Publications by authors named "Carlo Pirola"

19 Publications

  • Page 1 of 1

Sonophotocatalytic degradation of sodium diclofenac using low power ultrasound and micro sized TiO.

Ultrason Sonochem 2020 Oct 7;67:105123. Epub 2020 Apr 7.

Università degli Studi di Milano, Dipartimento di Chimica, via Golgi, 19 - 20133 Milano, Italy. Electronic address:

The nonsteroidal anti-inflammatory drug sodium diclofenac (DC) is an emerging water pollutant which resists conventional wastewater treatments. Here the sonophotocatalytic degradation of DC was carried out using micrometric TiO (both pristine and Ag-decorated), UV-A irradiation and 20 kHz pulsed ultrasound. Sonophotocatalytic tests were compared with photolysis, sonolysis, sonophotolysis, sonocatalysis and photocatalysis data performed in the same conditions. A synergy index of over 2 was determined for tests with pristine TiO, while values close to 1.3 were observed for Ag-TiO. Reaction intermediates were studied by HPLC-MS, showing degradation mechanisms activated by hydroxyl radicals. Similar pathways were identified for photocatalytic and sonophotocatalytic tests, although the latter led to more oxidized compounds. Different reactor configurations (static and dynamic set ups) were studied. Sequential and simultaneous application of UV light and ultrasound led to similar performance. The role of water matrix was investigated using ultrapure and drinking water, showing marked detrimental effects of electrolytes on the DC degradation. Overall, the combined treatment proved more efficient than photocatalysis alone especially in demanding working conditions, like in drinking water matrices.
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http://dx.doi.org/10.1016/j.ultsonch.2020.105123DOI Listing
October 2020

Effect of Carbon Support, Capping Agent Amount, and Pd NPs Size for Bio-Adipic Acid Production from Muconic Acid and Sodium Muconate.

Nanomaterials (Basel) 2020 Mar 11;10(3). Epub 2020 Mar 11.

Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133 Milan, Italy.

The effect of support, stabilizing agent, and Pd nanoparticles (NPs) size was studied for sodium muconate and t,t-muconic acid hydrogenation to bio-adipic acid. Three different activated carbons (AC) were used (Norit, KB, and G60) and carbon morphology did not affect the substrate conversion, but it greatly influenced the adipic acid yield. 1% Pd/KB Darco catalyst, which has the highest surface area and Pd surface exposure, and the smallest NPs size displayed the highest activity. Furthermore, the effect of the amount of the protective agent was studied varying metal/protective agent weight ratios in the range of 1/0.00-1/1.20, using KB as the chosen support. For sodium muconate reduction 1% Pd/KB_1.2 catalyst gave the best results in terms of activity (0.73 s), conversion, and adipic acid yield (94.8%), while for t,t-muconic acid hydrogenation the best activity result (0.85 s) was obtained with 1% Pd/KB_0.0 catalyst. Correlating the results obtained from XPS and TEM analyses with catalytic results, we found that the amount of PVA (polyvinyl alcohol) influences mean Pd NPs size, Pd(0)/Pd(II) ratio, and Pd surface exposure. Pd(0)/Pd(II) ratio and Pd NPs size affected adipic acid yield and activity during sodium muconate hydrogenation, respectively, while adipic acid yield was related by exposed Pd amount during t,t-muconic acid hydrogenation. The synthesized catalysts showed higher activity than commercial 5% Pd/AC.
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http://dx.doi.org/10.3390/nano10030505DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7153248PMC
March 2020

Experimental Characterization of Polymer Surfaces Subject to Corona Discharges in Controlled Atmospheres.

Polymers (Basel) 2019 Oct 10;11(10). Epub 2019 Oct 10.

Ricerca sul Sistema Energetico (RSE S.p.A.), 20134 Milano, Italy.

