15 research outputs found

    Controlling Surface Termination and Facet Orientation in Cu<sub>2</sub>O Nanoparticles for High Photocatalytic Activity: A Combined Experimental and Density Functional Theory Study

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    Cu<sub>2</sub>O nanoparticles with controllable facets are of great significance for photocatalysis. In this work, the surface termination and facet orientation of Cu<sub>2</sub>O nanoparticles are accurately tuned by adjusting the amount of hydroxylamine hydrochloride and surfactant. It is found that Cu<sub>2</sub>O nanoparticles with Cu-terminated (110) or (111) surfaces show high photocatalytic activity, while other exposed facets show poor reactivity. Density functional theory simulations confirm that sodium dodecyl sulfate surfactant can lower the surface free energy of Cu-terminated surfaces, increase the density of exposed Cu atoms at the surfaces and thus benefit the photocatalytic activity. It also shows that the poor reactivity of the Cu-terminated Cu<sub>2</sub>O (100) surface is due to the high energy barrier of holes at the surface region

    Dye-Assisted Transformation of Cu<sub>2</sub>O Nanocrystals to Amorphous Cu<i><sub>x</sub></i>O Nanoflakes for Enhanced Photocatalytic Performance

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    Amorphous Cu<i><sub>x</sub></i>O nanoflakes with a thickness of 10ā€“50 nm were synthesized through dye-assisted transformation of rhombic dodecahedral Cu<sub>2</sub>O nanocrystals using a facile solution process. The morphology evolution observed by electron microscopy is highly dependent on the reaction between the surface and the dye. The crystal grain shrinks during the process until the formation of a purely amorphous nanoflake. The amorphous Cu<i><sub>x</sub></i>O nanoflake consists of a combination of CuĀ­(I) and CuĀ­(II) with a ratio close to 1:1. It shows enhanced photocatalytic reactivity toward the degradation of methyl orange compared to that of rhombic dodecahedral Cu<sub>2</sub>O nanocrystals with all active (110):Cu facets. The chemical composition and architecture remain the same after repeating degradation tests. The high surface-to-volume ratio contributes to its superior photocatalytic performance, whereas its low surface energy, confirmed by density functional theory simulations, explains its improved stability. The nanoflakes also show the ability of degrading nitrobenzene effectively, thus demonstrating great promise as a highly stable and active photocatalyst for environmental applications

    Improving the Fire Performance of Nylon 6,6 Fabric by Chemical Grafting with Acrylamide

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    Our previous study has demonstrated that photografting can enhance the flame retardancy of both polyamide and polyester fabric. In this work, efforts to use chemical grafting with acrylamide (AM) as the monomer and dibenzoyl peroxide (BPO) as the initiator were made to improve the homogeneity of the grafting chains and the flame retardancy of nylon 6,6 fabric. The effects of reaction time, reaction temperature, and monomer concentration on the percentage of grafting (PG) were investigated. The effect of PG on the fire performance of AM-<i>g</i>-nylon 6,6 fabric was also studied. The flame retardancy and thermal behavior were characterized in terms of the limiting oxygen index (LOI), UL 94 test, cone calorimetry, thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The results showed that the after-flame time and char length were significantly reduced after grafting. The heat release rate (HRR) of grafted sample was decreased by 28% compared to that of the ungrafted sample. The optimal grafting conditions were obtained as follows: reaction time, 1.5 h; reaction temperature, 70 Ā°C; and concentration of total monomer, 15 wt %. The chemical structure and microstructure of AM-<i>g</i>-nylon 6,6 fabric were analyzed by attenuated-total-reflection Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. A possible grafting mechanism is proposed and discussed

    Tetrahedral Silver Phosphate/Graphene Oxide Hybrids as Highly Efficient Visible Light Photocatalysts with Excellent Cyclic Stability

