1,186 research outputs found
Advanced oxidation processes (AOPs) for the mineralization of azo-dyes from wastewaters: homogeneous vs. heterogeneous photocatalytic processes
No full textAdvanced oxidation processes (AOPs) for the mineralization of azo-dyes from wastewaters: homogeneous vs. heterogeneous photocatalytic processes
Francesco Conte 1, Cristina Calloni 2, Ilenia Rossetti 3 and Gianguido Ramis 4*
1 Chemical Plants and Industrial Chemistry Group, Dipartimento di Chimica, Università degli Studi di Milano, Milan, Italy
2 Chemical Plants and Industrial Chemistry Group, Dipartimento di Chimica, Università degli Studi di Milano, Milan, Italy
3 Chemical Plants and Industrial Chemistry Group, Dipartimento di Chimica, Università degli Studi di Milano, Milan, Italy
4* DICCA, Università degli Studi di Genova, Genoa, Italy, presenting author, corr. author ([email protected])
INTRODUCTION
Textiles industries huge production determines a strong environmental impact: the yearly total impact per person is estimated to be 1.3 tonnes of raw material and over 100 m3 of water. Ca. 700,000 – 1,000,000 tons/years of dyes are produced and more than 280,000 tons are lost in the effluent and often remain as persistent pollutants. Heterogeneous and homogeneous phototreatments can be efficiently used as Advanced Oxidation Processes to degrade such contaminants and a comparison between different technologies has been carried out on the azo-dye Dystar’s Levafix Brilliant Red E-6BA.
EXPERIMENTAL
Oas a model molecule for this study because it is characterized by low biodegradability
TiO2 P25 was employed as a commercial nanostructured material supplied by Evonik and compared with TiO2 FSP, prepared through a homemade flame spray pyrolysis apparatus. Metallic co-catalysts were deposited over the surface by wet impregnation and then reduced at different temperature (Ag, Au, Pt, Pd, Fe).
The catalysts were characterised by XRD, N2 physisorption and DR-UV-VIS analyses.
The photo-degradation tests were carried out in different cylinder-type double-wall glass reactors of 300-1000 mL capacity, open to air and equipped with a suitable lamp in case of photocatalyzed processes.
The Fenton process was carried out either in light or dark conditions by adding Fe salts and H2O2 and compared with UV/H2O2 and Heterogeneous photodegradation processes with the above described catalysts.
The light sources employed were characterized by different emission wavelength and power output: a LED-type lamp (white light, 30 W, 2700 lm), an external UV lamp (200W, maximum emission at 365 nm) and two different low power immersed-UV lamp (125 W, maximum emission at 365 nm); natural sunlight. The average irradiance was measured for the different setups through a photo-radiometer sensitive to the UVA fraction and were 116 W/m2 in case of the external-UV lamp and respectively 60 and 260 W/m2 for the low irradiance (lamp 1) and high irradiance (lamp 2) immersed-UV lamp. The progress of the reaction was monitored by UV-Vis and Total Organic Carbon (TOC).
Toxicity tests on the treated solutions were also carried out using the Crustacean Daphnia magna.
RESULTS AND DISCUSSION
The fastest degradation process was Photo-Fenton with the highest power immersion UV lamp (10 min to 97.4% conversion), strictly followed by the UV/H2O2 process (20 min to 100% conversion). The degradation time increased with the other light sources, i.e. sun and LED, but overall, the total reaction time did not exceed 30 min. On the other hand, when it comes to the heterogeneous process, the titania synthetized via flame pyrolysis takes longer time to reach full conversion. At first glance it seems that the homogeneous treatment outperforms the heterogeneous ones, however, in the first case these results were achieved using a large amount of hydrogen peroxide, about 3.5 equivalents, which of course boost the reaction and lowers the time required to achieve a good conversion of the substrate.
Figure 9: Degradation of Levafix dye: comparison.
No organic carbon was detected after the treatment, except when employing gold deposited catalyst. Acute toxicity tests revealed that the Levafix Briliant Red resulted in a 48h-LC50 of 117 mg/L. The toxic response was dramatic in case of the solutions treated with UV/H2O2 and (Photo)Fenton processed, since a higher mortality of Daphnia magna specimens was observed due to the residual amounts of hydrogen peroxide. Overall, the best toxicity results were achieved in case of the samples treated with titania photocatalyst (P25), since the toxicity of the solutions was lower than the ones containing the bare dye.
