Bicontinuous microemulsions (BCME) were used to synthesize hierarchical superstructures (HSs) of Pt-Co3O4 by reduction/precipitation. BCMEs possess water and oil nanochannels, and therefore, both hydrophilic and lipophilic precursors can be used. Thus, PtAq-CoAq, PtAq-CoOi, PtOi-CoAq and PtOi-CoOi were prepared (where Aq and Oi stand for the precursor present in aqueous or oily phase, respectively). The characterization of the Pt-Co3O4-HS confirmed the formation of metallic Pt and Co3O4 whose composition and morphology are controlled by the initial pH and precursor combination, determining the presence of the reducing/precipitant species in the reaction media. The electrocatalytic activity of the Pt-Co3O4-HSs for oxygen evolution reaction (OER) was investigated using linear sweep voltammetry in 0.1 M KOH and compared with Pt-HS. The lowest onset overpotentials for Pt-Co3O4-Hs were achieved with PtOi-CoOi (1.46 V vs. RHE), while the lowest overpotential at a current density of 10 mA cm−2 (η10) was obtained for the PtAq-CoAq (381 mV). Tafel slopes were 102, 89, 157 and 92 mV dec−1, for PtAq-CoAq, PtAq-CoOi, PtOi-CoAq and PtOi-CoOi, respectively. The Pt-Co3O4-HSs showed a better performance than Pt-HS. Our work shows that the properties and performance of metal–metal oxide HSs obtained in BCMEs depend on the phases in which the precursors are present.

Self-cleaning coatings are advanced materials for the removal of pollutants and microorganisms by combining wettability, photocatalytic degradation, and antimicrobial activity. In this work, we propose a rational design of self-cleaning films based on TiO2 synthesized by sol–gel on commercial glazed ceramic tiles for building’s indoor applications. The synthesis strategy is based on hydrolysis and condensation of Ti-isopropoxide in the presence of W­(VI) precursors to tune defects and crystallinity of the resulting W–TiO2 thin film. From the microstructure and surface composition analysis for different tungsten contents and annealing temperatures, we conclude that the film is composed by sintered TiO2 particles with adsorbed polytungstates (WO x ) that inhibit anatase/rutile transformation. Polytungstates on TiO2 also induce surface defects that enhance water contact angle and inactivation of Escherichia coli under visible light. The presence of W­(VI) has a negligible effect toward crystal violet degradation either under visible or under UV light. These results provide evidence on the existence of at least two different types of defects: (i) intrinsic defect from a sol–gel route and (ii) induced defect by tungsten species on the surface. Understanding the correlation between composition, structure, and self-cleaning properties provides a base for an efficient design of low-cost self-cleaning ceramic tiles that can be fully manufactured in an industrial plant.

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Plasmonic superstructures may concentrate hot spots both on the external surface and within the inner gaps of the assembly. However, these materials are usually obtained by two-steps procedures from synthesis of plasmonic nanoparticles to their 3D assembly. The interconnected nano-network of water and oil channels in a bicontinuous microemulsion (BµE) may act as a preorganized reaction system giving reticulated materials. In this work, a silver hierarchical superstructure (HSS-AgCt) was obtained in the water channels of a BµE in a one-pot procedure. The characterization of the morphology and crystalline structure revealed that this superstructure is composed of silver nanoparticles embedded in polymeric silver citrate forming a 3D mesh of interconnected fibers with mean width of 30 nm. The aging of HSS-AgCt in the BµE allowed the degradation of the citrate fibers giving rise to interconnected spherical silver nanoparticles (HSS-Ag) of 8 nm as measured from TEM images. Rhodamine 6-G was detected by SERS up to 10 -12 M with an analytical enhancement factor of 10 9 for both materials using a 633 nm laser operating at 0.85 mW (5% of the nominal power). These results introduce a novel route to obtain highly sensitive SERS substrates in one-pot procedures by using BµE as a nanoreactor and template.

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Supporting a photocatalyst, such as titania nanoparticles (TiO 2 NPs), is a good strategy to improve its performance since it can facilitate the photocatalyst recovery from the aqueous media and provides a high surface area for pollutant adsorption. Among the several advanced functional materials used as TiO 2 NP support, the hierarchical meso/macroporous SiO 2 spheres not only show the advantages associated to its chemical nature but also the dendritic fibrous structure provides a porous network that offers many benefits to be exploited in optical and catalytic devices. In this chapter, different synthetic approaches to design hierarchical meso/macroporous silica and the strategies to support TiO 2 NPs regarding the photocatalytic performance of these materials are shown.

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