic stresses. This study suggested the great potential of CDs in protecting crops against abiotic stress.