FineCat : a meeting fostering progress in frontier research and sustainable development from and within Sicily

Scientific meetings on topics of socioeconomic and environmental global relevance such as the \u201cFineCat Symposium on heterogeneous catalysis for fine chemicals\u201d held in Sicily between 2012 and 2017 may actively promote sustainable development and progress in frontier research from and within developing areas of the world

Photocatalytic and oxidative synthetic pathways for highly efficient PANI-TIO2 nanocomposites as organic and inorganic pollutant sorbents

Polyaniline (PANI)-materials have recently been proposed for environmental remediation applications thanks to PANI stability and sorption properties. As an alternative to conventional PANI oxidative syntheses, which involve toxic carcinogenic compounds, an eco-friendly procedure was here adopted starting from benign reactants (aniline-dimer and H2O2) and initiated by ultraviolet (UV)-irradiated TiO2. To unlock the full potential of this procedure, we investigated the roles of TiO2 and H2O2 in the nanocomposites synthesis, with the aim of tailoring the properties of the final material to the desired application. The nanocomposites prepared by varying the TiO2:H2O2:aniline-dimer molar ratios were characterized for their thermal, optical, morphological, structural and surface properties. The reaction mechanism was investigated via mass analyses and X-ray photoelectron spectroscopy. The nanocomposites were tested on both methyl orange and hexavalent chromium removal. A fast dye-sorption was achieved also in the presence of interferents and the recovery of the dye was obtained upon eco-friendly conditions. An efficient Cr(VI) abatement was obtained also after consecutive tests and without any regeneration treatment. The fine understanding of the reaction mechanism allowed us to interpret the pollutant-removal performances of the different materials, leading to tailored nanocomposites in terms of maximum sorption and reduction capability upon consecutive tests even in simulated drinking water

Triply green polyaniline: UV irradiation-induced synthesis of highly porous PANI/TiO2 composite and its application in dye removal

An environmentally benign procedure for the preparation of polyaniline/TiO2 composites is presented. The UV irradiation-induced synthesis leads to materials with good crystallinity and tailored morphology, showing promising sorption and recycle properties in dye removal tests. A reaction mechanism is proposed on the basis of LC-MS and FT-IR investigations

Polyaniline/TiO2 composites: green photocatalysic synthesis and application in wastewater remediation

In recent years, polyaniline (PANI) composites and nanocomposites with metal and metal-oxide materials have received growing attention for electrochemical and photoelectrochemical applications (Gu 2013). Among them, PANI/TiO2 composites are probably the most interesting systems due to synergistic effects between the conductive polymer and the oxide photocatalyst in terms of photogenerated charge separation and photocatalytic efficiency (Bae 2011). Moreover, polyaniline has been reported to possess favourable sorption properties, which can be exploited for pollutant remediation (Alcaraz-Espinoza 2015, Janaki 2012). PANI/TiO2 composites are thus promising candidates for wastewater treatment combining different pollutant remediation approaches. Polyaniline is classically synthesised via oxidative polymerization (Tran 2011), which involves noxious reagents (aniline and peroxydisulfates) and leads to toxic and carcinogenic byproducts (such as benzidine and trans-azobenzidine). In recent years, greener alternatives have been reported, such as a synthetic process starting from aniline dimer ((4-aminophenil)aniline) and using Fe3+ as catalyst and H2O2 as oxidant (Della Pina 2018). Unfortunately, this alternative procedure does not offer any control over the polymer morphology, leading to compact materials with low surface area and, as a consequence, poor dye-sorption capability. Very recently, we proposed a new photocatalytically induced green synthesis leading to stable polyaniline/TiO2 composites with porous morphology, wide surface area, high crystallinity and, most important, excellent dye removal performance and reusability (Cionti 2018). The reaction is carried out in two steps: at first, the aniline dimer is dissolved in a HCl aqueous solution and TiO2 is added while starting UV irradiation. In the second step, H2O2 is added in the dark, leading to the final product. In this work, we shed light on the photocatalytic nature of the synthetic mechanism, highlighting the different roles of TiO2 and of H2O2 on the composite structural and morphological features as well as on the composite performance for pollutant abatement. The reaction mechanism was investigated by a combination of spectrometric techniques, radical scavenger tests, and surface characterizations (Fig.1). By sampling the reaction mixture at different irradiation times, we demonstrated that under UV irradiation the growth of the oligomers occurs at the TiO2 particle surfaces. The same experiment carried out without UV irradiation showed the intrinsic photocatalytic nature of the process: in the dark, only short oligomers without appropriate chain conjugation were produced. However, even after prolonged UV irradiation, the final green product could be obtained only upon addition of H2O2, showing that, while oligomer formation is initiated by radicals produced by TiO2 photocatalysis, small amounts of an oxidant (H2O2) are still needed for the polymer chain growth. The role of the H2O2 amount proved to be especially crucial with respect to the composite properties. Increasing the H2O2 amount together with that of TiO2 led to composites with low surface area and reduced dye removal capability (Fig.2 a) due to a faster polymerization step. On the other hand, when only the photocatalyst amount was increased, neither the product morphology, nor its dye-removal ability were affected. This enables to increase the TiO2 content within the composite with the aim of enhancing its photocatalytic performance. In this respect, the composite stability was tested in water under prolonged UV irradiation, showing that the material optical, structural and morphological properties remained unchanged. The composite was tested towards the removal of anionic azo dyes in aqueous solution, evaluating the effect of the matrix composition and the composite reusability (Fig.2 b), showing promising results

Polyaniline (PANI): an innovative support for sampling and removal of VOCs in air matrices

