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The incorporation of silica nanoparticles (Si-NPs) into the polymer matrix is a growing area of interest research to produce high-performance polymer nanocomposites (NCs) across a wide range of nanotechnology applications. This improvement is due to the Si-NPs capability to self-assembly giving rise to specific well-organized structures with both short- and long-range order across a hierarchy of spatial scales, determined by both NP-NP and NP-matrix interactions, involving a careful balance among attractive driving forces, repulsive forces, and directional forces. Respect to this, the aim of the present paper is to systematically review the use of Si-NPs in polymer NCs and on the role of NPs self-assembly in determining the final material properties. Firstly, we explored the synthesis and modification of both isotropic and anisotropic Si-NPs in relation with use in NC materials, focusing on NPs dispersion and distribution, as well as on the functionalization strategies of Si-NPs. Besides Si-NPs functionalization with conventional small organic molecules, a large section is devoted to an emerging class of functionalized Si-NPs with macromolecules, namely silica hairy NPs (Si-HNPs), able to give rise a rich variety of complex assemblies and materials with new structures and functionalities. Successively, NCs materials containing Si-NPs and Si-HNPs have been explored in terms of synthetic preparation and properties. The self-organization of Si-NPs and Si-HNPs in polymer matrices has been reported and its effect on the functional materials properties have been evaluated with a critical point of view on the results, limits, and future perspectives. Our review can be considered a tutorial work, aiming at providing useful insights to researchers in the field of nanotechnology and nanoscience, taking into consideration the fundamental role of NPs self-assembly processes in determining the functional material properties.

Ladder-like polysilsesquioxanes (LPSQs) are characterized by a double-stranded siloxane backbone, whose chemical and structural properties depend on both the synthesis parameters and the nature of the organic side-chains. In the case of ladder-like (methacryloxypropyl) polysilsesquioxanes (LPMASQ), polymer matrices can be produced by exploiting the presence of photocurable methacrylate groups. Consequently, they can be used to prepare functional nanocomposites (NCs), either by blending with organic polymers such as polybutadiene or exploiting the inorganic fillers’ dispersion. Since the properties of LPMASQ-based NCs are strongly related to their structure, the structural changes of polymerized LPMASQ were investigated upon addition of low loadings of TiO2 nanoparticles (up to 3 wt%) by solid state nuclear magnetic resonance and X-ray diffraction. The filler addition leads to the reduction of the polymerization capacity of the LPMASQ organic side-chains. Moreover, a different organization of ladder chains has been highlighted, ascribable to the increase in fully condensed linear ladder units at the expenses of folded chains and defective structures. The methodological approach here adopted can be extended to other composite systems and may help to describe the properties at the filler-matrix interface, offering valuable hints for a better design of these materials. Graphical Abstract

The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO

ZnO nanoparticles grown on highly porous silica with spherical and rod-like morphology were investigated by radioluminescence and photoluminescence measurements to assess the influence of intrinsic defectiveness on the optical properties. Spectroscopic analysis of ZnO/SiO2 systems unveils defect-related luminescence and a very weak excitonic emission. The samples display peculiar optical properties with unlike intensity and energy emissions, disclosing the occurrence of inequivalent defect centers in ZnO nanoparticles supported onto silica with different morphology.

The localization of the rubber vulcanization reaction close to the silica filler surface was investigated in isoprene rubber composites (IR NCs): the main goal was to highlight the role of curing agents’ dispersion and filler surface features on the spatial propagation of the rubber cross-links and the resulting mechanical behavior of the material. The study was realized by tailoring the morphology of the curing activator, i.e. by vulcanizing IR NCs with Zn@SiO2 double function filler, composed of Zn(II) single sites anchored on SiO2 filler, in comparison to silica filled IR NCs vulcanized with microcrystalline ZnO. The microscopic cross-links distribution was measured by Transmission Electron Microscopy for network visualization (NVTEM) and Time Domain Nuclear Magnetic Resonance (TD-NMR). Besides the NCs mechanical behavior was characterized both at small strain and at fracture. In the presence of Zn@SiO2, higher cross-link density in proximity to SiO2 particles was evidenced, which gradually spreads from the filler surface to the bulk, induced by localization of the Zn(II) centers. IR NCs with Zn@SiO2 resulted stiffer (+45%) and with a lower fracture toughness (less than one third), compared to m-ZnO based NCs, which shows a quite homogeneous structure of the rubber cross-links network. The results highlighted the correlation between the composites structural features and their macroscopic behavior, paving the way to modulating the mechanical properties of elastomeric materials by tuning the nature of the curing agents.

