Self-assembly of noble metal nanoparticles into sub-100 nm colloidosomes with collective optical and catalytic properties.

Self-assembly at the nanoscale represents a powerful tool for creating materials with new structures and intriguing collective properties. Here, we report a novel strategy to synthesize nanoscale colloidosomes of noble metals by assembling primary metal nanoparticles at the interface of emulsion droplets formed by their capping agent. This strategy produces noble metal colloidosomes of unprecedentedly small sizes (<100 nm) in high yield and uniformity, which is highly desirable for practical applications. In addition, it enables the high tunability of the composition, producing a diversity of monometallic and bimetallic alloy colloidosomes. The colloidosomes exhibit interesting collective properties that are different from those of individual colloidal nanoparticles. Specifically, we demonstrate Au colloidosomes with well-controlled interparticle plasmon coupling and Au-Pd alloy colloidosomes with superior electrocatalytic performance, both thanks to the special structural features that arise from the assembly. We believe this strategy provides a general platform for producing a rich class of miniature colloidosomes that may have fascinating collective properties for a broad range of applications

Agenda 21.

A Agenda 21 Brasileira é um processo e, ao mesmo tempo, instrumento de planejamento participativo para o desenvolvimento sustentável e que tem como eixo central a sustentabilidade, compatibilizando a conservação ambiental, a justiça social e o crescimento econômico. O documento e resultado de uma vasta consulta a população brasileira, sendo construída a partir das diretrizes da Agenda 21 global. Trata-se, portanto, de um instrumento fundamental para a construção da democracia ativa e da cidadania participativa no pais. A primeira fase foi a construção da Agenda 21 Brasileira. Esse processo, que se deu de 1996 a 2002, foi coordenado pela Comissão de Politicas de Desenvolvimento Sustentável e da Agenda 21 Nacional - CPDS e teve o envolvimento de cerca de 40.000 pessoas de todo o Brasil. O documento Agenda 21 Brasileira foi concluído em 2002. A partir de 2003, a Agenda 21 Brasileira não somente entrou na fase de implementação assistida pela CPDS, como também foi elevada a condição de Programa do Plano Plurianual, PPA 2004-2007, pelo atual governo. Como programa, ela adquire mais foça politica e institucional, passando a ser instrumento fundamental para a construção do Brasil Sustentável, estando coadunada com as diretrizes da politica ambiental do Governo-transversalidade, desenvolvimento sustentável, fortalecimento do Sistema e participação social, adotando referenciais importantes como a Carta da Terra. Portanto, a Agenda 21, que tem provado ser um guia eficiente para processos de união da sociedade, compreensão dos conceitos de cidadania e de sua aplicação, e hoje um dos grandes instrumentos de formação de politicas públicas no Brasil.Agenda 21 Brazilian is a process and, at the same time, instrument of participative planning for the sustainable development and that it has as central axle the sustentabilidade, compatibizando the ambient conservation, social justice and the economic growth. The document is resulted of a vast one consults the Brazilian population, being constructed from the lines of direction of global Agenda 21. It is treated, therefore, of a basic instrument for the construction of the active democracy and the participative citizenship in the Country. The first phase was the construction of Agenda 21 Brazilian. This process, that if gave of 1996 the 2002, was co-ordinated by the Commission of Politics of Sustainable Development and the National Agenda 21 - CPDS and had the envolvement of about 40.000 people of all Brazil. The document Agenda 21 Brazilian was concluded in 2002. From 2003, Agenda 21 Brazilian not only entered in the phase of implementation attended for the CPDS, as also condition of Program of the Puritanical Plan was raised a, PPA 2004-2007, for the current government. As program, it it acquires more force institutional politics and, starting to be basic instrument for the construction of Sustainable Brazil, being coadunate with the lines of direction of the ambient politics of the Government-transversaldade, sustainable development, fortalecimento of the System and social participation, adopting referenciais important as the Letter of the Land. Therefore, Agenda 21, that it has proven being an efficient guide for processes of union of the society, understanding of the concepts of citizenship and its application, is today one of the great instruments of formation of public politics in Brazi

Customizable Ligand Exchange for Tailored Surface Property of Noble Metal Nanocrystals.

It is highly desirable, while still challenging, to obtain noble metal nanocrystals with custom capping ligands, because their colloidal synthesis relies on specific capping ligands for the shape control while conventional ligand exchange processes suffer from "the strong replaces the weak" limitation, which greatly hinders their applications. Herein, we report a general and effective ligand exchange approach that can replace the native capping ligands of noble metal nanocrystals with virtually any type of ligands, producing flexibly tailored surface properties. The key is to use diethylamine with conveniently switchable binding affinity to the metal surface as an intermediate ligand. As a strong ligand, it in its original form can effectively remove the native ligands; while protonated, it loses its binding affinity and facilitates the adsorption of new ligands, especially weak ones, onto the metal surface. By this means, the irreversible order in the conventional ligand exchange processes could be overcome. The efficacy of the strategy is demonstrated by mutual exchange of the capping ligands among cetyltrimethylammonium, citrate, polyvinylpyrrolidone, and oleylamine. This novel strategy significantly expands our ability to manipulate the surface property of noble metal nanocrystals and extends their applicability to a wide range of fields, particularly biomedical applications

Porous Au–Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis

Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au–Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ∼1.3 × 10⁷ on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications

Porous Au–Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis

Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au–Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ∼1.3 × 10⁷ on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications