1. Degradation of microplastics in the environment : dissertationVaibhav Budhiraja, 2024, doctoral dissertation Abstract: Plastics are based on organic polymers that are sensitive to the environment in which they find themselves and will gradually decay through a variety of chemical reactions. This process is of great importance for the transformation and persistence of microplastics (MPs) that pollute the environment. The rate of degradation depends on two major factors: Firstly, the intrinsic properties of the polymers, such as chemical structure, molecular weight, crystallinity and the presence of additives, fillers or reinforcement and secondly, the environment to which they are exposed. The degradation rate of plastic will vary in different environmental matrices like soil, freshwater, seawater, wastewater, land etc., as well as in diverse environmental conditions like UV radiation, temperature, humidity, the effect of pollutants etc. Plastic mainly undergoes two fundamental reactions: oxidation and hydrolysis and the chemical structure of the polymer and its additives plays a key role in the degradation mechanism of plastic. Polyolefins having a carbon-only main chain are resistant to hydrolysis but susceptible to oxidation, whereas polyesters and polyamides containing heteroatoms are sensitive to hydrolysis and much more resistant to oxidation.
In the context of the present work, five different studies were done involving both naturally degraded plastic and accelerated weathering of plastics in the form of small particles, MPs. In the first study, natural degraded polyethylene (PE) and polypropylene (PP) samples with a life span of more than forty years were collected from the environment and their physiochemical properties were analysed. The results show that red coloured PE samples were more degraded as compared to blue coloured samples, indicating that pigment plays a key role in the degradation. The PP sample shows extreme surface degradation, leading to fragmentation and the generation of MPs. In the second study, the effect of hydrodynamic cavitation on MPs in waste water treatment plant sludge was evaluated. PE, PP, polyethylene terephthalate and polyamide were extracted from the sludge. It was found that hydrodynamic cavitation does not disintegrate the MPs, although it removes some toxic metals and shows cell disruption mechanisms.
Other studies were done with accelerated weathered MPs, which include PE, PP and tire wear particles (TWP), that were treated in accordance with an ISO 4892 standard weathering procedure that mimics natural weathered conditions. In the third study, we used weathered PE films to evaluate the synergistic adsorption behaviour of two pollutants, namely triclosan (TCS) and methylparaben (MeP). It was found that weathered MPs adsorb more pollutants and the adsorption behaviour of TCS is enhanced in the presence of MeP. In the fourth study, the magnetic extraction of pristine and weathered PE and TWP particles was performed. The results confirmed that the magnetic
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extraction of weathered MPs is difficult as compared to pristine MPs as their surface becomes more hydrophilic with weathering. In the fifth study, the effect of weathering on the density of PE and PP was evaluated. We found that weathering enhances the density of polyolefins, which is one of the main reasons for the observed sinking of polyolefin MPs in water.
Keywords: accelerated weathering, aging, density, magnetic separation, pigment, plastic degradation, pollutants, polyethylene, polyolefin, polypropylene, sinking, tire wear particles, dissertations
Published in RUNG: 04.06.2024; Views: 346; Downloads: 0
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2. Uncovering the nature of transient and metastable nonequilibrium phases in 1T − ▫$TaS_2$ ▫Tanusree Saha, Arindam Pramanik, Barbara Ressel, Alessandra Ciavardini, Fabio Frassetto, Federico Galdenzi, Luca Poletto, Arun Ravindran, Primož Rebernik Ribič, Giovanni De Ninno, 2023, original scientific article Abstract: Complex systems are characterized by strong coupling between different microscopic degrees of freedom. Photoexcitation of such materials can drive them into new transient and metastable hidden phases that may not have any counterparts in equilibrium. By exploiting femtosecond time- and angle-resolved photoemission spectroscopy, we probe the photoinduced transient phase and the recovery dynamics of the ground state in a complex material: the charge density wave (CDW)–Mott insulator 1T-TaS2. We reveal striking similarities between the band structures of the transient phase and the (equilibrium) structurally undistorted metallic phase, with evidence for the coexistence of the low-temperature Mott insulating phase and high-temperature metallic phase. Following the transient phase, we find that the restorations of the Mott and CDW orders begin around the same time. This highlights that the Mott transition is tied to the CDW structural distortion, although earlier studies have shown that the collapses of Mott and CDW phases are decoupled from each other. Interestingly, as the suppressed order starts to recover, a metastable phase emerges before the material recovers to the ground state. Our results demonstrate that it is the CDW lattice order that drives the material into this metastable phase, which is indeed a commensurate CDW–Mott insulating phase but with a smaller CDW amplitude. Moreover, we find that the metastable phase emerges only under strong photoexcitation (∼3.6 mJ/cm2) and has no evidence when the photoexcitation strength is weak (∼1.2 mJ/cm2).