Polyaniline (PANI)-based materials for both removal and sampling of volatile organic compounds (VOCs) from air by rapid adsorption/desorption processes have been developed. The polymer was synthesized in form of emeraldine as both salt and base using different synthetic approaches, a traditional one and a "green" one. VOCs adsorption/desorption efficiency was evaluated for all the materials analyzing the desorbed VOCs fractions by GC/MS technique and obtaining results similar to the presently adopted method employing commercial activated carbon. Most important, in this work it has been demonstrated for the first time that the use of PANI-based sorbents allowed the substitution of the toxic CS2, recommended in official methods, with the less hazardous CH3OH as the VOCs extraction solvent. Moreover, a complete regeneration of the polymers could be realized by a few rapid washing steps. Finally, the best PANI-based material was subjected to recycling tests thereby showing a high adsorption/desorption efficiency retention up to four runs

Sustainable Approaches for Polyaniline and Polypyrrole Synthesis

: Among the conducting organic polymers (COPs), polyaniline (PANI) and polypyrrole (PPY) are the most investigated. Even though many efforts have been done to overcome the traditional synthetic methods typically based on the use of strong stoichiometric oxidants, the growing environmental sensitivity and the necessity of pure products, especially in medical and biological fields, make the COPs “green†synthesis a topic of the utmost importance. Herein, we report a brief overview of our results in the synthesis of PANI and PPY operating under mild conditions, using H2O2 and O2 as the oxidants in the presence of different catalysts: colloidal Au nanoparticles (AuNPs), AuNPs/TiO2, AuNPs/C, metallic Cu, Cu salts and Fe3O4 NPs

Inkjet printed doped polyaniline: navigating through physics and chemistry for the next generation devices

Innovative benzidine-free PANI-based inks for electrically conducive inkjet printed devices were developed and tested and the results compared with those obtained by traditional PANI. NMR investigations evidenced the presence of quinones and phenolic groups on the backbone of the innovative PANIs that are thought being responsible for the higher solubility in DMSO. A mechanism of reaction was proposed. The numerous characterizations (NMR, UV-Vis, FTIR, XPS and electrical investigations) allowed to compare protonation level, doping level, valence band maximum for both the type of PANI. The correlation among structural properties, printability, conductivity and solubility was discussed

Clean transformation of ethanol to useful chemicals : the behavior of a gold-modified silicalite catalyst

Upon addition of gold to silicalite-1 pellets (a MFI-type zeolite), the vapor phase oxidation of ethanol could be addressed to acetaldehyde or acetic acid formation. By optimizing the catalyst composition and reaction conditions, the conversion of ethanol could be tuned to acetaldehyde with 97% selectivity at 71% conversion or to acetic acid with 78% selectivity at total conversion. Considering that unloaded silicalite-1 was found to catalyze the dehydration of ethanol to diethylether or ethene, a green approach for the integrated production of four important chemicals is herein presented. This is based on renewable ethanol as a reagent and a modular catalytic process

PANI-TiO2 composites: the mechanism behind a green process

Polyaniline (PANI) is an important member of the family of organic conductive polymers, which holds potential in numerous fields, such as electronics, optics and photovoltaics [1]. In recent years, PANI has received increasing attention for application in wastewater treatment due to its sorption properties enabling the removal of a broad range of pollutants [2,3]. Polyaniline is classically synthesized by oxidative polymerization [4], which involves noxious reagents (aniline as starting compound and persulfates as oxidant) and gives rise to toxic and carcinogenic by-products (such as benzidine and trans-azobenzene). A great deal of effort has been devoted to find alternative green routes: in particular, some of us reported a benign synthesis based on aniline dimer ((4-aminophenyl)aniline), H2O2 as oxidant and Fe3+ as catalyst [5]. However, this procedure yields no control on the polymer morphology, leading to a compact PANI with low surface area and poor dye sorption capability. We have recently developed an alternative green synthesis based on TiO2 photocatalysis, enabling a morphological control of the polymer [6]. In this work, the reaction mechanism has been investigated in depth via LC-MS, FT-IR and z-potential analyses. In the first stage, carried out under UV irradiation, the growth of oligomers from the aniline dimer takes place on the TiO2 particle surfaces, activated by the photocatalytic generated radicals. In the second step, the addition of H2O2 (80% less than in the Fe-catalyzed synthesis) activates the polymer growth, giving rise to the final product. By separating the oligomerization and polymerization steps, polymer composites with high crystallinity and porous morphology could be prepared. The dye sorption capability of the samples was tested toward methyl orange as model for anionic azo dyes: promising results were obtained both in terms of dye removal and product reusability. The creation of PANI-TiO2 composites opens the door to future applications exploiting the complementary properties of the two materials, such as pollutant removal processes based on combined sorption and photocatalytic degradation

Alkaline glucose oxidation on nanostructured gold electrodes

The electrocatalytic properties of nanostructured gold electrodes for glucose electro-oxidation in KOH were investigated by cyclic voltammetry and compared with a commercially available polycrystalline gold electrode. These electrodes were prepared by depositing gold nanoparticles from a sol onto different carbonaceous conductive supports: glassy carbon, carbon cloth and graphite paper. The gold sol was prepared reducing an aqueous solution of tetrachloroauric acid with sodium borohydride. In order to improve gold nanoparticle adhesion, the substrate surfaces were treated with warm concentrated nitric acid. Gold on treated carbon cloth turned out to be a very promising anode for glucose electro-oxidation. In order to better understand the glucose oxidation its pH dependence as well as sorbitol (the glucose reduction product) electroxidation were investigated