Journal of Materials Chemistry (v.21, #31)

Front cover (11441-11441).

Inside front cover (11442-11442).

Contents list (11443-11453).

Themed issue: Chemical transformations of nanoparticles by Dmitri V. Talapin; Yadong Yin (11454-11456).

Formation and morphology control of nanoparticles via solution routes in an autoclave by Yongchun Zhu; Tao Mei; Yan Wang; Yitai Qian (11457-11463).
Formation and morphology control of nanomaterials is a crucial issue in nanoscience research in the exploitation of novel properties. This article presents a review of some research activities on the formation and morphology control of nanoparticles via solution routes in an autoclave over the last decade. Several solution systems, including hydrothermal, solvothermal and mixed solvothermal routes, are specifically discussed and highlighted. A helical belt template mechanism was proposed for the formation of the Te nanotubes in aqueous ammonia. Assisted by the surfactant of sodium dodecyl benzenesulfonate (SDBS), nickel nanobelts were hydrothermally synthesized. Ethylenediamine (En) and n-butylamine can be used as shape controllers to one-dimensional (1D) semiconductor nanostructures in the solvothermal process. The phase of metastable and stable MnS crystallites can be controlled by solvothermal reaction in various solvents. Selective preparation of 1D to 3D CdS nanostructures was achieved by controlling the volume ratio of the mixed solvents. With poly(vinylpyrrolidone) (PVP) serving as a soft template, the transformation from nanowires to nanotubes, then to nanowires was observed in the mixed solvents of distilled water and ethanolamine (EA).

Fluorescent magnetic nanoparticles based on a ruthenium complex and Fe3O4 by Pinxian Xi; Kai Cheng; Xiaolian Sun; Zhengzhi Zeng; Shouheng Sun (11464-11467).
A fluorescent ruthenium (Ru) complex is coupled to magnetic Fe3O4 nanoparticles (NPs) via 3-(3,4-dihydroxyphenyl) propanoic acid (DHPPA) and O,O′-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol (PPG-PEG-PPG-diamine). The resultant Ru–Fe3O4 NP conjugate shows excellent colloidal, photochemical and magnetic stability, and is promising as a dual functional probe for biological imaging applications.

Synthesis and evaluation of gold nanoparticle-modified polyelectrolyte capsules under microwave irradiation for remotely controlled release for cargo by Loretta L. del Mercato; Edgar Gonzalez; Azhar Z. Abbasi; Wolfgang J. Parak; Victor Puntes (11468-11471).
The Layer-by-Layer fabrication of polyelectrolyte capsules with and without Au nanoparticles embedded into their walls is reported. We have studied the behaviour of these capsules under microwave irradiation. Their properties have been investigated by transmission electron microscopy and dynamic light scattering measurements. We demonstrate that microwaves affect the structure of both capsules types by inducing remarkable damage to the multilayer wall. We also show that upon microwave exposure the walls of polyelectrolyte capsules which are modified with Au nanoparticles undergo rapid damage compared to capsules without incorporated nanoparticles. These results indicate that microwaves can be used to control the opening of cargo-loaded capsules, which could be harnessed for drug delivery purposes.

Transformation of hydrophobic iron oxide nanoparticles to hydrophilic and biocompatible maghemite nanocrystals for use as highly efficient MRI contrast agent by Yong Il Park; Yuanzhe Piao; Nohyun Lee; Byeongjun Yoo; Byung Hyo Kim; Seung Hong Choi; Taeghwan Hyeon (11472-11477).
We report a transformation of hydrophobic iron oxide nanoparticles to hydrophilic and biocompatible maghemite nanocrystals by controlled thermal treatment followed by dextran coating. Sodium sulfate salt was used as matrix for preventing aggregation during the thermal treatment at high temperature. Through the thermal treatment and subsequent isolation process, highly crystalline bare maghemite nanocrystals with high magnetization were produced. Subsequent coating with dextran derivatives produced hydrophilic and biocompatible iron oxide nanocrystals. Among various kinds of dextran derivatives, polyanionic carboxymethyl dextran (CM-dextran) was most efficient for stabilizing the nanocrystals in aqueous media. CM-dextran coated nanocrystals exhibited high relaxivity originating from the high magnetization and assembled structure.