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.

The interaction between activators (ZnO) and co-activators (stearic acid, SA) represents a key step in the vulcanization process, to generate Zn(II) intermediate complexes that enhance the reaction kinetic and promote the shortening of sulfur bridges, leading to highly cross-linked materials. To understand the influence of the structural, morphological and surface properties of ZnO in the reactivity with SA, in this work, pure ZnO nanoparticles (NPs) and ZnO NPs anchored on SiO2 (ZnO/SiO2) were prepared through soft chemistry techniques. Tailoring of morphology and surface features was accomplished through a fine control of the synthetic parameters, as demonstrated by the careful characterization of the activators. Then, the interaction of pure ZnO and ZnO/SiO2 activators with SA in the absence of rubber was investigated by using Differential Scanning Calorimetry (DSC). The occurrence of Zn(II)-SA complexes with different thermal stability and structural properties was assessed by a comprehensive thermogravimetric and spectroscopic survey. The generation and the chemical structure of these specific vulcanization intermediates was related to the peculiar characteristics of the ZnO/SiO2 systems and, in turn, to their ability in imparting faster kinetics and higher curing efficiency to isoprene rubber nanocomposites, compared to bare ZnO. These results, besides proposing a valid benchmark for achieving further insights on the interaction of stearic acid with activators, pave the way to provide specific protocols for a better design and implementation of ZnO-based materials able to effectively enhance the rubber vulcanization process, with significant economic and environmental advantages.

The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO2 substrates (ZnO/SiO2) has been performed in the view to create nanosystems potentially suitable in X-ray activated photodynamic therapy. Indeed, cytotoxic porphyrin dyes with increasing concentrations have been anchored on ZnO/SiO2 nanoparticles through amino-silane moieties. Chemical and structural analyses correlated with photoluminescence reveal that radiative energy transfer between ZnO and porphyrins is the principal mechanism prompting the excitation of photosensitizers. The use of soft X-ray excitation results in a further sensitization of the porphyrin emission, due to augmented energy deposition promoted by ZnO in the surroundings of the chemically bound porphyrin. This finding unveils the cruciality of the design of hybrid nanoparticles in ruling the efficacy of the interaction between ionizing radiation and inorganic/organic moieties, and thus of the final nanomaterial performances towards the foreseen application.

Photocatalytic chemical transformations in the presence of irradiated TiO

Hybrid silica-based nanofillers were synthesised by grafting short chains of poly(ethylene glycol) (PEG) with different molecular weight on the surface of SiO2 porous nanoparticles. Based on this approach, homogeneous poly(ethylene oxide) (PEO)-based ceramic-in-polymer solid-state electrolytes with SiO2 loadings up to 23 wt% were obtained, thanks to the high compatibility between the two phases endowed by the grafted PEG chains. These electrolytes showed satisfying ionic conductivity and excellent resistance against dendrite piercing that enabled long operation, for more than 350 h, under continuous stripping/plating of lithium in symmetric Li/electrolyte/Li cells. Additionally, the operating life of these devices was improved by the self-healing reaction between Li dendrites and silica fillers, being able to reinstate the cycling after short circuit. Finally, a lithium metal full cell, equipped with LiFePO4 positive material and the solid-state electrolyte containing 18 wt% of SiO2, demonstrated high stability against dendrite penetration and discharge capacity at 70 °C comparable to cells based on liquid analogues.

The crosslink density and distribution inside the polymer matrix affect the mechanical properties of rubber nanocomposites (NCs). Since the catalytic activity of zinc has a central role in the formation of crosslinks, this study focuses on the effect that the structure of the catalytic sites and their localization inside the polymer matrix have on the mechanical behavior of rubber materials. To do this, a new highly efficient activator, Zn@SiO2 based on zinc single sites anchored onto the silica surface, is used as double function filler, acting as both activator and reinforcing filler. The mechanical properties of rubber NCs prepared with Zn@SiO2 are compared to NCs conventionally cured with ZnO particles. The results suggest that localizing the catalytic sites at different distance from the filler particles dispersed in the rubber matrix is a promising tool to control the crosslinking density and distribution, which means tuning the mechanical properties of rubber NCs.

