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Rechargeable zinc-air batteries (ZABs) have been considered promising as next-generation sustainable energy storage devices; however, their large-scale deployment is hampered by the unsatisfactory cyclic lifespan. Employing neutral and mild-acidic electrolytes is effective in extending the cyclability, but the rapid performance degradation of the bifunctional catalysts owing to different microenvironmental requirements of the alternative oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a serious limitation of their cyclic life. Herein, we propose a "self-decoupling" strategy to significantly improve the stability of the bifunctional catalysts by constructing a smart interface in the bifunctional air electrode. This smart interface, containing a resistance-switchable sulfonic acid doped polyaniline nanoarray interlayer, is nonconductive at high potential but conductive at low potential, which enables spontaneous electrochemical decoupling of the bifunctional catalyst for the ORR and OER, respectively, and thus protects it from degradation. The resulting self-decoupled mild-acidic ZAB delivers stable cyclic performances in terms of a negligible energy efficiency loss of 0.015% cycle -1 and 3 times longer cycle life (∼1400 h) compared with the conventional mild-acidic ZAB using a normal bifunctional air electrode and the same low-cost ZnCo phosphide/nitrogen-doped carbon bifunctional catalyst. This work provides an effective strategy for tolerating alternative oxidation-reduction reactions and emphasizes the importance of smart nanostructure design for more sustainable batteries.

Dual-band electrochromic devices (DBEDs), which can selectively modulate near-infrared (NIR) and visible (VIS) light transmittance through electrochromism, have gained increasing interest as a building energy saving technology. The technology is strongly dependent on the progress in electrochromic materials. Most current research has focused on the dual-band properties of the cathode materials, leaving the charge-balancing anode materials under-explored by comparison. This is a report of our study on the suitability of tin-doped indium oxide (ITO) nanocrystals (NCs) as a capacitive anode material for DBEDs. The ITO NCs are electrically conductive and VIS light transparent throughout the device operating range. As a result, they would not affect the NIR-selective modulation of the electrochromic device like most other anode materials do. The high surface area and good conductivity of the ITO NCs facilitate the adsorption/desorption of anions; thereby increasing their effectiveness as an ion storage thin film on the anode to balance the cathode charge. The best DBED prototype assembled from an ITO NC anode and a WO 3- x cathode showed effective and independent control of VIS light and NIR transmittance with high optical modulation (71.1% at 633 nm, 58.1% at 1200 nm), high coloration efficiency (95 cm 2 C -1 at 633 nm, 220 cm 2 C -1 at 1200 nm), fast switching speed, good bistability, and cycle stability.

Most issues with Li-S batteries are caused by the slowness of the multielectron sulfur electrochemical reaction resulting in the loss of sulfur as soluble polysulfides to the electrolyte and the redox shuttling of polysulfides between the cathode and anode during battery charge and discharge. The acceleration of the polysulfide conversion reaction to their end products via electrocatalysis has the appeal of a root-cause solution. However, the polysulfide electrocatalysts developed to date have rarely considered polysulfide conversion as a multistep reaction and, as such, were not optimized to target specific steps in the overall S 8 ↔ Li 2 S n ↔ Li 2 S conversion. The targeting approach is however beneficial, as it can be used to design multicatalyst systems to reduce as many rate-limiting steps in the overall catalysis as effectively possible. This article demonstrates the concept and implementation of stepwise electrocatalysis in polysulfide conversion, using Fe-N and Co-N co-doped carbons to selectively catalyze the long-chain polysulfide conversion (S 8 ↔ Li 2 S 4 ) and the short-chain polysulfide conversion reactions (Li 2 S 4 ↔ Li 2 S), respectively. The two electrocatalysts were deployed in the sulfur cathode as a dual layer, using an ordered spatial separation to synergize their catalytic effects. A sulfur electrode designed as such could utilize ∼90% of the sulfur theoretical specific capacity and support a high areal capacity of ∼8.3 mAh cm -2 and a low electrolyte/sulfur ratio of 5 μL mg -1 .

Lithium-sulfur batteries, with their high theoretical energy density and the low material cost of sulfur, are highly promising as a post-lithium ion battery contender. Their current performance is however compromised by sulfur loss and polysulfide shuttle to result in low energy efficiency and poor cycle stability. Herein, a catalytic material (Co 9 S 8- x /CNT, nanoparticles with a metallic Co 9 S 8 core and a sulfur-deficient shell on a CNT support) was applied as an interlayer on the sulfur cathode to retain migratory polysulfides and promote their reutilization. The Co 9 S 8- x /CNT catalyst is highly effective for the conversion of polysulfides to insoluble end products (S or Li 2 S/Li 2 S 2 ), and its deployment as a cathode-integrated interlayer was able to retain the polysulfides in the cathode for reuse. The accumulation of polysulfides in the electrolyte and the polysulfide shuttle were significantly reduced as a result. Consequently, a host-free sulfur cathode with the Co 9 S 8- x /CNT interlayer had a low capacity fade rate of 0.049% per cycle for 1000 cycles at a 0.3C rate, a significant improvement of the capacity fade rate without it (0.28% per cycle for 200 cycles). The results here provide not only direct evidence for the contributions of sulfur deficiencies on the catalytic activity of Co 9 S 8 in polysulfide conversion reactions but also the methodology on how the catalyst should be deployed in a Li-S battery for the best catalytic outcome.

