Calcium hydroxide nanoparticles and hypogeum environment: test to understand the best way of application

For a long time the conservation of archaeological artefacts has been based on the principles of compatibility and minimal intervention. This involves a series of partially unsolved problems, concerning the products used for deteriorated structures consolidation. The choice of materials depends on several factors such as: microclimatic conditions, application methods, and reaction time of products. Recently the employment of nanolime in the consolidation treatments of decorative carbonate matrix surfaces had a great development, thanks to multifunctional use in calcium standard-sized particles treatments. However, while the use of the nanostructured materials is described in several specialized papers, the information about the best conditions of applicability of the nanolime and its related potentiality for the consolidation in hypogeum environment is rarely considered. The present work is devoted to represent a case study with the aim to give useful elements in order to evaluate the application of nanolime. The funerary inscriptions coming from St. Callixtus Catacombs have been the object of the research carried out in situ and in laboratory, checking indirectly in the short run and in the long run the porosity variation in the materials. The present study intends to indicate the best suspension concentration on consolidation in relationship with hypogeum environment

DESIGN AND SYNTHESIS OF NEW COMPOUNDS FOR PHOTOVOLTAICS APPLICATIONS AND PHOTOCATALYTIC H2 PRODUCTION

The phenomenon of global warming, coupled with the progressive depletion of fossil fuels reserves, demand their rapid replacement with renewable energy sources. Among them, solar energy appears very appealing since it is abundant, ubiquitous and practically inexhaustible. Furthermore, solar energy can be exploited in several different ways, since it can be converted both to electricity and fuels. The most promising method for solar electricity production is based on photovoltaic cells and related devices. Among new-generation photovoltaic devices, dye-sensitized solar cells (DSSC) emerged for their simple manufacturing and peculiar working mechanism, making them particularly suitable for building integration and indoor electricity generation; perovskite solar cells (PSCs), on the other hand, currently attract great attention due to their high efficiencies, which almost rival those of traditional silicon-based modules. Concerning the field of fuels, H2 seems to be the perfect candidate to replace fossil fuels since it is carbonfree, can be produced from water and has a high energy content. Contrary to traditional electrolysis, photocatalytic H2 production can be considered a promising and cheap alternative to produce H2 in a green and sustainable way. The work presented in this Ph. D. thesis was focused on the development of new light responsive materials that can be employed in all the fields described above. The first part of the work deals with the modification of well-known organic DSSC sensitizers featuring a donor-π-acceptor structure. In particular, we modified their acceptor moiety by introducing one or more sulfur atoms. The presence of a sulfur atom in the anchoring group induced a red-shift and a broadening of the absorption spectrum compared to typical carboxylic dyes, but did not affect the charge injection capability of the sensitizers, resulting in DSSCs of similar efficiency. The second part of the thesis analyzes the effect of alkaline cation size on the efficiency of quasi solid-state DSSCs built with a commercial organic dye (D35). For this purpose, five different gel electrolytes containing I2 and five different alkaline iodides (LiI, NaI, KI, RbI, CsI) were prepared and characterized. Incorporation of the different alkaline ions induced changes in the conductivity of the gels, altering the performance of the corresponding DSSCs in function of the charge density of the cations. In the third part, the synthesis and characterization of two new Hole Transporting Materials (HTMs) for PSCs are described. A common pillar[5]arene scaffold was functionalized with two different triarylamine fragments, in order to obtain two innovative multi-branched HTMs. The materials were fully characterized and a preliminary screening of the properties of the corresponding solar cells was carried out, highlighting the crucial role of additives to boost their performances. Finally, the last part of this thesis is focused on the synthesis of three new D-π-A organic dyes, bearing a dithienosilole core, suitable for photocatalytic H2 production by adsorption on a nanostructured Pt/TiO2 catalyst. Structure-activity relationships for such dyes were investigated by evaluating the effect of the introduction of alkyl chains on different positions of their scaffold, which were found to influence several properties such as solubility, aggregation, shielding and wettability of the semiconductor surface

Organic dye-sensitized solar cells containing alkaline iodide-based gel polymer electrolytes: Influence of cation size