Polymeric dielectrics are employed extensively in the power transmission industry, thanks to their excellent properties; however, under normal operating conditions these materials tend to degrade and fail. In this study, samples of low-density polyethylene, polypropylene, polymethyl methacrylate, and polytetrafluorethylene were subjected to corona discharges under nitrogen and air atmospheres. The discharges introduced structural modifications over the polymer surface. From a chemical perspective, the alterations are analogous among the non-fluorinated polymers (i.e., polyethylene (PE), polypropylene (PP), and polymethyl methacrylate (PMMA)). A simulation of the corona discharge allowed the identification of highly reactive species in the proximity of the surface. The results are consistent with the degradation of insulating polymers in high-voltage applications due to internal partial discharges that ultimately lead to the breakdown of the material.
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http://dx.doi.org/10.3390/polym11101646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836313PMC
October 2019

Photocatalytic porcelain grés large slabs digitally coated with AgNPs-TiO.

Environ Sci Pollut Res Int 2019 Dec 25;26(36):36117-36123. Epub 2019 Apr 25.

IrisCeramica Group, Via Ghiarola Nuova 119, 41042, Fiorano M.se (MO), Italy.

TiO is employed as both photocatalytic and structural materials, leading to its applications in external coatings or in interior furnishing devices, including cement mortar, tiles, floorings, and glass supports. The authors have already demonstrated the efficiency of photoactive micro-sized TiO and here its industrial use is reported using the digital printing to coat porcelain grés slabs. Many advantages are immediately evident, namely rapid and precise deposition, no waste of raw materials, thus positively affecting the economy of the process. Data for the thin films deposited by digital printing were compared with those obtained for the conventional spray method. The use of metal-doped TiO is also reported so that the photoactivity of these materials can be exploited even under LED light. The digital inkjet printed coatings exhibited superior photocatalytic performance owing to both higher exposed surface area and greater volume of deposited anatase, as well as the greater areal distribution density of thinly and thickly coated regions. Moreover, the presence of TiO doped silver increased the efficiency of the materials in NOx degradation both under UVA and LED lights.
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http://dx.doi.org/10.1007/s11356-019-05218-7DOI Listing
December 2019

Ultrasound-assisted impregnation for high temperature Fischer-Tropsch catalysts.

Ultrason Sonochem 2018 Nov 23;48:523-531. Epub 2018 Jun 23.

Department of Chemical Engineering, Polytechnique Montréal, 2500, chemin de Polytechnique, Montréal, H3T 1J4 Québec, Canada. Electronic address:

A fraction of the petroleum extracted from oil reservoirs contains associated natural gas. Rather than building infrastructure to recover low volumes of this natural gas, the industry flares or vents it to the atmosphere, which contributes to atmospheric greenhouse gas emissions but also reduces the air quality locally because it contains gaseous sulphur and nitrogen compounds. Converting the natural gas (NG) to hydrocarbons with a small-scale two-step gas-to-liquids process, is an alternative to flaring and venting. In the first step, NG reacts with oxygen to form syngas (Catalytic Partial Oxidation) and in the second step the syngas reacts over metallic catalysts to form higher paraffins at 210 °C to 300 °C-Fischer Tropsch synthesis (FT). For the first time, we synthesize bimetallic FeCo FT catalysts with ultrasound. An ultrasonic horn agitates the solution during the entire impregnation process. The active phase dispersion of the sonicated catalysts was superior to the catalyst synthesized without ultrasound, while reducing the impregnation time by a factor of three. We tested our catalysts in a lab-scale, fixed-bed reactor at 270 °C and 300 °C, and achieved 80% conversion over 3-days on stream and a 40% yield of C.
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http://dx.doi.org/10.1016/j.ultsonch.2018.06.017DOI Listing
November 2018

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

Nanomaterials (Basel) 2018 Mar 19;8(3). Epub 2018 Mar 19.

Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, I-20133 Milano, Italy.

