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Constructing the strong interaction between the matrix and the active centers dominates the design of high-performance electromagnetic wave (EMW) absorption materials. However, the interaction-relevant absorption mechanism is still unclear, and the design of ultrahigh reflection loss (

Cryogenic electron microscopy is one of the fastest and most robust methods for capturing high-resolution images of proteins, but stringent sample preparation, imaging conditions, and in situ radiation damage inflicted during data acquisition directly affect the resolution and ability to capture dynamic details, thereby limiting its broader utilization and adoption for protein studies. We addressed these drawbacks by introducing synthesized giant carbon nano-test tubes (GCNTTs) as radiation-insulating materials that lessen the irradiation impact on the protein during data acquisition, physical molecular concentrators that localize the proteins within a nanoscale field of view, and vessels that create a microenvironment for solution-phase imaging. High-resolution electron microscopy images of single and aggregated hemoglobin molecules within GCNTTs in both solid and solution states were acquired. Subsequent scanning transmission electron microscopy, small-angle neutron scattering, and fluorescence studies demonstrated that the GCNTT vessel protected the hemoglobin molecules from electron irradiation-, light-, or heat-induced denaturation. To demonstrate the robustness of GCNTT as an imaging platform that could potentially augment the study of proteins, we demonstrated the robustness of the GCNTT technique to image an alternative protein, d-fructose dehydrogenase, after cyclic voltammetry experiments to review encapsulation and binding insights. Given the simplicity of the material synthesis, sample preparation, and imaging technique, GCNTT is a promising imaging companion for high-resolution, single, and dynamic protein studies under electron microscopy.

Compared to traditional electric double-layer capacitors, redox-enhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g-1 charging rate and fast discharge rate produces the best overall performance.

The addition of redox-active molecules into electrochemical-capacitor electrolytes provides increased specific energy density. Here we illustrate the underlying operational mechanisms and design pr...

The chemical reactivity and/or the diffusion of Ag atoms or ions during thermal processing can cause irreversible structural damage, hindering the application of Ag nanowires (NWs) in transparent c...

Redox-enhanced electrochemical capacitors (redox ECs) are a class of augmented electric double-layer capacitors utilizing reversible redox reactions of soluble redox couples in the electrolyte. These systems offer increased energy density, efficient power delivery, and simple construction. In this Perspective, we provide an overview of the emerging field of redox ECs, including the current status, advantages, and outstanding problems confronting their development. Our discussion is primarily focused on operating mechanisms and how they affect performance. We also provide a perspective on the advantage of dual-redox ECs and how to improve them based on fundamental design principles including self-discharge suppression strategies. Finally, we comment on best practices for device characterization, suggest performance-reporting protocols for redox ECs, and examine future directions for the field.

Research in electric double-layer capacitors (EDLCs) and rechargeable batteries is converging to target systems that have battery-level energy density and capacitor-level cycling stability and power density. This research direction has been facilitated by the use of redox-active electrolytes that add faradaic charge storage to increase energy density of the EDLCs. Aqueous redox-enhanced electrochemical capacitors (redox ECs) have, however, performed poorly due to cross-diffusion of soluble redox couples, reduced cycle life, and low operating voltages. In this manuscript, we propose that these challenges can be simultaneously met by mechanistically designing a liquid-to-solid phase transition of oxidized catholyte (or reduced anolyte) with confinement in the pores of electrodes. Here we demonstrate the realization of this approach with the use of bromide catholyte and tetrabutylammonium cation that induces reversible solid-state complexation of Br2/Br3–. This mechanism solves the inherent cross-diffusion i...

While silver and gold have been the dominant plasmonic metals used for surface-enhanced Raman spectroscopy (SERS) since the field’s inception. We argue that virtually any metal, when appropriately nanostructured as a grating, has the potential to be an efficient SERS substrate. This conclusion provides the basis for making SERS a general tool for studying surface processes and catalysis and allows SERS substrates to be routinely based on earth-abundant, low-cost, and chemically interesting metals. We illustrate the above premise by producing highly performing SERS substrates using aluminum, nickel, and copper in addition to silver and gold as benchmarks. All five metals were found to yield high SERS intensities. The approximately three orders enhancement variation among the five substrates based on differing metals is ascribed mainly to local field effects associated with individual grating elements. This conclusion is supported by local field calculations. This suggests that the largest contribution to t...