The electrolyte used in dye-sensitized solar cells (DSSCs) plays a key role in the process of current generation, and hence the analysis of charge-transfer mechanisms both in its bulk and at its interfaces with other materials is of fundamental importance. Because of solvent confinement, gel polymer electrolytes are more practical and convenient to use with respect to liquid electrolytes, but in-depth studies are still necessary to optimize their performances. In this work, gel polymer electrolytes of general formulation polyacrylonitrile (PAN)/ethylene carbonate (EC)/propylene carbonate (PC)/MI, where M+is a cation in the alkaline series Li-Cs, were prepared and used in DSSCs. Their ionic conductivities were determined by impedance analysis, and their temperature dependence showed Arrhenius behavior within the experimental window. FT-IR studies of the electrolytes confirmed the prevalence of EC coordination around the cations. Photo-anodes were prepared by adsorbing organic sensitizer D35 on nanocrystalline TiO2thin films, and employed to build DSSCs with the gel electrolytes. Nanosecond transient spectroscopy results indicated a slightly faster dye regeneration process in the presence of large cations (Cs+, Rb+). Moreover, a negative shift of TiO2flat-band potential with the decreasing charge density of the cations (increasing size) was observed through Mott-Schottky analysis. In general, results indicate that cell efficiencies are mostly governed by photocurrent values, in turn depending on the conductivity increase with cation size. Accordingly, the best result was obtained with the Cs+-containing cell, although in this case a slight reduction of photovoltage compared to Rb+was observed

Green/Yellow-Emitting Conjugated Heterocyclic Fluorophores for Luminescent Solar Concentrators

In this study, we report on the synthesis of new organic fluorophores containing either the benzo[1,2-d:4,5-d]bisthiazole or the dithieno[3,2-b:2,3-d]silole heterocyclic unit, and on their application for the fabrication of luminescent solar concentrators (LSCs) made of poly(methyl methacrylate) (PMMA) thin films. In solution, the new compounds absorbed light in the visible region and displayed a brilliant green emission in the 500-600 nm range with moderate-to-good fluorescence quantum yields (0.25-0.68). Dispersions of selected fluorophores in PMMA thin films mostly maintained the light absorption features observed in solution, although in the case of benzobisthiazole-based fluorophore 1a an evident fluorescence red-shift was observed when increasing the compound concentration in the film. In agreement with its promising optical properties, LSCs prepared with the latter compound yielded interesting optical efficiencies up to 6.42%, not far from those of state-of-the-art PMMA LSC devices

Azobenzene-based optoelectronic transistors for neurohybrid building blocks

Abstract Exploiting the light–matter interplay to realize advanced light responsive multimodal platforms is an emerging strategy to engineer bioinspired systems such as optoelectronic synaptic devices. However, existing neuroinspired optoelectronic devices rely on complex processing of hybrid materials which often do not exhibit the required features for biological interfacing such as biocompatibility and low Young’s modulus. Recently, organic photoelectrochemical transistors (OPECTs) have paved the way towards multimodal devices that can better couple to biological systems benefiting from the characteristics of conjugated polymers. Neurohybrid OPECTs can be designed to optimally interface neuronal systems while resembling typical plasticity-driven processes to create more sophisticated integrated architectures between neuron and neuromorphic ends. Here, an innovative photo-switchable PEDOT:PSS was synthesized and successfully integrated into an OPECT. The OPECT device uses an azobenzene-based organic neuro-hybrid building block to mimic the retina’s structure exhibiting the capability to emulate visual pathways. Moreover, dually operating the device with opto- and electrical functions, a light-dependent conditioning and extinction processes were achieved faithful mimicking synaptic neural functions such as short- and long-term plasticity

Correction to “Combining Dithienosilole-Based Organic Dyes with a Brookite/Platinum Photocatalyst toward Enhanced Visible-Light-Driven Hydrogen Production”

Correction to “Combining Dithienosilole-Based Organic Dyes with a Brookite/Platinum Photocatalyst toward Enhanced Visible-Light-Driven Hydrogen Production