Two-dimensional MXene materials have demonstrated attractive electrical and electrochemical properties in energy storage applications. Adding stretchability to MXene remains challenging due to its high mechanical stiffness and weak intersheet interaction, so the assembling techniques for mechanically stable MXene architectures require further development. We report a simple fabrication by harnessing the interfacial instability to generate higher dimensional MXene nanocoatings capable of programmed crumpling/unfolding. A sequential patterning approach enabled the design of sequence-dependent MXene textures across multiple length scales, which were utilized for controllable wetting surfaces and high-areal-capacitance electrodes. We next transferred the crumpled MXene nanocoating onto an elastomer to fabricate an MXene/elastomer electrode with high stretchability. The accordion-like MXene can be reversibly folded/unfolded and still preserve efficient specific capacitances. We further fabricated asymmetric MXene supercapacitors, and the devices demonstrated efficient electrochemical performance and large deformability (180° bendability, 100% stretchability). Our texturing techniques can be applied to large MXene families for designing stretchable architectures in wearable electronics.

The organic foulants and bacteria in secondary wastewater treatment can seriously impair the membrane performance in a water treatment plant. The embedded electrode approach using an externally applied potential to repel organic foulants and inhibit bacterial adhesion can effectively reduce the frequency of membrane replacement. Electrode embedment in membranes is often carried out by dispensing a conductor (e.g., carbon nanotubes, or CNTs) in the membrane substrate, which gives rise to two problems: the leaching-out of the conductor and a percolation-limited membrane conductivity that results in an added energy cost. This study presents a facile method for the embedment of a continuous electrode in thin-film composite (TFC) forward osmosis (FO) membranes. Specifically, a conducting porous carbon paper is used as the understructure for the formation of a membrane substrate by the classical phase inversion process. The carbon paper and the membrane substrate polymer form an interpenetrating structure with good stability and low electrical resistance (only about 1Ω/□). The membrane-electrode assembly was deployed as the cathode of an electrochemical cell, and showed good resistance to organic and microbial fouling with the imposition of a 2.0 V DC voltage. The carbon paper-based FO TFC membranes also possess good mechanical stability for practical use.

In comparison with nonaqueous Li-air batteries, aqueous Li-air batteries are kinetically more facile and there is more variety of non-noble metal catalysts available for oxygen electrocatalysis, especially in alkaline solution. The alkaline battery environment is however vulnerable to electrolyte carbonation by atmospheric CO2 resulting in capacity loss over time. The acid aqueous solution is immune to carbonation but is limited by the lack of effective non-noble metal catalysts for the oxygen evolution reaction (OER). This is contrary to the oxygen reduction reaction (ORR) in acid solution where a few good candidates exist. We report here the development of a N-Co-O triply doped carbon catalyst with substantial OER activity in acid solution by the thermal codecomposition of polyaniline, cobalt salt and cyanamide in nitrogen. Cyanamide and the type of cobalt precursor salt were found to determine the structure, crystallinity, surface area, extent of Co doping and consequently the OER activity of the final carbon catalyst in acid solution. We have also put forward some hypotheses about the active sites that may be useful for guiding further work.

Co(OH)2 in the form of hexagonal nanoplates synthesized by a simple hydrothermal reaction has shown even greater activity than cobalt oxides (CoO and Co3O4) in oxygen reduction and oxygen evolution reactions (ORR and OER) under alkaline conditions. The bifunctionality for oxygen electrocatalysis as shown by the OER-ORR potential difference (ΔE) could be reduced to as low as 0.87 V, comparable to the state-of-the-art non-noble bifunctional catalysts, when the Co(OH)2 nanoplates were compounded with nitrogen-doped reduced graphene oxide (N-rGO). The good performance was attributed to the nanosizing of Co(OH)2 and the synergistic interaction between Co(OH)2 and N-rGO. A zinc-air cell assembled with a Co(OH)2-air electrode also showed a performance comparable to that of the state-of-the-art zinc-air cells. The combination of bifunctional activity and operational stability establishes Co(OH)2 as an effective low-cost alternative to the platinum group metal catalysts.

α-MnO2 nanowires modified with dispersed poly(3,4-ethylenedioxythiophene)-protected Au and Ag nanoclusters (Au-MnO2 and Ag-MnO2) were used for the first time as hybrid oxygen electrocatalysts for nonaqueous lithium-oxygen batteries. The Au-MnO2 and Ag-MnO2 hybrid catalysts surpassed the performance of pristine α-MnO2 nanowires in full-cell tests in the following order: Au-MnO2 > Ag-MnO2 > pristine α-MnO2. Specifically, cells with the Au-MnO2 catalyst could reduce the discharge/charge overpotentials at 100 mA g(-1) to 0.23/1.02 V and deliver discharge/charge capacities of 5784/5020 mAh g(-1). They could also be cycled for at least 60 times at the depth of discharge of 1000 mAh g(-1). The good full cell performance demonstrated the effectiveness of Au/Ag nanoclusters in promoting oxygen electrocatalysis on α-MnO2; forming discharge products with more reactive morphologies. It is therefore worthwhile to explore the use of Au and Ag nanoclusters in other catalyst systems for oxygen electrocatalysis in nonaqueous solutions.

