Edgar González

Carving at the Nanoscale: Sequential Galvanic Exchange and Kirkendall Growth at Room Temperature

Processes used in colloidal chemistry can be jointly exploited to make complex metal alloy nanoparticles. Shape control of inorganic nanocrystals is important for understanding basic size- and shape-dependent scaling laws and is useful in a wide range of applications. With minor modifications in the chemical environment, it is possible to control the reaction and diffusion processes at room temperature, opening up a synthetic route for the production of polymetallic hollow nanoparticles with very different morphology and composition, obtained by the simultaneous or sequential action of galvanic replacement and the Kirkendall effect.

Shape matters: effects of silver nanospheres and wires on human alveolar epithelial cells

BackgroundIn nanotoxicology, the exact role of particle shape, in relation to the composition, on the capacity to induce toxicity is largely unknown. We investigated the toxic and immunotoxic effects of silver wires (length: 1.5 - 25 μm; diameter 100 - 160 nm), spherical silver nanoparticles (30 nm) and silver microparticles (<45 μm) on alveolar epithelial cells (A549).MethodsWires and nanoparticles were synthesized by wet-chemistry methods and extensively characterized. Cell viability and cytotoxicity were assessed and potential immunotoxic effects were investigated. To compare the effects on an activated and a resting immune system, cells were stimulated with rhTNF-α or left untreated. Changes in intracellular free calcium levels were determined using calcium imaging. Finally, ion release from the particles was assessed by ICP-MS and the effects of released ions on cell viability and cytotoxicity were tested.ResultsNo effects were observed for the spherical particles, whereas the silver wires significantly reduced cell viability and increased LDH release from A549 cells. Cytokine promoter induction and NF-κB activation decreased in a concentration dependent manner similar to the decrease seen in cell viability. In addition, a strong increase of intracellular calcium levels within minutes after addition of wires was observed. This toxicity was not due to free silver ions, since the samples with the highest ion release did not induce toxicity and ion release control experiments with cells treated with pre-incubated medium did not show any effects either.ConclusionsThese data showed that silver wires strongly affect the alveolar epithelial cells, whereas spherical silver particles had no effect. This supports the hypothesis that shape is one of the important factors that determine particle toxicity.

Effect of cerium dioxide, titanium dioxide, silver, and gold nanoparticles on the activity of microbial communities intended in wastewater treatment

Growth in production and use of nanoparticles (NPs) will result increased concentrations of these in industrial and urban wastewaters and, consequently, in wastewater-treatment facilities. The effect of this increase on the performance of the wastewater-treatment process has not been studied systematically and including all the microbial communities involved in wastewater treatment. The present work investigates, by using respiration tests and biogas-production analysis, the inhibitory effect of four different commonly used metal oxide (CeO(2) and TiO(2)) and zero-valent metal (Ag and Au) nanoparticles on the activity of the most important microbial communities present in a modern wastewater-treatment plant. Specifically, the actions of ordinary heterotrophic organisms, ammonia oxidizing bacteria, and thermophilic and mesophilic anaerobic bacteria were tested in the presence and absence of the nanoparticles. In general, CeO(2) nanoparticles caused the greatest inhibition in biogas production (nearly 100%) and a strong inhibitory action of other biomasses; Ag nanoparticles caused an intermediate inhibition in biogas production (within 33-50%) and a slight inhibition in the action of other biomasses, and Au and TiO(2) nanoparticles caused only slight or no inhibition for all tested biomasses.

Chromium VI adsorption on cerium oxide nanoparticles and morphology changes during the process.

In this study, suspended cerium oxide nanoparticles stabilized with hexamethylenetetramine were used for the removal of dissolved chromium VI in pure water. Several concentrations of adsorbent and adsorbate were tested, trying to cover a large range of possible real conditions. Results showed that the Freundlich isotherm represented well the adsorption equilibrium reached between nanoparticles and chromium, whereas adsorption kinetics could be modeled by a pseudo-second-order expression. The separation of chromium-cerium nanoparticles from the medium and the desorption of chromium using sodium hydroxide without cerium losses was obtained. Nanoparticles agglomeration and morphological changes during the adsorption-desorption process were observed by TEM. Another remarkable result obtained in this study is the low toxicity in the water treated by nanoparticles measured by the Microtox(®) commercial method. These results can be used to propose this treatment sequence for a clean and simple removal of drinking water or wastewater re-use when a high toxicity heavy metal such as chromium VI is the responsible for water pollution.

Synthesis and evaluation of gold nanoparticle-modified polyelectrolyte capsules under microwave irradiation for remotely controlled release for cargo

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.