Gratings have been widely investigated both theoretically and experimentally as surface-enhanced Raman spectroscopy (SERS) substrates, exhibiting, under appropriate circumstances, increased far-field extinctions and near-field intensities over those of an appropriately equivalent number of isolated particles. When the grating order transitions from evanescent to radiative, narrow resonance peaks are observed in the extinction spectrum whose properties can be manipulated by controlling the grating's geometric parameters. Here we report the application of the architectural principles of grating fabrication using a square two-dimensional array of gold-coated nanostructures that achieves SERS enhancements of 10(7) uniformly over areas of square centimeters. The high-performance grating substrates were fabricated using commonly available foundry-based techniques that have been chosen for their applicability to large-scale wafer processing. Additionally, we restricted ourselves to a parametric regime that optimizes SERS performance in a repeatable and reproducible manner.

The performance of redox-enhanced electrochemical capacitors (redox ECs) is substantially improved when oxidized catholyte (bromide) and reduced anolyte (viologen) are retained within the porous electrodes through reversible counterion-induced solid complexation. Investigation of the mechanism illustrates design principles and identifies pentyl viologen/bromide (PV/Br) as a new high-performance electrolyte. The symmetric PV/Br redox EC produces a specific energy of 48.5 W·h/kgdry at 0.5 A/gdry (0.44 kW/kgdry) with 99.7% Coulombic efficiency, maintains stability over 10 000 cycles, and functions identically when operated with reversed polarity.

Plasmonic metal/semiconductor heterostructures show promise for visible-light-driven photocatalysis. Gold nanorods (AuNRs) semi-coated with TiO2 are expected to be ideally structured systems for hydrogen evolution. Synthesizing such structures by wet-chemistry methods, however, has proved challenging. Here we report the bottom-up synthesis of AuNR/TiO2 nanodumbbells (NDs) with spatially separated Au/TiO2 regions, whose structures are governed by the NRs' diameter, and the higher curvature and lower density of CnTAB surfactant at the NRs' tips than on their lateral surfaces, as well as the morphology's dependence on concentration, and alkyl chain length of CnTAB. The NDs show plasmon-enhanced H2 evolution under visible and near-infrared light.

We propose a nanostructured Mn-doped V2O5 lithium-ion battery cathode material that facilitates cathodic charge transport. The synthesis strategy uses a layered compound, vanadium(III) jarosite, as the precursor, in which the Mn2+ ions are doped uniformly between the vanadium oxide crystal layers. Through a two-step transformation, the vanadium jarosite was converted into Mn2+-doped V2O5. The resulting aliovalent doping of the larger Mn cations in the modified V2O5 structure increases the cell volume, which facilitates diffusion of Li+ ions, and introduces oxygen vacancies that improve the electronic conductivity. Comparison of the electrochemical performance in Li-ion batteries of undoped and the Mn2+-doped V2O5 hierarchical structure made from layered vanadium jarosite confirms that the Mn-doping improves ion transport to give a high cathodic columbic capacity (253 mAhg–1 at 1C, 86% of the theoretical value, 294 mAhg–1) and excellent cycling stability.

We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx -/I- couple and a redox couple of H2O/Had on the negative electrode, respectively. Here, we, for the first time, report utilizing IOx -/I- redox couple for the positive electrode, which pins the positive electrode potential to be 0.4-0.5 V vs. Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach -1.1 V vs. Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectrometry and Raman spectrometry confirm the formation of IO3 - ions (+5) from I- (-1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between -20 to 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14,000 cycles.

The optical resonances of plasmonic nanostructures depend critically on the geometrical details of the absorber. We show that this unique property of plasmons can potentially be used to create panchromatic absorbers covering most of the useful solar spectrum, by measuring the light-to-hydrogen conversion capabilities of a series multielectrode photocatalytic devices, based on functionalized gold nanorods of appropriately chosen aspect ratios. Judiciously combining nanorods of various aspect ratios almost doubles the H2 production of the device over what is optimally possible with a device using gold nanorods of a single aspect ratio (all other key parameters being equal). The estimated quantum efficiency (absorbed photons-to-hydrogen) averaged over the entire solar spectrum of the best performing plasmonic multielectrode array was approximately 0.1%, and the measured H2 production rate for all of the devices was found to be approximately proportional to the hot electron generation. The device was monitored continuously for over 200 hr of operation without measurable diminution in the rate.