Amphiphilicity is a surface property that has yet to be explored for the noble metal nanoclusters (NCs). This article shows how amphiphilicity may be added to sub-2-nm metal NCs by patching hydrophilic NCs (e.g., Au25(MHA)18 NCs where MHA is 6-mercaptohexanoic acid) with hydrophobic cations (e.g., cetyltrimethylammonium ion, CTA(+)) to about half of a monolayer coverage. Specifically we demonstrate the preparation of amphiphilic Au25(MHA)18@xCTA NCs (x = 6-9 where x is the number of CTA(+) per NC) by the phase-transfer (PT) driven ion-paring reaction between CTA(+) and -COO(-) (derived from the deprotonation of the terminal carboxyl group of MHA). Due to the coexistence of flexible hydrophilic MHA and hydrophobic MHA···CTA ligands in comparable amounts on the NC surface, the Au25(MHA)18@xCTA NCs (x = 6-9) exhibit good amphiphilicity, which enabled them to dissolve in solvents with distinctly different polarities and to self-assemble like a molecular amphiphile. Consequently, the amphiphilic Au25(MHA)18@xCTA NCs (x = 6-9) could self-organize into stacked bilayers at the air-liquid interface, similar to the formation of lyotropic liquid crystalline phases by common surfactants. The good solubility and molecular-amphiphile-like self-assembly properties can significantly increase the utility of noble metal NCs in basic and applied research.

CONSPECTUS: Heterogeneous metal nanocrystals (HMNCs) are a natural extension of simple metal nanocrystals (NCs), but as a research topic, they have been much less explored until recently. HMNCs are formed by integrating metal NCs of different compositions into a common entity, similar to the way atoms are bonded to form molecules. HMNCs can be built to exhibit an unprecedented architectural diversity and complexity by programming the arrangement of the NC building blocks ("unit NCs"). The architectural engineering of HMNCs involves the design and fabrication of the architecture-determining elements (ADEs), i.e., unit NCs with precise control of shape and size, and their relative positions in the design. Similar to molecular engineering, where structural diversity is used to create more property variations for application explorations, the architectural engineering of HMNCs can similarly increase the utility of metal NCs by offering a suite of properties to support multifunctionality in applications. The architectural engineering of HMNCs calls for processes and operations that can execute the design. Some enabling technologies already exist in the form of classical micro- and macroscale fabrication techniques, such as masking and etching. These processes, when used singly or in combination, are fully capable of fabricating nanoscopic objects. What is needed is a detailed understanding of the engineering control of ADEs and the translation of these principles into actual processes. For simplicity of execution, these processes should be integrated into a common reaction system and yet retain independence of control. The key to architectural diversity is therefore the independent controllability of each ADE in the design blueprint. The right chemical tools must be applied under the right circumstances in order to achieve the desired outcome. In this Account, after a short illustration of the infinite possibility of combining different ADEs to create HMNC design variations, we introduce the fabrication processes for each ADE, which enable shape, size, and location control of the unit NCs in a particular HMNC design. The principles of these processes are discussed and illustrated with examples. We then discuss how these processes may be integrated into a common reaction system while retaining the independence of individual processes. The principles for the independent control of each ADE are discussed in detail to lay the foundation for the selection of the chemical reaction system and its operating space.

The organization of nanoscale materials as building units into extended structures with specific geometry and functional properties is a challenging endeavor. Hereby, an environmentally benign, simple, and scalable method for preparation of stable, linker-free, self-supported, high-order 3D meso-oblate spheroids of CuO nanoparticle aggregates with size-tunable building nanounits for reversible lithium-ion storage is reported. In contrast to traditional spherical nanoparticle aggregation, a unique oblate spheroid morphology is achieved. The formation mechanism of the unusual oblate spheroid of aggregated nanoparticles is proposed. When tested for reversible lithium ion storage, the unique 3D meso-oblate spheroids of CuO nanoparticle aggregate demonstrated highly improved electrochemical performance (around ∼600 mAh/g over 20 cycles), which could be ascribed to the nanoporous aggregated mesostructure with abundant crystalline imperfection. Furthermore, the size of building units can be controlled (12 and 21 nm were tested) to further improve their electrochemical performance.

TiO2 nanoparticles aggregated into a regular ball-in-ball morphology were synthesized by hydrothermal processing and converted to carbon-encapsulated F-doped Li4Ti5O12 (LTO) composites (C-FLTO) by solid state lithiation at high temperatures. Through the careful control of the amount of carbon precursor (D(+)-glucose monohydrate) used in the process, LTO encapsulated with a continuous layer of nanoscale carbon was formed. The carbon encapsulation served a dual function: preserving the ball-in-ball morphology during the transformation from TiO2 to LTO and decreasing the external electron transport resistance. The fluoride doping of LTO not only increased the electron conductivity of LTO through trivalent titanium (Ti(3+)) generation, but also increased the robustness of the structure to repeated lithiation and delithiation. The best-performing composite, C-FLTO-2, therefore delivered a very satisfying performance for a LTO anode: a high charge capacity of ∼158 mA h g(-1) at the 1 C rate with negligible capacity fading for 200 cycles and an extremely high rate performance up to 140 C.

LiMn1-xFexPO4/C (x = 0 and 0.3) with a uniform carbon coating and interspersed carbon particles was prepared by a high-energy ball-milling (HEBM)-assisted solid-state reaction. The as-synthesized LiMn0.7Fe0.3PO4/C delivered an excellent rate performance as a LiMnPO4 class of materials. Specifically, the specific discharge capacity was 164 mAh/g (96% of theoretical value) at the 0.05 C rate and 107 mAh/g at the 5 C rate (1 C = 170 mA/g). Electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements indicated improvements in the transport of electrons and Li(+) as well as the emergence of a single-phase region in lithium extraction and insertion reactions.