Potential use of CeO2, TiO2 and Fe3O4 nanoparticles for the removal of cadmium from water

Abstract Inorganic nanoparticles (NPs) of cerium oxide (CeO2), iron oxide (Fe3O4) and titanium oxide (TiO2) were studied for the removal of dissolved cadmium from water at concentrations ranging from 25 to 350 mg/L. Adsorption was the predominant mechanism for sequestration, and particularly efficient cadmium removal was demonstrated for Fe3O4 NPs. Experimental data were fitted to three different adsorption isotherms: Langmuir, Freundlich and Temkin. The best fit was obtained for the Freundlich isotherm (R 2 > 0.96 for all NPs). Adsorption was shown to follow pseudo second-order kinetics (R 2 ⩾ 0.91 for all NPs). All three NPs showed some removal of cadmium in aqueous solution, but after 72 h of process, Fe3O4 NPs showed a higher capacity of cadmium adsorption (101.1 mg Cd/g NP) than CeO2 NPs (49.1 mg Cd/g NP) or TiO2 NPs (12.2 mg Cd/g NP). These results demonstrate the potential use of this NPs to remove dissolved cadmium at high concentrations.

Preliminary study of phosphate adsorption onto cerium oxide nanoparticles for use in water purification; nanoparticles synthesis and characterization.

In this study, the synthesis and characterization of cerium oxide nanoparticles (CeO(2)-NPs) and their adsorption potential for removing phosphate from water was evaluated using a multi-factor experimental design to explore the effect of various factors on adsorption. The objective function selected was the percentage of phosphate removed from water, in which the phosphate concentration and the CeO(2)-NP concentration are quantitative variables (factors in the experimental design). A lineal polynomial fitted the experimental results well (R(2) = 0.9803). The nanostructure was studied by transmission electron microscopy (TEM) and high-resolution TEM techniques before and after the adsorption process. During the adsorption and desorption processes several changes in the morphology and surface chemistry of the CeO(2)-NPs were observed.

Exploring New Synthetic Strategies for the Production of Advanced Complex Inorganic Nanocrystals

Abstract The design of new protocols for the colloidal synthesis of complex nanocrystals (NCs) with advanced functionalities, comprising both hybrid and hollow structures, and the study of their fundamental properties is of paramount importance for the development of a new generation of nanostructured materials. The possibility of tailoring the dimensional regime of NCs, along with its composition and structure, represents a landmark achievement in the control of their unique physico-chemical properties. These properties, alongside with the ability to cheaply produce high quality NCs in fairly large amounts by wet-chemistry techniques, leads to their potential applicability from materials science to nanomedicine. Within this context, this review is focused on describing a successful framework for designing synthetic strategies for the production of advanced complex NCs, integrating the development of new synthetic methods with its structural characterization, monitoring of their properties, and study of its reactivity. As a result, it is expected to provide new routes to produce robust and easy-to-process NCs in a wide range of sizes, shapes and configurations that can be explored to achieve the combination of all degrees of control, aiming to produce a complete and diverse library of material combinations that will expand its applicability in a wide diversity of fields.

Inorganic nanoparticles and the environment: balancing benefits and risks.

Abstract Environmental remediation issues, although being essential, are partially and incompletely solved by conventional technologies. Critical points include ensuring access to clean water, removing air pollutants and cleaning up industrial- or military-contaminated soils, among others. A series of laboratory demonstrations have shown how nanoparticles (NPs) are efficient in carrying out these works. However, a deeper understanding of the processes at the molecular level and the transfer to the larger scales of real application are still needed. Exploiting material properties at the nanoscale for environmental remediation, apart from contributing to the benefits of living in a cleaner world, has the potential to promote economic growth and innovation, while allowing a sustainable development of nanotechnologies. Of course, benefits obtained have to be balanced with the potential risks of introducing large amounts of NPs in the environment. Whether the unknown risks of engineered NPs, which are currently an established field of research called nanotoxicology, outweigh their benefits for the society is a question still being solved. In this chapter, properties that make NPs appealing for environmental remediation, safety aspects and potential-associated toxicity are described. Moreover, some model cases of environmental applications using inorganic NPs are shown.

Hollow metal nanostructures for enhanced plasmonics(Conference Presentation)

Complex metal nanoparticles offer a great playground for plasmonic nanoengineering, where it is possible to cover plasmon resonances from ultraviolet to near infrared by modifying the morphologies from solid nanocubes to nanoframes, multiwalled hollow nanoboxes or even nanotubes with hybrid (alternating solid and hollow) structures. We experimentally show that structural modifications, i.e. void size and final morphology, are the dominant determinants for the final plasmonic properties, while compositional variations allow us to get a fine tuning. EELS mappings of localized surface plasmon resonances (LSPRs) reveal an enhanced plasmon field inside the voids of hollow AuAg nanostructures along with a more homogeneous distributions of the plasmon fields around the nanostructures. With the present methodology and the appropriate samples we are able to compare the effects of hybridization at the nanoscale in hollow nanostructures. Boundary element method (BEM) simulations also reveal the effects of structural nanoengineering on plasmonic properties of hollow metal nanostructures. Possibility of tuning the LSPR properties of hollow metal nanostructures in a wide range of energy by modifying the void size/shell thickness is shown by BEM simulations, which reveals that void size is the dominant factor for tuning the LSPRs. As a proof of concept for enhanced plasmonic properties, we show effective label free sensing of bovine serum albumin (BSA) with some of our hollow nanostructures. In addition, the different plasmonic modes observed have also been studied and mapped in 3D.