CONCLUSION
Photo-degradation of Levafix Brilliant Red was compared for different AOPs. The homogeneous treatments were more efficient in the degradation of the selected dye, but the main advantages of employing solid nanostructured photocatalyst is that it is not compulsory to add hydrogen peroxide (low toxicity) and the catalyst can be recovered easily
Electronic and spectral properties of clean and C60-covered atom-thick Chromium oxide at the Fe(001) surface
No full textChemisorption of a single atomic layer of oxygen on the Fe(001) surface yields a highly ordered and reproducible benchmark substrate [1] for theoretical and experimental studies, and for the epitaxial growth of metal oxides, including atom-thick CrxOy layers, and hybrid interfaces with foreseen applications e.g. in organic spintronics.
This talk initially presents ab initio investigations that have supplemented microscopy and spectroscopy experiments of the electronic and magnetic properties of two-dimensional Chromium oxides of Cr3O4 and Cr4O5 stoichiometry grown on Fe(001), featuring antiferromagnetic magnetic configurations with underlying Fe(001) [2,3]. Despite Cr / CrO systems are notoriously difficult for mean field approaches, generalized-gradient results are found to explain most experimental findings, with a rigid shift of oxygen bands accounting for electronic correlation effects.
We eventually consider the effect of inserted Cr4O5 layers at the interface between the prototypical C60 organic semiconductor and Fe(001), which is shown to enhance the magnetic hybridization between the molecule and the surface through x-ray magnetic circular dichroism (XMCD) [4,5]. By means of ab initio calculation we characterize the local interface morphology, the magnetic configuration of the surface and the induced spin dependent electronic properties of the molecule, the latter reflecting the magnetic electronic properties of the surface at the relevant energy range. As seen from the substrate, adsorbates can influence the magnitude and even orientation of surface Cr magnetic moments. The interest in this interface is then twofold: on one side the thin magnetic oxide allows tailoring the magnetic properties of the organic layer, on the other side the adsorption of C60 can be envisioned as a tool to control the magnetic ordering of Cr atoms at the interface.
[1] A. Picone, M. Riva, A. Brambilla, A. Calloni, G. Bussetti, M. Finazzi, F. Ciccacci, L. Duò, Surface Science Reports 71, 32 (2016).
[2] A. Picone, G. Fratesi, M. Riva, G. Bussetti, A. Calloni, A. Brambilla, M. I. Trioni, L. Duò, F. Ciccacci, and M. Finazzi, Phys. Rev. B 87, 085403 (2013).
[3] A. Calloni, G. Fratesi, S. Achilli, G. Berti, G. Bussetti, A. Picone, A. Brambilla, P. Folegati, F. Ciccacci, and L. Duò, Phys. Rev. B 96, 085427 (2017).
[4] A. Brambilla, A. Picone, D. Giannotti, A. Calloni, G. Berti, G. Bussetti, S. Achilli, G. Fratesi, M. I. Trioni, G. Vinai, P. Torelli, G. Panaccione, L. Duò, M. Finazzi, and F. Ciccacci, Nano Lett. 17, 7440 (2017).
[5] A. Brambilla, A. Picone, S. Achilli, G. Fratesi, A. Lodesani, A. Calloni, G. Bussetti, M. Zani, M. Finazzi, L. Duò, and F. Ciccacci, Journal of Applied Physics 125, 142907 (2019)
Contrast enhanced ultrasound as a new tool to estimate the performance of midline catheters in the single patient
No full textBackground: Contrast enhanced ultrasound (CEUS) through MicroBubbles Time (MBT) (time from infusion of saline with addition of micro-bubbles of air to visualization of first bubbles in right atrium (RA), visualized by subxiphoid or apical echocardiography) is an alternative to Intracavitary ECG and chest X-ray in evaluation of tip location in central venous catheters. Objective: To evaluate feasibility and variability of CEUS in peripheral catheters (Midline-MC) in a cohort of patients and in a subgroup where tip location was also performed through chest X-ray. Secondary outcomes were verifying the correlation between MBT and distance between tip of MC and RA (anthropometric and radiological measures), body mass index (BMI), vein diameter at point of insertion. Methods: Patients with insertion of MC were enrolled in this prospective cohort. After catheter insertion, CEUS was performed recording MBT. Results: One hundred thirty-two MCs were inserted, 45 performed Chest X-ray. MBT wasn’t feasible in 7 (5%) because of low quality echocardiographic images. Subcostal view was available in 114 patients (91.2%), while 11 patients (8.8%) were examined through apical four-chamber view. Mean MBT in the whole population was 2.3 ± 0.8 s. Significant correlation between anthropometric and radiological measures, BMI and MBT was found. 32.8% of MC had a MBT ⩽2 s. Conclusions: CEUS could be useful to estimate tip position. Our study showed how 2 s is not a suitable cutoff to confirm central catheter’s tip
Conformational properties of the aggregation precursor state of HypF-N.