We report a method for preparing p-type silicon germanium bulk alloys directly from a boron-doped silica germania nanocomposite. This is the first successful attempt to produce and characterize the thermoelectric properties of SiGe-based thermoelectric materials prepared at temperatures below the alloy's melting point through a magnesiothermic reduction of the silica-germania nanocomposite. We observe a thermoelectric power factor that is competitive with the literature record obtained for high energy ball milled nanocomposites. The large grain size in our hot pressed samples limits the thermoelectric figure of merit to 0.5 at 800 C for an optimally doped Si80Ge20 alloy. © 2013 American Chemical Society.

A key challenge for the materials chemist is the development of controllable and straightforward synthetic methodologies that will integrate multiple phases/compositions with scalar designed physical properties. The intent of this Perspective is to give a brief summary of some of the current bulk-scaled approaches that might help guide researchers in the design of optimal heterostructures in large quantity for the further improvement of thermoelectric conversion efficiency. Examples of two-phase combinations on different length scales will be discussed with a focus on the hot carrier filtering effect that results from the selective scattering of carriers with different energies. On the basis of this strategy, heterostructures fabricated by both the bottom-up solution approaches at low temperature and top-down solid-state deposition routes that show promise in improving the thermoelectric figure of merit are highlighted. © 2013 American Chemical Society.

Methyl bromide is used as feed in a process that converts it to gasoline. It is prepared by the gas-phase reaction of CH4 with Br2, a reaction that produces, besides the desired CH3Br, large amounts of CH2Br2. The latter cokes the catalyst used for gasoline production. The separation of CH2Br2 by distillation makes gasoline production too expensive. It is therefore important to increase the selectivity of the bromination reaction. We show that a small amount of I 2 catalyzes the reaction CH2Br2 + CH 4 → 2CH3Br, which leads to higher CH4 conversion and higher selectivity to CH3Br. These findings are promising for developing a low-cost integrated bromine-iodine based dual-halogen pathway to convert stranded natural gas into fuels and chemicals. © 2013 American Chemical Society.

Propane oxidative dehydrogenation is a promising candidate for on-purpose propylene production. However, in oxidative dehydrogenation the propylene yield is limited by the simultaneous oxidization of propane to multiple oxygenated byproducts. We show that a small amount of I2 is highly effective in catalyzing the dehydrogenation of propane into propylene, using dibromomethane (DBM), a byproduct of the activation of methane by bromine, as the oxidant. Single-pass “C3H6+C3H7X” (X = Br, I; C3H7X can be easily converted to C3H6 and HX) yields of up to 80% can be easily achieved, with the highly selective conversion of DBM to methyl bromide, which is readily converted into either high-market-value petrochemicals or liquid fuels. Bearing in mind that the formation of DBM is one of the major undesirable byproducts in the bromine-mediated gas-to-liquid technology, our findings create a win-win situation. On the one hand, this approach is promising for developing a low-cost, on-purpose propylene technology using n...

CH3Br, like CH3OH in the Methanol-To-Gasoline process, can be readily directly converted to petrochemicals and liquid fuels. CH3Br can be obtained in high yields by the direct bromination of methane using relatively low reaction temperatures and pressure, but with the formation of dibromomethane (DBM) as a primary side product. Here, we report that DBM can be highly selectively converted to higher hydrocarbons and methyl bromide via a catalytic hydrodebromination process. Silica-supported palladium carbide shows a high selectivity for the conversion of DBM to higher hydrocarbons, mainly light olefins. Silica-supported ruthenium has a high selectivity for the conversion of DBM to methyl bromide, which can then be converted to fuels or light olefins. These reactions offer pathways to increase the overall useful product yield of the methane bromination reaction, thus taking an important step toward the potential industrial application of bromine mediated Gas-To-Liquid technology.

Ultrafine MoO2 nanorods with a diameter of ∼5 nm were successfully synthesized by a nanocasting method using mesoporous silica SBA-15 as hard template. This material demonstrates high reversible capacity, excellent cycling performance, and good rate capacity as an anode electrode material for Li ion batteries. The significant enhancement in the electrochemical Li storage performance in ultrafine MoO2 nanorods is attributed to the nanorod structure with small diameter and efficient one-dimensional electron transport pathways. Moreover, density functional theory calculations were performed to elucidate the Li uptake/removal mechanism in the MoO2 electrodes, which can help us understand the unique cycling behavior of MoO2 material.

