Centimeter-sized diamond composites with high electrical conductivity and hardness.

Achieving high-performance materials with superior mechanical properties and electrical conductivity, especially in large-sized bulk forms, has always been the goal. However, it remains a grand challenge due to the inherent trade-off between these properties. Herein, by employing nanodiamonds as precursors, centimeter-sized diamond/graphene composites were synthesized under moderate pressure and temperature conditions (12 GPa and 1,300 to 1,500 °C), and the composites consisted of ultrafine diamond grains and few-layer graphene domains interconnected through covalently bonded interfaces. The composites exhibit a remarkable electrical conductivity of 2.0 × 104 S m-1 at room temperature, a Vickers hardness of up to ~55.8 GPa, and a toughness of 10.8 to 19.8 MPa m1/2. Theoretical calculations indicate that the transformation energy barrier for the graphitization of diamond surface is lower than that for diamond growth directly from conventional sp2 carbon materials, allowing the synthesis of such diamond composites under mild conditions. The above results pave the way for realizing large-sized diamond-based materials with ultrahigh electrical conductivity and superior mechanical properties simultaneously under moderate synthesis conditions, which will facilitate their large-scale applications in a variety of fields.

Supramolecular Aggregation of Carbon Nanodots.

Supramolecular aggregation has provided the archetype concept to understand the variants in an emerging systems property. Herein, we have achieved the supramolecular assembly of carbon nanodots (CDs) for the first time and employ supramolecular aggregation to understand their alteration in photophysical properties. In detail, we have employed the CDs as a block to construct the supramolecular assembly of aggregates in the CDs' antisolvent of ethanol. The CD-based aggregates exhibit complex and organized morphologies with another long-wavelength excitation-dependent emission band. The experimental results and density functional theoretical calculations reveal that the supramolecular assembly of CDs can decrease the energy gap between the ground and excited states, contributing to the new long-wavelength excitation-dependent emission. The supramolecular aggregation can be employed as one universal strategy to manipulate and understand the luminescence of CDs. These findings cast new light to build the emerging systems and understand the light emission of CDs through supramolecular chemistry.

In Situ Confining Citric Acid-Derived Carbon Dots for Full-Color Room-Temperature Phosphorescence.

Room-temperature phosphorescence has received much attention owing to its potential applications in information encryption and bioelectronics. However, the preparation of full-color single-component-derived phosphorescent materials remains a challenge. Herein, a facile in situ confining strategy is proposed to achieve full-color phosphorescent carbon dots (CDs) through rapid microwave-assisted carbonization of citric acid in NaOH. By tuning the mass ratio of citric acid and NaOH, the obtained CDs exhibit tunable phosphorescence wavelengths ranging from 483 to 635 nm and alterable lifetimes from 58 to 389 ms with a synthesis yield of up to 83.7% (>30 g per synthesis). Theoretical calculations and experimental results confirm that the formation of high-density ionic bonds between cations and CDs leads to efficient afterglow emission via the dissociation of CD arrangement, and the evolution of the aggregation state of CDs results in redshifted phosphorescence. These findings provide a strategy for the synthesis of new insights into achieving and manipulating room-temperature phosphorescent CDs, and prospect their applications in labeling and information encryption.

Ga2O3-Based Solar-Blind Position-Sensitive Detector for Noncontact Measurement and Optoelectronic Demodulation.

As a kind of photodetector, position-sensitive-detectors (PSDs) have been widely used in noncontact photoelectric positioning and measurement. However, fabrications and applications of solar-blind PSDs remain yet to be harnessed. Herein, we demonstrate a solar-blind PSD developed from a graphene/Ga2O3 Schottky junction with a 25-nanometer-thick Ga2O3 film, in which the absorption of the nanometer-thick Ga2O3 is enhanced by multibeam interference. The graphene/Ga2O3 junction exhibits a responsivity of 48.5 mA/W and a rise/decay time of 0.8/99.8 µs at zero bias. Moreover, the position of the solar-blind spot can be determined by the output signals of the PSD. Using the device as a sensor of noncontact test systems, we demonstrate its application in measurement of angular, displacement, and light trajectory. In addition, the position-sensitive outputs have been used to demodulate optical signals into electrical signals. The results may prospect the application of solar-blind PSDs in measurement, tracking, communication, and so on.