Facile synthesis of hybrid nanostructures from nanoparticles, nanorods and nanowires by Jiayuan Mao; Xueqin Cao; Junwei Zhen; Huilin Shao; Hongwei Gu; Jianmei Lu; Jackie Y. Ying (11478-11481).
We show the anisotropic selective growth of gold particles onto various nanomaterials to form heterodimers, tadpole-like and necklace-like hybrid structures via simple nucleation. The morphology of these hybrid nanostructures can be easily controlled. Necklace-like Pt–Au nanostructures demonstrated high stabilities as electrocatalysts for oxygen-reduction reaction.

Pd nanoparticles were generated in situ in a mesoporous Zr-modified SiO2 film and transformed into PdHx (x≈ >0–0.7) nanoparticles by dipping in aqueous NaBH4 solution in ambient conditions, and the adsorbed hydrogen can be released to regenerate the original Pd nanoparticles at 120 °C.

Size-dependent CO2 capture in chemically synthesized magnesium oxide nanocrystals by Anne M. Ruminski; Ki-Joon Jeon; Jeffrey J. Urban (11486-11491).
The carbon dioxide storage capacity of magnesium oxide (MgO) particles was examined as a function of particle size, shape, and surface area. Two types of MgO nanocrystals (5 nm spheres and 23 nm disks) were synthesized and compared against commercially available MgO (325 mesh/44 μm and 40 mesh/420 μm). The surface area of the four types of particles was determined by N2 gas adsorption. Carbon dioxide capture was measured at 60 °C and 600 °C using thermogravimetric analysis, with results indicating enhanced CO2 capacity correlating with increased surface area.

Switchable photoconductivity of quantum dot films using cross-linking ligands with light-sensitive structures by G. Daniel Lilly; Adam C. Whalley; Sergio Grunder; Cory Valente; Matthew T. Frederick; J. Fraser Stoddart; Emily A. Weiss (11492-11497).
This paper describes the use of a diarylethylene (DAE) ligand, which adopts structures that are sensitive to the wavelength of light, to cross-link films of CdSe quantum dots (QDs) within electrical junctions with photoswitchable conductivity. These QD-DAE films are deposited on indium-tin-oxide/poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (ITO/PEDOT:PSS) electrodes and have eutectic Ga-In top-contacts. The photocurrent density of the cross-linked QD films is enhanced by a factor of 6.5 (averaged over all applied voltages) when the DAE ligand is switched from its open, non-conductive form (by illumination with 500–650 nm light) to its closed, conductive form (by illumination with 300–400 nm light). This enhancement is accomplished by changing the inter-particle electronic coupling, not the inter-particle distance. Identical QD films cross-linked with dibenzenedithiol ligands have a photoconductivity that is insensitive to the wavelength of light.

The structural evolution and diffusion during the chemical transformation from cobalt to cobalt phosphide nanoparticles by Don-Hyung Ha; Liane M. Moreau; Clive R. Bealing; Haitao Zhang; Richard G. Hennig; Richard D. Robinson (11498-11510).
We report the structural evolution and the diffusion processes which occur during the phase transformation of nanoparticles (NPs), ε-Co to Co2P to CoP, from a reaction with tri-n-octylphosphine (TOP). Extended X-ray absorption fine structure (EXAFS) investigations were used to elucidate the changes in the local structure of cobalt atoms which occur as the chemical transformation progresses. The lack of long-range order, spread in interatomic distances, and overall increase in mean-square disorder compared with bulk structure reveal the decrease in the NP’s structural order compared with bulk structure, which contributes to their deviation from bulk-like behavior. Results from EXAFS show both the Co2P and CoP phases contain excess Co. Results from EXAFS, transmission electron microscopy, X-ray diffraction, and density functional theory calculations reveal that the inward diffusion of phosphorus is more favorable at the beginning of the transformation from ε-Co to Co2P by forming an amorphous Co-P shell, while retaining a crystalline cobalt core. When the major phase of the sample turns to Co2P, the diffusion processes reverse and cobalt atom out-diffusion is favored, leaving a hollow void, characteristic of the nanoscale Kirkendall effect. For the transformation from Co2P to CoP theory predicts an outward diffusion of cobalt while the anion lattice remains intact. In real samples, however, the Co-rich nanoparticles continue Kirkendall hollowing. Knowledge about the transformation method and structural properties provides a means to tailor the synthesis and composition of the NPs to facilitate their use in applications.