No full textThe conversion of specific proteins or protein fragments into insoluble, ordered fibrillar aggregates is a fundamental process in protein chemistry, biology, medicine and biotechnology. As this structural conversion seems to be a property shared by many proteins, understanding the mechanism of this process will be of extreme importance. Here we present a structural characterisation of a conformational state populated at low pH by the N-terminal domain of Escherichia coli HypF. Combining different biophysical and biochemical techniques, including near- and far-UV circular dichroism, intrinsic and 8-anilinonaphthalene-1-sulfonate-derived fluorescence, dynamic light scattering and limited proteolysis, we will show that this state is largely unfolded but contains significant secondary structure and hydrophobic clusters. It also appears to be more compact than a random coil-like state but less organised than a molten globule state. Increase of the total ionic strength of the solution induces aggregation of such a pre-molten globule state into amyloid-like protofibrils, as revealed by thioflavin T fluorescence and atomic force microscopy. These results show that a premolten globule state can be, among other possible conformational states, one of the precursor states of amyloid formation. In addition, the possibility of triggering aggregation by modulating the ionic strength of the solution provides one a unique opportunity to study both the initial precursor state and the aggregation process
First results on an adaptive optics pre-mode cleaning system based on interferometric phase-front detection
No full textWe present an adaptive optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack–Hartman-based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations such as, for instance, the control of the input beam of gravitational waves interferometric detectors
Oxygen contribution to the magnetic response of ultrathin Fe/Ni multilayers grown on Fe-p(1x1)O
No full textWe investigated the magnetic behaviour of an Fe overlayer on a Ni buffer layer (Fe/Ni multilayer system) grown on top of the Fe-p(1×1)O surface, with a particular focus on the modifications observed in the spin-resolved electronic structure and the role of oxygen, introduced in the system in a well-defined amount at the substrate preparation stage. The structural properties are investigated by means of low energy electron diffraction, that confirms the formation of an epitaxial system featuring a metastable surface lattice. Spin-resolved photoemission spectroscopy testifies a strong decrease of the spectral spin polarization for increasing thickness of the Ni buffer layer, reaching a minimum from a nominal thickness of 6 Ni atomic layers. Surprisingly, the growth of a single Fe overlayer is sufficient to restore most of the original polarization signal, thus creating an ultrathin bcc Fe film seemingly decoupled from the substrate. Ab initio calculations track the modifications of the magnetic moments of the surface layers that quench upon Ni deposition and restore with additional Fe growth. Spin-resolved inverse photoemission highlights a notable reduction of the density of majority states just above the Fermi level, possibly influencing the magnetic response of the system
Titanium(IV)-(R,R,R)-tris(2-phenylethoxy)amine-alkylperoxo complex mediated oxidations: The biphilic nature of the oxygen transfer to organic sulfur compounds
No full textThe enantioselective sulfoxidation of methyl p-tolyl sulfide by Ti(IV)/ N(CH2CHPhO)3(OiPr), 1, and cumyl hydroperoxide yields both the corresponding sulfoxide and sulfone with comparable reaction rates (kS/kSO=3.2). Such a behavior stands in contrast with the remarkably high selectivity usually exhibited by d0 transition metal peroxocomplexes. Hammett correlations show that peroxocomplex 2, derived from the addition of cumylhydroperoxide to 1, has a biphilic nature, behaving as an electrophilic oxidant towards sulfides (rho=-0.60) while a nucleophilic pathway dominates the oxidation of sulfoxides (rho =+0.45). Kinetic evidence and theoretical calculations [RHF/3-21G(*)] indicate that the mechanistic modification of the reactivity is triggered by coordination of the sulfoxide to the metal center occurring with a calculated stabilization energy of 19.3 Kcal/mol. According to this mechanistic picture, the Lewis acid Ti(IV) metal center activates the hydroperoxide and the sulfoxide in a template intramolecular oxidative process
The effect of cyclic voltammetry speed on anion intercalation in HOPG
No full textIt is generally accepted that anion intercalation occurs when HOPG is kept at high electrochemical potentials in oxidant electrolytes, such as perchloric and sulfuric acids. The graphite surface undergoes a detriment, made also evident by the swelling of the uppermost layers (blisters formation) caused by gas evolution in standard electrochemical conditions (namely, by cycling the HOPG voltage at speeds up to 25 mV/s). Surface swelling is therefore considered as being indicative of anion intercalation. Recently, suppression of blister formation when the potential is swept at larger speeds (such as 600 mV/s) has been observed, raising the question as to whether this phenomenon might be able to suppress anion intercalation. In this work, by combining atomic force microscopy and X-ray photoemission spectroscopy, we unequivocally show that the HOPG electrode undergoes similar chemical modifications, regardless of the chosen electrochemical conditions and consequently of the morphological evolution at the surface
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