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There is a growing concern within the medical community about the potential burden of microplastics on human organs and tissues. In this study, we investigated by microRaman spectroscopy the presence of microplastics in human kidneys and urine. Moreover, an open-access software was developed and validated for the project, which enabled the comparison between the investigated spectra and a self-created spectral database, thus enhancing the ability to characterize polymers and pigments in biological matrices. Healthy portions of ten kidneys obtained from nephrectomies, as well as ten urine samples from healthy donors were analyzed: 26 particles in both kidney and urine samples were identified, with sizes ranging from 3 to 13 µm in urine and from 1 to 29 µm in kidneys. The most frequently determined polymers are polyethylene and polystyrene, while the most common pigments are hematite and Cu-phthalocyanine. This preclinical study proves the presence of microplastics in renal tissues and confirms their presence in urine, providing the first evidence of kidney microplastics deposition in humans.
Subject(s)
Microplastics , Water Pollutants, Chemical , Humans , Plastics/chemistry , Water Pollutants, Chemical/analysis , Environmental Monitoring/methods , Polymers , Spectrum Analysis , Kidney/chemistryABSTRACT
The increasing energy demand and the ever more pressing need for clean technologies of energy conversion pose one of the most urgent and complicated issues of our age. Thermoelectricity, namely the direct conversion of waste heat into electricity, is a promising technique based on a long-standing physical phenomenon, which still has not fully developed its potential, mainly due to the low efficiency of the process. In order to improve the thermoelectric performance, a huge effort is being made by physicists, materials scientists and engineers, with the primary aims of better understanding the fundamental issues ruling the improvement of the thermoelectric figure of merit, and finally building the most efficient thermoelectric devices. In this Roadmap an overview is given about the most recent experimental and computational results obtained within the Italian research community on the optimization of composition and morphology of some thermoelectric materials, as well as on the design of thermoelectric and hybrid thermoelectric/photovoltaic devices.
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The crystallographic and transport properties of thin films fabricated by pulsed laser deposition and belonging to the Smy(FexNi1-x)4Sb12filled skutterudite system were studied with the aim to unveil the effect exerted by temperature and duration of thermal treatments on structural and thermoelectric features. The importance of annealing treatments in Ar atmosphere up to 523 K was recognized, and the thermal treatment performed at 473 K for 3 h was selected as the most effective in improving the material properties. With respect to the corresponding bulk compositions, a significant enhancement in phase purity, as well as an increase in electrical conductivity and a drop in room temperature thermal conductivity, were observed in annealed films. The low thermal conductivity, in particular, can be deemed as deriving from the reduced dimensionality and the consequent substrate/film interfacial stress, coupled with the nanometric grain size.
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The structural, microstructural, Raman and ionic conductivity properties of (Gd,Sm)-doped ceria were studied and compared to the ones of similar ceria systems with the aim of deepening the comprehension of the correlations between defect chemistry and movement of oxygen vacancies in such materials, which are ideal candidates as electrolytes in solid oxide cells. The system was chosen as it combines the advantages of using the most effective doping ions for ceria, namely Sm3+ and Gd3+, and the expected positive effects of multiple doping. The main effect of double doping on the structure is the enlargement of the compositional region where ionic conductivity takes place, due to the entrance of the smaller doping ions into defect clusters, mainly trimers and dimers (RE ≡ rare earth). On the other hand, the formation of such clusters also affects ionic conductivity, as it causes the occurrence of a double activation energy with a temperature threshold located at â¼770 K. The dissociation of trimers above this temperature induces the appearance of a high temperature activation energy which is lower than the one observed in singly-doped systems, such as Sm- and Nd-doped ceria, showing the unique value of this parameter.
ABSTRACT
Filled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Smy(FexNi1-x)4Sb12-filled skutterudite system. Films were deposited under vacuum conditions by the pulsed laser deposition (PLD) method on fused silica substrates, and the deposition temperature was varied. The effect of the annealing process was studied by subjecting a set of films to a thermal treatment for 1 h at 423 K. Electrical conductivity σ and Seebeck coefficient S were acquired by the four-probe method using a ZEM-3 apparatus performing cycles in the 348-523 K temperature range, recording both heating and cooling processes. Films deposited at room temperature required three cycles up to 523 K before being stabilized, thus revealing the importance of a proper annealing process in order to obtain reliable physical data. XRD analyses confirm the previous result, as only annealed films present a highly crystalline skutterudite not accompanied by extra phases. The power factor of annealed films is shown to be lower than in the corresponding bulk samples due to the lower Seebeck coefficients occurring in films. Room temperature thermal conductivity, on the contrary, shows values comparable to the ones of doubly doped bulk samples, thus highlighting the positive effect of interfaces on the introduction of scattering centers, and therefore on the reduction of thermal conductivity.