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 measurements.
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http://dx.doi.org/10.3390/nano8030176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5869667PMC
March 2018

Simultaneous photodegradation of VOC mixture by TiO powders.

Chemosphere 2018 Feb 5;193:198-206. Epub 2017 Nov 5.

GranitiFiandre SpA, Via Ghiarola Nuova 119, 42014 Castellarano, Italy.

Volatile and semi volatile organic compounds' concentration have dramatically increased in indoor environments in recent years. UV light promotes titanium dioxide, which oxidises various molecules; however, most of the studies report the degradation of a single VOC. Here, we investigate the photo-oxidation of 17 molecules in mixture to have a realistic test of TiO efficacy. We compare P25, a nanometric catalyst, and 1077, a micrometric sample, that poses less health concerns. A proton-transfer-reaction mass spectrometer measured online the concentration of all the pollutants simultaneously. Aldehydes compete for the adsorption on both the catalyst's active sites and thus they degrade 70% and 55% with P25 and 1077 respectively. Considering the single pollutant oxidation, instead, aldehydes fully oxidize. Even though benzene is recalcitrant to degradation, P25 and 1077 reduced toluene's concentration to 97% and 96% in 55 min, respectively. Acetonitrile is refractory to photocatalysis.
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http://dx.doi.org/10.1016/j.chemosphere.2017.11.003DOI Listing
February 2018

Micro-sized TiO as photoactive catalyst coated on industrial porcelain grès tiles to photodegrade drugs in water.

Environ Sci Pollut Res Int 2018 Jul 27;25(21):20348-20353. Epub 2017 Apr 27.

GranitiFiandre SpA, Via Radici Nord 112, 42014, Castellarano, Italy.

Pharmaceutical compounds and their metabolites raise worrying questions because of their continuous release and lack of efficient removal by conventional wastewater treatments; therefore, they are being detected in groundwater, surface water and drinking water in increasing concentrations. Paracetamol and aspirin are two of the most commonly used drugs employed as fever reducer, analgesic and anti-inflammatory. They and their metabolites are very often found in river water, so their degradation is necessary in order to render water suitable for human consumption. The present work is focused on the comparison of the photocatalytic performance of industrial active grés porcelain tiles covered with a commercial micro-sized TiO by industrial process using either conventional spray deposition or innovative digital printing methods. The photodegradation of two commonly used drugs, namely aspirin and paracetamol, was investigated both individually and as a mixture, in both deionized and tap water. The results reveal the full conversion of the drugs and the significant role of the photocatalytic tiles in the mineralization processes leading to harmless inorganic species. In particular, the digitally printed tiles exhibited better photodegradation performance for both drugs compared to the spray deposited tiles. No deactivation was observed on both photocatalytic tiles.
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http://dx.doi.org/10.1007/s11356-017-9066-6DOI Listing
July 2018

Fe-based heterogeneous catalysts for the Fischer-Tropsch reaction: Sonochemical synthesis and bench-scale experimental tests.

Ultrason Sonochem 2017 01 19;34:774-780. Epub 2016 Jul 19.

University of Illinois at Urbana-Champaign, School of Chemical Sciences, 505 S. Mathews Av., Urbana, IL 61801, USA.

The sonochemical synthesis of nanostructured materials owes its origins to the extreme conditions created during acoustic cavitation, i.e., the formation of localized hot spots in the core of collapsing bubbles in a liquid irradiated with high intensity ultrasound (US). In particular, in the present work a sonochemical synthesis has been investigated for the production of three different iron-based samples supported on SiO and loaded with different metals and promoters (10 %wt of Fe; 30 %wt of Fe; 30 %wt of Fe, 2 %wt of K and 3.75 %wt of Cu) active in the Fischer-Tropsch (FT) process. Sonochemically synthesized heterogeneous catalysts were characterized by BET, XRPD, TPR, ICP, CHN, TEM, SEM and then tested in a fixed bed FT-bench-scale rig fed with a mixture of H and CO at a H/CO molar ratio equal to 2, at activation temperatures of 350-400°C and reaction temperatures of 250-260°C. The experimental results showed that the ultrasonic samples are effective catalysts for the FT process. Notably, increasing the activation temperature increased CO conversion, while product selectivity did not diminish. All the sonochemically prepared samples presented in this work provided better catalytic results compared to the corresponding traditional FT impregnated catalysts.
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http://dx.doi.org/10.1016/j.ultsonch.2016.07.012DOI Listing
January 2017