Substituted metal oxides containing ionic species have been attracting a great deal of attention because of their potential ability to reduce the usage of precious metals in heterogeneous catalysts. We investigate Pd-substituted CeO2 for C–H bond activation reactions including the partial oxidation and dry reforming of CH4. This catalyst has been previously studied for CO oxidation, NOx reduction, and the water-gas shift reaction. Pd-substituted CeO2, Ce1–xPdxO2−δ, was prepared as a powder with high surface area and a hollow sphere morphology using ultrasonic spray pyrolysis. The catalysts were extensively characterized using synchrotron X-ray diffraction and other techniques, confirming phase pure samples up to 10 mol % Pd substitution. Ce0.95Pd0.05O2−δ was found to be active for partial oxidation of CH4 around 500 °C and higher. Our studies, including postcatalytic synchrotron diffraction, suggest that the single-phase Ce1–xPdxO2−δ material is not the active species and that catalysis occurs instead ove...

Chemical gardens form when ferrous chloride hydrate seed crystals are added or concentrated solutions are injected into solutions of sodium silicate and potassium phosphate. Various precipitation morphologies are observed depending on silicate and phosphate concentrations, including hollow plumes, bulbs, and tubes. The growth of precipitates is controlled by the internal osmotic pressure, fluid buoyancy, and membrane strength. Additionally, rapid bubble-led growth is observed when silicate concentrations are high. ESEM/EDX analysis confirms compositional gradients within the membranes, and voltage measurements across the membranes during growth show a final potential of around 150-200 mV, indicating that electrochemical gradients are maintained across the membranes as growth proceeds. The characterization of chemical gardens formed with iron, silicate, and phosphate, three important components of an early earth prebiotic hydrothermal system, can help us understand the properties of analogous structures that likely formed at submarine alkaline hydrothermal vents in the Hadean-structures offering themselves as the hatchery of life.

Photovoltaic devices based on organic semiconductors require charge-separating networks (bulk heterojunctions) for optimal performance. Here we report on the fabrication of organic-inorganic photovoltaic devices with tailored (n-type) CdSe nanorod arrays aligned perpendicularly to the substrate. The nanorod lengths varied from 58 ± 12 to 721 ± 15 nm, while the diameters and inter-rod spacings were kept constant at 89.5 ± 7.5 and 41.3 ± 9.9 nm, respectively. Short-circuit densities improved linearly with nanorod length, resulting in power conversion efficiencies of up to 1.38% for cells with nanorods 612 ± 46 nm long. Notably, the cell's efficiency was dominated by exciton generation in the CdSe nanorods.

Gold nanoparticles ∼2 nm in diameter were synthesized with, on average, between 0 and ∼5.4 anionic thiols per particle. An electrochemical quartz-crystal microbalance was used to monitor the motion of ions and electrons during redox cycling (charging) of thin films of these nanoparticles. When the electrochemistry was performed using a polyanion electrolyte too large to penetrate the nanoparticle film, the degree of oxidation that was possible was found to be dictated by the average number of anionic ligands on the particle surface available for charge compensation. These anionic nanoparticle thin films were combined with previously reported/synthesized cationic nanoparticles into solution-processed nanoparticle film bilayers. We demonstrate using these bilayers that the control over charge compensation kinetics afforded by the use of a polyelectrolyte supporting electrolyte in conjunction with ionic surface functionalization allows for the selective charging of one layer of nanoparticles over the other a...

Exceptionally sensitive hydrogen sensors were produced using Pd-nanoparticle-decorated, single vanadium dioxide nanowires. The high-sensitivity arises from the large downward shift in the insulator to metal transition temperature following the adsorption on and incorporation of atomic hydrogen, produced by dissociative chemisorption on Pd, in the VO(2), producing approximately 1000-fold current increases. During a rapid initial process, the insulator to metal transition temperature is decreased by10 degrees C even when exposed to trace amounts of hydrogen gas. Subsequently, hydrogen continues to diffuse into the VO(2) for several hours before saturation is achieved with only a modest change in the insulator to metal transition temperature but with a significant increase in the conductivity. The two time scales over which H-related processes occur in VO(2) likely signal the involvement of two distinct mechanisms influencing the electronic structure of the material one of which involves electron-phonon coupling pursuant to the modification of the vibrational normal modes of the solid by the introduction of H as an impurity.

In this work, we report a facile solution-phase synthesis of hollow cubic phase α-NaYF4 nanoparticles by a controlled ion exchange process from cubic phase Y2O3 nanospheres. We demonstrate that hol...

