New Insights into the SnO₂ Sensing Mechanism Based on the Properties of Shape Controlled Tin Oxide Nanoparticles

We report on the sensing behavior of SnO₂ shape controlled nanocrystals in order to evaluate the role of their exposed crystal surfaces in the sensing mechanism. Octahedral (OCT), elongated dodecahedral (DOD), and nanobar shaped (NBA) nanocrystals were synthesized by previously reported procedures and their performances were evaluated in the sensing toward CO. Singly ionized oxygen vacancies (V_O^•) were detected by electron spin resonance (ESR), and their abundance and reactivity were associated to the exposed crystal faces and, in turn, to the sensing responses of the nanocrystals. Results indicated that the electrical properties and the formation/reactivity of the V_O^• centers are interconnected and are relatable to the nanoparticle specific surfaces. Two different temperature-dependent sensing mechanisms were proposed, depending on the prevalence of the surface structure or of the specific surface area on the sensing ability of shape controlled SnO₂ nanoparticles

Crystal Surfaces and Fate of Photogenerated Defects in Shape-Controlled Anatase Nanocrystals: Drawing Useful Relations to Improve the H₂ Yield in Methanol Photosteam Reforming

We comprehensively explored the photocatalytic properties, in H₂ production by methanol photosteam reforming, of anatase nanocrystals with nearly rectangular (<i>RC</i>), rhombic (<i>R</i>), and nanobar (<i>NB</i>) shapes having exposed {001}, {101}, and {010} surfaces. The aim was to relate the reactivity both to the type of crystal facets and to the photogenerated defects. The electron spin resonance (ESR) spectra reveal that the amount of Ti³⁺ (electron traps) is parallel to the H₂ evolution rate and becomes a maximum for the <i>RC</i> nanocrystals, which display the highest area of {001} surfaces and the lowest {101} area but also involve a significant area of {010} facets. This points out that the H₂ production cannot be related only to the envisaged reducing {101} facets, but that the {010} facets also play a key role. We suggest that the contiguous {001}, {101}, and {010} facets form a highly effective “surface heterojunction” within a <i>RC</i> nanoparticle which drives the electrons photogenerated on {001} facets not just toward the {101} but also to the {010} facets, while the holes are driven toward the {001} facets. This transfer improves the charge separation, thus boosting the photoefficiency of <i>RC</i> nanocrystals compared to that of <i>NB</i> and <i>R</i> nanocrystals. The ESR spectra performed after ultraviolet excitation in the presence of MeOH show the partial annihilation of the Ti³⁺ features, mainly for highly reactive <i>RC</i> nanocrystals. Because H₂ production involves an electron transfer to the proton, a relevant role in H⁺ photoreduction of the Ti³⁺ centers present on the exposed {010} and {101} surfaces is suggested. These findings underline the importance of determining the relationship between the photogenerated defects and the exposed crystal surfaces to optimize the photocatalytic properties of anatase nanocrystals

Mineralogy and geochemistry of Devonian ultramafic minor intrusions of the southern Kola Peninsula, Russia: implications for the petrogenesis of kimberlites and melilitites

Rechargeable sodium-ion batteries are becoming a viable alternative to lithium-based technology in energy storage strategies, due to the wide abundance of sodium raw material. In the past decade, this has generated a boom of research interest in such systems. Notwithstanding the large number of research papers concerning sodium-ion battery electrodes, the development of a low-cost, well-performing anode material remains the largest obstacle to overcome. Although the well-known anatase, one of the allotropic forms of natural TiO₂, was recently proposed for such applications, the material generally suffers from reduced cyclability and limited power, due to kinetic drawbacks and to its poor charge transport properties. A systematic approach in the morphological tuning of the anatase nanocrystals is needed, to optimize its structural features toward the electrochemical properties and to promote the material interaction with the conductive network and the electrolyte. Aiming to face with these issues, we were able to obtain a fine tuning of the nanoparticle morphology and to expose the most favorable nanocrystal facets to the electrolyte and to the conductive wrapping agent (graphene), thus overcoming the intrinsic limits of anatase transport properties. The result is a TiO₂-based composite electrode able to deliver an outstandingly stability over cycles (150 mA h g^–1 for more than 600 cycles in the 1.5–0.1 V potential range) never achieved with such a low content of carbonaceous substrate (5%). Moreover, it has been demonstrated for the first time than these outstanding performances are not simply related to the overall surface area of the different morphologies but have to be directly related to the peculiar surface characteristics of the crystals