Aspirin and paracetamol removal using a commercial micro-sized TiO catalyst in deionized and tap water.

Environ Sci Pollut Res Int 2017 May 21;24(14):12646-12654. Epub 2016 Oct 21.

GranitiFiandre SpA, Via Radici Nord 112, 42014, Castellarano, Italy.

Micro-sized TiO catalyst was employed to degrade pharmaceutical compounds, i.e. aspirin and paracetamol, two of the most widely used drugs, purchasable without prescription. Their active agents, acetylsalicylic acid and acetaminophen, are characterized by different substituent groups, linked to the aromatic ring, which affect both the photodegradation and mineralization processes. The experimental conditions highlight the relationship between the nature of the pristine molecules, their degradation mechanisms, their mutual interference and the water's role. The research started from model systems with a single pollutant to the mixture of them and finally by moving from deionized water to tap water.
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http://dx.doi.org/10.1007/s11356-016-7781-zDOI Listing
May 2017

Copper NPs decorated titania: A novel synthesis by high energy US with a study of the photocatalytic activity under visible light.

Ultrason Sonochem 2016 Jul 15;31:295-301. Epub 2016 Jan 15.

GranitiFiandre SpA, Castellarano (MO), Italy.

The most important drawback of the use of TiO2 as photocatalyst is its lack of activity under visible light. To overcome this problem, the surface modification of commercial micro-sized TiO2 by means of high-energy ultrasound (US), employing CuCl2 as precursor molecule to obtain both metallic copper as well as copper oxides species at the TiO2 surface, is here. We have prepared samples with different copper content, in order to evaluate its impact on the photocatalytic performances of the semiconductor, and studied in particular the photodegradation in the gas phase of some volatile organic molecules (VOCs), namely acetone and acetaldehyde. We used a LED lamp in order to have only the contribution of the visible wavelengths to the TiO2 activation (typical LED lights have no emission in the UV region). We employed several techniques (i.e., HR-TEM, XRD, FT-IR and UV-Vis) in order to characterize the prepared samples, thus evidencing different sample morphologies as a function of the various copper content, with a coherent correlation between them and the photocatalytic results. Firstly, we demonstrated the possibility to use US to modify the TiO2, even when it is commercial and micro-sized as well; secondly, by avoiding completely the UV irradiation, we confirmed that pure TiO2 is not activated by visible light. On the other hand, we showed that copper metal and metal oxides nanoparticles strongly and positively affect its photocatalytic activity.
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http://dx.doi.org/10.1016/j.ultsonch.2016.01.015DOI Listing
July 2016

Porous TiO2 microspheres with tunable properties for photocatalytic air purification.

Ultrason Sonochem 2013 Jan 20;20(1):445-51. Epub 2012 Jul 20.

CNR-Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milano, Italy.

The synthesis of highly-crystalline porous TiO(2) microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO(2) template particles surface and TiO(2) precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO(2) to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO(2) microspheres were tested in the photocatalytic degradation of nitrogen oxides (NO(x)) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa).
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http://dx.doi.org/10.1016/j.ultsonch.2012.07.003DOI Listing
January 2013

Photocatalytic NOx abatement: the role of the material supporting the TiO2 active layer.

J Hazard Mater 2012 Apr 10;211-212:203-7. Epub 2011 Nov 10.

Università degli Studi di Milano, Dipartimento di Chimica Fisica ed Elettrochimica, Via Golgi 19, 20133 Milano, Italy.