Through a series of carefully executed experiments, we discovered the prevalence of anisotropic shell growth in many upconversion NaREF4 systems caused by a combination of factors: selective adsorption of ligands on the core surface due to the core crystal structure, ligand etching, and the lattice mismatch between core and shell components. This could lead to incomplete shell formation in core-shell nanocrystals under certain conditions. Shell growth is always faster in the a and b crystallographic directions than in the c direction. In the case of a larger lattice mismatch between the core and shell, shell growth only occurs in the a and b directions resulting in an oblong core-shell structure. These findings are useful for rationalizing shell-dependent emission properties, understanding the emission mechanisms in complex core-shell nanostructures, and for creating accurate models of core-shell designs for multifunctionality and optimal performance in applications.

A fundamental understanding of the luminescence of Au-thiolate nanoclusters (NCs), such as the origin of emission and the size effect in luminescence, is pivotal to the development of efficient synthesis routes for highly luminescent Au NCs. This paper reports an interesting finding of Au(I)-thiolate complexes: strong luminescence emission by the mechanism of aggregation-induced emission (AIE). The AIE property of the complexes was then used to develop a simple one-pot synthesis of highly luminescent Au-thiolate NCs with a quantum yield of ~15%. Our key strategy was to induce the controlled aggregation of Au(I)-thiolate complexes on in situ generated Au(0) cores to form Au(0)@Au(I)-thiolate core-shell NCs where strong luminescence was generated by the AIE of Au(I)-thiolate complexes on the NC surface. We were able to extend the synthetic strategy to other thiolate ligands with added functionalities (in the form of custom-designed peptides). The discovery (e.g., identifying the source of emission and the size effect in luminescence) and the synthesis protocols in this study can contribute significantly to better understanding of these new luminescence probes and the development of new synthetic routes.

The design of an efficient synthesis for large-scale production of atomically precise nanoclusters (NCs) is pivotal in realizing the size-dependent properties of the NCs. A simple and versatile method for producing atomically precise thiolated gold NCs (Au(25)(SR)(18) NCs) in large quantities (~200 mg) is demonstrated in this study. It uses a gaseous reducing agent, carbon monoxide (CO), to support a slow and size-controlled growth of Au(25)(SR)(18) NCs. Absorption measurements of the reaction solution, which underwent distinct color changes (colorless → yellow → orange → brown → red-brown), allowed the formation of thiolated Au(25) NCs to be reconstructed from several key intermediates. The unique reaction environment provided by gaseous CO presents a new synthetic route to fabricate atomically precise metal NCs in quantities large enough for application explorations.

Mastery of the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the synthesis of metal nanomaterials with hollow interiors or cage-bell structures based on the inside-out diffusion of Ag in core-shell structured nanoparticles. It begins with the synthesis of core-shell Ag-M or core-shell-shell M(A)-Ag-M(B) nanoparticles in an organic solvent. Ag is then extracted from the core or the inner shell by bis(p-sulfonatophenyl)phenylphosphane, which binds strongly with Ag(I)/Ag(0) to allow the complete removal of Ag in 24-48 h, leaving behind an organosol of hollow or cage-bell structured metal nanomaterials. Because of their relatively lower densities, which usually translate to a higher surface area than their solid counterparts, the hollow and cage-bell structured metal nanomaterials are especially relevant to catalysis. For example, cage-bell structured Pt-Ru nanoparticles were found to display outstanding methanol tolerance for the cathode reaction of direct methanol fuel cells (DMFCs) as a result of the differential diffusion of methanol and oxygen in the cage-bell structure.

This paper describes the synthesis of ion-pair-reinforced semi-interpenetrating polymer networks (SIPNs) as proton exchange membranes (PEMs) for the direct methanol fuel cells (DMFCs). Specifically, sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), a linear polymer proton source, was immobilized in a brominated PPO (BPPO) network covalently cross-linked by ethylenediamine (EDA). The immobilization of SPPO in the SIPN network was accomplished not only by the usual means of mechanical interlocking but also by ion pair formation between the sulfonic acid groups of SPPO and the amine moieties formed during the cross-linking reaction of BPPO with EDA. Through the ion pair interactions, the immobilization of SPPO polymer in the BPPO network was made more effective, resulting in a greater uniformity of sulfonic acid cluster distribution in the membrane. The hydrophilic amine-containing cross-links also compensated for some of the decrease in proton conductivity caused by ion pair formation. The SIPN membranes prepared as such showed good proton conductivity, low methanol permeability, good mechanical properties, and dimensional stability. Consequently, the PPO based SIPN membranes were able to deliver a higher maximum power density than Nafion, demonstrating the potential of the SIPN structure for PEM designs.