Keywords: angle resolved photoemission, time resolved photoemission, 2D materials, charge density wave, Mott insulator
Published in RUNG: 15.01.2024; Views: 709; Downloads: 4
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3. Giant and tunable out-of-plane spin polarization of topological antimonenePolina M. Sheverdyaeva, Conor Hogan, Gustav Bihlmayer, Jun Fujii, Ivana Vobornik, Matteo Jugovac, Asish K. Kundu, Sandra Gardonio, Zipporah Rini Benher, Giovanni di Santo, 2023, original scientific article Keywords: density functional theory, spin-resolved ARPES, electronic structure, topological insulators, 2D materials, antimonene
Published in RUNG: 18.07.2023; Views: 1108; Downloads: 4
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5. ULTRAFAST ELECTRON DYNAMICS IN CORRELATED SYSTEMS PROBED BY TIME-RESOLVED PHOTOEMISSION SPECTROSCOPYTanusree Saha, 2023, doctoral dissertation Abstract: Complex systems in condensed matter are characterized by strong coupling
between different degrees of freedom constituting a solid. In materials
described by many-body physics, these interactions may lead to
the formation of new ground states such as excitonic insulators, Mott
insulators, and charge and spin density waves. However, the inherent
complexity in such materials poses a challenge to identifying the
dominant interactions governing these phases using equilibrium studies.
Owing to the distinct timescales associated with the elementary interactions,
such complexities can be readily addressed in the non-equilibrium
regime. Additionally, these materials might also show the emergence
of new, metastable “hidden“ phases under non-equilibrium. The thesis
investigates the ultrafast timescales of fundamental interactions in candidate
systems by employing time-and angle-resolved photoemission spectroscopy
in the femtosecond time domain. In the (supposed) excitonic
insulator model system Ta2NiSe5, the timescale of band gap closure
and the dependence of rise time (of the photoemission signal) on the
photoexcitation strength point to a predominantly electronic origin of
the band gap at the Fermi level. The charge density wave (CDW) -
Mott insulator 1T-TaS2 undergoes photoinduced phase transition to two
different phases. The initial one is a transient phase which resembles
the systems’s high temperature equilibrium phase, followed by a long-lived
“hidden“ phase with a different CDW amplitude and is primarily
driven by the CDW lattice order. For the spin density wave system
CaFe2As2 where multiple bands contribute in the formation of Fermi surfaces,
selective photoexcitation was used to disentangle the role played
by different electron orbitals. By varying the polarization of photoexcitation
pulses, it is observed that dxz/dyz orbitals primarily contribute to
the magnetic ordering while the dxy orbitals have dominant role in the
structural order. The findings of the present study provide deeper perspectives
on the underlying interactions in complex ground phases of
matter, therefore, initiating further experimental and theoretical studies
on such materials.
