Growth of Horizontal Semiconducting SWNT Arrays with Density Higher than 100 tubes/μm using Ethanol/Methane Chemical Vapor Deposition

Horizontally aligned semiconducting single-walled carbon nanotube (s-SWNT) arrays with a certain density are highly desirable for future electronic devices. However, obtaining s-SWNT arrays with simultaneously high purity and high density is extremely challenging. We report herein a rational approach, using ethanol/methane chemical vapor deposition, to grow SWNT arrays with a s-SWNT ratio over 91% and a density higher than 100 tubes/μm. In this approach, at a certain temperature, ethanol was fully thermally decomposed to feed carbon atoms for Trojan-Mo catalysts growing high density SWNT arrays, while the incomplete pyrolysis of methane provided appropriate active H radicals with the help of catalytic sapphire surface to inhibit metallic SWNT (m-SWNT) growth. The synergistic effect of ethanol/methane mixtures resulted in enriched semiconducting SWNTs and no obvious decrease in nanotube density due to their milder reactivity and higher controllability at suitable growth conditions. This work represents a step forward in large-area synthesis of high density s-SWNT arrays on substrates and demonstrates potential applications in scalable carbon nanotube electronics

Versatile Cutting Method for Producing Fluorescent Ultrasmall MXene Sheets

As a recently created inorganic nanosheet material, MXene has received growing attention and has become a hotspot of intensive research. The efficient morphology control of this class of material could bring enormous possibilities for creating marvelous properties and functions; however, this type of research is very scarce. In this work, we demonstrate a general and mild approach for creating ultrasmall MXenes by simultaneous intralayer cutting and interlayer delamination. Taking the most commonly studied Ti₃C₂ as an illustrative example, the resulting product possessed monolayer thickness with a lateral dimension of 2–8 nm and exhibited bright and tunable fluorescence. Further, the method could also be employed to synthesize ultrasmall sheets of other MXene phases, for example, Nb₂C or Ti₂C. Importantly, although the strong covalent M–C bond was to some extent broken, all of the characterizations suggested that the chemical structure was composed of well-maintained host layers without observation of any serious damages, demonstrating the superior reaction efficiencies and safeties of our methods. This work may provide a facile and general approach to modulate various nanoscale materials and could further stimulate the vast applications of MXene materials in many optical-related fields

Graphene-Patched CNT/MnO₂ Nanocomposite Papers for the Electrode of High-Performance Flexible Asymmetric Supercapacitors

MnO₂ has been widely studied as the pseudo-capactive electrode material of high-performance supercapacitors for its large operating voltage, low cost, and environmental friendliness. However, it suffers from low conductivity and being hardly handle as the electrodes of supercapacitors especially with flexibility, which largely limit its electrochemical performance and application. Herein, we report a novel ternary composite paper composed of reduced graphene sheet (GR)-patched carbon nanotube (CNT)/MnO₂, which has controllable structures and prominent electrochemical properties for a flexible electrode of the supercapacitor. The composite paper was prepared by electrochemical deposition of MnO₂ on a flexible CNT paper and further adsorption of GR on its surface to enhance the surface conductivity of the electrode and prohibit MnO₂ nanospheres from detaching with the electrode. The presence of GR was found remarkably effective in enhancing the initial electrochemical capacitance of the composite paper from 280 F/g to 486.6 F/g. Furthermore, it ensures the stability of the capacitance after a long period of charge/discharge cycles. A flexible CNT/polyaniline/CNT/MnO₂/GR asymmetric supercapacitor was assembled with this composite paper as an electrode and aqueous electrolyte gel as the separator. Its operating voltage reached 1.6 V, with an energy density at 24.8 Wh/kg. Such a composite structure derived from a multiscale assembly can offer not only a robust scaffold loading MnO₂ nanospheres but also a conductive network for efficient ionic and electronic transport; thus, it is potentially promising as a novel electrode architecture for high-performance flexible energy storage devices

Facile Assembly of Ni–Co Hydroxide Nanoflakes on Carbon Nanotube Network with Highly Electrochemical Capacitive Performance