ABSTRACT
Defect aggregates in doped ceria play a crucial role in blocking the movement of oxygen vacancies and hence in reducing ionic conductivity. Nevertheless, evaluation of their amount and the correlation between domain size and transport properties is still an open issue. Data derived from a high-pressure X-ray diffraction investigation performed on the Ce1-x(Nd0.74Tm0.26)xO2-x/2 system are employed to develop a novel approach aimed at evaluating the defect aggregate content; the results are critically discussed in comparison to the ones previously obtained from Sm- and Lu-doped ceria. Defect clusters are present even at the lowest considered x value, and their content increases with increasing x and decreasing rare earth ion (RE3+) size; their amount, distribution, and spatial correlation can be interpreted as a complex interplay between the defects' binding energy, nucleation rate, and growth rate. The synoptic analysis of data derived from all of the considered systems also suggests that the detection limit of the defects by X-ray diffraction is correlated to the defect size rather than to their amount, and that the vacancies' flow through the lattice is hindered by defects irrespective of their size and association degree.
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The structural and thermoelectric properties of the filled skutterudite (Sm,Gd)y(FexNi1-x)4Sb12 were investigated and critically compared to the ones in the Sm-containing system with the aim of unravelling the effect of double filling on filling fraction and thermal conductivity. Several samples (x = 0.50-0.90 and y = 0.15-0.48) were prepared by melting-sintering, and two of them were densified by spark plasma sintering in order to study their thermoelectric features. The crystallographic study enables the recognition of the role of the filler size in ruling the filling fraction and the compositional location of the p/n crossover: It has been found that the former lowers and the latter moves toward lower x values with the reduction of the filler ionic size, as a consequence of the progressively weaker interaction of the filler with the Sb12 cavity. The analysis of thermoelectric properties indicates that, despite the Sm3+/Gd3+ small mass difference, the contemporary presence of these ions in the 2a site significantly affects the thermal conductivity of both p- and n-compositions. This occurs by reducing its value with respect to the Sm-filled compound at each temperature considered, and making the overall thermoelectric performance of the system comparable to several multi-filled (Fe, Ni)-based skutterudites described in the literature.
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Rare-earth (RE)-doped ceria systems, in particular when RE ≡ Nd, Sm, or Gd, are well-known to be characterized by high values of ionic conductivity in the intermediate temperature range, which, in principle, makes them ideal solid electrolytes in solid oxide fuel and electrolysis cells. Defect chemistry turns out to be a pivotal issue in this framework because ionic conductivity is driven by the ability of oxygen vacancies to move through the lattice, and any form of defect clustering tends to depress the efficiency of oxygen transport. In this viewpoint, not only are factors at the average scale assessed, such as the compositional extent of the CeO2-like solid solution, but also the occurrence of local inhomogeneities due to vacancy-dopant association is discussed in correlation with its central role in hindering the migration of vacancies. The relationship between the stability of the hybrid phase and the RE3+ ionic size is presented, and the highly complementary role of Raman spectroscopy toward X-ray diffraction is described in detail. The key points of the whole discussion are finally used to identify the most relevant structure-related parameters affecting ionic conductivity in the studied material.
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Samples belonging to the series Sm(y)(Fe(x)Ni(1−x)4Sb12 were heated in Ar atmosphere up to 400 °C and cooled down to room temperature several times, with the aim to evaluate the effect of thermal cycles on microhardness. The treatment temperature was chosen in correspondence of the maximum ZT value, in order to simulate the operating conditions of the material in a thermoelectric device. Vickers measurements allowed to detect the effect of both composition and thermal treatments on the microhardness properties of the material. A decrease in the microhardness value was observed prior to thermal treatments with increasing Fe amount, due to the substitution of Ni by the larger Fe atom. Moreover, almost all compositions show an increase in the hardness of the skutterudite phase as a consequence of thermal cycles, accounting for the Sb enrichment of skutterudite. This evidence suggests also a possible improvement of the preparation procedure in order to obtain a stoichiometric Sb amount within the skutterudite. Samples were prepared by direct reaction of pure elements at 950 °C followed by thermal treatment at 620 °C. The composition and microstructure of the obtained samples were investigated by X-ray powder diffraction, and by optical and electronic microscopy.
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A room temperature structural study has been performed through the whole compositional range of the (Ce1-xLux)O2-x/2 system by synchrotron X-ray diffraction and µ-Raman spectroscopy. Samples were synthesized by thermal treatment in air at 1373 K of coprecipitated mixed oxalates. A CeO2-based solid solution with a fluorite-type structure (F) was found to be stable up to x = 0.4, while at higher Lu content a (F + C) biphasic region was observed, with C being the cubic atomic arrangement typical of sesquioxides of the heaviest rare earths. A comparative approach including also results deriving from other (Ce1-xREx)O2-x/2 systems (RE ≡ Gd and Sm) allowed us to conclude that the compositional extent of the F solid solution is a complex function of RE3+ size and RE compressibility. On this basis, the dependence of ionic conductivity on the RE identity was interpreted as related both to the Ce4+/RE3+ size closeness and to RE compressibility. Ce4+/RE3+ dimensional issues were also revealed to rule the appearance of the hybrid structure observed in the two aforementioned systems, consisting of the intimate intergrowth of C microdomains within the F-based host lattice. Moreover, a more extended definition of F-based solid solution, including also the hybrid structure, is formulated; the latter is meant as a modification of the former, occurring when mainly RE-vacancy aggregates are incorporated into the host lattice in spite of isolated RE ions. By µ-Raman spectroscopy it was possible to demonstrate that the mechanism of oxygen vacancy formation is common to all the systems studied, provided that the structure of the F-based solid solution, also including the hybrid structure, is retained.
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A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and µ-Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x ≈ 0.63 and y ≈ 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and µ-Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques.
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A structural study of Sm- and Gd-doped ceria was performed with the aim to clarify some unexplained structural features. (Ce1-xREx)O2-x/2 samples (RE ≡ Sm, Gd; x = 0, 0.1, ..., 1) were prepared by coprecipitation of mixed oxalates and subsequent thermal treatment at 1473, 1173, or 1073 K in air; they were then analyzed at room temperature both by synchrotron X-ray diffraction and µ-Raman spectroscopy. Two structural models were adopted to fit the experimental data, namely, a fluoritic one, resembling the CeO2 structure at low RE content, and a hybrid one at higher RE content, intermediate between the CeO2 and the RE2O3 structures. Two main transitions were detected along the compositional range: (a) an RE-dependent transition at the boundary between the fluoritic and the hybrid regions, of a chemical nature; (b) an RE-independent transition within the hybrid region at â¼0.5, having a purely geometrical nature. The presence of two finely interlaced F- and C-based structures within the hybrid region was confirmed, and hints of their composition were obtained by µ-Raman spectroscopy. The obtained results indicate a possible explanation for the non-Vegard behavioral trend of the cell parameters.
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The crystallographic features of Gd-doped ceria were investigated at the operating temperature of solid oxides fuel cells, where these materials are used as solid electrolytes. (Ce(1-x)Gd(x))O(2-x/2) samples (x = 0.1, 0.3, 0.5, 0.7) were prepared by coprecipitation of mixed oxalates, treated at 1473 K in air, and analyzed by synchrotron X-ray diffraction in the temperature range 673 K ≤ T ≤ 1073 K at the Elettra synchrotron radiation facility located in Trieste, Italy. In the whole temperature span a boundary was found at x â¼ 0.2 between a CeO2-based solid solution (for x ≤ 0.2) and a structure where Gd2O3 microdomains grow within the CeO2 matrix, taking advantage of the similarity between Gd(3+) and Ce(4+) sizes; the existence of the boundary at x â¼ 0.2 was confirmed also by measurements of ionic conductivity performed by impedance spectroscopy. Similar to what observed at room temperature, the trend of the cell parameter shows the presence of a maximum; with increasing temperature, the composition corresponding to the maximum moves toward lower Gd content. This evidence can be explained by analyzing the behavior of the coefficient of thermal expansion as a function of composition.