Photooxidation triggered ultralong afterglow in carbon nanodots.

It remains a challenge to obtain biocompatible afterglow materials with long emission wavelengths, durable lifetimes, and good water solubility. Herein we develop a photooxidation strategy to construct near-infrared afterglow carbon nanodots with an extra-long lifetime of up to 5.9 h, comparable to that of the well-known rare-earth or organic long-persistent luminescent materials. Intriguingly, size-dependent afterglow lifetime evolution from 3.4 to 5.9 h has been observed from the carbon nanodots systems in aqueous solution. With structural/ultrafast dynamics analysis and density functional theory simulations, we reveal that the persistent luminescence in carbon nanodots is activated by a photooxidation-induced dioxetane intermediate, which can slowly release and convert energy into luminous emission via the steric hindrance effect of nanoparticles. With the persistent near-infrared luminescence, tissue penetration depth of 20 mm can be achieved. Thanks to the high signal-to-background ratio, biological safety and cancer-specific targeting ability of carbon nanodots, ultralong-afterglow guided surgery has been successfully performed on mice model to remove tumor tissues accurately, demonstrating potential clinical applications. These results may facilitate the development of long-lasting luminescent materials for precision tumor resection.

FGF21 alleviates adipose stem cell senescence via CD90 glycosylation-dependent glucose influx in remodeling healthy white adipose tissue.

The senescence of adipose stem cells (ASCs) impairs healthy adipose tissue remodeling, causing metabolic maladaptation to energy surplus. The intrinsic molecular pathways and potential therapy targets for ASC senescence are largely unclear. Here, we showed that visceral ASCs were prone to senescence that was caused by reactive oxygen species (ROS) overload, especially mitochondrial ROS. These senescent ASCs failed to sustain efficient glucose influx, pentose phosphate pathway (PPP) and redox homeostasis. We showed that CD90 silence restricted the glucose uptake by ASCs and thus disrupted their PPP and anti-oxidant system, resulting in ASC senescence. Notably, fibroblast growth factor 21 (FGF21) treatment significantly reduced the senescent phenotypes of ASCs by augmenting CD90 protein via glycosylation, which promoted glucose influx via the AKT-GLUT4 axis and therefore mitigated ROS overload. For diet-induced obese mice, chronic administration of low-dose FGF21 relieved their visceral white adipose tissue (VAT) dysfunction and systemic metabolic disorders. In particular, VAT homeostasis was restored in FGF21-treated obese mice, where ASC repertoire was markedly recovered, accompanied by CD90 elevation and anti-senescent phenotypes in these ASCs. Collectively, we reveal a molecular mechanism of ASC senescence by which CD90 downregulation interferes glucose influx into PPP and redox homeostasis. And we propose a FGF21-based strategy for healthy VAT remodeling, which targets CD90 glycosylation to correct ASC senescence and therefore combat obesity-related metabolic dysfunction.

Colorful Triplet Excitons in Carbon Nanodots for Time Delay Lighting.

Time delay lighting offers an added period of buffer illumination for human eyes upon switching off the light. Long-lifetime emission from triplet excitons has outstanding potential, but the forbidden transition property due to the Pauli exclusion principle makes them dark, and it stays challenging to develop full-color and bright triplet excitons. Herein, triplet excitons emission from ultraviolet (UV) to near infrared (NIR) in carbon nanodots (CNDs) is achieved by confining multicolor CNDs emitters in NaCNO crystal. NaCNO crystal can isolate the CNDs, triplet excitons quenching caused by the excited state electrons aggregation induced energy transfer is suppressed, and the confinement crystal can furthermore promote phosphorescence of the CNDs by inhibiting the dissipation of the triplet excitons due to non-radiative transition. The phosphorescence from radiative recombination of triplet excitons in the CNDs covers the spectral region from 300 nm (UV) to 800 nm (NIR), the corresponding lifetimes can reach 15.8, 818.0, 239.7, 168.4, 426.4, and 127.6 ms. Furthermore, the eco-friendly luminescent lampshades are designed based on the multicolor phosphorescent CNDs, time delay light-emitting diodes are thus demonstrated. The findings will motivate new opportunities for the development of UV to NIR phosphorescent CNDs and time delay lighting applications.

