Air-stable Aluminum Research Articles

Synthesis and hydrogen production kinetics of temperature-responsive aluminum-poly(N-isopropylacrylamide) core-shell nanoparticles

We report here on the synthesis of air-stable aluminum nanoparticles (Al NPs) capped with a temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM). These core-chell particles display temperature-dependent hydrogen production kinetics upon hydrolysis. Kinetic studies show that the bimolecular rate constant below the critical solution temperature (CST) is 2.85 × 10−4 L mol−1 s−1 (at 20 °C), which is nearly twice that of the rate constant (1.6 × 10−4 L mol−1 s−1) above the CST (at 40 °C). This non-Arrhenius behavior is proposed to originate from collapse of the capping layer above the CST which creates a less permeable capping layer. The core-shell nanoparticles were characterized with powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy with total attenuated reflection (FTIR-ATR), and differential scanning calorimetry coupled with thermogravimetric analysis (DSC/TGA). Transmission electron microscopy (TEM) confirms the Al NPs are core-shell structures and the composite particle size distribution ranges from 22 nm to 40 nm.

Synthesis of aluminum nanoparticles capped with copolymerizable epoxides

We report on the synthesis of air-stable aluminum nanoparticles (Al NPs) capped with 1,2-epoxy-9-decene. Long-chain epoxides have proven to be effective capping agents for Al NPs as the epoxide ring is highly susceptible to ring-opening polymerization, leading to the formation of putative polyether loops on the nascent Al NP surface. However, these materials are observed to degrade within several hours to days following exposure to ambient air. By inducing polymerization of the additional terminal alkene functionality on the epoxide, we have produced Al NPs that exhibit both a shelf life of ~6 weeks and a high active Al content. Transmission electron microscopy confirms that these spherical nanostructures, ~25 nm in diameter, are embedded in a covalently bound polymer matrix that serves as a prophylactic barrier against water/air (H2O/O2) degradation, and 27Al solid-state NMR is used to nondestructively confirm the presence of both metallic Al0 and oxidized Al3+. In addition, we have induced polymerization of the epoxide terminal alkene functionality with a long-chain diene monomer, 1,13-tetradecadiene, leading to the formation of Al NPs protected by an extremely hydrophobic polymer matrix. These core–shell nanomaterials also have high active Al contents along with extremely long shelf lives (up to 6 months upon air exposure).

Alcohol‐Processable Organic Amorphous Electrolytes as an Effective Electron‐Injection Layer for Organic Light‐Emitting Diodes

A new series of monoammonium-based organic electrolytes with the tetrafluoroborate (BF(4)(-)) counteranion have been synthesized. Replacing the pendant ethyl groups in the fluorenyl unit with 4-ethoxyphenyl groups dramatically improves both solubility and morphological stability. The characterization of the alcohol-processable amorphous ionic compounds as an electron-injection layer in organic light-emitting diodes (OLEDs) reveals that the organic electrolyte that comprises a rigid linear-conjugated unit provides better device performance, with respect to its counterpart containing a branched bulky moiety. The capability of these compounds to facilitate electron injection from air-stable aluminum metal is preliminarily discussed on the basis of the investigations of the electron-only devices and photovoltaic experiments.

Multispectroscopic (FTIR, XPS, and TOFMS−TPD) Investigation of the Core−Shell Bonding in Sonochemically Prepared Aluminum Nanoparticles Capped with Oleic Acid

Organically capped metal nanoparticles are an attractive alternative to more conventional oxide-passivated materials, due to the lower reaction temperatures and the possibility of tuning the organic coating. Sonochemical methods have been used to produce small (∼5 nm average size) air-stable aluminum nanoparticles capped with oleic acid. In order to understand the nature of the metal−organic bonding in the nanoparticles, we have used FTIR, XPS, and TOFMS−TPD techniques to study the organic passivation layer and its desorption at elevated temperatures. In the present case we find that the organic layer appears to be attached via Al−O−C bonds with the C atom formerly involved in the carboxylic acid functional group.

