Progress in Nanoporous Templates: Beyond Anodic Aluminum Oxide and Towards Functional Complex Materials

Successful synthesis of ordered porous, multi-component complex materials requires a series of coordinated processes, typically including fabrication of a master template, deposition of materials within the pores to form a negative structure, and a third deposition or etching process to create the final, functional template. Translating the utility and the simplicity of the ordered nanoporous geometry of binary oxide templates to those comprising complex functional oxides used in energy, electronic, and biology applications has been met with numerous critical challenges. This review surveys the current state of commonly used complex material nanoporous template synthesis techniques derived from the base anodic aluminum oxide (AAO) geometry

Enhancing the Catalytic Activity of Palladium Nanoparticles via Sandwich-Like Confinement by Thin Titanate Nanosheets

As atomically thin oxide layers deposited on flat (noble) metal surfaces have been proven to have a significant influence on the electronic structure and thus the catalytic activity of the metal, we sought to mimic this architecture at the bulk scale. This could be achieved by intercalating small positively charged Pd nanoparticles of size 3.8 nm into a nematic liquid crystalline phase of lepidocrocite-type layered titanate. Upon intercalation the galleries collapsed and Pd nanoparticles were captured in a sandwichlike mesoporous architecture showing good accessibility to Pd nanoparticles. On the basis of X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) Pd was found to be in a partially oxidized state, while a reduced Ti species indicated an electronic interaction between nanoparticles and nanosheets. The close contact of titanate sandwiching Pd nanoparticles, moreover, allows for the donation of a lattice oxygen to the noble metal (inverse spillover). Due to the metal–support interactions of this peculiar support, the catalyst exhibited the oxidation of CO with a turnover frequency as high as 0.17 s–1 at a temperature of 100 °C

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

Atomic layer deposition (ALD) offers exciting possibilities for controlling the structure and composition of surfaces on the atomic scale in heterogeneous catalysts and solid oxide fuel cell (SOFC) electrodes. However, while ALD procedures and equipment are well developed for applications involving flat surfaces, the conditions required for ALD in porous materials with a large surface area need to be very different. The materials (e.g., rare earths and other functional oxides) that are of interest for catalytic applications will also be different. For flat surfaces, rapid cycling, enabled by high carrier-gas flow rates, is necessary in order to rapidly grow thicker films. By contrast, ALD films in porous materials rarely need to be more than 1 nm thick. The elimination of diffusion gradients, efficient use of precursors, and ligand removal with less reactive precursors are the major factors that need to be controlled. In this review, criteria will be outlined for the successful use of ALD in porous materials. Examples of opportunities for using ALD to modify heterogeneous catalysts and SOFC electrodes will be given

Development of a lift-off process for sub-micrometer structures implemented on ultra-thin film Cu(In,Ga)Se2 (CIGS) solar cells

Cu(In,Ga)Se2 (CIGS) solar cells have been gathering increased attention by the scientific and the industrial community, with values of efficiency reaching a record value of 23.35%. Nevertheless, the use of the scarce elements as In and Ga might translate into a higher production cost in the near future. The reduction of the absorber thickness is a solution to this problem. However, some studies point that for sub-micrometer thicknesses, rear contact recombination vastly increases, and the light absorption is incomplete. In order to tackle these problems, several passivation and optical techniques are being developed. The focus of this thesis is to develop a lift-off process for the implementation of a novel structure with the objective of increasing the optical reflection on the rear contact, increasing the optical path. The structure consisted on a metal/dielectric stack patterned with Mo lines that will make the electrical contact with CIGS. Through the use of several metals (Pd, Pt, Cu, Ta) encapsulated with a dielectric layer (SiO2), that were then patterned with Mo lines, using a lithographic step, we managed to enhance both External Quantum Efficiency and the Short Circuit Current (4.13 mA/cm2 abs. increase) on the modified CIGS solar cells, in comparison to an ultrathin reference

Layer-by-Layer Thin Films and Coatings Containing Metal Nanoparticles in Catalysis

The layer-by-layer (LbL) technique is one of the most promising ways of fabricating multilayer thin films and coatings with precisely controlled composition, thickness, and architecture on a nanometer scale. This chapter considers the multilayer thin films and coatings containing metal nanoparticles. The main attention was paid to LbL films containing metal nanoparticles assembled by convenient methods based on the different intermolecular interactions, such as hydrogen bonding, charge transfer interaction, molecular recognition, coordination interactions, as driving force for the multilayer buildup. Much attention has paid to the LbL films containing metal nanocomposites for multifunctional catalytic applications, in particular, photocatalysis, thermal catalysis, and electrocatalysis. The preparation protocol of LbL-assembled multilayer thin films containing metal nanoparticles (such as Au, Ag, Pd, Pt), metal oxides (Fe3O4), and sulfides (CdS) that are supported on the various surfaces of nanotubes of TiO2, Al2O3 membranes, graphene nanosheets, graphene oxide and further applications as catalysts with respect to photocatalytic, electrocatalytic performances is discussed. The systematization and analysis of literature data on synthesis, characterization, and application of multilayer thin films and coatings containing metal nanoparticles on the diverse supports may open new directions and perspectives in this unique and exciting subject

PHOTOCATALYTIC DEGRADATION OF PHENOL IN WATER BY SILVER/TITANIUM DIOXIDE NANORODS COATED WITH AN ULTRATHIN MAGNESIUM OXIDE LAYER

Phenol is one of the most widespread, toxic, and recalcitrant compounds commonly found in water sources. Due to its persistent nature, conventional wastewater treatment methods are not effective to remove or degrade phenol from water. In this work, a novel photocatalyst is developed to degrade phenol under simulated sunlight. The catalyst is composed of a 1D titanium dioxide (TiOv2) nanorod decorated with elemental silver (Ag) nanoparticles, coated in an ultrathin magnesium oxide (MgO) layer through an atomic layer deposition (ALD) method. The prepared catalyst was characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-vis diffuse reflectance spectroscopy (UV-Vis DRS). The solar light photocatalytic performance of the material was evaluated and correlated with the material properties. The Ag decoration promoted light absorption and transfer of photo-induced electron-hole pairs from within TiOv2 nanorods to the catalyst surface. The ultrathin MgO layer with a subnanometer thickness further increased the light absorption and inhibited surface charge recombination through a surface passivation effect, promoting phenol degradation. The photocatalytic reaction mechanism was investigated by the examination of hydroxyl and superoxide radical production in the photocatalytic system. The results from this work demonstrate a new strategy for fabricating efficient sunlight-driven photocatalysts for the degradation of persistent water contaminants