CX3CR1hi macrophages sustain metabolic adaptation by relieving adipose-derived stem cell senescence in visceral adipose tissue.

Adipose-derived stem cells (ASCs) drive healthy visceral adipose tissue (VAT) expansion via adipocyte hyperplasia. Obesity induces ASC senescence that causes VAT dysfunction and metabolic disorders. It is challenging to restrain this process by biological intervention, as mechanisms of controlling VAT ASC senescence remain unclear. We demonstrate that a population of CX3CR1hi macrophages is maintained in mouse VAT during short-term energy surplus, which sustains ASCs by restraining their senescence, driving adaptive VAT expansion and metabolic health. Long-term overnutrition induces diminishment of CX3CR1hi macrophages in mouse VAT accompanied by ASC senescence and exhaustion, while transferring CX3CR1hi macrophages restores ASC reservoir and triggers VAT beiging to alleviate the metabolic maladaptation. Mechanistically, visceral ASCs attract macrophages via MCP-1 and shape their CX3CR1hi phenotype via exosomes; these macrophages relieve ASC senescence by promoting the arginase1-eIF5A hypusination axis. These findings identify VAT CX3CR1hi macrophages as ASC supporters and unravel their therapeutic potential for metabolic maladaptation to obesity.

Hepatocyte TIPE2 is a fasting-induced Raf-1 inactivator that drives hepatic gluconeogenesis to maintain glucose homeostasis.

BACKGROUND: The liver regulates metabolic balance during fasting-feeding cycle. Hepatic adaptation to fasting is precisely modulated on multiple levels. Tumor necrosis factor-α-induced protein 8-like 2 (TIPE2) is a negative regulator of immunity that reduces several liver pathologies, but its physiological roles in hepatic metabolism are largely unknown. METHODS: TIPE2 expression was examined in mouse liver during fasting-feeding cycle. TIPE2-knockout mice, liver-specific TIPE2-knockout mice, liver-specific TIPE2-overexpressed mice were examined for fasting blood glucose and pyruvate tolerance test. Primary hepatocytes or liver tissues from these mice were evaluated for glucose production, lipid accumulation, gene expression and regulatory pathways. TIPE2 interaction with Raf-1 and TIPE2 transcription regulated by PPAR-α were examined using gene overexpression or knockdown, co-immunoprecipitation, western blot, luciferase reporter assay and DNA-protein binding assay. RESULTS: TIPE2 expression was upregulated in fasted mouse liver and starved hepatocytes, which was positively correlated with gluconeogenic genes. Liver-specific TIPE2 deficiency impaired blood glucose homeostasis and gluconeogenic capacity in mice upon fasting, while liver-specific TIPE2 overexpression elevated fasting blood glucose and hepatic gluconeogenesis in mice. In primary hepatocytes upon starvation, TIPE2 interacted with Raf-1 to accelerate its ubiquitination and degradation, resulting in ERK deactivation and FOXO1 maintenance to sustain gluconeogenesis. During prolonged fasting, hepatic TIPE2 deficiency caused aberrant activation of ERK-mTORC1 axis that increased hepatic lipid accumulation via lipogenesis. In hepatocytes upon starvation, PPAR-α bound with TIPE2 promoter and triggered its transcriptional expression. CONCLUSIONS: Hepatocyte TIPE2 is a PPAR-α-induced Raf-1 inactivator that sustains hepatic gluconeogenesis and prevents excessive hepatic lipid accumulation, playing beneficial roles in hepatocyte adaptation to fasting.

Chemiluminescent carbon nanodots for dynamic and guided antibacteria.