Keywords: complex systems, charge density wave, excitonic insulator, metastable phase, Mott insulator, non-equilibrium, spin density wave, timescales, time- and angle-resolved photoemission, ultrafast dynamics
Published in RUNG: 01.06.2023; Views: 1617; Downloads: 30
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6. Infrared spectra in amorphous alumina : a combined ab initio and experimental studyLuigi Giacomazzi, Nikita S. Shcheblanov, Mikhail E. Povarnitsyn, Yanbo Li, Andraž Mavrič, Barbara Zupančič, Jože Grdadolnik, Alfredo Pasquarello, 2023, original scientific article Abstract: We present a combined study based on the experimental measurements of an infrared (IR) dielectric function and first-principles calculations of IR spectra and the vibrational density of states (VDOS) of amorphous alumina (am−Al2O3). In particular, we show that the main features of the imaginary part of the dielectric function ε2(ω) at ∼380 and 630 cm−1 are related to the motions of threefold-coordinated oxygen atoms, which are the vast majority of oxygen atoms in am-Al2O3. Our analysis provides an alternative point of view with respect to an earlier suggested assignment of the vibrational modes, which relates them to the stretching and bending vibrational modes of AlOn (n=4, 5, and 6) polyhedra. Our assignment is based on the additive decomposition of the VDOS and ε2(ω) spectra, which shows that (i) the band at ∼380cm−1 features oxygen motions occurring in a direction normal to the plane defined by the three nearest-neighbor aluminum atoms, i.e., out-of-plane motions of oxygen atoms; (ii) Al-O stretching vibrations (i.e., in-plane motions of oxygen atoms) appear at frequencies above ∼500cm−1, which characterize the vibrational modes underlying the band at ∼630cm−1. Aluminum and fourfold-coordinated oxygen atoms contribute uniformly to the VDOS and ε2(ω) spectra in the frequency region ∼350–650 cm−1 without causing specific features. Our numerical results are in good agreement with the previous and presently obtained experimental data on the IR dielectric function of am−Al2O3 films. Finally, we show that the IR spectrum can be modeled successfully by assuming isotropic Born charges for aluminum atoms and fourfold-coordinated oxygen atoms, while requiring the use of three parameters, defined in a local reference frame, for the anisotropic Born charges of threefold-coordinated oxygen atoms.
Keywords: dielectric properties, microstructure, amorphous materials, density functional calculations, infrared techniques, aluminium oxide
Published in RUNG: 10.05.2023; Views: 1445; Downloads: 7
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7. Ultrafast relaxation of photoexcited superfluid He nanodropletsM. Mudrich, A.C. LaForge, A. Ciavardini, P. O'Keeffe, C. Callegari, M. Coreno, A. Demidovich, M. Devetta, M. Di Fraia, M. Drabbels, P. Finetti, O. Gessner, C. Grazioli, A. Hernando, D.M. Neumark, Y. Ovcharenko, P. Piseri, O. Plekan, K.C. Prince, R. Richter, M.P. Ziemkiewicz, T. Moller, J. Eloranta, M. Pi, M. Barranco, F. Stienkemeier, 2020, original scientific article Keywords: helium, helium nanodroplet, nanomaterial, density functional theory, dipole, excitation, ionization, photoelectron spectroscopy, photoexcitation, photon, simulation, ultraviolet radiation, ultrafast photoemission, free electron laser, ultrafast spectrscopy
Published in RUNG: 20.01.2022; Views: 1902; Downloads: 0
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8. Carbon and Nitrogen K-Edge NEXAFS Spectra of Indole, 2,3-Dihydro-7-azaindole, and 3-FormylindoleAurora Ponzi, Elisa Bernes, Daniele Toffoli, Giovanna Fronzoni, Carlo Callegari, Alessandra Ciavardini, Michele Di Fraia, Robert Richter, Kevin Charles Prince, Hanan Sa'adeh, Michele Devetta, Davide Faccialà, Caterina Vozzi, Lorenzo Avaldi, Paola Bolognesi, Mattea Castrovilli, Daniele Catone, Marcello Coreno, Oksana Plekan, 2021, original scientific article Keywords: Carbon and nitrogen, General description, Hybrid functional, Near-edge X-ray absorption fine structure spectrum, Relevant features, Rydberg character, Theoretical spectra, Time dependent density functional theory
Published in RUNG: 19.01.2022; Views: 2034; Downloads: 0
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