This paper reports a simple and scalable method for the synthesis of highly fluorescent Ag, Au, Pt, and Cu nanoclusters (NCs) based on a mild etching environment made possible by phase transfer via electrostatic interactions. Using Ag as a model metal, a simple and fast (total synthesis time < 3 h) phase transfer cycle (aqueous → organic (2 h incubation) → aqueous) has been developed to process originally polydisperse, nonfluorescent, and unstable Ag NCs into monodisperse, highly fluorescent, and extremely stable Ag NCs in the same phase (aqueous) and protected by the same thiol ligand. The synthetic protocol was successfully extended to fabricate highly fluorescent Ag NCs protected by custom-designed peptides with desired functionalities (e.g., carboxyl, hydroxyl, and amine). The facile synthetic method developed in this study should largely contribute to the practical applications of this new class of fluorescence probes., (© 2011 American Chemical Society)

Graphene-encapsulated ordered aggregates of Fe(3)O(4) nanoparticles with nearly spherical geometry and hollow interior were synthesized by a simple self-assembly process. The open interior structure adapts well to the volume change in repetitive Li(+) insertion and extraction reactions; and the encapsulating graphene connects the Fe(3)O(4) nanoparticles electrically. The structure and morphology of the graphene-Fe(3)O(4) composite were confirmed by X-ray diffraction, scanning electron microscopy, and high-resolution transmission microscopy. The electrochemical performance of the composite for reversible Li(+) storage was evaluated by cyclic voltammetry and constant current charging and discharging. The results showed a high and nearly unvarying specific capacity for 50 cycles. Furthermore, even after 90 cycles of charge and discharge at different current densities, about 92% of the initial capacity at 100 mA g(-1) was still recoverable, indicating excellent cycle stability. The graphene-Fe(3)O(4) composite is therefore a capable Li(+) host with high capacity that can be cycled at high rates with good cycle life. The unique combination of graphene encapsulation and a hollow porous structure definitely contributed to this versatile electrochemical performance.

The shape-controlled synthesis of noble metal nanocrystals (NCs) bounded by high-index facets is a current research interest because the products have the potential of significantly improving the catalytic performance of NCs in industrially important reactions. This study reports a versatile method for synthesizing polyhedral NCs enclosed by a variety of high-index Pd facets. The method is based on the heteroepitaxial growth of Pd layers on concave trisoctahedral (TOH) gold NC seeds under careful control of the growth kinetics. Polyhedral Au@Pd NCs with three different classes of high-index facets, including concave TOH NCs with {hhl} facets, concave hexoctahedral (HOH) NCs with {hkl} facets, and tetrahexahedral (THH) NCs with {hk0} facets, can be formed in high yield. The Miller indices of NCs are also modifiable, and we have used the THH NCs as a demonstrative example. The catalytic activities of these NCs were evaluated by the structure-sensitive reaction of formic acid electro-oxidation. The results showed that the high-index facets are generally more active than the low-index facets. In summary, a seeded growth process based on concave high-index faceted monometallic TOH NC templates and careful control of the growth kinetics is a simple and effective strategy for the synthesis of noble metal NCs with high-index facets. It also offers tailorability of the surface structure in shape-controlled synthesis.

We have developed a unique metal nanoparticle (mNPs)-based assay to detect sequence-specific interactions between transcription factor and its corresponding DNA-binding elements. This assay exploits the interparticle-distance dependent optical properties of noble mNPs as sensing element and utilizes specific protein-DNA interactions to control the dispersion status of the mNPs. The assay involves two sets of double-stranded (ds)DNA modified-mNPs, each carrying a half site segment of a functional DNA sequence for the protein of interest. Each of these half sites is designed to contain a short complementary sticky end that introduces base-pairing forces to facilitate particle aggregation and to form a transient full dsDNA sequence. The detection of specific protein-DNA binding is founded on the premise that the mixture of these two sets of dsDNA-mNPs experiences a remarkable particle aggregation under certain salt conditions; whereas the aggregation can be retarded in the presence of a specific protein that binds and stabilizes the transient full dsDNA structure and therefore introduces steric protection forces between particles. We have demonstrated the concept using estrogen receptor α and its response elements, with gold and silver NPs as the sensing platform. UV-vis spectroscopy, transmission electron spectroscopy, and dynamic light scattering measurements were conducted to provide full characterization of the particle aggregation/dispersion mechanism. Differing from most of the mNP-based colorimetric sensors that are designed based on the analyte-induced aggregation mechanism, current protein binding-stabilization sensing strategy reduces the false signals caused by unrelated particle destabilizing effects. It is expected that this assay principle can be directed toward other transcription factors by simply changing the recognition sequence to form different segmented dsDNA-mNP constructs.

Peptides are multifunctional reagents (reducing and capping agents) that can be used for the synthesis of biocompatible metal nanoparticles under relatively mild conditions. However, the progress in peptide synthesis of metal nanoparticles has been slow due to the lack of peptide design rules. It is difficult to establish sequence-reactivity relationships from peptides isolated from biological sources (e.g., biomineralizing organisms) or selected by combinatorial display libraries because of their widely varying compositions and structures. The abundance of random and inactive amino acid sequences in the peptides also increases the difficulty in knowledge extraction. In this study, a "bottom-up" approach was used to formulate a set of rudimentary rules for the size- and shape-controlled peptide synthesis of gold nanoparticles from the properties of the 20 natural alpha-amino acids for AuCl(4)(-) reduction and binding to Au(0). It was discovered that the reduction capability of a peptide depends on the presence of certain reducing amino acid residues, whose activity may be regulated by neighboring residues with different Au(0) binding strengths. Another finding is the effect of peptide net charge on the nucleation and growth of the Au nanoparticles. On the basis of these understandings, several multifunctional peptides were designed to synthesize gold nanoparticles in different morphologies (nanospheres and nanoplates) and with sizes tunable by the strategic placement of selected amino acid residues in the peptide sequence. The methodology presented here and the findings are useful for establishing the scientific basis for the rational design of peptides for the synthesis of metal nanostructures.