Nanometer-sized liquid droplets formed at temperatures below the bulk melting point become supercooled as they grow through Ostwald ripening or coalescence and can be exploited to grow nanowires without any catalyst. We used this simple approach to synthesize a number of highly crystalline metal oxide nanowires in a chemical or physical vapor deposition apparatus. Examples of nanowires made in this way include VO(2), V(2)O(5), RuO(2), MoO(2), MoO(3), and Fe(3)O(4), some of which have not been previously reported. Direct evidence of this new mechanism of nanowire growth is found from in situ 2-dimensional GISAXS (grazing incidence small angle X-ray scattering) measurements of VO(2) nanowire growth, which provides quantitative information on the shapes and sizes of growing nanowires as well as direct evidence of the presence of supercooled liquid droplets. We observe dramatic changes in nanowire growth by varying the choice of substrate, reflecting the influence of wetting forces on the supercooled nanodroplet shape and mobility as well as substrate-nanowire lattice matching on the definition of nanowire orientation. Surfaces with defects can also be used to pattern the growth of the nanowires. The simplicity of this synthesis concept suggests it may be rather general in its application.

We present a simple, solution-based synthetic route to hollow cerium oxide spheres. Thin layers (∼12 nm) of cerium oxide are deposited onto ∼200 nm silica colloids using cerium nitrate and the silica cores are subsequently removed to yield hollow spheres. The spheres are composed of ∼4 nm ceria nanocrystals. Nitrogen adsorption isotherms indicate that the spheres are microporous with pore sizes of approximately 10 A. The spheres are thermally stable to collapse and ripening up to 700 °C and are active for the catalytic combustion of carbons. The hollow ceria spheres developed in this work are attractive as building blocks for multicomponent catalysts.

Perpendicularly aligned semiconducting CdSe nanorod arrays were fabricated on ITO-coated glass substrate using porous aluminum oxide (PAO) as a hard template. Nanorod lengths were varied between 50 and 500 nm, while keeping the diameter at 65 nm. The electrochemical photovoltaic performance was found to depend critically on nanorod length and crystallinity. Arrays of rods annealed at 500 degrees C showed an order of magnitude improvement in white light power conversion efficiency over unannealed samples. The largest power conversion efficiency of 0.52% was observed for nanorods 445 +/- 82 nm in length annealed at 500 degrees C. The technique described is generally applicable to fabricating highly aligned nanorods of a broad range of materials on a robust transparent conductor.

The electrocatalytic activity of gold-platinum (Au-Pt) clusters was investigated in acidic and alkaline electrolytes. The clusters were synthesized by electrodeposition on fluorinated tin oxide (FTO) substrates and carbon disks with dimensions from 50 to 200 nm. Methanol electrooxidation (fuel cell anode) and oxygen electroreduction (fuel cell cathode) activities were measured using cyclic voltammetry and chronoamperometry. The results for methanol electrooxidation showed that platinum could be partially substituted by gold to achieve higher resistance to poisoning without affecting the activity in acid electrolyte, while in alkaline environment, a significant overall improvement in performance was observed. On the other hand, for the oxygen electroreduction, kinetic results obtained using a rotating disk electrode (RDE) indicated that Au alloying with Pt does not significantly alter the catalytic activity in acidic electrolyte, while a significant improvement in activity was observed in an alkaline electrolyte, which is attributed to a synergistic effect between the Au and Pt.

Electrostatic interactions between the imidazole-based cationic homopolymer, polyvinylimidazole (PVIm), and anionic polysaccharide, sodium alginate, lead to the formation of colloidal aggregates known as complex coacervates in the pH range 4–6.5. PVIm was labeled with the fluorescent reporter pyrene to investigate the coacervation-induced changes in and around PVIm chains. While the pyrene-tagged PVIm had blue fluorescence in water, the coacervate phase exhibited an additional broad band around 492 nm (green) due to formation of pyrene excimers. Fluorescence spectroscopic investigations point toward aggregation of PVIm chains and desolvation upon coacervation. Highly anisotropic fluorescence emission indicates tight packing of the polymer chains in the coacervate. Confocal microscopy of fluorescein-labeled alginate and rhodamine-labeled PVIm shows coacervates as dense aggregates with uniform distribution of the polymers. Fluorescence spectroscopy offers sensitive and easy investigation into polyelectrolyte interactions.

