Synergic photocatalytic effect between TiO2 and a fluorinated transparent ionomeric material in the oxidation of hydrosoluble pollutants in turbid suspensions

The crystal violet (CV) dye has been chosen to study the photooxidation activity of titanium dioxide immobilized into a transparent fluoropolymeric matrix toward organic pollutants. The photoactive matrix was directly coated on the UV source by applying a TiO2 containing fluorinated ionomeric dispersion and a perfluorinated transparent amorphous polymer in an appropriate sequence. The photocatalytic activity of the multilayered coating towards the hydrosoluble organic CV dye was evaluated in transparent solution and in highly turbid suspension. The turbidity was obtained by dispersing insoluble microparticles of calcium sulfate in the polluted aqueous solution. The photoabatement rates obtained in transparent and in turbid conditions were 0.0918 min-1 and 0.0300 min-1, respectively. The TiO2 nanoparticle dispersed in the fluorinated matrix revealed a higher photocatalytic activity than simple dispersed TiO2 in both transparent as well as turbid conditions. The immobilization of the catalyst in a stable fluorinated matrix avoided the TiO2 separation and prevented catalyst losses. The synergism in the activity between the TiO2-based photocatalyst and the fluorinated matrix was particularly evident at low pollutant concentrations

Comparison of Branched and Linear Perfluoropolyether Chains Functionalization on Hydrophobic, Morphological and Conductive Properties of Multi-Walled Carbon Nanotubes

The functionalization of multi-walled carbon nanotubes (MW-CNTs) was obtained by generating reactive perfluoropolyether (PFPE) radicals that can covalently bond to MW-CNTs’ surface. Branched and linear PFPE peroxides with equivalent molecular weights of 1275 and 1200 amu, respectively, have been thermally decomposed for the production of PFPE radicals. The functionalization with PFPE chains has changed the wettability of MW-CNTs, which switched their behavior from hydrophilic to super-hydrophobic. The low surface energy properties of PFPEs have been transferred to MW-CNTs surface and branched units with trifluoromethyl groups, CF3, have conferred higher hydrophobicity than linear units. Porosimetry discriminated the effects of PFPE functionalization on meso-porosity and macro-porosity. It has been observed that reactive sites located in MW-CNTs mesopores have been intensively functionalized by branched PFPE peroxide due to its low average molecular weight. Conductivity measurements at different applied pressures have showed that the covalent linkage of PFPE chains, branched as well as linear, weakly modified the electrical conductivity of MW-CNTs. The decomposed portions of PFPE residues, the PFPE chains bonded on carbon nanotubes, and the PFPE fluids obtained by homo-coupling side-reactions were evaluated by mass balances. PFPE-modified MW-CNTs have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), static contact angle (SCA), surface area, and porosity measurement

Absorption and photocatalytic degradation of VOCs by perfluorinated ionomeric coating with TiO2 nanopowders for air purification

In this work, we propose a transparent multilayered perfluoropolymeric coating as immobilization method for TiO2 nanoparticles, and evaluate its suitability in the gas phase photocatalytic degradation of six different volatile organic compounds. The coating was made of a layer of TiO2-containing perfluorosulfonic acid polymer on a layer of perfluorinated amorphous polymer. The chemical stability of perfluoropolymeric materials to UV radiation and UV-activated TiO2 overcomes the possible degradation of the polymeric immobilization system which is typical of more traditional polymeric coatings. Moreover, the TiO2-containing ionomeric perfluorosulfonic layer worked as selective membrane for pollutants absorption and catalyst preservation, depending on the interactions between the superacidic polar heads of the ionomer and the pollutants, in particular those capable of hydrogen bonding. Gas-phase photocatalytic degradation tests were performed using pentane, methanol, 2-propanol, toluene, dichloromethane and pyridine as reference volatile organic pollutants, thus ranging on different polarity properties. Results indicate performances comparable to other approaches reported in the literature and show a strong influence of both atmospheric conditions (namely, humidity) and pollutant nature – polarity, proticity – on the actual kinetics of photodegradation, also depending on the interactions regulating the affinity between the ionomeric layer of the coating and pollutants. The high potential of the coating in the photodegradation was confirmed by the observed values of the photoabatement rates: all approximatively above 10−5 s−1 and maximum for alcohols (1.4 × 10−4 and 1.7 × 10−4 s−1 in dry and humid conditions, respectively)