The activity and selectivity of carbon-supported Pt-decorated PdFe nanoparticles in the oxygen reduction reaction (ORR) were investigated in the presence and absence of methanol. The Pt-decorated PdFe nanoparticles, which consist of a PdPt surface and a PdFe interior, were prepared by the galvanic reaction between PdFe/C alloy nanoparticles and PtCl4(2-) in aqueous solution. The presence of a Pt-enriched surface after the replacement reaction was independently confirmed by several microstructural characterization techniques and cyclic voltammetry. The catalyst with such heterogeneous architecture is catalytically more active than a bulk PdFePt alloy catalyst with the same overall composition. The observed enhancements in catalyst performance can be attributed to the lattice strain effect between the shell and core components. The Pt-decorated PdFe (PdFe@PdPt/C) catalyst also compares favorably with a commercial Pt/C catalyst with four times as much Pt in terms of ORR activity, cost, and methanol tolerance.

One-dimensional (1-D) nanomaterials are basic building blocks for the construction of nanoscale devices. However, the fabrication and alignment of 1-D nanomaterials with specific geometry and composition on a given substrate is a significant challenge. Herein we show a successful example of fabricating a family of aligned 1-D C-curved nanoarches of different compositions on an extended Si surface by a simple and scalable method. The nanoarches are made up of either single-crystalline Sn nanorods encapsulated in carbon nanotubes (CNTs), SnO(2) nanotubes, or CNTs. The aligned 1-D C-curved nanoarches of single-crystalline Sn nanorods in CNTs are prepared first by a facile in situ reduction of SnO(2) nanoparticles under standard chemical vapor deposition conditions. Nanoarches of CNTs and SnO(2) nanotubes were then derived from the Sn@CNT nanoarches by acid etching and by calcination in air, respectively.

A simple one-pot template-free synthesis was used to form porous Pt networks from the CO-induced self-organization of monodisperse primary Pt nanoparticles. Spherical, rod-shaped, knot-like, multibranched, and hyperbranched porous networks could be obtained under different conditions through changes in the reaction temperature and citrate ion concentration. The formation of these porous platinum networks could be rationalized by a mechanism where citrate ions and Chini-like platinum carbonyl clusters formed upon CO exposure are the most important contributors.

This paper reports the synthesis and self-assembly of monodisperse icosahedral Ag, Au, and Pd nanoparticles with tunable sizes. Ag nanoparticles were first prepared by a modified polyol method. The as-synthesized Ag nanoparticles were all icosahedral multiply twinned particles (MTPs) with notable size variations. The variability was reduced to less than 5% after a digestive ripening post treatment. The nearly monodisperse Ag nanoparticles were then used in replacement reactions with Au and Pd precursors to produce monodisperse icosahedral Au and Pd nanoparticles. The size of the monodisperse icosahedral Ag, Au, and Pd nanoparticles could also be increased thereafter by seed-mediated growth. The closely matched geometrical attributes of these icosahedral nanoparticles allowed them to easily self-assemble into 3-D superlattices either in the solution phase or on a solid substrate.

This paper reports a simple, one-pot, template-free synthesis of flower-like Au nanoparticles (three-dimensional branched nanoparticles with more than 10 tips) with high yield and good size monodispersity at room temperature. The size of the Au nanoflowers could be tuned by controlling the composition of the starting reaction mixture. The key synthesis strategy was to use a common Good's buffer, HEPES, as a weak reducing and particle stabilizing agent to confine the growth of the Au nanocrystals in the special reaction region of limited ligand protection (LLP). Time-course measurements by UV-vis spectroscopy and TEM were used to follow the reaction progress and the evolution of the flower-like shape. The Au nanoflowers exhibited strong surface-enhanced effects which were utilized in the design of an efficient, stable, and nontoxic Raman-active tag for in vivo applications.

One of the methods to render CdSe/ZnS core-shell quantum dots(QDots) water-soluble is to functionalize the surface with carboxylate groups by the use of heterobifunctional ligands such as 3-mercaptopropionic acid, where the thiolic end binds onto the outer ZnS shell. However, currently available ligand-exchange procedures starting with TOPO-capped quantum dots often lead to significant loss of quantum yields and poor stability of the colloids in water. As part of our efforts to overcome these problems, we used computational methods to understand the nature of binding between alkyl thiols and ZnS wurtzite surfaces. Guided by the computational results, we modified the ligand-exchange method and increased the reactivity of 3-mercaptopropionic acid toward the ZnS surface in chloroform. The functionlization reaction required only mild reaction conditions and led to QDot nanoparticles that were individually dispersed in water with good colloidal stability. Importantly, the photoluminescence performance of the QDots was highly preserved.

This paper describes the synthesis of single-crystalline Ag nanoplates using the extract of unicellular green alga Chlorella vulgaris at room temperature. Proteins in the extract were involved in the biological synthesis, providing the dual function of Ag ion reduction and shape-controlled synthesis of nanosilver. Hydroxyl groups in Tyr residues and carboxyl groups in Asp and/or Glu residues were further identified as the most active functional groups for Ag ion reduction and for directing the anisotropic growth of Ag nanoplates, respectively. The kinetics of Ag ion reduction in biological systems was discussed and probed by using custom-designed peptides. The results showed the Tyr content (the reduction source) and the content of Ag complexers (the reaction inhibitors, e.g., His and Cys) in the protein molecules as important factors affecting the reduction kinetics. The comprehensive system identification effort has led to the design of a simple bifunctional tripeptide (DDY-OMe) with one Tyr residue as the reduction source and two carboxyl groups in the Asp residues as shape-directors, which could produce small Ag nanoplates with low polydispersivity in good yield (>55%). The roles of the carboxyl groups in the formation of Ag nanoplates were also discussed.

