Nickel@Siloxene catalytic nanosheets for high-performance CO2 methanation.

Two-dimensional (2D) materials are of considerable interest for catalyzing the heterogeneous conversion of CO2 to synthetic fuels. In this regard, 2D siloxene nanosheets, have escaped thorough exploration, despite being composed of earth-abundant elements. Herein we demonstrate the remarkable catalytic activity, selectivity, and stability of a nickel@siloxene nanocomposite; it is found that this promising catalytic performance is highly sensitive to the location of the nickel component, being on either the interior or the exterior of adjacent siloxene nanosheets. Control over the location of nickel is achieved by employing the terminal groups of siloxene and varying the solvent used during its nucleation and growth, which ultimately determines the distinct reaction intermediates and pathways for the catalytic CO2 methanation. Significantly, a CO2 methanation rate of 100 mmol gNi-1 h-1 is achieved with over 90% selectivity when nickel resides specifically between the sheets of siloxene.

Synthesis and sensing properties of D5h pentagonal silver star nanoparticles.

In this work, we use silver decahedral nanoparticle (AgDeNP) seeds to synthesize pentagonal silver stars (AgStDeNPs) and study the sensing properties of these nanoparticles. The regrowth process of AgStDeNPs is kinetically-controlled, so the purity of the seed NPs is critical to avoid secondary deposition in the highly non-equilibrium reduction. To control the regrowth process, surface blocking with sodium polyacrylate (PANa) was implemented. PANa moderates rough silver nanostructures typically obtained by reduction with ascorbic acid. To modulate polymer binding to the surface and thus to tune surface blocking, pH served as a key synthetic parameter. Under optimal regrowth conditions, new sliver was deposited on the highest energy sites of the decahedra - the vertices of the rims - to yield pentagonal stars. The universality of this regrowth process was established with several different seed particles. The sharpness and size of the stellated tips are tunable by the amount of added silver. Gold deposition onto AgStDeNPs enables the preparation of diverse structures with enhanced stability. Ease of transformation, e.g. rounding, of star branches opens a promising venue for enhanced SPR sensing. Also, AgStDeNPs enable femtomolar detection of 5,5-dithiobis(2-nitrobenzoic acid) in SERS.

A design strategy for the hierarchical fabrication of colloidal hybrid mesostructures.

Advances in nanotechnology depend upon expanding the ability to create new and complex materials with well-defined multidimensional mesoscale structures. The creation of hybrid hierarchical structures by combining colloidal organic and inorganic building blocks remains a challenge due to the difficulty in preparing organic structural units of precise size and shape. Here we describe a design strategy to generate controlled hierarchical organic-inorganic hybrid architectures by multistep bottom-up self-assembly. Starting with a suspension of large inorganic nanoparticles, we anchor uniform block copolymer crystallites onto the nanoparticle surface. These colloidally stable multi-component particles can initiate the living growth of uniform cylindrical micelles from their surface, leading to three-dimensional architectures. Structures of greater complexity can be obtained by extending the micelles via addition of a second core-crystalline block copolymer. This controlled growth of polymer micelles from the surface of inorganic particles opens the door to the construction of previously inaccessible colloidal organic-inorganic hybrid structures.

Gold plating of silver nanoparticles for superior stability and preserved plasmonic and sensing properties.

Gold-plated silver nanoparticles (Au@AgNPs, shell@core) with high stability in various environments detrimental to AgNPs have been produced with preserved plasmonic and sensing properties.

Ultrathin gold nanoframes through surfactant-free templating of faceted pentagonal silver nanoparticles.

Ultrathin gold nanoframes (up to 1.6 nm) were prepared via templating upon well-defined faceted silver morphologies. Starting with silver decahedra, small quantities of gold (1-10 mol% relative to the amount of silver) were selectively deposited on the nanoparticle edges under optimized reducing conditions. Silver dissolution in hydrogen peroxide yielded well-defined gold frames that retained their structural integrity in the ultrathin nanowire regime below 2 nm. The frame formation protocol was also successfully applied to other silver nanoparticle shapes featuring pentagonal twinning and (111) facets (e.g., pentagonal faceted rods and icosahedra). The demonstrated approach can be applied in the controlled preparation of ultrathin metal nanowires complementary to lithography and in the production of ultrafine noble-metal nanostructures for catalytic applications.

Microgels for the encapsulation and stimulus-responsive release of molecules with distinct polarities.

A microfluidic strategy for the encapsulation and stimulus-responsive release of molecules with distinct polarities from the interior of microgels is reported. The approach relies on (i) the generation of a primary O/W emulsion by the ultrasonication method, (ii) MF emulsification of the primary emulsion, and (iii) photopolymerization of the monomer present in the aqueous phase of the droplets, thereby transforming them into microgels. Non-polar molecules are dissolved in oil droplets embedded in the microgels. Polar molecules are physically associated with the hydrogel network. Upon heating, the microgels contract and release polar and non-polar cargo molecules. The approach paves the way for stimuli-responsive vehicles for multiple drug delivery.

Hybrid porous material produced by polymerization-induced phase separation.

Herein we demonstrate a new, straightforward method for the synthesis of macroporous hybrid polymers coated with gold nanorods, which are strongly and uniformly attached to the surface of pores.

A study of polymerization-induced phase separation as a route to produce porous polymer-metal materials.

We report the results of the experimental study of the preparation of hybrid porous polymer material carrying gold nanorods (NRs) on the surface of pores. The material was prepared by utilizing two effects occurring concurrently: the photoinitiated polymerization-induced phase separation in the polymer-solvent mixture and the migration of the NRs to the interface between the polymer and the porogen solvent. We show that the enrichment of the interface with the NRs is enhanced at high polymerization rate leading to the rapid phase separation. By contrast, more rapid increase in viscosity achieved at high polymerization rate does not have a significant effect on the segregation of NRs to the surface of pores.

Lamellar envelopes of semiconductor nanocrystals.

We report the solution-phase formation of ordered lamellar nanocrystal (NC) arrays. These semiconductor lamellae exhibit structural integrity and temporal stability, without recourse to chemical cross-linking. They are many micrometers in diameter yet only two or three nanocrystal layers in thickness. We show that these structures can integrate a cargo of water-soluble ions, molecules, metal nanoparticles, or biomolecules. Encapsulation of gold nanoparticles is found to cause photoluminescence enhancement of the host CdSe nanocrystals. These easily prepared nanocrystal "envelopes" promise properties modulated through the integration of a vast array of water-soluble species. Our approach marks a step toward ordered, compartmentalized, NC-based complexes with controlled architectures.