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    The degradation efficiency and recyclability of photocatalysts are the key for their practical applications. Tetrahedral silver phosphate (Ag<sub>3</sub>PO<sub>4</sub>) is a superior visible-light photocatalyst, while graphene oxide (GO) sheets with high specific surface area and abundant functional groups are expected to further enhance the photocatalytic efficiency and improve the recyclability of Ag<sub>3</sub>PO<sub>4</sub>. Herein, we demonstrate an eco-friendly and kinetically controlled approach to synthesize Ag<sub>3</sub>PO<sub>4</sub>/GO hybrids. Tetrahedral Ag<sub>3</sub>PO<sub>4</sub> are grown in situ on the GO sheets in mixed solvents, and their microstructures are controlled by the slow dissolution and ionization of H<sub>3</sub>PO<sub>4</sub> and the adjustment of the volume ratios of ethanol/water solvents. The hybrid with 5 wt % of GO exhibits an extraordinary photocatalytic efficiency and satisfactory recyclability for the degradation of organic dyes. Approximately 99% of methylene blue could be degraded in 4 min, and the degradation percentage is still as high as 97% even after 5 cycles of photocatalytic degradations. The mechanism of reinforcement of the photocatalytic performance was also studied. This hybridization of tetrahedral Ag<sub>3</sub>PO<sub>4</sub> with GO sheets provides an efficient solution to the photocorrosion of Ag<sub>3</sub>PO<sub>4</sub> and is an efficient approach for synthesizing Ag<sub>3</sub>PO<sub>4</sub>-based semiconducting hybrids as highly efficient and recyclable photocatalysts

    Fine Tuning Water States in Hydrogels for High Voltage Aqueous Batteries

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    Hydrogels are widely used as quasi-solid-state electrolytes in aqueous batteries. However, they are not applicable in high-voltage batteries because the hydrogen evolution reaction cannot be effectively suppressed even when water is incorporated into the polymer network. Herein, by profoundly investigating the states of water molecules in hydrogels, we designed supramolecular hydrogel electrolytes featuring much more nonfreezable bound water and much less free water than that found in conventional hydrogels. Specifically, two strategies are developed to achieve this goal. One strategy is adopting monomers with a variety of hydrophilic groups to enhance the hydrophilicity of polymer chains. The other strategy is incorporating zwitterionic polymers or polymers with counterions as superhydrophilic units. In particular, the nonfreezable bound water content increased from 0.129 in the conventional hydrogel to >0.4 mg mgā€“1 in the fabricated hydrogels, while the free water content decreased from 1.232 to āˆ¼0.15 mg mgā€“1. As a result, a wide electrochemical stability window of up to 3.25 V was obtained with the fabricated hydrogels with low concentrations of incorporated salts and enhanced hydrophilic groups or superhydrophilic groups. The ionic conductivities achieved with our developed hydrogel electrolytes were much higher than those in the conventional highly concentrated salt electrolytes, and their cost is also much lower. The designed supramolecular hydrogel electrolytes endowed an aqueous K-ion battery (AKIB) system with a high voltage plateau of 1.9 V and contributed to steady cycling of the AKIB for over 3000 cycles. The developed supramolecular hydrogel electrolytes are also applicable to other batteries, such as aqueous lithium-ion batteries, hybrid sodium-ion batteries, and multivalent-ion aqueous batteries, and can achieve high voltage output

    Rational Design and Modification of Highā€‘<i>k</i> Bis(double-stranded) Block Copolymer for High Electrical Energy Storage Capability

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    High dielectric constant (high-<i>k</i>) polymers have important application in advanced electronic devices such as energy storage, wearable electronics, artificial muscles, and electrocaloric cooling because of their excellent flexibility and ease of processing. However, most of the commercially available polymers have low-<i>k</i> values and the designed strategies for enhancing <i>k</i> are usually at the cost of the increase of dielectric loss. In this work, novel high-<i>k</i> and low loss bisĀ­(double-stranded) block copolymers, containing the ionic-conjugated hybrid conductive segments (HCS) with narrow band gap and the insulating segments with wide band gap, were synthesized by tandem metathesis polymerizations. The novel copolymers exhibited enhanced dielectric constant of 33ā€“28 accompanied by low dielectric loss of 0.055ā€“0.02 at 10<sup>2</sup>ā€“10<sup>6</sup> Hz, and thus greatly increased stored energy density of 9.95 J cm<sup>ā€“3</sup> was achieved at relatively low electric field of 370 MV m<sup>ā€“1</sup>, which is significantly higher than that of the commercial biaxially oriented polypropylene (BOPP) (about 1.6 J cm<sup>ā€“3</sup> at 400 MV m<sup>ā€“1</sup>). In addition, by doping with I<sub>2</sub>, the <i>k</i> values of the HCS-contained block copolymer can increase further to 36.5ā€“29 with low dielectric loss of 0.058ā€“0.026, and the stored energy density maintained at a high level of 8.99 J cm<sup>ā€“3</sup> at 300 MV m<sup>ā€“1</sup> with suitable I<sub>2</sub> content. The excellent dielectric and energy storage capability were attributed to the unique macromolecular structure and well-defined nanomorphology, which not only enhanced the dipolar, electronic, and interfacial polarizations but also significantly suppressed the leakage current and increased the breakdown strength by wrapping the narrow band gap segments in the wide band gap segments