Herein, we demonstrate the high-density assembly of Ni–Co hydroxide nanoflakes on conductive carbon nanotube (CNT) network through a simple and rapid chemical precipitation method, presenting a low-cost and high-performance scaffold for pseudosupercapacitor. It is found that the Ni–Co layered double hydroxide (LDH) nanoflakes prefer to proliferate around large-diameter CNTs (diameter > 50 nm), with conductive CNT network well-maintained. Such hierarchical nanostructures show greatly improved specific surface areas compared with bare CNT network and are freestanding without other organic binder, which can be directly employed as a binder-free compact electrode assembly. By optimizing the chemical composition of as-precipitated LDH nanoflakes, the resultant Co_0.4Ni_0.6(OH)₂ LDH/CNT composite nanostructures exhibit the largest specific electrochemical capacitance and the best rate performance, with their capacitance up to 1843 F/g under a low current density of 0.5 A/g and maintained at 1231 F/g when the current density is increased 20 times to 10 A/g. Importantly, such hierarchical nanostructures tend to prevent the electrode from severe structural damage and capacity loss during hundreds of charge/discharge under a high rate (2 A/g), ensuring the electrode with high-energy density (51 W h/kg) at power density of 3.3 kW/kg

Data_Sheet_1_Associations of healthy eating index-2015 with osteoporosis and low bone mass density in postmenopausal women: a population-based study from NHANES 2007–2018.docx

PurposeThe current study aimed to explore the associations of diet quality assessed by healthy eating index-2015 (HEI-2015) with risks of osteoporosis and low bone mineral density (BMD) among American postmenopausal women aged 50 years and older.MethodsPostmenopausal women aged 50 years and older in the National Health and Nutrition Examination Survey from 2007 through 2018 were included in the final sample. Analysis of variance and Rao-Scott adjusted chi-square tests were used to compare the characteristics across tertiles of HEI-2015. Univariate and multivariate weighted logistic regression models were employed to explore the associations of HEI-2015 tertiles and continuous HEI-2015 with the risks of osteoporosis and low BMD. Nonlinear dose-response associations were evaluated using weighted restricted cubic spline analyses, and the contributions of various HEI-2015 components were assessed using weighted quantile sum regression models.ResultsThe final sample included 3,421 postmenopausal women aged 50 years and older representative for approximately 28.38 million non-institutionalized U.S. postmenopausal women. Osteoporosis prevalence decreased with HEI-2015 tertiles while the prevalence of low BMD showed no significant decrease. Compared with postmenopausal women in the first tertile of HEI-2015, those with the second (OR: 0.57, 95%CI: 0.38–0.84) and third (OR: 0.48, 95%CI: 0.29–0.78) HEI-2015 tertiles were associated with reduced osteoporosis risk after multivariate adjustments, but no significant association of HEI-2015 with the risk of BMD was identified. Furthermore, similar effects were confirmed in the sensitivity analyses and subgroup analyses and interaction effects. Moreover, significant nonlinear associations were observed between HEI-2015 with osteoporosis risk, and total vegetables, refined grains and greens and beans demonstrated the strongest protective effect among HEI-2015 components against osteoporosis.ConclusionsThis study strongly suggests the significant negative associations of HEI-2015 with osteoporosis risk in American postmenopausal women. These findings highlight the importance of adherence to the dietary guidelines for Americans in reducing the risk of osteoporosis.</p

Synergy of W₁₈O₄₉ and Polyaniline for Smart Supercapacitor Electrode Integrated with Energy Level Indicating Functionality

Supercapacitors are important energy storage technologies in fields such as fuel-efficient transport and renewable energy. State-of-the-art supercapacitors are capable of supplanting conventional batteries in real applications, and supercapacitors with novel features and functionalities have been sought for years. Herein, we report the realization of a new concept, a smart supercapacitor, which functions as a normal supercapacitor in energy storage and also communicates the level of stored energy through multiple-stage pattern indications integrated into the device. The metal-oxide W₁₈O₄₉ and polyaniline constitute the pattern and background, respectively. Both materials possess excellent electrochemical and electrochromic behaviors and operate in different potential windows, −0.5–0 V (W₁₈O₄₉) and 0–0.8 V (polyaniline). The intricate cooperation of the two materials enables the supercapacitor to work in a widened, 1.3 V window while displaying variations in color schemes depending on the level of energy storage. We believe that our success in integrating this new functionality into a supercapacitor may open the door to significant opportunities in the development of future supercapacitors with imaginative and humanization features