Thin photovoltaics based on chalcopyrite film, Cu(In,Ga)Se2 (CIGS) and related alloys, have exhibited so far efficiency over 22,3% on the laboratory scale. However, the CIGS solar cells scale-up is expected to be hampered because of the low availability of In and Ga in the Earth crust. The most promising next leader in the chalcogenide thin film technology seems to be the kesterite compound Cu2ZnSnS4 (CZTS), as it is based on earth-abundant elements and it shows the better results when low-cost solution processable techniques are employed in the fabrication. Solution-processed inorganic semiconductors, in fact, offer a rising route for the low-cost mass production of solar cells In this context, we present a new chemical procedure to obtain a superior quality Cu2ZnSnS4 and Cu2FeSnS4 thin films composed of highly soluble and inexpensive precursors in a non-toxic and environmentally friendly solvent. The films were prepared by a Sol-Gel method and the deposition was carried out by in situ gel formation on fluorine doped tin oxide coated glass. The films obtained were characterized by Raman spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, photoluminescence spectroscopy and by electronic scanning microscopy. The developed methodology has successfully identified an innovative way to achieve high-quality kesterite thin films for photovoltaic applications; relate devices optimization is currently underway.

Conventional methods for fabricating chalcogenide-based solar cells involve vacuum processes, e.g. co-evaporation and sputtering, even if the most performing devices based on the kesterite compound Cu2ZnSn(S,Se)4 have been realized using a solution-based methodology. Moreover, non-vacuum processes present significant advantages as lower production costs, higher productivity and uniformity of the final stoichiometry composition. In this context, we present a new chemical procedure to obtain a superior quality Cu2ZnSnS4 and Cu2FeSnS4 films composed by highly soluble and inexpensive precursors in a non-toxic and environmentally friendly solvent. Therefore, the films were prepared by a Sol-Gel method, starting from the metal salts in organic solvent (dimethylsulfoxide); thiourea was used as a source of sulphur. The influence of the composition of solutions containing metal ions was studied: solutions of metal salts containing non-coordinating anions and coordinates ones were compared to evaluate the role of anions and their coordination with metal ions in the formation of a pure and homogeneous phase. To obtain information about the complex mechanism of interaction between the metals and the various components of the solution Raman measurements and electronic paramagnetic resonance (EPR) were performed. The film deposition was carried out by in situ gel formation on fluorine doped tin oxide coated glass. The subsequent heat treatment guarantees the formation of the correct crystalline phase, without sulfurization but in Argon atmosphere [and at temperature suitable also for flexible and plastic substrates]. The films obtained were characterized by Raman spectroscopy, X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX), morphologically by electronic scanning electron microscopy (SEM). Raman and EPR measurements have shown that thiourea plays a primary role in coordinating metallic ions in solution, also highlighting the reductive power on copper; the coordinating effect of acetate ions, employed as precursors, plays a primary role in ensuring homogeneity in solution and consequently in the film. XRD confirms the absence of secondary phases. Therefore, the developed methodology has successfully identified an innovative way to achieve high quality kesterite thin films for photovoltaic applications; relate devices optimization is currently underway.

Nowadays environmental pollution has become a very diffuse topic for scientific research and several articles deal with the development of innovative techniques and materials for treatments of both wastewaters and polluted air. In this context, photocatalysis has a great potential as green technique for the depollution of several organic and inorganic toxic molecules. Zinc oxide has been introduced in heterogeneous photocatalytic treatments as an alternative material to TiO2, thanks to its similar properties: high photosensitivity, non-toxicity, low cost, competitive photocatalytic activity (band gap of 3.37 eV). Recently, along with their traditional application fields (e.g. coatings, cosmetics), ZnO nanopowders have been used as photocatalysts (second only to TiO2) for environmental remediation both in aqueous and gas phases (Pudukudy et al., 2013 and Pifferi et al., 2014). The best performances for nanosized ZnO can be reached either modifying the strategy of synthesis or doping the material with different species, including transition metals (Mn, Cu) but also rare earth elements (La, Er) (Sin et al., 2014 and Zamiri et al., 2014). Also bismuth has been tested as dopant, proving its ability to shift the adsorption edge of ZnO (reducing the band gap of the material) to lower energy, exploiting solar light and modifying the separation rate of photoinduced charge carriers (Chandraboss et al., 2013 and Senthilraja et al., 2015). In the present paper photocatalytic mineralization of o-toluidine in aqueous media under UV/solar irradiation was achieved by bare and bismuth doped zinc oxide nanoparticles. By adopting different analytical approaches a reaction mechanism is proposed, explaining the differences in photodetoxification performances.