Sonochemically Assisted Thermal Decomposition of Alane N,N-Dimethylethylamine with Titanium (IV) Isopropoxide in the Presence of Oleic Acid to Yield Air-Stable and Size-Selective Aluminum Core−Shell Nanoparticles

Using sonochemistry to provide the thermal energy and mixing, we demonstrate the ability to synthesize air-stable aluminum nanoparticles of two different size distributions from the titanium-catalyzed thermal decomposition of alane. Characterization data indicate the presence of spherical face-centered-cubic aluminum nanoparticles with average sizes of either 5 or 30 nm that are capped with an organic shell. The average size of the nanoparticles correlates with the concentration of the passivation agent oleic acid, where a higher concentration results in smaller particles. Thermal analysis data demonstrates that at elevated temperatures (>550 °C), these particles react via a typical aluminum oxidation mechanism, whereas at low temperatures (<550 °C), the behavior of these particles is unique and directly related to the presence of the organic shell.

Soft-chemistry Route to P-I-N Heterostructured Quantum Dot Electroluminescence Device: All Solution-processed Polymer-Inorganic Hybrid QD-EL Device

ABSTRACTp-i-n heterostructured quantum-dot electroluminescence (QD-EL) device was fabricated by soft-chemical process, which shows a low turn-on voltage comparable to OLEDs. To construct the multilayered device structure, p-type polymer semiconductor was deposited on the ITO glass by sequential process of coating and thermal curing, thereupon a few monolayers of QD was spin-coated. n-type metal-oxide film was deposited on top of the QD luminescence layer by sol-gel method, providing a facile and low-cost route for the ETL fabrication. Prior to solution-processed ETL construction, a post-treatment is performed using cross-linking agent, in order to chemically-immobilize the QDs. As a cathodic electrode, relatively air-stable aluminum was deposited. The constituent material as well as the electronic band structure of the integrated device guarantees operating stability in air and low turn-on voltage.

High-efficiency red electrophosphorescent devices based on new osmium(II) complexes

In this paper, we report on highly efficient red-phosphorescent light-emitting diodes using a series of osmium complexes 1–3 doped into poly( N-vinyl-carbazole) (PVK) matrix as emitters, thermally stable 1,3,5-tris(4′-fluorobiphenyl-4-yl)benzene (F-TBB) as a hole-blocking layer, and Alq 3 as an electron injection layer. The CIE 1931 chromaticity coordinates of complexes 1–3 are around (0.650, 0.347), (0.681, 0.317), and (0.696, 0.302), respectively, and remain almost unchanged over a wide range of operation voltages. The maximum luminous efficiencies reached 7.0, 3.5, and 1.2 cd/A for devices based on 10 wt.% of osmium complexes 1, 2 and 3, respectively, even with air stable aluminum as the cathode. We systematically studied the dependence of device performance on the osmium doping concentrations. It was found that the best device performance was observed at 10 wt.% doping concentration for all three osmium complexes. Both maximum luminance and luminous efficiency increased with increasing osmium complex concentrations in the beginning and reached maximum at 10 wt.% doping concentration. However, a further increase in the doping level resulted in a reduction in both device brightness and efficiency due to concentration quenching and triplet–triplet annihilation. This is consistent with the absolute photoluminescence quantum yields of PVK thin films doped with different concentration of osmium complexes.

New Series of Blue-Emitting and Electron-Transporting Copolymers Based on Cyanostilbene

A novel series of conjugated copolymers having fluorene and binaphthyl moieties in the main chain and based on cyanostilbene were synthesized in good yields by a palladium-catalyzed Suzuki coupling reaction, a new approach different from the traditional Knoevenagel condensation polymerization. Through controllable modification of the main chain structures, not only were the thermal, electronic, and optical properties of the polymers tuned, but also the structure−property relationships were studied. All these polymers possess excellent thermal stability with glass-transition temperatures of 60−159 °C and onset decomposition temperatures of 411−417 °C. Cyclic voltammetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from −2.92 to −3.08 eV and low-lying HOMO energy levels ranging from −6.01 to −6.13 eV, and they may be promising candidates for electron-transporting or hole-blocking materials in light-emitting diodes (LEDs). The polymers in thin films emit strong blue luminance around 457−489 nm with narrow bandwidth upon photoexcitation. The single-layer LED fabricated with a copolymer F−CN composed of fluorene and cyanostilbene units using an air-stable aluminum electrode emits blue light with an external quantum efficiency of 0.006%. A double-layer LED, fabricated using a blend of poly(N-vinylcarbazole) and F−CN as emitting layer and tris(8-hydroxyquinolinato)aluminum as electron transporting layer, shows an external quantum efficiency of 0.2%. Preliminary electroluminescent results show that these polymers are new candidates for blue emissive materials in polymeric LEDs.

Novel Cyclohexylsilyl- or Phenylsilyl-Substituted Poly(p-phenylene vinylene)s via the Halogen Precursor Route and Gilch Polymerization

Novel cyclohexylsilyl- or phenylsilyl-substituted poly(1,4-phenylene vinylene) (PPV) derivatives, poly[2,5-bis(dimethylcyclohexylsilyl)-1,4-phenylene vinylene] (BDMCyS−PPV), poly[2,5-bis(dimethylphenylsilyl)-1,4-phenylene vinylene] (BDMPS−PPV), poly[2-dimethylcyclohexylsilyl-1,4-phenylene vinylene] (DMCyS−PPV), and poly[2-dimethylphenylsilyl-1,4-phenylene vinylene] (DMPS−PPV), were synthesized via the bromine precursor route (BPR) and Gilch dehydrohalogenation polyaddition. Thin films of the insoluble BDMCyS−PPV and BDMPS−PPV were fabricated from soluble polymer precursor materials by thermal conversion, and the electronic properties of these films were investigated. Monosilyl-substituted DMCyS−PPV and DMPS−PPV exhibited good solubility in the conjugated state, good film-forming properties, and high molecular weights. Moreover, they showed better thermal stability and higher values of Tg (DMCyS−PPV, 125 °C; DMPS−PPV, 127 °C) than other PPV derivatives including alkylsilyl-substituted PPVs; this improved mechanical stability led to good electroluminescence performance. Monocyclohexylsilyl- or phenylsilyl-substituted DMCyS−PPV and DMPS−PPV exhibited sharp PL emissions at about 511 and 513 nm, respectively, along with extremely high photoluminescence (PL) efficiencies in both solution and film (DMCyS−PPV, Φfilm = 0.83; DMCPS−PPV, Φfilm = 0.82). LED devices fabricated from DMCyS−PPV and DMPS−PPV using the configuration ITO/polymer/Al showed electroluminescence (EL) maxima at 510 and 515 nm, respectively, with external EL quantum efficiencies of 0.02% and 0.03%. Incorporation of PVK as a hole-transporting layer between the ITO and polymer with an air-stable aluminum cathode caused a substantial improvement in the EL quantum efficiencies, increasing the values to 0.07% for DMCyS−PPV and 0.08% for DMPS−PPV.

Violet–blue electroluminescent diodes utilizing conjugated polymer blends

We report violet–blue emission from light-emitting diodes (LEDs) fabricated by dispersing a soluble conjugated polymer poly(2,5-dibutoxyphenylene) (PPP) and an organic electron-transporting material 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) into a hole-transporting polymer poly( N-vinylcarbazole) (PVK). The emission film can be spin-coated by the blend solution. The air-stable aluminum is used as the cathode material. The electroluminescent efficiency of the device reaches 1.2%, which is more than 100 times that of the device made with only PPP. The LEDs turn on at about 20 V and have a peak emission wavelength in the violet–blue region at 424 nm.