Smartly designed photoreactive silica nanoparticles and their reactivity by Anna Peled; Maria Naddaka; Jean-Paul Lellouche (11511-11517).
Monodisperse, colloidal silica nanoparticles (NPs) are being widely investigated due to a variety of applications in various fields of chemistry. Many works utilize incorporation of various functional groups to silica NPs for their further modifications. However, at present no benzophenone (BPh) or phenyl azide (PA) containing silica NPs exist. Upon UV irradiation BPh and PA form highly reactive species that react with any organic material. Here we present a convenient method for the preparation of novel hybrid photoreactive silica NPs (denoted as SiO2@photoreactive group) prepared by co-condensation of photoreactive organosilanes and tetraethyl orthosilicate (TEOS) to obtain SiO2@PA and SiO2@BPh NPs. The reactivity of these two types of silica NPs is compared to that of perfluorinated phenyl azide (PFPA) based SiO2 NPs. The reactivity evaluation is carried out by the reaction of the three types of SiO2 NPs with highly inert poly(2-chloro-paraxylelene) films. It is found that, in contrast to what is stated in the literature, PA is much more reactive than PFPA, when dealing with solid state photochemical reactions. Next, photoreactive silica NPs on polymer films are used as an intermediate functional phase for a second modification step using silane-based chemistry. A successful incorporation of amine functionality onto silica NPs is achieved by their reaction with 3-aminopropyltriethoxysilane (APTES) and is verified by fluorescence microscopy. This strategy provides a general and versatile route to efficient functionalization of silica by light.

Pt nanocrystal evolution in the presence of Au(iii)-salts at room temperature: spontaneous formation of AuPt heterodimers by Stephanie I. Lim; Miriam Varon; Isaac Ojea-Jiménez; Jordi Arbiol; Victor Puntes (11518-11523).
Room temperature synthesis of AuPt heterodimers is reported using a simple protocol. The role of oleylamine and Pt NCs in the reduction and nucleation of Au has been investigated. There are two unique aspects in this synthesis. Firstly, the synthesis was conducted at room temperature, which enabled the heterodimer growth to progress at a slower rate and thus allowed monitoring of the Au nucleation process. Secondly, these conditions allowed epitaxial growth with no crystal modification at the Au–Pt interphase. The presence of Pt NC seeds markedly accelerated the reaction, serving both as nucleation platforms and as an initial catalytic reducer of the Au ions in solution. The growth of Au on Pt NCs was monitored at different times by UV-vis, HRTEM and XRD.

Effect of the treatment with (di-)amines and dithiols on the spectroscopic, electrochemical and electrical properties of CdSe nanocrystals' thin films by Aurélie Lefrançois; Elsa Couderc; Jérôme Faure-Vincent; Saïd Sadki; Adam Pron; Peter Reiss (11524-11531).
In recent years the treatment of thin films of nanocrystals (NCs) with short monofunctional or bifunctional bridging ligands has commonly been used to improve the conductivity within the NCs' assemblies. How does this surface ligand exchange in the solid state influence the electronic energy levels of the system? We show that electrochemical studies and in particular differential pulse voltammetry (DPV) can be used to give an answer to this question. Combined UV-vis, DPV and cyclic voltammetry data reveal that a shift of several tens of meV of the NCs' HOMO and LUMO levels takes place upon surface ligand exchange. As objects of our study we have selected thin solid films of stearic acid and oleylamine capped CdSe NCs, which were treated with acetonitrile solutions of 1,2-ethanedithiol, butylamine, phenylenediamine, benzenedithiol and pyridine to induce the ligand exchange in the solid state, confirmed by FTIR spectroscopy. The resulting modified films exhibit strongly enhanced conductivity as compared to the films constituted of pristine NCs.

Uniform AgCl nanocubes with an average edge length of 85 nm have been prepared by a facile reverse micelle method. Partially reducing the as-produced AgCl nanocubes enables us to achieve a class of sunlight-driven plasmonic AgCl : Ag nanophotocatalysts. The optical absorption spectrum of the thus-achieved nanophotocatalyst exhibits strong absorption in the visible region due to surface plasmon resonance (SPR) of silver nanoparticles. Under sunlight illumination the hybrid AgCl : Ag nanoparticles exhibit high activity and durability towards decomposition of organic pollutant, e.g., methyl orange. The catalyst can be reused for 19 times without loss of activity. The possible photocatalytic mechanism is discussed, which indicates that metallic silver nanograins (or nanoparticles) play a critical role in enhancing photocatalytic performance and stabilizing the photocatalyst. These features mean the present nanophotocatalyst can be applied in environmental remediation, and waste water disinfection.

