Keys for designing hematite/plasmonic metal hybrid nanostructures with enhanced photoactive properties

Photoactive hybrid nanostructures composed of metal oxides and plasmonic metals are able to perform the conversion of radiant (solar) energy into electrical or chemical energy. However, their use in large-scale practical applications still requires their photoconversion efficiency to be improved. In this work, the light-harvesting properties of hematite/plasmonic metal rodlike hybrid nanostructures are investigated on the basis of discrete dipole approximation simulations. The effects of the length and nature of the metallic counterpart on the far- and near-field optical properties of the hybrid nanostructure are analyzed in detail. The implemented methodology allowed us to assess the contribution of each component of the hybrid nanostructure to the absorption efficiency, Qabs, separately. In turn, the Qabs values obtained were employed to determine the absorbed photon flux, ø, within the α-Fe2O3 component, a relevant quantity directly related to the photoconversion efficiency. It was found that both absorption efficiency Qabs and absorbed photon flux ø can be largely enhanced through a proper selection of the length and nature of the metallic counterpart of the nanostructure, evidencing plasmon-enhanced light absorption in the α-Fe2O3 component, which is attributed to a plasmon-induced energy transfer mechanism based on near-field enhancements. Importantly, it was found that the highest ø values achieved for nanostructures composed of Ag and Al (∼11 × 1016 photons cm-2 s-1) are nearly 3 times larger than those corresponding to nanostructures composed of Au (∼4 × 1016 photons cm-2 s-1). In addition, a direct relationship between the absorbed photon flux, ø, and optical characteristics of the nanostructures, that is, the bandgap energy of α-Fe2O3 and the energy and radiative line width of the localized surface plasmon resonance, was empirically obtained. Such a relationship not only complements but also overcomes the limitations of the reported useful criteria and provides helpful guidelines for the optimum design of hybrid nanostructures with enhanced photoactive properties.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Near-Field Enhancement Contribution to the Photoactivity in Magnetite-Gold Hybrid Nanostructures

Hybrid nanostructures composed of magnetic iron oxides and plasmonic metals can convert light energy into chemical energy, and they can be easily manipulated through magnetic fields. As a consequence of these multifunctional features, they can be employed as magnetically recyclable heterogeneous photocatalysts. Herein, we report a two-step method for the preparation of magnetite (Fe3O4)-gold (Au) hybrid nanostructures in aqueous media. The obtained material resembles a core-satellite morphology of 60 nm Fe3O4 nanoparticles surrounded by nearly 20 nm spherical Au nanoparticles attached to their surface. The synthesized hybrid material exhibits enhanced capabilities for methylene blue photodegradation compared with bare Fe3O4 nanoparticles. Detailed electrodynamics simulations were performed to achieve further insight into the improved photoactive properties of the Fe3O4-Au hybrid nanostructures. The theoretical results show that the excitation of localized surface plasmon resonances in the Au component leads to greater light absorption in the Fe3O4 component, which ultimately impacts the improved photocatalytic properties of the hybrid nanostructure. Overall, this work provides a complementary approach toward a complete understanding of the enhanced photoactive properties of hybrid nanostructures and highlights the importance of considering their actual morphology into simulations.Fil: Guzman, Federico Valentin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Mercadal, Pablo Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Conversión de energía solar mediante nanomateriales híbridos

Los nanomateriales híbridos compuestos por materiales semiconductores y metales plasmónicos permiten utilizar eficientemente luz del Sol para fotocatalizar reacciones químicas de relevancia ambiental y energética, tales como la degradación de contaminantes y la generación de H2. El desarrollo de tecnologías basadas en estos compuestos podría satisfacer la demanda de soluciones sustentables. En este trabajo se presenta un resumen del estado actual del conocimiento respecto al proceso de fotocatálisis heterogénea usando luz solar como fuente de energía, y nanoestructuras híbridas, como catalizadores. Se exponen los principales mecanismos que conducen a mejoras en la eficiencia de conversión de luz y se describen las estrategias más ampliamente utilizadas para sintetizar tales nanoestructuras.Hybrid nanomaterials composed of semiconductor materials and plasmonic metals allow the efficient use of sunlight to photocatalyst chemical reactions of environmental and energetic relevance, such as the degradation of pollutants and the generation of H2. The development of technologies based on these compounds could satisfy the demand for sustainable solutions. This paper presents a summary of the current state of knowledge regarding the process of heterogeneous photocatalysis using sunlight as a source of energy, and hybrid nanostructures, as catalysts. The main mechanisms that lead to improvements in light conversion efficiency are described and the most widely used strategies to synthesize such nanostructures are described.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Plasmon coupling in silver nanosphere pairs