Tailoring the Dielectric and Mechanical Properties of Polybutadiene Nanocomposites by Using Designed Ladder-like Polysilsesquioxanes

In this study, the preparation of polybutadiene/polysilsesquioxane nanocomposites (NCs) having tunable thermomechanical and dielectric properties is reported. This was achieved by using different amounts of a filler consisting of a silsesquioxane with a defined ladder-like molecular structure (LPMASQ) bearing reactive methacrylate functionalities. In detail, solid-state nuclear magnetic resonance (NMR) investigation revealed that an increasing amount of filler leads to a progressive homopolymerization of LPMASQ units resulting in the generation of domains in the composites, which induce a kind of polymer chain confinement in proximity of the hybrid interface. The evolution of the molecular organization of the inorganic nanobuilding blocks as a function of their concentration has been highlighted also by small-angle X-ray scattering (SAXS) experiments. The gradual assembly of LPMASQ units gives rise to peculiar dielectric properties along with enhanced thermal and mechanical stability of the final NCs, thus supplying suitable materials for applications in high performance dielectrics. Furthermore, these outcomes support the idea that a careful control of the molecular architecture and organization of the silsesquioxanes in a polymer matrix allows to simultaneously modulate two or more distinct functional features of polymer NCs

New Insights into the Photocatalytic Properties of RuO₂/TiO₂ Mesoporous Heterostructures for Hydrogen Production and Organic Pollutant Photodecomposition

Photocatalytic activities of mesoporous RuO₂/TiO₂ heterojunction nanocomposites for organic dye decomposition and H₂ production by methanol photoreforming have been studied as a function of the RuO₂ loading in the 1–10 wt % range. An optimum RuO₂ loading was evidenced for both kinds of reaction, the corresponding nanocomposites showing much higher activities than pure TiO₂ and commercial reference P25. Thus, 1 wt % RuO₂/TiO₂ photocatalyst led to the highest rates for the degradation of cationic (methylene blue) and anionic (methyl orange) dyes under UV light illumination. To get a better understanding of the mechanisms involved, a comprehensive investigation on the photogenerated charge carriers, detected by electron spin resonance (ESR) spectroscopy in the form of O^–, Ti³⁺, and O₂^– trapping centers, was performed. Along with the key role of superoxide paramagnetic species in the photodecomposition of organic dyes, ESR measurements revealed a higher amount of trapped holes in the case of the 1 wt % RuO₂/TiO₂ photocatalyst that allowed rationalizing the trends observed. On the other hand, a maximum average hydrogen production rate of 618 μmol h^–1 was reached with 5 wt % RuO₂/TiO₂ photocatalyst to be compared with 29 μmol h^–1 found without RuO₂. Favorable band bending at the RuO₂/TiO₂ interface and the key role of photogenerated holes have been proposed to explain the highest activity of the RuO₂/TiO₂ photocatalysts for hydrogen production. These findings open new avenues for further design of RuO₂/TiO₂ nanostructures with a fine-tuning of the RuO₂ nanoparticle distribution in order to reach optimized vectorial charge distribution and enhanced photocatalytic hydrogen production rates

Synthesis and Characterization of Alkoxysilane-Bearing Photoreversible Cinnamic Side Groups: A Promising Building-Block for the Design of Multifunctional Silica Nanoparticles

The present study reports on the synthesis of a new alkoxysilane-bearing light-responsive cinnamyl group and its application as a surface functionalization agent for the development of SiO2 nanoparticles (NPs) with photoreversible tails. In detail, cinnamic acid (CINN) was activated with N-hydroxysuccinimide (NHS) to obtain the corresponding NHS-ester (CINN–NHS). Subsequently, the amine group of 3-aminopropyltriethoxysilane (APTES) was acylated with CINN–NHS leading to the generation of a novel organosilane, CINN-APTES, which was then exploited for decorating SiO2 NPs. The covalent bond to the silica surface was confirmed by solid state NMR, whereas thermogravimetric analysis unveiled a functionalization degree much higher compared to that achieved by a conventional double-step post-grafting procedure. In light of these intriguing results, the strategy was successfully extended to naturally occurring sepiolite fibers, widely employed as fillers in technological applications. Finally, a preliminary proof of concept of the photoreversibility of the obtained SiO2@CINN-APTES system has been carried out through UV diffuse reflectance. The overall outcomes prove the consistency and the versatility of the methodological protocol adopted, which appears promising for the design of hybrid NPs to be employed as building blocks for photoresponsive materials with the ability to change their molecular structure and subsequent properties when exposed to different light stimuli