Advanced antibacterial technologies are needed to counter the rapid emergence of drug-resistant bacteria. Image-guided therapy is one of the most promising strategies for efficiently and accurately curing bacterial infections. Herein, a chemiluminescence (CL)-dynamic/guided antibacteria (CDGA) with multiple reactive oxygen species (ROS) generation capacity and chemiexcited near-infrared emission has been designed for the precise theranostics of bacterial infection by employing near-infrared emissive carbon nanodots (CDs) and peroxalate as CL fuels. Mechanistically, hydrogen peroxide generated in the bacterial microenvironment can trigger the chemically initiated electron exchange between CDs and energy-riched intermediate originated from the oxidized peroxalate, enabling bacterial induced inflammation imaging. Meanwhile, type I/II photochemical ROS production and type III ultrafast charge transfer from CDs under the self-illumination can inhibit the bacteria proliferation efficiently. The potential clinical utility of CDGA is further demonstrated in bacteria infected mice trauma model. The self-illuminating CDGA exhibits an excellent in vivo imaging quality in early detecting wound infections and internal inflammation caused by bacteria, and further are proven as efficient broad-spectrum antibacterial nanomedicines without drug-resistance, whose sterilizing rate is up to 99.99%.

Pentaheptite diamond: a new carbon allotrope.

The search forsp3-hybridized carbon allotropes other than diamond has attracted extensive interest because of their fascinating properties. In this paper, an orthorhombic carbon phase insp3bonding, named pentaheptite diamond, by combining the particle swarm optimization method with first-principles calculations has been predicted. The phonon spectra, total energy and elastic constants calculations of the pentaheptite diamond confirm its dynamical, thermal and mechanical stability at zero pressure, respectively. It possesses a high bulk modulus of 385 GPa and Vickers hardness of 72.6 GPa, comparable to diamond. Electronic band structure calculations show that the pentaheptite diamond has a direct band gap of 4.18 eV.

Regulating Na deposition by constructing a Au sodiophilic interphase on CNT modified carbon cloth for flexible sodium metal anode.

Na metal anode has attracted increasing attentions as the anode of sodium ion batteries (SIBs) due to its high theoretical capacity, low redox potential and high abundance. However, the formation of uncontrollable Na dendrite during repeated plating/stripping cycles hinders its further development and application. Herein, a sodiophilic Na metal anode host is developed by sputtering gold nanoparticles (Au NPs) into interconnected carbon nanotube modified carbon cloth (CNT/CC) to form a Au-CNT/CC architecture. Sodiophilic Au NPs effectively guide the Na metal uniform deposition and three-dimensional (3D) microporous structure offers a large surface area for nucleation and reducing the current densities. The regulated uniform Na metal deposition mechanism is investigated by the in-situ optical microscopy and simulation analysis. As a result, Au-CNT/CC electrode exhibits a low nucleation overpotential (2.2 mV) and stable cycle performance for 1600 h at 1 mA cm-2 with 2 mAh cm-2. Moreover, it even exhibits a long cycle stability for more than 800 h at 5 mA cm-2 with 2 mAh cm-2. To explore its application, a full cell coupled with a sodium vanadium phosphate coated with carbon layer (NVP@C) cathode is assembled and delivers an average discharge capacity of 80.6 mAh g-1 and coulombic efficiency of 99.6% for 400 cycles at 100 mAh g-1. Furthermore, a flexible pouch cell with Na@Au-CNT/CC as the anode is fabricated and demonstrated good flexibility and future application of wearable electronics.

Localized Excitonic Electroluminescence from Carbon Nanodots.

Localized excitons are expected to achieve high-performance electroluminescence and have been widely investigated in GaN-based light-emitting diodes (LEDs). Although carbon nanodot (CD) based LEDs have been achieved with the radiative recombination of electrons and holes, localized excitonic electroluminescence has been not reported before. In this Letter, localized excitonic electroluminescent devices have been fabricated using fluorescent CDs as an active layer. The CDs show strong localized excitonic yellow emission with a fluorescence quantum yield of 76% and Stokes shift of 2.1 eV. The CD-based LEDs present a sub-bandgap turn-on voltage of 2.4 V and a maximum luminance of 60.2 cd m-2, which is the lowest driving voltage among the CD-based electroluminescent devices. Localized centers trap carriers effectively, resulting in sub-bandgap light emission. The current results manifest that localized excitons may furnish a promising approach to boost the development of CD-based LEDs.

Defect-Engineered 3D hierarchical NiMo3S4 nanoflowers as bifunctional electrocatalyst for overall water splitting.