Thermodynamics of aqueous perfluorooctanoic acid (PFOA) and 4,8-dioxa-3H-perfluorononanoic acid (DONA) from DFT calculations: Insights into degradation initiation

Modern fluorosurfactants introduced during and after perfluoroalkyl carboxylates/sulfonates phase-out present chemical features designed to facilitate abatement, hence reducing persistence. However, the implications of such features on environmental partitioning and stability are yet to be fully appreciated, partly due to experimental difficulties inherent to the handling of their (diluted) aqueous solutions. In this work, rigorous quantum chemistry calculations were carried out in order to provide theoretical insights into the thermodynamics of hydroperfluorosurfactants in aqueous medium. Estimates of acid dissociation constant (pKa), standard reduction potential (E0), and bond dissociation enthalpy (BDE) and free energy (BDFE) were computed for perfluorooctanoic acid (PFOA), 4,8-dioxa-3H-perfluorononanoic acid (DONA) and their anionic forms via ensemble averaging at density functional theory level with implicit solvent models. A ‹pKa› in the neighborhood of zero and a E0of about 2.2 V were obtained for PFOA. Predictions for the acidic function of DONA compare well with PFOA's, with a pKaof 0.8–1.5 and a E0of 2.07–2.15 V. Deprotonation thus represents the dominant phenomenon at environmental conditions. Calculations indicate that H-abstraction of the aliphatic proton of DONA by a hydroxyl radical is the thermodynamically favored reaction path in oxidative media, whereas hydrolysis is not a realistic scenario due to the high dissociation constant. Short intramolecular interactions available to the peculiar hydrophobic tail of DONA were also reviewed, and the relevance of the full conformational space of the fluorinated side chain discussed

Photoactive Perfluorinated Ionomeric Transparent Coatings in the Oxidative Abatement of Hydrosoluble Pollutants in Turbid Suspensions

Photoactive perfluorinated ionomeric transparent coatings in the oxidative abatement of hydrosoluble pollutants in turbid suspensions Walter Navarrini*(1,2), Federico Persico(1,2), Maurizio Sansotera(1,2) (1) Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”, Politecnico di Milano, Via Mancinelli 7, 20131, Milano, Italy. (2) Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, Via G. Giusti 9, 50121 Firenze, Italy. *Walter Navarrini: Tel: +39.02.2399.3035; email address: [email protected]; The abatement of organic pollutants in water phase promoted by photoactive titanium dioxide has been widely studied in the last decade [1]. Despite the high photodegradative rates guaranteed by slurry TiO2, its industrial use is strongly limited by the catalyst recovery cost. To overcome this obstacle powder TiO2 was immobilized into a multilayer ionomeric-perfluorinated matrix and the activity of this Photoactive Coating (PAC) was studied. In order to obtain the correct interaction between the activated TiO2 and the polluted aqueous solutions the polymeric matrix must be characterized by high chemical resistance, high transparency towards UV light, good wettability and good permeability to oxygen and water vapor [2,3]. The multilayer coating photocatalytic activity towards hydrosoluble organic pollutants was evaluated in clear as well as in highly turbid conditions obtained by dispersing barium sulphate microparticles in the polluted solution. The perfluorinated multilayer photoactive coating was applied directly on the UV source and employed as substrate for immobilization of the photocatalyst. A TFE/perfluorodioxole copolymer double-layer acted as primer; a dispersion of TiO2 in the perfluorinated ionomeric solution of a copolymer between TFE/perfluorosulphonylvinylether acted as photoactive layer. The strong acidity of the ionomeric side chains conferred hydrophilicity to the coating , allowing a good interaction with the polluted aqueous solutions. Rhodamine B-base (RhB) and Crystal Violet (CV) were used as organic hydrosoluble pollutants and their concentration in solution was monitored by UV-Vis spectroscopy and HPLC-MS technique. In both clear and turbid conditions, TiO2-embedded transparent fluorinated coating revealed higher photocatalytic activity than merely dispersed TiO2 (Image1). This behavior was particularly evident at low pollutant concentrations. In addition, catalyst immobilization prevented TiO2 separation and catalyst losses, allowing the development of a simple and efficient continuous apparatus. I Image 1. Degradative efficiency of PAC compared to the performances obtained with slurry TiO2 References [1] M. Sansotera, et al., Appl. Catal., B, 148 (2014) 29. [2], F. Persico, et al., Thin Solid Films, 545 (2013) 210. [3] W. Navarrini, et al., Prog. Org. Coat., 74 (2012) 794