Free-standing and supported films with a lateral gradient in composition were prepared using blends of poly(acrylic acid) (PAA)/sodium salt and its copolymers with acrylamide (AAm) in an applied electric field. The gradients were stabilized by complexation of carboxylate groups with metal species. To find the favorable conditions and components for successful blending and interaction with Fe and Ce species, we studied blending of the two PAA samples with molecular weights of 2000 and 15 000 Da with two copolymers of AA and AAm (with 10 and 70 wt % of AA units) and interaction of these blends with Fe(III) and Ce(IV) ions. The structure of the hybrid (blend) films was studied using differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, X-ray diffraction, and optical microscopy. To ensure blend miscibility and efficient interaction with metal ions, the copolymer containing 70 wt % AA units has been used. The surface enrichment with metal species was observed at all experimental conditions studied in this work. For lateral gradient film formation, 15 000 Da PAA has been used to avoid uneven distribution of the homopolymer in the film, observed for 2000 Da PAA. The gradient films were characterized by XPS. The lateral gradient of functionality such as COONa group or Fe content has been obtained at different strengths of electric field applied during film formation. The use of lower voltage allows one to prevent NaOH formation and creates more favorable conditions for development of a gradient polymer film. The Ce content gradient was not observed due to formation of large Ce oxide particles (or = 750 nm), masking the gradient of functionality. For the first time, free-standing films with a lateral gradient in composition were prepared using an applied electric field.

Electrochemical methods for the codeposition of Cr or Mo with α-Fe2O3 (hematite) have been developed to produce doped iron oxide films with varying compositions of Cr and Mo which are active photoanodes for photoelectrochemical (PEC) water decomposition (“water splitting”). The films were characterized by scanning electron microscopy, X-ray diffraction, UV−vis optical spectroscopy, and X-ray photoelectron spectroscopy to determine the effect of the dopants on the hematite structure and PEC performance. Upon doping, the microstructures of the films varied; however, no preferred crystallographic orientation or dopant phase segregation was observed. The best performing samples were 5% Cr and 15% Mo doped which had Incident Photon Conversion Efficiencies (IPCE’s) at 400 nm of 6% and 12%, respectively, with an applied potential of 0.4V vs Ag/AgCl. These IPCE values were 2.2× and 4× higher than the undoped sample for the 5% Cr and 15% Mo samples, respectively. The increase in performance is attributed to an imp...

Several naturally occurring biomacromolecular structures, particularly those containing histidine-rich proteins, have been shown to depend on metal ion complexation for hardness and stiffness. In this study, water-soluble metal-binding polymers and copolymers based on vinylimidazole were utilized to mimic the glycine- and histidine-rich proteins of ragworm jaws. Blends of these polymers with agarose exhibited a significant capacity for Zn(II) and Cu(II) complexation. Rheological and uniaxial tensile tests as well as nanoindentational analysis of the blends revealed a more than 10-fold improvement in the tensile strength, along with increases in the hardness of the dried samples, upon metal ion addition. Pronounced differences in mechanical effects, however, were associated with Cu(II) and Zn(II) complexation, and the latter provided much better overall mechanical performance.

We demonstrate that ionic surface functionalization is well-suited for controlling the electrochemical charging of nanoparticle assemblies. Gold nanoparticles approximately 2 nm in diameter were functionalized with between 0 and approximately 3.3 cationic thiols per particle and the coupled motion of ions and electrons during redox cycling (charging) was followed in situ using an electrochemical quartz-crystal microbalance. When the electrochemistry is performed using a polycation electrolyte too large to penetrate the nanoparticle film, the degree of reduction possible was found to be dictated by the number of cationic ligands on the particle surface available for charge compensation. This route to reduced particles might be useful for electronic device fabrication, since the negative electronic charge is precisely compensated by immobile cationic ligands.

We developed a simple sol−gel chemistry-based opal infiltration method for the fabrication of high-quality planar titania photonic crystals. Polystyrene synthetic opals were infiltrated with a hydrophobic and air/moisture-stable liquid titania precursor. The high stability and hydrophobicity of the titania precursor enabled a new “lift-off/turn-over” backfilling technique that after calcination gives planar titania inverse opals with a flat and completely open surface, without the need for additional processing steps to remove any excess surface coating of the backfilling material. We also compare two different infiltration strategies and their influence on the structural and photonic properties. The obtained inverse opals display excellent photonic properties as evidenced by the presence of first-, second-, and third-order Bragg reflection peaks in accordance with theoretical photonic band structure calculations.