Protein microarrays are promising tools that can potentially enable high throughput proteomic screening in areas such as disease diagnosis and drug discovery. A critical aspect in the development of protein microarrays is the optimization of the array's surface chemistry to achieve the high sensitivity required for detection of proteins in cell lysate and other complex biological mixtures. In the present study, a high-density antibody array with minimal nonspecific cellular protein adsorption was prepared using a glass surface coated with a poly(propyleneimine) dendrimer terminated with carboxyl group (PAMAM-COOH). The carboxyl-terminated dendrimer-modified surface has almost similar nonspecific cellular protein adsorption when compared to an inert PEG-modified surface. In addition, the multiple functional sites available for reaction on the dendrimer surface facilitated high-density immobilization of antibodies and efficient capture of bioanalytes. Various molecules were tested for their ability to block or deactivate the reactive carboxyl surface after antibody immobilization to further reduce the nonspecific binding. A short oligoethylene glycol (NH2-d4-PEG-COOH), was found to significantly improve the signal-to-noise ratio of the assay, resulting in higher sensitivity. The properties and functional qualities of the various surfaces were characterized by contact angle and AFM measurements. Nonspecific protein adsorption and protein immobilization as a function of dendrimer generations and sensitivity of antigen capturing from a buffer (1 pM) as well as from the complex cell lysate (10 pM) system were examined. Our detailed experimental studies demonstrated a facile method of preparing surfaces with high protein loading and low nonspecific protein binding for the development of high sensitivity protein microarrays.

It is a significant challenge to develop proton exchange membranes (PEMs) possessing both desired proton conductivity and low methanol permeability for the direct methanol fuel cells (DMFC). In this work, a composite PEM was fabricated from a predominantly hydrophobic framework of three-component polymer blend (TCPB) of acrylic polymers and a dispersed proton-conducting hydrophilic copolymer network. The hydrophilic copolymer was designed to contain three co-monomer units of complementary functionalities: 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA), and 2-hydroxyl-3-(diethanolamino)propylmethacrylate (DEAPMA). The resultant PEMs were macroscopically homogeneous but contained microscopic heterogeneity in the form of dispersed nanosize AMPS domains with radiating (HEMA-DEAPMA) segments in the TCPB matrix, forming an overall amphiphilic matrix. Formation of such a texture was consequential upon the association of AMPS units and hydrogen bonding between the HEMA and DEAPMA short blocks of the hydrophilic copolymer with TCPB. The polymer blend membranes therefore acquired dual functionalities, i.e., effective proton transport between AMPS granules through interconnecting (HEMA-DEAPMA) segments, resulting in proton conductivity of the order of 10(-2) S/cm, and low water uptake and inhibited methanol passage in the continuous amphiphilic matrix, resulting in methanol permeability of (1.25-8) x 10(-7) cm2/s, which is about 3-8 times smaller than that of Nafion117.

Core-shell Au-Pt nanoparticles with intimate contact of Pt and Au were prepared by a displacement reaction without formation of monometallic Au nanoparticles. The Au-Pt nanoparticles were dispersed on carbon (Au@Pt/C) and were used to catalyze methanol electrooxidation in acidic solutions at room temperature. The core-shell nanostructure was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy, and specific catalytic activities were evaluated by CO anodic stripping voltammetry in 0.5 M H(2)SO(4) and by cyclic voltammetry in 1 M CH(3)OH + 0.5 M H(2)SO(4). The Au@Pt/C catalyst demonstrated enhanced specific activity in methanol electrooxidation and showed multiple CO stripping peaks which were all negatively shifted with respect to a similarly prepared Ag@Pt/C catalyst. The activity enhancement is attributed to the presence of Au underneath a very thin Pt shell where electron exchange between Au and Pt had promoted the formation of active oxygen species on Pt, which facilitated the removal of inhibiting CO-like reaction intermediates.

High-quality, monodisperse PbS-Au(1), PbS-Au(4), and PbS-Au(n) nanostructures have been synthesized via a facile and convenient solution chemistry approach. HRTEM images of these nanostructures showed good selectivity of gold deposition on the semiconductor in several spatially correlated directions. The formation of these regular nanostructures can be explained by the difference in polarity of crystal facets that led to the selective growth of metal on the semiconductor surface. Owing to their narrow size distribution and intrinsic high-symmetry, the resulting PbS-Au(4) and PbS-Au(n) heterogeneous nanostructures could spontaneously self-assemble into ordered arrays with different symmetries. From the results of the pump-probe measurements, the presence of Au in PbS-Au(4) nanostructures has substantially altered the nonlinear optical response of PbS nanocrystals.