In this work we study the optical properties of silver metal nanosphere pairs by means of rigorous electrodynamics calculations based on the generalized multiparticle Mie theory. By correlating the dipole longitudinal plasmon wavelength with its corresponding value of the real part of the dielectric constant, and based on the dipole quasi-electrostatic approximation, we were able to derive a new plasmon ruler equation for the longitudinal dipole plasmon resonance of Ag dimers, suitable for a wide range of interparticle distances and radii. The new resonance condition equation, at variance with previous work on noble metal nanoparticle pairs, takes into account empirically retardation effects and multipole interactions, being a novel, accurate, and potentially useful tool for future applications in plasmonic Nanometrology or sensor devices.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Near field enhancement in Ag Au nanospheres heterodimers

The near field enhancement in Ag Au nanospheres heterodimers excited at their respective resonance wavelengths is studied in detail using rigorous electrodynamics calculations based on the Generalized Multiparticle Mie theory. The effect of incident polarization, nanosphere radius, and interparticle separation on the distribution pattern and magnitude of the near field enhancement is analyzed. As in the homodimer case, the highest enhancement values are found for incident polarization parallel to the dimer axis. However, there are significant different enhancement patterns around the dimer according to the excitation wavelength. Analyzing the vector field plot of the enhancement, and comparing it with those corresponding to Ag and Au nanospheres homodimers, the differences observed are rationalized in terms of multipole excitations to explain the effect of breaking the symmetry of the plasmonic heterodimer. The results presented could be a useful tool for future design and engineering of plasmonic devices based on the near field properties such as substrates for enhanced spectroscopies and sensing. © 2011 American Chemical Society.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Size Optimization of Iron Oxide@Noble Metal Core-Shell Nanohybrids for Photothermal Applications

The optical properties of several iron oxide@noble metal core-shell nanohybrids (NHs) have been systematically studied by means of electrodynamics simulations applying Mie theory for coated spheres. Focus has been made in analyzing the dependence of the absorption cross section Cabs on the composition as well as on the variables that determine the NHs size, that is, the core radius, R, and the shell thickness, S. The absorption spectra are characterized by an intense peak attributed to a plasmon resonance mode for which the spectral position can be finely tuned in the Vis-NIR range according to the NH size and composition. The absorption cross-section peak intensity, Cabs,max, a key quantity regarding photothermal applications, also presents a strong dependence on the NH size and composition. In general, it is found that α-Fe2O3@Au and α-Fe2O3@Ag lead to larger Cabs,max values than Fe3O4@Au and Fe3O4@Ag core-shell NHs, which is attributed to the lower imaginary refractive index of α-Fe2O3 in comparison to that of Fe3O4. The theoretical Cabs,max values were then used to calculate the temperature change ΔT experienced by the NH when its plasmon resonance mode is excited on resonance. This information has been summarized in diagrams that relate, for each NH composition, the core radius R, the shell thickness S, its resonance wavelength, and the temperature change ΔT experienced at their resonance wavelength. This set of diagrams summarizes relevant information that allows us to predict, for instance, the size and composition that a NH should have to produce the largest ΔT upon illumination at a certain wavelength. The results presented in this work should be helpful to guide and optimize the design of magnetic-plasmonic core-shell NHs with potential photothermal applications.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Light Harvesting in Magnetite-Coated Plasmonic Metal Nanospheres