The development of one- and two-photon induced polymerization using CdS semiconductor quantum dots (QDs) and amine co-initiators to promote radical generation and subsequent polymerization is presented. Two-photon absorption (TPA) cross-section measurements, linear absorption, and transmission electron microscopy are used to characterize the QDs. The effectiveness of the co-initiators in increasing the efficiency of photopolymerization (polymer chains formed per excitation) is examined. Triethylamine was observed to be most effective, yielding quantum efficiencies of initiation of >5%. The interactions between the co-initiators and QDs are investigated with steady-state photoluminescence and infrared spectroscopies. Possible initiation mechanisms are discussed and supported by electrochemical data. Making use of the surface chemistry developed here and the large QD TPA cross-sections, two-photon induced polymerization is demonstrated. The large TPA cross-sections coupled with modest quantum efficiencies for initiation reveal the unique potential of molecularly passivated QDs as efficient two-photon photosensitizers for polymerization.

CdSe nanorod electrode arrays with the nanorods aligned normal to the substrate were fabricated using porous aluminum oxide (PAO) templates. Photovoltaic characteristics were determined electrochemically in an aqueous solution using polysulfide (Sn2−) as the redox mediator. Isolating the back electrode from the electrolyte with a 100-nm-thick TiO2 barrier layer increased the open circuit voltage from −0.23 to −0.34 V and the fill factor from 0.42 to 0.57. Depending on the electrolyte concentration, IPCE values between 2.5 and 8% were observed at an incident wavelength of 500 nm. Internal quantum efficiencies were estimated to approach 50%. This architecture could be beneficial for the fabrication of bulk-heterojunction photovoltaic devices in conjunction with solution-deposited semiconducting inorganic nanoparticles or organic semiconductors.

We report a novel strategy for writing volume holograms by photoacid generation and subsequent acid-catalyzed degradation leading to increased free volume/refractive index modulation in the exposed regions of a cross-linked rigid polymeric matrix. This strategy offers nondestructive read out and high diffraction efficiency and allows optical-quality, millimeter thick films to be fabricated that possess excellent thermal and dimensional stability. A key feature of this approach is the efficient acid-catalyzed degradation of functional groups in the cross-linked matrix leading to release of volatile products which diffuse readily out of the thick films. Furthermore, the reported data storage material is lightweight and inexpensive and can be easily processed into different shapes, making it an attractive candidate for data storage applications.

Molecular assembly enables the formation of material systems with multiple compositions and functions that are structured at the mesoscale (2−50 nm) and beyond. This approach allows structure control through the competitive tuning of bulk and surface interactions to yield new mechanical, catalytic, optoelectronic, biological, and other properties. The molecular-assembly process is governed by the interactions between different components of the assembling system and with their external environment. This review summarizes the fundamental principles of molecular assembly in the synthesis of mesostructured inorganic–organic materials and focuses on recent attempts to utilize external fields (magnetic, electric, or mechanical) and dimensional confinement (in one, two, and three dimensions) to direct the molecular assembly of mesostructured organic–inorganic hybrids with astonishing complexity.

Membrane proteins are a class of nanoscopic entities that control the matter, energy, and information transport across cellular boundaries. Electrostatic interactions are shown to direct the rapid co-assembly of proteorhodopsin (PR) and lipids into long-range crystalline arrays. The roles of inherent charge variations on lipid membranes and PR variants with different compositions are examined by tuning recombinant PR variants with different extramembrane domain sizes and charged amino acid substitutions, lipid membrane compositions, and lipid-to-PR stoichiometric ratios. Rational control of this predominantly electrostatic assembly for PR crystallization is demonstrated, and the same principles should be applicable to the assembly and crystallization of other integral membrane proteins.

This work reports on progress in controlling the size and porosity of spontaneously assembled composite polyelectrolyte microspheres for their potential use in targeted drug delivery applications. ...

Efficient encapsulation of functionalized spherical nanoparticles by viral protein cages was found to occur even if the nanoparticle is larger than the inner cavity of the native capsid. This result raises the intriguing possibility of reprogramming the self-assembly of viral structural proteins. The iron oxide nanotemplates used in this work are superparamagnetic, with a blocking temperature of about 250 K, making these virus-like particles interesting for applications such as magnetic resonance imaging and biomagnetic materials. Another novel feature of the virus-like particle assembly described in this work is the use of an anionic lipid micelle coat instead of a molecular layer covalently bound to the inorganic nanotemplate. Differences between the two functionalization strategies are discussed.