The design and construction of bifunctional electrocatalysts with high activity and durability is essential for overall water splitting. Herein, a unique 3D hierarchical NiMo3S4 nanoflowers with abundant defects and reactive sites were grown directly on carbon textiles (NiMo3S4/CTs) using a facile hydrothermal synthesis method. The defect-rich NiMo3S4 nanoflakes, prepared by doping Ni2+ in the lattice of Mo-S, displays extended d-spacing of (002) crystal plane, resulting in the electrocatalytic activity of hydrogen evolution and oxygen evolution reaction (HER and OER) was improved under alkaline conditions. The self-supported NiMo3S4/CTs electrode delivers a small overpotential of 149.5 mV for HER and 126.2 mV for OER at 10 mA cm-2, respectively. Based on detailed structure analysis and density functional theory (DFT) calculations, the excellent HER and OER activities can be attributed to the unique structure of the nanoflowers, where the metallic characteristics for Ni-doped Mo-S lead to the enhancement of intrinsic conductivity and the rich abundance of Ni3+ active sites. As a result, the NiMo3S4/CTs as efficient bifunctional electrocatalysts for overall water-splitting was performed in alkaline electrolyte, where the system required only 1.55, 1.66 and 1.76 V to deliver current densities of 10, 50 and 100 mA cm-2, respectively. This study provides a new method for improving the electrocatalysis properties of transition metal sulfides by metal-ion doping to generate more active defect sites, thus promoting the development of non-noble-metal electrocatalysts for overall water splitting.

3D-Printed Sodiophilic V2CTx/rGO-CNT MXene Microgrid Aerogel for Stable Na Metal Anode with High Areal Capacity.

Featuring a high theoretical capacity, low cost, and abundant resources, sodium metal has emerged as an ideal anode material for sodium ion batteries. However, the real feasibility of sodium metal anodes is still hampered by the uncontrolled sodium dendrite problems. Herein, an artificial three-dimensional (3D) hierarchical porous sodiophilic V2CTx/rGO-CNT microgrid aerogel is fabricated by a direct-ink writing 3D printing technology and further adopted as the matrix of Na metal to deliver a Na@V2CTx/rGO-CNT sodium metal anode. Upon cycling, the V2CTx/rGO-CNT electrode can yield a superior cycling life of more than 3000 h (2 mA cm-2, 10 mAh cm-2) with an average Coulombic efficiency of 99.54%. More attractively, it can even sustain a stable operation over 900 h at 5 mA cm-2 with an ultrahigh areal capacity of 50 mAh cm-2. In situ and ex situ characterizations and density functional theory simulation analyses prove that V2CTx with abundant sodiophilic functional groups can effectively guide the sodium metal nucleation and uniform deposition, thus enabling a dendrite-free morphology. Moreover, a full cell pairing a Na@V2CTx/rGO-CNT anode with a Na3V2(PO4)3@C-rGO cathode can deliver a high reversible capacity of 86.27 mAh g-1 after 400 cycles at 100 mA g-1. This work not only clarifies the superior Na deposition chemistry on the sodiophilic V2CTx/rGO-CNT microgrid aerogel electrode but also offers an approach for fabricating advanced Na metal anodes via a 3D printing method.

Interface engineering of nickel Hydroxide-Molybdenum diselenide nanosheet heterostructure arrays for efficient alkaline hydrogen production.

The stacking of Molybdenum Diselenide (MoSe2) nanomaterials as well as its poor intrinsic conductivity lead to sluggish water dissociation kinetics, which limit the performance of the alkaline hydrogen evolution reaction (HER). Herein, we constructed Nickel Hydroxide Ni(OH)2-MoSe2 heterostructures directly on 3D self-supporting carbon cloth (CC) substrate via a simple hydrothermal and the subsequent chemical bath deposition process, then systemically studied the effect of the Ni(OH)2 deposition time on the HER performance. The synergistic effect between Ni(OH)2 and MoSe2 in the Ni(OH)2-MoSe2 heterostructures optimizes the poor conductivity and Gibbs free energy for water adsorption, thus improving the water dissociation kinetics and giving rise to fast electron transfer in the HER process. The Ni(OH)2-MoSe2/CC constructed in this way with a Ni(OH)2 deposition times of 30 min performs good catalytic activities with a low overpotential of 130 mV at -10 mA cm-2, a low Tafel slope of 78.2 mV dec-1 and good stability. Our results suggest that interface engineering combining with conductive substrate are conducive to enhance alkaline HER activity of MoSe2 and other similar transition metal dichalcogenides.