The design of hybrid nanostructures composed of plasmonic metals and semiconductor oxides plays a major role in determining their efficiency for the conversion of solar energy. In this work, the light-harvesting properties of spherical core–shell hybrid nanostructures composed of a plasmonic metal core (Au, Ag, and Al) coated by a magnetite (Fe3O4) shell have been investigated through systematic discrete dipole approximation simulations. The diameter of the plasmonic core D was varied in the range of 5–90 nm, while the thickness of the Fe3O4 shell S was varied in the range of 2–40 nm. It was found that for a given set of D and S values, the absorbed photon flux within the Fe3O4 shell, ϕ, increases in the order Al, Au, and Ag. Furthermore, for a given size, which is D + 2S = constant, the largest ϕ value is approximately achieved when D/S = 3, 4, and 5 for Al, Au, and Ag as the core material, respectively. In addition, it was empirically found that ϕ correlates directly with the predictor K, a quantity that depends on D, S, and the resonance energy of the plasmon. The results presented contribute to expanding the tool kit that allows optimizing the design of hybrid nanostructures in order to improve their photoactive properties.Fil: Gonzalez Ochea, Rocio Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Plasmon enhanced light absorption in aluminium@Hematite core shell hybrid nanocylinders: the critical role of length

The light absorption as well as the near field enhancements properties of Al@α-Fe2O3 core shell hybrid nanocylinders (HNs) have been systematically studied by means of Discrete Dipole Approximation simulations. The Al@α-Fe2O3 HNs consist of a right circular cylinder Al core, wrapped by a circular section of an α-Fe2O3 shell, both having the same finite length L. A general and useful methodology has been implemented to assess separately the partial contributions to the absorption spectrum of each component of the Al@α-Fe2O3 HN. The employed methodology can be applied not only to those HNs studied here but also to any other nanostructure with arbitrary geometry and several components providing relevant information not accessible through standard spectroscopic techniques. The absorption spectra have been employed to calculate the absorbed photon flux ϕ within the α-Fe2O3 shell. According to the HN size, plasmon enhanced light absorption in the α-Fe2O3 shell of the Al@α-Fe2O3 HNs is evidenced, which is attributed to a plasmon-induced energy transfer mechanism based on near field enhancements. The effect of the HN length on the absorbed photon flux ϕ is an important issue that has not been addressed yet, as only infinitely long HN has been considered in previous studies. It is demonstrated that the HN length L has a crucial influence on the absorbed photon flux ϕ, as it is the main structural parameter that allows us to tune the dipole plasmon resonance of the Al core into the visible region. Furthermore, it is shown that Al cores lead to larger ϕ values than the typical plasmonic metals Ag and Au. The results presented in this work point out that the HN length should be explicitly taken into account for an optimum design of core shell hybrid cylindrical nanostructures with enhanced or improved photoactive properties.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Passarelli, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Colloidal SERS Substrate for the Ultrasensitive Detection of Biotinylated Antibodies Based on Near-Field Gradient within the Gap of Au Nanoparticle Dimers

Surface-enhanced Raman spectroscopy (SERS) has demonstrated to be a powerful technique for the ultrasensitive detection of different types of analytes and particularly biomolecules, with the rational design of SERS substrates being one of the most relevant issues for the development of effective detection protocols. In this work, a colloidal SERS substrate consisting of a pair of Au nanorods linked by the molecular bridge biotin/streptavidin/biotin has been obtained and employed for the detection of picomolar quantities of the biotinylated antibodies gliadin IgG and Ara h1 IgG, which is of great interest in food science. As a consequence of the bioconjugation strategy implemented, the SERS substrate, that is, the Au nanorod dimer, presents the advantage of combining in a single nanostructure the capabilities for both direct and indirect detection of the biotinylated antibodies. Furthermore, the experimental results are supported by detailed electrodynamics simulations which takes into account not only the gradient of the near-field enhancements within the hot spot but also the volume occupied by the respective biomolecules. The SERS substrate presented here could be straightforwardly employed for the ultrasensitive detection of other biotinylated biomolecules.Fil: Mercadal, Pablo Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Near-field enhancement of multipole plasmon resonances in Ag and Au nanowires

In this paper, we investigate theoretically the electromagnetic field enhancement arising from excitation of silver and gold nanowires (NWs) of finite length, capable of sustaining surface plasmon resonances of different multipole order, using the Discrete Dipole Approximation (DDA). The influence of NW length on the degree of enhancement and confinement of the electromagnetic field for each surface plasmon mode is analyzed by a 3D mapping of the near field for different planes around the NW as well by calculating its variation with distance along two different directions, one parallel to and the other perpendicular to the NW axis, outside of the NW. It was found that the enhancement is still significant at relative large distances from the NW end, its decay being of much longer range than that predicted by a simple dipole approximation, especially at near-infrared wavelengths.Fil: Encina, Ezequiel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Perassi, Eduardo Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coronado, Eduardo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin