LIQUIDI IONICI E FULLERENI: PIATTAFORME PER NUOVI MATERIALI

The synthesis of innovative catalysts based on different carbon nanoforms (CNFs), namely fullerene C60 and carbon nanotubes (CNTs), and their application in Suzuki and Heck C-C coupling reactions, constitutes the common thread of the first part (Chapter 1 and 2) of this thesis. C60 and CNTs were functionalized with ionic liquids (ILs) and poly-amidoamine (PAMAM) dendrimers, respectively, and used as supports for palladium nanoparticles (PdNPs). Moreover, additional supported catalytic systems based on one of the synthesized C60-IL hybrids were prepared and successfully employed in the title coupling reactions. The final part (Chapter 3) of the thesis deals on the microwave-mediated synthesis optimization of some fullerene-based acceptors species for organic photovoltaics (OPV). In such a way, the main C60- and C70-based acceptor derivatives for organic solar cells, such as PCBM, DPM6, BHN and ICBA, were obtained in higher yields and shorter reaction times with respect to the data reported in literature. These findings represent a step forward toward the wide production of cheaper organic solar cells as a consequence of the cost abatement of the acceptors given by higher yields, lower waste production, and reduced reaction time which means a strong energy saving

A study on the stability of carbon nanoforms–polyimidazolium network hybrids in the conversion of co2 into cyclic carbonates:Increase in catalytic activity after reuse

Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO(2) into cyclic carbonate under high temperature and CO(2) pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved catalytic activity. Beside the low catalytic loading (0.05–0.09 mol%) and the absence of Lewis acid co-catalysts, all the materials showed high TON values (up to 1154 for epichlorohydrin with SW-1:2). Interestingly, despite the loss of part of the polymeric coating for crumbling or peeling, the activity increases upon recycling of the materials, and this behaviour was ascribed to their change in morphology, which led to materials with higher surface areas and with more accessible catalytic sites. Transmission electron microscopy analysis, along with different experiments, have been carried out in order to elucidate these findings

First Evidence of Tris(catecholato)silicate Formation from Hydrolysis of an Alkyl Bis(catecholato)silicate

The hydrolysis of 3-ammoniumpropylbis(catecholato)silicate 1, giving two different silica-based materials containing different amounts of tris(catecholato)silicate, is reported. The latter species can be formed through an attack of catechol to the silicon atom in the pentacoordinate complex, in which the silicon-carbon bond is further activated toward electrophilic proton cleavage. The Knoevenagel reaction was used as a probe in order to test the availability of functional groups on the surface of such materials

Modified Nanocarbons for Catalysis

Nanocarbons represent useful scaffolds in the preparation of last generation nanostructured catalysts, and their chemical functionalization through covalent or non-covalent modification is becoming an important tool for introducing well-distributed anchoring points and, in the meantime, could be the first step toward the assembling of hybrid nanostructured materials with a hierarchical order. In this Review are reported synthesis and catalytic applications of chemically modified nanocarbons such as fullerene, carbon nanotubes, graphene, nanohorns and nanodiamonds in organocatalytic and metal-based (metal nanoparticles, organometallic complexes) reactions, covering major chemical reactions encompassing, the oxidation of alcohols, aldehydes, olefins, and silanes, hydrogenation reactions of aldehydes, ketones, and alkenes, dehydrogenative coupling of silanes, C 12C coupling reactions, epoxidation of alkenes, CO2 fixation into cyclic carbonates, and asymmetric reactions, among others

Improved performance in flexible organic solar cells by using copolymeric phase-separation modulators

One of the main problems related to the low performance of the organic solar cells (OSCs), concerns the low mobility of the materials constituting the heterojunction. Indeed, the poor charge transport in the active layer is the principal cause of a competition between separation and recombination of the photogenerated carriers. In this regard, a major obstacle to enhance OSCs efficiency is developing strategies to optimize the exciton dissociation and, consequently, the charge collection at the electrodes. Donor and acceptor systems must be well mixed on the length scale of 5 – 20 nm (exciton diffusion length) to meet the criteria for efficient exciton dissociation. In addition, the network structure should involve continuous donor-acceptor pathways for efficient carrier transport. The most common practice to achieve this goal is by thermal or solvent annealing of active layer.[1] However, this approach often leads to an unwanted phase segregation with formation of large domains where only a small fraction of excitons could diffuse to the donor-acceptor interface.[2] In this work, we show how this challenge is achievable by incorporating phase-separation modulators into bulk heterojunction (BHJ). In particular, three copolymers based on polythiophene and C60 units have been designed, easily synthesized, characterized, and employed as additive in P3HT:PCBM devices. The effect of the thienyl spacer length between C60 monomers on optoelectronic properties, morphology, and structure of heterojunction has been examined using several techniques (NMR, FTIR, XPS, XRD and AFM). We observed that small quantities of these systems can play a critical role in tuning the device morphology by improving the phase separation in thin film heterojunction.[3] In particular, these copolymers act as phase separation modulators by controlling the growth of donor/acceptor domains in the heterojunction, during the thermal annealing process. Indeed, by employing copolymers containing oligothiophenic chains with size of about 8 nm, a large number of domains with a size comparable to the length scale of exciton diffusion are generated, resulting in the highest power conversion efficiency (PCE) (4.46 %) and short current density (JSC) (16.15 mA cm-2) values reported so far for P3HT:PCBM solar cells on plastic substrates. Moreover, the results obtained in preliminary investigations on the other devices containing different fullerene acceptors seem to show the effectiveness and the generality of our approach. Finally, bending tests showed that OSCs with copolymers maintain higher level of performance than reference devices, thus giving new perspectives to applications of flexible photovoltaics

Efficient microwave-mediated synthesis of fullerene acceptors for organic photovoltaics

Two different processes, namely the Bamford–Stevens and [4 + 2] Diels Alder reactions, have been optimized under microwave irradiation for the functionalization of fullerenes. In this manner, all the main C60- and C70-based acceptor derivatives for organic solar cells such as PCBM, DPM, BHN and ICBA, have been prepared in higher yields and shorter reaction times with respect to the reported data. These findings represent a step forward toward the wide production of cheaper organic solar cells as a consequence of the cost abatement of the acceptors given by higher yields, lower waste production, and reduced reaction time which means a strong energy saving