    Vertically Aligned Carbon Nanotubes on Carbon Nanofibers: A Hierarchical Three-Dimensional Carbon Nanostructure for High-Energy Flexible Supercapacitors

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    Hierarchical structures enable high-performance power sources. We report here the preparation of vertically aligned carbon nanotubes directly grown on carbon nanofibers (VACNTs/CNFs) by combining electrospinning with pyrolysis technologies. The structure and morphology of VACNTs/CNFs could be precisely tuned and controlled by adjusting the percentage of reactants. The desired VACNTs/CNFs could not only possess high electric conductivity for efficient charge transport but could also increase surface area for accessing more electrolyte ions. When using an ionic liquid electrolyte, VACNTs/CNFs-based electric double layer (EDL) flexible supercapacitors can deliver a high specific energy of 70.7 Wh/kg at a current density of 0.5 A/g and at 30 Ā°C, and an ultrahigh-energy density of 98.8 Wh/kg at a current density of 1.0 A/g and at 60 Ā°C. Even after 20ā€Æ000 charging/discharging cycles, the EDL capacitor still retains 97.0% of the initial capacitance. The excellent performance highlights the important role of the branched VACNTs in storing and accumulating charge and the CNF backbone in transporting charge, thereby boosting both power density and energy density

    Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman

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    High load-bearing capacity is one of the crucial indicators for liquid superlubricants to move toward practicality. However, some of the current emerging systems not only have low contact pressures but also are highly susceptible to further degradation due to water adsorption and even superlubricity failure. Herein, a novel choline chloride-based ionic liquid analogues (ILAs) of a superlubricant with triethanolamine (TEOA) as the H-bond donor is reported for the first time; it obtains an ultralow coefficient of friction (0.005) and high load-bearing capacity (360 MPa, more than 2 times that of similar systems) due to adsorption of a small amount of water (<5 wt %) from the air. In situ Raman combined with 1H NMR and FTIR techniques reveals that adsorbed water competes with the hydroxyl group of TEOA for coordination with Clā€“, leading to the conversion of some strong H-bonds to weak H-bonds in ILAs; the localized strong H-bonds and weak H-bonds endow the ILAs with high load-bearing capacity and the formation of ultralow shear-resistance sliding interfaces, respectively, under the shear motion. This study proposes a strategy to modulate the interactions between liquid species using adsorbed water from air as a competing ligand, which provides new insights into the design of ILA-based macroscopic liquid superlubricants with a high load-bearing capacity

    Flexible Waterproof Rechargeable Hybrid Zinc Batteries Initiated by Multifunctional Oxygen Vacancies-Rich Cobalt Oxide

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    Although both are based on Zn, Znā€“air batteries and Znā€“ion batteries are good at energy density and power density, respectively. Here, we adopted Arā€“plasma to engrave a cobalt oxide with abundant oxygen vacancies (denoted as Co<sub>3</sub>O<sub>4ā€“<i>x</i></sub>). The introduction of oxygen vacancies to cobalt oxide not only promotes its reversible Coā€“O ā†” Coā€“Oā€“OH redox reaction but also leads to good oxygen reduction reaction and oxygen evolution (ORR/OER) performance (a half-wave potential of 0.84 V, four-electron transfer process for ORR, and 330 mV overpotential, 58 mVĀ·dec<sup>ā€“1</sup> Tafel slope for OER). We then constructed a battery system based on both Znā€“Co<sub>3</sub>O<sub>4ā€“<i>x</i></sub> and Znā€“air electrochemical reactions. The hybrid battery reveals both a high-power density of 3200 WĀ·kg<sup>ā€“1</sup> and high-energy density of 1060 WhĀ·kg<sup>ā€“1</sup>. Furthermore, the developed flexible solid-state hybrid batterydemonstrates good waterproof and washable ability (99.2% capacity retention of after 20 h water soaking test and 93.2% capacity retention after 1 h washing test). Interestingly, the fabricated flexible battery can work under water, and after the power is exhausted, the battery can automatically recover electricity output as long as it is exposed to air. The developed device is suitable for wearable applications considering its electrochemical performances, great environmental adaptation, and ā€œair recoverabilityā€. In addition, this study underscores the approach to develop hybrid energy-storage technologies through modification of electrode materials
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