Carbon Nanodots with Nearly Unity Fluorescent Efficiency Realized via Localized Excitons.

Carbon nanodots (CDs) have emerged as an alternative option for traditional nanocrystals due to their excellent optical properties and low toxicity. Nevertheless, high emission efficiency is a long-lasting pursuit for CDs. Herein, CDs with near-unity emission efficiency are prepared via atomic condensation of doped pyrrolic nitrogen, which can highly localize the excited states thus lead to the formation of bound excitons and the symmetry break of the π-electron conjugation. The short radiative lifetimes (<8 ns) and diffusion lengths (<50 nm) of the CDs imply that excitons can be efficiently localized by radiative recombination centers for a defect-insensitive emission of CDs. By incorporating the CDs into polystyrene, flexible light-converting films with a high solid-state quantum efficiency of 84% and good resistance to water, heating, and UV light are obtained. With the CD-polymer films as light conversion layers, CD-based white light-emitting diodes (WLEDs) with a luminous efficiency of 140 lm W-1 and a flat-panel illumination system with lighting sizes of more than 100 cm2 are achieved, matching state-of-the-art nanocrystal-based LEDs. These results pave the way toward carbon-based luminescent materials for solid-state lighting technology.

Meter-scale chemiluminescent carbon nanodot films for temperature imaging.

Chemiluminescence (CL), as one class of luminescence driven by chemical reaction, exhibits obvious temperature-dependence in its light emission process. Herein, temperature-dependent CL emission of carbon nanodots (CDs) in the chemical reaction of peroxalate and hydrogen peroxide is demonstrated and temperature imaging based on the temperature-dependent CL has been established for the first time. In detail, the temperature-dependent CL emission of CDs in the chemical reaction of peroxalate and hydrogen peroxide is observed, and the linear relationship between the CL intensity and temperature is demonstrated in both the CL solution and film, enabling their applications in temperature sensing and imaging capabilities. The increase of the CL emission with temperature can be attributed to the accelerated electron exchange between the CDs and intermediate generated in the peroxalate system. Meter-scale chemiluminescent CD films have been constructed. The CL sensor based on the films presents a high spatial resolution of 0.4 mm and an outstanding sensitivity of 0.08 °C-1, which is amongst the best values for the thermographic luminophores. With the unique temperature response and flexible properties, non-planar, meter-scale and sensitive palm temperature imaging has been achieved. These findings present new opportunities for designing CL-based temperature probes and thermography.

Ultraviolet phosphorescent carbon nanodots.

Phosphorescent carbon nanodots (CNDs) have generated enormous interest recently, and the CND phosphorescence is usually located in the visible region, while ultraviolet (UV) phosphorescent CNDs have not been reported thus far. Herein, the UV phosphorescence of CNDs was achieved by decreasing conjugation size and in-situ spatial confinement in a NaCNO crystal. The electron transition from the px to the sp2 orbit of the N atoms within the CNDs can generate one-unit orbital angular momentum, providing a driving force for the triplet excitons population of the CNDs. The confinement caused by the NaCNO crystal reduces the energy dissipation paths of the generated triplet excitons. By further tailoring the size of the CNDs, the phosphorescence wavelength can be tuned to 348 nm, and the room temperature lifetime of the CNDs can reach 15.8 ms. As a demonstration, the UV phosphorescent CNDs were used for inactivating gram-negative and gram-positive bacteria through the emission of their high-energy photons over a long duration, and the resulting antibacterial efficiency reached over 99.9%. This work provides a rational design strategy for UV phosphorescent CNDs and demonstrates their novel antibacterial applications.

Humidity Sensors Realized via Negative Photoconductivity Effect in Nanodiamonds.

Herein, the negative photoconductivity (NPC) effect has been observed in nanodiamonds (NDs) for the first time, and with illumination under a 660 nm laser lamp, the conductivity of the NDs decreases significantly. The NPC effect has been attributed to the trapping of carriers by the absorbed water molecules on the ND surfaces. A humidity sensor has been constructed based on the NPC effect of the NDs, and the sensitivity of the sensor can reach 106%, which is the highest value ever reported for carbon-based humidity sensors.