The importance of the choice of a suitable substrate as supporting material for photoactive TiO(2), either in the form of powders or thin films or in photoactive paints, is frequently disregarded. In this paper four different supports (stainless steel, sand-blasted stainless steel, Teflon and glass) are object of investigation. The final aim is to verify the presence of interactions between the photocatalyst (AEROXIDE(®) TiO(2) P25 by Evonik Degussa Corporation) and the support, directly involved in the photocatalytic activity in the NO(x) abatement. The characterization results have been correlated with the photoactivity of the different samples. In particular, a coating of about 6-9 μm seems to allow a photocatalytic result free from any positive or negative interference with the supporting material, therefore giving reliable results about the photoactivity of the TiO(2) under investigation.
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http://dx.doi.org/10.1016/j.jhazmat.2011.10.095DOI Listing
April 2012

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO(2) Prepared by Ultrasound.

Nanoscale Res Lett 2008 Nov 25;4(2):97-105. Epub 2008 Nov 25.

Nanocrystalline TiO(2) samples were prepared by promoting the growth of a sol-gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NO(x) in air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p(3/2) region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energy per volume (E(tot)/V) and not the acoustic intensity or the pulsed/continuous mode.
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http://dx.doi.org/10.1007/s11671-008-9208-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2894369PMC
November 2008

Efficiency of 1,4-dichlorobenzene degradation in water under photolysis, photocatalysis on TiO2 and sonolysis.

J Hazard Mater 2008 May 25;153(3):1136-41. Epub 2007 Sep 25.

Dipartimento di Chimica Fisica ed Elettrochimica and Center of Excellence CIMAINA, Università degli Studi di Milano, Via Golgi 19, I-20133 Milano, Italy.

The rate of 1,4-dichlorobenzene (1,4-DCB) degradation and mineralization in the aqueous phase was investigated either under direct photolysis or photocatalysis in the presence of commercial or sol-gel synthesized TiO2, or under sonolysis at 20 kHz with different power inputs. Two lamps, both emitting in the 340-400 nm wavelength range with different energy, were employed as irradiation sources. Photocatalysis ensured faster removal of 1,4-DCB with respect to sonolysis and direct photolysis. The highest degradation and mineralization rate was attained with the combined use of photocatalysis and sonolysis, i.e. under sonophotocatalytic conditions. The efficiency of the employed advanced oxidation techniques in 1,4-DCB degradation is discussed also in relation to their energy consumption, which might be decisive for their practical application.
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http://dx.doi.org/10.1016/j.jhazmat.2007.09.071DOI Listing
May 2008

The beneficial influence of ultrasound in the polymerization of epsilon-caprolactam to polyamide-6 (Nylon 6). Part I: primary experimental results.

Ultrason Sonochem 2007 Sep 20;14(6):680-8. Epub 2006 Dec 20.

Department of Physical Chemistry and Electrochemistry, University of Milan, via Golgi n. 19, I-20133 Milano, Italy.

Epsilon-caprolactam (CL) polymerization to polyamide-6 (Nylon 6) was studied at different contents of water in CL (0.01-2 wt%), with or without epsilon-amino-caproic acid (ACA) as an activator, applying to the mixture an initial treatment of Ultrasound (US) (17.5-20 kHz) at low temperatures (70-110 degrees C) and for short times (max 10 min). It was verified that polymerization at 260 degrees C produces a polymer having a much higher molecular weight (MW) when US is applied with respect to silent (SIL) conditions i.e. without the use of ultrasound. This constitutes a "pre-sonication effect". The ratio (MW)(US)/(MW)(SIL) is inversely proportional to the initial content of water in CL. The action of US converts CL at very low temperatures (70-110 degrees C) and water content, in comparison with silent conditions where CL was unconverted. Optimized conditions are studied with respect to nature and pressure of gas inside the reactor, temperature, time and frequency of US irradiation, energy consumption and nature of activator.
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http://dx.doi.org/10.1016/j.ultsonch.2006.12.008DOI Listing
September 2007

The beneficial influence of ultrasound in the polymerization of epsilon-caprolactam to polyamide-6 (Nylon 6). Part II: additional experiment to understand the "pre-sonication effect".