Transverse oxidation of gold nanorods assisted by selective end capping of silver oxide by Zhihong Bao; Zhenhua Sun; Manda Xiao; Huanjun Chen; Linwei Tian; Jianfang Wang (11537-11543).
An approach for the transverse oxidation of Au nanorods has been demonstrated by selectively capping the ends of the nanorods with Ag2O through a hydrothermal reaction. The tight Ag2O capping protects the ends of the nanorods and restricts oxidation to occurring only at the side surfaces. Such transverse oxidation leads to a gradual reduction in the effective diameter of the nanorods, an increase in the effective aspect ratio, and therefore a red shift in the longitudinal plasmon resonance. The red shift in the longitudinal plasmon resonance can reach up to 250 nm and be controlled by varying the oxidation time. In addition, the Ag2O capping and transverse oxidation process is also applicable for Au nanorods with different longitudinal plasmon resonance wavelengths. Furthermore, the transverse oxidation is nonuniform. It produces dimples on the side surfaces of the Au nanorods. Numerical electrodynamic calculations indicate that the oxidized nanorods exhibit stronger electric field intensity enhancements at the dimples for both the longitudinal and transverse plasmon resonances in comparison to the unoxidized nanorods. We believe that this transverse oxidation approach will be beneficial to the design and preparation of Au nanostructures for various biotechnological applications.

Reshaping and LSPR tuning of Au nanostars in the presence of CTAB by Laura Rodríguez-Lorenzo; José M. Romo-Herrera; Jorge Pérez-Juste; Ramón A. Alvarez-Puebla; Luis M. Liz-Marzán (11544-11549).
Gold nanostars can easily undergo reshaping into spherical particles by simply adding a small amount of CTAB. Such reshaping can be understood in terms of Ostwald ripening involving dissolution of weakly bound surface atoms at areas with high convex curvature and re-deposition at concave areas. This process can be stopped at any time by adding silver ions, which block bromide and stabilize the surface. Because the localized surface plasmon resonance (LSPR) band of the nanostars colloid gradually changes during etching, stabilization of intermediate morphologies allows fine LSPR tuning, which can be exploited for plasmonic applications.

Gradated alloyed CdZnSe nanocrystals with high luminescence quantum yields and stability for optoelectronic and biological applications by Subhendu K. Panda; Stephen G. Hickey; Christian Waurisch; Alexander Eychmüller (11550-11555).
Graded, high-quality ternary CdZnSe quantum dots (QDs) have been successfully prepared by the alloying of CdSe/ZnSe core/shell QDs at high temperatures. By increasing the alloying time, a gradient distribution of components was obtained, which leads to tunable emission across most of the visible spectrum through a systematic blue-shift in emission wavelength. The resultant alloyed QDs show a gradated quasi core/shell structure in which the core is CdSe rich and the shell is rich in ZnSe. This distinctive structure results in a photoluminescence (PL) quantum yield (QY) up to 55% and moreover, the alloyed nanocrystals can retain their high luminescence when dispersed in aqueous solutions. They also demonstrate high photo and thermal stability. The peak shape and spectral position remains unchanged under all experimental conditions undertaken in this study.

Thermally induced atomic reconstruction of PbSe/CdSe core/shell quantum dots into PbSe/CdSe bi-hemisphere hetero-nanocrystals by Dominika Grodzińska; Francesca Pietra; Marijn A. van Huis; Daniel Vanmaekelbergh; Celso de Mello Donegá (11556-11565).
The properties of hetero-nanocrystals (HNCs) depend strongly on the mutual arrangement of the nanoscale components. In this work we have investigated the structural and morphological evolution of colloidal PbSe/CdSe core/shell quantum dots upon annealing under vacuum. Prior to annealing the PbSe core has an approximately octahedral morphology with eight {111} facets, and the CdSe shell has zinc-blende crystal structure. Thermal annealing under vacuum at temperatures between 150 °C and 200 °C induces a structural and morphological reconstruction of the HNCs whereby the PbSe core and the CdSe shell are reorganized into two hemispheres joined by a common {111} Se plane. This thermally induced reconstruction leads to considerable changes in the optical properties of the colloidal PbSe/CdSe HNCs.