We report herewith the synthesis of hollow Pt nanospheres by using bis(p-sulfonatophenyl)phenylphosphine to selectively remove the Ag cores of Ag-Pt core-shell nanoparticles. Core-shell Ag-Pt nanoparticles were first obtained by the successive reduction method with a discontinuous Pt shell to allow the BSPP passage. Transmission electron microscopy imaging of the core-shell Ag-Pt nanoparticles before and after BSPP dissolution showed little changes in the particle size, indicating that the removal of the Ag cores had occurred isomorphously. The hollow Pt nanospheres, together with the predecessor Ag-Pt core-shell particles of the same size, were transferred from water to toluene and surface modified by dodecylamine in toluene. This allows the catalytic activities of solid and hollow Pt particles in room temperature methanol oxidation reaction to be compared under conditions of identical particle size and the same surface environment. The measured higher specific activity of the Pt hollow nanospheres could then be attributed unambiguously to the larger specific surface area prevalent in the porous hollow structure.

This paper describes a facile hydrothermal procedure capable of aligning CdS nanocrystals on multiwalled carbon nanotubes (MWCNTs) without the use of organic bridging molecules such as cysteamine and carboxylates. The direct placement of CdS on MWCNTs allows good mixing and better interfacing between the two nanophases. The synthesis conditions can in principle be tuned to produce modulations in compositions, phases, and crystal orientations to the need of optoelectronic and photonic applications.

We conducted a computational adsorption study of methylamine on various surface models of a gold nanoparticle which is facetted by multiple [111] and [100] planes. In addition to these flat surfaces, our models include the stepped surfaces (ridges) formed along the intersections of these planes. Binding on the flat surfaces was fairly weak, but substantially stronger on the ridges by an average of 4.4 kcal/mol. This finding supports the idea that ssDNA's interaction with gold nanoparticles occurs through the amines on the purine/pyrimidine rings. Also, this typically undesirable interaction between DNA and gold nanoparticles is expected to increase as the particle size decreases. Our analysis suggests that particle size is an important controlling parameter to reduce this interaction.

In this study, ordered macroporous carbon with a three-dimensional (3D) interconnected pore structure and a graphitic pore wall was prepared by chemical vapor deposition (CVD) of benzene using inverse silica opal as the template. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectrometry, nitrogen adsorption, and thermogravimetric analysis techniques were used to characterize the carbon samples. The electrochemical properties of the carbon materials as a carbon-based anode for lithium-ion batteries and as a Pt catalyst support for room-temperature methanol electrochemical oxidation were examined. It was observed that the CVD method is a simple route to fabrication of desired carbon nanostructures, affording a carbon with graphitic pore walls and uniform pores. The graphitic nature of the carbon enhances the rate performance and cyclability in lithium-ion batteries. The specific capacity was found to be further improved when SnO(2) nanoparticles were supported on the carbon. The specific activity of Pt catalyst supported on the carbon materials for room-temperature methanol electrochemical oxidation was observed to be higher than that of a commercial Pt catalyst (E-TEK).

The replacement reaction between hydrophobized Ag nanoparticles and hydrophobized AuCl4- in toluene has been examined in detail. The conclusions obtained under our experimental conditions are different from those reported in the literature in three aspects: (1) a detectable contraction of the Ag nanoparticle sacrificial templates during the course of the reaction is shown; (2) the deposition of Au on the shrunken Ag templates inhibits further Ag oxidation, resulting in the formation of core-shell Ag-Au nanoparticles instead of Au nanoshells; and (3) the significant red-shift in the surface plasmon resonance (SPR) band is more of a consequence of shape and chemical composition changes rather than as an indication of Au nanoshell formation. Solvent and temperature are influential environmental factors that determine the structure and composition of nanoparticles formed by the replacement reaction.

Ag-Pt nanoparticles with a confirmed core-shell structure could only be formed by the successive reduction method using Ag nanoparticles as the seeds. The core-shell structure could be conveniently inferred from the transferability of the particles from water to toluene. Independent measurements by UV-vis spectroscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used to validate the experimental results. The reverse order of synthesis using Pt nanoparticles as the seeds did not result in any core-shell product. Instead a physical mixture of Ag nanoparticles and the original Pt seeds was obtained under the same experimental conditions.

Acetate-stabilized ruthenium nanoparticles were prepared by the NaBH4 reduction of the metal precursor salt at room temperature. Nanoparticles with a mean diameter of 2.20 nm and a standard deviation of 1.03 nm could be obtained under experimental conditions. The Ru nanoparticles so obtained could be easily extracted to a toluene solution of alkylamine, giving rise to alkylamine-stabilized Ru nanoparticles with a mean diameter of 2.96 nm and a standard deviation of 0.92 nm. The new found role of acetate stabilization was used to formulate a mechanism for the formation of metal (Pt, Ru) nanoparticles in ethylene glycol. In this mechanism metal nanoparticles are stabilized in ethylene glycol by adsorbed acetate ions, which are produced as a product of the OH- catalyzed reaction between the metal precursor salt and ethylene glycol.

PtRu nanoparticles supported on Vulcan XC-72 carbon and carbon nanotubes were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which were uniformly dispersed on carbon, were 2-6 nm in diameter. All PtRu/C catalysts prepared as such displayed the characteristic diffraction peaks of a Pt face-centered cubic structure, excepting that the 2theta values were shifted to slightly higher values. XPS analysis revealed that the catalysts contained mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV), and Ru(IV). The electro-oxidation of methanol was studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both PtRu/C catalysts had high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell single stack test cell using the Vulcan-carbon-supported PtRu alloy as the anode catalyst showed high power density.