Mesostructured non-silicate oxides, with well-defined organization on the 2–50 nm size scale, may play a pivotal role in advancing vital disciplines such as catalysis, energy conversion, and biotechnology. Herein, we present selected methodologies for utilizing the sol–gel process, in conjunction with organic-directed assembly, to synthesize a variety of mesostructured oxides. The nature of the inorganic precursor is critical for this process. We discuss the development of general routes for yielding stable, nanoscopic, hydrophilic, inorganic precursors compatible with organic co-assembly. In particular, we highlight the use and characterization of organic-acid-modified transition metal oxide sol–gel precursors that allow for the synthesis and processing of designer mesostructured oxides such as titania hybrids for optical applications and porous multicomponent metal oxides useful for catalysis.

Multicomponent metal oxides have attracted attention for their potential use in electronic, (photo)catalytic, photovoltaic, and energy storage applications. The ability to simultaneously control the nanoscale structure and composition of such materials using simple and inexpensive routes is important for that potential to be realized. Here we introduce a simple and widely applicable methodology for the synthesis of multicomponent mesostructured metal oxides (MMMOs) from the combination of inexpensive and commercially available polymers with metal alkoxides solubilized in a sol−gel solution consisting of acetic acid, hydrochloric acid, and ethanol (AcHE). MMMOs obtained utilizing the AcHE system have tunable pore structures, a high degree homogeneity, and in certain cases thermal stability above 1000 °C. The ability to easily process these diverse MMMOs in the form of thin films, free-standing membranes, and monoliths provides distinct advantages over previously reported MMO synthesis proceduresespecially ...

The outstanding mechanical properties of impact-bearing tissues, such as Nereis jaws, make their morphology and chemical composition a subject of particular interest. The complex structure of the jaw was recently reported to exhibit molecular gradients that were closely correlated with stiffness and hardness.(18) Accordingly, we have explored the spatial distribution and bonding chemistries of Zn and the halogens in the surface structure of the jaws. Using secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM), we found that Cl, Br, and I distributions are enhanced in surface layers of the basal protected portion of the jaw but are shifted to greater depths toward the exposed jaw tip. There are thus two complementary halogen gradients in the jaw: one on the surface that decreases from the base to the tip, coupled to an increasing one in the subsurface layers. The outer surface coating appeared to have granular morphology, in contrast to the anisotropic, fibrous core that dominates the subarchitecture. Using X-ray photoelectron spectroscopy (XPS), we discovered that Zn, I, and Br in the jaws have single chemical environments whereas chlorine is present in two distinct modes (Cl-Zn and Cl-C). Given the inverse relationship between surface exposure and halogen abundance in the jaws, it is unlikely that the halogens contribute directly to mechanical properties such as wear and hardness.

Gold nanorods and bipyramids have been synthesized using the seed-mediated approach in aqueous cetyltriethylammonium bromide (CTEAB) solutions in the presence of silver nitrate. Gold nanoparticle seeds that are stabilized with either CTEAB or sodium citrate have been used. The use of the CTEAB-stabilized seeds gives gold nanorods in high yield in one step with the longitudinal plasmon wavelength ranging from 750 to 1030 nm, depending on the amount of the seeds. The longitudinal plasmon wavelength can be extended to 1100 nm by the use of a two-step growth method. The growth of gold nanorods in CTEAB solutions takes 5-10 h, more than 5 times slower than that in cetyltrimethylammonium bromide solutions at the same concentration of surfactants. The use of the citrate-stabilized seeds gives both gold bipyramids and a small percentage of gold nanorods. The longitudinal plasmon wavelength of the bipyramids is tunable from 700 to 1100 nm by varying the amount of the citrate-stabilized seeds. The growth of gold bipyramids takes more than 1 day. Transmission electron microscopy characterizations reveal that the gold nanorods grown from both types of gold nanoparticle seeds are single-crystalline and that the gold bipyramids are penta-twinned.

High-optical-quality titania-based mesostructured films with cubic or 2D-hexagonal symmetry were fabricated by combining trifluoroacetate (TFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers. The distribution, dynamics, and local environments of the TFA-modified titania, PEO, and PPO components of the hybrid were investigated. IR/Raman spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy studies indicate that TFA coordinates the titanium center and forms a stable complex that is subsequently organized by the block copolymer species into ordered mesostructures. Solid-state NMR (19)F--(1)H cross-polarization, (13)C{(1)H} two-dimensional heteronuclear correlation, and (1)H relaxation techniques were used to determine that PEO is predominantly incorporated within the TFA-modified titania, and that PPO environments encompass both microphase separated regions and interfacial regions composed of mixed PPO and TFA-modified titania. NMR (19)F multiple-quantum spin counting measurements suggest that -CF(3) groups of the trifluoroacetate ligands do not form clusters but instead randomly distribute within the inorganic component of the hybrid.