Thermodynamic modelling of nanomorphologies of hematite and goethite by Haibo Guo; Amanda S. Barnard (11566-11577).
Iron oxide and oxyhydroxide nanoparticles are among the most important mobile and catalytic agents in a variety of biogeochemical environments, and are being increasingly synthesized for energy, electronic, catalyst, environmental and medical applications. The morphologies at nanoscale are relevant to the control of shapes and sizes, surface chemistry, and performance of these nanoparticles, as well as our understanding of naturally occurring processes. Therefore, we have begun to develop this understanding by studying the relationship between size, shape, and thermodynamic stability of unpassivated hematite (α-Fe2O3) and goethite (α-FeOOH) nanoparticles, using a robust thermodynamic morphology model with input parameters from reliable first-principles calculations and thermochemical data. The results revealed the thermodynamic stable shapes of hematite and goethite nanoparticles, and demonstrated that the phase transformation from goethite to hematite is highly dependent on the particle size and temperature. Goethite nanoparticles are thermodynamically stable with small sizes, compared to hematite, but the equilibrium transformation temperature increases rapidly with decreasing particle size. The morphology sensitive phase transformation predicted by our model is a step further towards a nanophase diagram of iron oxides and oxyhydroxides.

Structure and stability of platinum nanocrystals: from low-index to high-index facets by Rao Huang; Yu-Hua Wen; Zi-Zhong Zhu; Shi-Gang Sun (11578-11584).
High index surfaces are introduced into Pt nanocrystals because they are expected to exhibit higher catalytic activity than low index planes such as {111}, {100}, and even {110}. This article presents a systematic investigation on the structure and stability of polyhedral Pt nanocrystals with both low-index and high-index facets by means of atomistic simulations. It has been found that the stability of Pt nanocrystals depends strongly on the particle shape and surface structures. Those nanocrystals, enclosed by high-index facets of {310}, {311}, and {331}, possess better stability and higher dangling bond density of surface compared with those ones with low-index facets, such as {100} and {110}, suggesting that they should become preferential candidates for nanocatalysts. The octahedral nanocrystals with {111} facets, though they have excellent structural and thermal stabilities, present the lowest dangling bond density of surface.

Coalescence of magic sized CdSe into rods and wires and subsequent energy transfer by Sucheta Sengupta; D. D. Sarma; Somobrata Acharya (11585-11591).
We report on the synthesis of CdSe magic-sized clusters (MSCs) and their evolution into 1D rod and wires retaining the diameter of the order of MSCs. At the beginning of the reaction, different classes of stable MSCs with band gaps of 3.02 eV and 2.57 eV are formed, which exhibit sharp band edge photoluminescence features with FWHM in the order of ∼13 nm. Reaction annealing time was carried out in order to monitor the shape evolution of the MSCs. We find that magic sized CdSe evolve into 1D rod and wires retaining the same diameter upon increasing annealing time. We observed the gradual emergence of new red shifted emission peaks during this shape evolution process, which emerge as a result of one dimensional energy transfer within the magic sized clusters during their subsequent transformation into rods and wires. The smallest, the second smallest sized MSC and the wires sequentially act as donors and acceptors during the size evolution from small MSCs to larger ones, and then eventually to wires. Steady-state and time-resolved luminescent spectroscopy revealed Forster resonance energy transfer (FRET) between the MSCs to the rods and wires.

Colloidal cadmium chalcogenide quantum dots can exhibit a drastic change in structure and conformation by addition of a metal cation with a positive redox potential. CdTe and CdSe nanoparticles mixed with a mercury cation were transformed into alloyed anisotropic structures with red-shifted optical properties. Additionally the same cation addition to CdSe nanorods caused oriented attachment and resulted in a series of end-to-end superstructures. In the case of gold cation addition, CdTe nanoparticles yielded gold based anisotropic structures which had poor solubility in the original solvent. CdTe nanoparticles mixed with lead, zinc and cadmium cations, however, kept their original optical properties after the same reaction procedure. Combining these observations with the previously reported chemical transformation from cadmium chalcogenides to silver/copper chalcogenides, we highlight the role of the redox potentials when describing the change in structural/optical property in colloidal cadmium chalcogenide nanocrystals.