Ultrason Sonochem 2007 Sep 20;14(6):689-94. Epub 2006 Dec 20.

Department of Physical Chemistry and Electrochemistry, University of Milan via Golgi no. 19, I-20133 Milano, Italy.

Ultrasound (US) "pre-sonication effect" is the beneficial effect of US in the hydrolytic polymerization of epsilon-caprolactam (CL) mixtures with very low water concentrations (about 0.1-1 wt%). It appears after a mild initial treatment of the mixtures with US [17.5-20 kHz, short times (5-15 min), low temperatures (70-110 degrees C)] followed by heating at 220-260 degrees C. An explanation is proposed on the basis of the formation in mild conditions (100 degrees C) of low concentrations of cyclic oligomers never detected in the literature at those conditions. These, under US irradiation, produce linear amino acid oligomers, which are strong activators of polymerization when the mixture of CL and water, after US irradiation, is heated at the suitable polymerization temperature indicated above.
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http://dx.doi.org/10.1016/j.ultsonch.2006.12.009DOI Listing
September 2007

Degradation of methyl tert-butyl ether in water: effects of the combined use of sonolysis and photocatalysis.

Ultrason Sonochem 2005 Apr;12(5):395-400

Dipartimento di Chimica Fisica ed Elettrochimica, Università di Milano, Via Golgi 19, I-20133 Milano, Italy.

The degradation of methyl tert-butyl ether (MTBE) in water was kinetically investigated in a O(2)/Ar 80:20 atmosphere employing either sonolysis at 20 kHz, or photocatalysis on TiO(2) (with 315 nm< lambda(irr) <400 nm), or simultaneous sonolysis and photocatalysis (i.e. sonophotocatalysis), as degradation techniques. In all investigated conditions, MTBE concentration decreased according to a first order rate law; under ultrasound the degradation rate was stirring-dependent. The time profile of the reaction intermediates gave information on the reaction paths prevailing under the different experimental conditions. The energy consumption of the employed degradation techniques was also evaluated, which might be decisive for their practical application.
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http://dx.doi.org/10.1016/j.ultsonch.2004.04.003DOI Listing
April 2005

Degradation of organic water pollutants through sonophotocatalysis in the presence of TiO(2).

Ultrason Sonochem 2003 Jul;10(4-5):247-54

Dipartimento di Chimica Fisica ed Elettrochimica, Università di Milano, Via Golgi 19, I-20133 Milano, Italy.

The degradation of 2-chlorophenol and of the two azo dyes acid orange 8 and acid red 1 in aqueous solution was investigated kinetically under sonolysis at 20 kHz and under photocatalysis in the presence of titanium dioxide particles, as well as under simultaneous sonolysis and photocatalysis, i.e. sonophotocatalysis. The influence on the degradation and mineralisation rates of the initial substrate concentration and of the photocatalyst amount was systematically investigated to ascertain the origin of the synergistic effect observed between the two degradation techniques. The evolution of hydrogen peroxide during kinetic runs was also monitored. Small amounts of Fe(III) were found to affect both the adsorption equilibria on the semiconductor and the degradation paths. Ultrasound may modify the rate of photocatalytic degradation by promoting the deaggregation of the photocatalyst, by inducing the desorption of organic substrates and degradation intermediates from the photocatalyst surface and, mainly, by favouring the scission of the photocatalytically and sonolytically produced H(2)O(2), with a consequent increase of oxidising species in the aqueous phase.
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http://dx.doi.org/10.1016/S1350-4177(03)00090-7DOI Listing
July 2003
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