Programmable Writing of Graphene Oxide/Reduced Graphene Oxide Fibers for Sensible Networks with <i>in Situ</i> Welded Junctions

Direct spinning of the graphene oxide (GO) dispersions from a moveable spinneret along the programmed track, <i>i.e.</i>, a “programmable writing” technique, was developed to make nonwoven, nonknitted, graphene-based networks with excellent mechanical properties. The resulting GO networks can be successfully converted into reduced GO (RGO) ones with better mechanical properties as well as excellent electrical conductivity <i>via</i> thermal/chemical reduction. <i>In situ</i> welded junctions formed during processing of the spun fibers have made the resulting networks with the integral structure, and outstanding mechanical properties and high electrical conductivities of the spun fibers and their web integrations have provided a great opportunity to remotely sense the external mechanical stimuli <i>via</i> electrical signal monitoring

Coupling Molecularly Ultrathin Sheets of NiFe-Layered Double Hydroxide on NiCo₂O₄ Nanowire Arrays for Highly Efficient Overall Water-Splitting Activity

Developing efficient but nonprecious bifunctional electrocatalysts for overall water splitting in basic media has been the subject of intensive research focus with the increasing demand for clean and regenerated energy. Herein, we report on the synthesis of a novel hierarchical hybrid electrode, NiFe-layered double hydroxide molecularly ultrathin sheets grown on NiCo₂O₄ nanowire arrays assembled from thin platelets with nickel foam as the scaffold support, in which the catalytic metal sites are more accessible and active and most importantly strong chemical coupling exists at the interface, enabling superior catalytic power toward both oxygen evolution reaction (OER) and additionally hydrogen evolution reaction (HER) in the same alkaline KOH electrolyte. The behavior ranks top-class compared with documented non-noble HER and OER electrocatalysts and even comparable to state-of-the-art noble-metal electrocatalysts, Pt and RuO₂. When fabricated as an integrated alkaline water electrolyzer, the designed electrode can deliver a current density of 10 mA cm^–2 at a fairly low cell voltage of 1.60 V, promising the material as efficient bifunctional catalysts toward whole cell water splitting

Direct Intertube Cross-Linking of Carbon Nanotubes at Room Temperature

Carbon nanotubes (CNTs) have long been regarded as an efficient free radical scavenger because of the large-conjugation system in their electronic structures. Hence, despite abundant reports on CNT reacting with incoming free radical species, current research has not seen CNT itself displaying the chemical reactivity of free radicals. Here we show that reactive free radicals can in fact be generated on carbon nanotubes via reductive defluorination of highly fluorinated single-walled carbon nanotubes (FSWNTs). This finding not only enriches the current understanding of carbon nanotube chemical reactivity but also opens up new opportunities in CNT-based material design. For example, spacer-free direct intertube cross-linking of carbon nanotubes was previously achieved only under extremely high temperature and pressure or electron/ion beam irradiation. With the free radicals on defluorinated FSWNTs, the nanotubes containing multiple radicals on the sidewall can directly cross-link with each other under ambient temperature through intertube radical recombination. It is demonstrated that carbon nanotube fibers reinforced via direct cross-linking displays much improved mechanical properties

Highly Uniform Carbon Nanotube Field-Effect Transistors and Medium Scale Integrated Circuits

Top-gated p-type field-effect transistors (FETs) have been fabricated in batch based on carbon nanotube (CNT) network thin films prepared from CNT solution and present high yield and highly uniform performance with small threshold voltage distribution with standard deviation of 34 mV. According to the property of FETs, various logical and arithmetical gates, shifters, and d-latch circuits were designed and demonstrated with rail-to-rail output. In particular, a 4-bit adder consisting of 140 p-type CNT FETs was demonstrated with higher packing density and lower supply voltage than other published integrated circuits based on CNT films, which indicates that CNT based integrated circuits can reach to medium scale. In addition, a 2-bit multiplier has been realized for the first time. Benefitted from the high uniformity and suitable threshold voltage of CNT FETs, all of the fabricated circuits based on CNT FETs can be driven by a single voltage as small as 2 V