Aqueous room-temperature synthesis of Au–Rh, Au–Pt, Pt–Rh, and Pd–Rh alloy nanoparticles: fully tunable compositions within the miscibility gaps by Elizabeth R. Essinger-Hileman; Danielle DeCicco; James F. Bondi; Raymond E. Schaak (11599-11604).
Many binary late transition metal systems have large bulk miscibility gaps, and a variety of synthetic strategies have been developed to generate these non-equilibrium alloys as nanoparticles. While many of these methods strive to co-nucleate both elements by exploiting fast reduction kinetics or co-sequestration within a confined space, we show here that simple room-temperature borohydride co-reduction of appropriate aqueous metal salt solutions yields alloy nanoparticles in the bulk-immiscible Au–Rh, Au–Pt, Pt–Rh, and Pd–Rh systems. The compositions can be tuned across the entire Au1−xRhx, Au1−xPtx, Pt1−xRhx, and Pd1−xRhx solid solutions by varying the ratio of metal salt reagents, and they form in the presence of a variety of molecular and polymeric surface stabilizers. Reaction pathway studies on the model Au–Rh system suggest that the alloy nanoparticles form via a “conversion chemistry” mechanism: Au nanoparticle templates nucleate first, followed by diffusion of Rh to form homogeneous Au–Rh alloy nanoparticles. The alloy nanoparticles tend to be agglomerated, but this can be minimized by forming the nanoparticles directly on catalytically relevant high surface area carbon and biological supports, e.g. Vulcan carbon and wild-type M13 bacteriophage.

Ligands affect the crystal structure and photovoltaic performance of thin films of PbSe quantum dots by Chih-Yin Kuo; Ming-Shin Su; Ching-Shun Ku; Shu-Min Wang; Hsin-Yi Lee; Kung-Hwa Wei (11605-11612).
We have prepared thin films of PbSe quantum dots (QDs) featuring three different ligands, oleic acid (OA), butylamine (BA), and 1,2-ethanedithiol (EDT), which have pronounced affects on the arrangement and photovoltaic performance of the PbSe QDs in the thin films. Transmission electron microscopy revealed that ligands that altered the inter-QD spacing induced significant changes in the packing of the PbSe QDs in localized regions of small areas (300 × 300 nm) of the thin films: from a superlattice of OA-capped PbSe QDs to a chaotic pattern of EDT-capped PbSe QDs. Using a synchrotron X-ray reflectivity probe and data fitting, we determined that the roughness decreased and the average densities increased for large-area (1.5 × 1.5 cm) PbSe QD thin films capped with BA and EDT, relative to those of the OA-capped PbSe QD film. In particular, the PbSe QDs' vertical packing density, which is critical for charge transport, increased substantially for the system incorporating EDT ligands. As a result, devices containing the EDT-treated PbSe QD film as the active layer displayed much improved power conversion efficiencies (PCEs) relative to those of corresponding devices featuring either the OA- or BA-capped PbSe QD films as active layers. Adopting a layer-by-layer technique, we fabricated a EDT-capped PbSe QD device that exhibited a PCE of 2.45%.

Statistical model for ensembles undergoing phase transformations by D. Vollath; F. D. Fischer (11613-11617).
A statistical model delivering average equilibrium concentrations and indications for the time evolution of ensembles of phase transforming nanoparticles, showing fluctuations, gives clues for a new approach. It is shown that the temporal evolution of transformation of the ensemble depends on the distinguishability of the particles. However, the equilibrium configuration of fluctuating ensembles does not depend on the distinguishability of the particles. The outcome of the presuppositionless statistical fluctuation model is the proof that any fluctuations connected to phase transformations occur in the minimum of the free enthalpy. Additionally, the analysis allows drafting a new fluctuation condition for ensembles.

Surfactant effect on the formation of CuInSe2 nanowires in solution phase synthesis by Stacey E. Wark; Chih-Hao Hsia; Zhiping Luo; Dong Hee Son (11618-11625).
Solution-phase synthesis of CuInSe2 nanowires without using metal nanocrystal catalysts has been demonstrated. The morphology of chalcopyrite CuInSe2 nanoparticles could be varied from spheres to highly anisotropic nanowires by varying the relative amount of strong and weak binding surfactants passivating the surface. For CuInSe2 nanowires, weakly binding dioctylphosphine oxide (DOPO) was found to be the key surfactant that enables the anisotropic 1-dimensional growth. Detailed analysis of the structure of the nanowires indicates that they grow perpendicular to (112) planes, with twinning around the growth axis by ∼60° rotation. The nanowires of CuInSe2 synthesized in this study exhibit saw-tooth surface morphology resembling a stack of truncated tetrahedra which show a continuous growth mechanism.

A facile one-step approach for the synthesis and assembly of copper and copper-oxide nanocrystals by Mahmud Diab; Brian Moshofsky; Ilan Jen-La Plante; Taleb Mokari (11626-11630).
A simple one-step approach for the formation of close packed films of copper and copper oxide nanoparticles is described. Thermal decomposition of copper cupferrate, a single-source precursor, on silicon produces a well-controlled, assembled film of Cu nanocrystals. Upon oxidation, Cu2O is formed with retention of the assembly. Similarly, the thermal decomposition of manganese cupferrate results in the formation of porous MnO nanowires. Various solvents were used to examine their influence on the composition and assembly of the nanoparticles. This approach enables an easy and reproducible process for the synthesis and assembly of metal oxide nanostructures.

Polyoxometalates and colloidal nanocrystals as building blocks for metal oxide nanocomposite films by Anna Llordes; Aaron T. Hammack; Raffaella Buonsanti; Ravisubhash Tangirala; Shaul Aloni; Brett A. Helms; Delia J. Milliron (11631-11638).
We report the preparation of solution-derived metal oxide nanocomposite films by combining polyoxometalates (POMs) and colloidal oxide nanocrystals. Polyniobates and vanadates were combined with Sn-doped In2O3 (ITO) nanocrystals leading to Nb2O5–ITO, V2O5–ITO and VO2–ITO nanocomposite films. Compared to other solution-phase methodologies, this approach offers excellent control of the nanoinclusion composition, size, morphology, and volume fraction. Two different methodologies have been used, which are based on the ex situ (in solution) and in situ (within the film) ligand exchange of the pristine organic capping ligands of the nanocrystals by POMs. A thorough structural and compositional characterization of the films at different stages of the ligand exchange process is also presented.

Reversible nanoparticle gels with colour switching by Soo-Hwan Jeong; Jung Woo Lee; Dengteng Ge; Kai Sun; Takuya Nakashima; Seong Il Yoo; Ashish Agarwal; Yao Li; Nicholas A. Kotov (11639-11643).
Assembly of semiconductor nanoparticles into gel structures and their subsequent behaviour is one of the less-developed areas in nanochemistry. We demonstrate here a simple luminescent gel from CdTe nanoparticles in aqueous solution. Its structure can be described as an infinite network from chainlike branched structures. The recrystallization into the solid monocrystalline nanowires is prevented by increasing content of sulphur in the nanoparticles, which drastically increases the recrystallization energy. Brief sonication returns the system into the sol state. This switching behaviour is reversible and is accompanied by equally reversible emission colour switching. Such properties are much needed in a variety of media-responsive (i.e.“smart”) optoelectronic materials. This system will also be useful as a convenient research tool for the observation of dynamics of aqueous nanoscale colloids.

Ripening of bimodally distributed AgCl nanoparticles by Sheng Peng; Yugang Sun (11644-11650).
Ripening of AgCl nanoparticles with a bimodal size distribution has been carefully studied in ethylene glycol containing poly(vinyl pyrrolidone) (PVP) as capping molecules and at elevated temperatures (e.g., 160 °C). The resulting AgCl particles exhibit high uniformity in size and cube-tetrapod morphology that are significantly different from the original AgCl nanoparticles. In addition, enhanced reducing ability of ethylene glycol at high temperature partially reduces AgCl to form Ag nanocrystalline domains in the AgCl particles, leading the AgCl particles to be efficiently absorbing visible light and to serve as a class of visible-light-driven photocatalysts due to the strong surface plasmon resonance (SPR) associated with the Ag nanocrystallites.

Inside back cover (11651-11651).

Back cover (11652-11652).