Abstract: There is a growing interest in the technological transfer of highly performing electrochemical sensors within portable analytical devices for the in situ monitoring of environmental contaminants, such as perfluorooctanesulfonic acid (PFOS). In the redesign of biomimetic sensors, many parameters should be taken into account from the working conditions to the electrode surface roughness. A complete characterization of the surface modifiers can help to avoid time-consuming optimizations and better interpret the sensor responses. In the present study, a molecularly imprinted polymer electrochemical sensor (MIP) for PFOS optimized on gold disk electrodes was redesigned on commercial gold screen-printed electrodes. However, its performance investigated by differential pulse voltammetry was found to be poor. Before proceeding with further optimization, a morphological study of the bare and modified electrode surfaces was carried out by scanning electron microscopy-energy-dispersive X-ray spectrometry (SEM-EDS), atomic force microscopy (AFM) and profilometry revealing an heterogeneous distribution of the polymer strongly influenced by the electrode roughness. The high content of fluorine of the target-template molecule allowed to map the distribution of the molecularly imprinted polymer before the template removal and to define a characterization protocol. This case study shows the importance of a multi-analytical characterization approach and identify significant parameters to be considered in similar redesigning studies.

Abstract: ​Food production is a cornerstone in contemporary industrial societies. Its production requires land, water and enormous amounts of fertilizers. These precious fertilizers enter the linear food chain and suffer from a cascade of inefficiencies, resulting in detrimental effects to the environment. A radical transforming of the current food production chain is, therefore, essential to guarantee a sustainable future for humanity. ​This thesis has studied the production of microbial protein (i.e. single-cell protein), which is the use of microorganisms such as yeast, fungi, algae and bacteria as protein ingredient for animal feed. The type of microorganisms targeted in this thesis were purple non-sulfur bacteria (PNSB). These bacteria are an extremely heterogenic group that contain photosynthetic pigments and are able to perform anoxygenic photosynthesis. The core focus of the thesis was technology development for the production of PNSB as a source of microbial protein on wastewater and fresh fertilizers. In the final stage of this research, it was the objective to explore the potential of PNSB as a nutritious feed ingredient for shrimp. ​Overall, this work has provided the building blocks to transform the conventional food production chain. The findings show that PNSB production and biomass valorization is within reach. Further pilot implementation and cost reduction will facilitate the introduction of PNSB production in future’s wastewater treatment plants and the valorization of the biomass as nutritious animal feed ingredient.​

Abstract: In the broad context of food and environmental safety, the development of selective and sensitive analytical tools for the detection of β-lactam antibiotics in milk down to their Maximum Residues Limits (MRL), is still an open challenge. To address this need, the design of new bio(mimetic) electrochemical sensors was investigated in the present thesis. These sensors are based on the intrinsic electrochemistry of β-lactam antibiotics, taking advantages of the characteristic electrochemical fingerprints of the core structures and redox active side chain groups. The electrochemistry of nafcillin (NAF) and the isoxazolyl penicillins (ISOXA) was investigated, identifying the peculiar electrochemical fingerprint of each antibiotic, proving that it is possible to use electrochemistry for the selective detection of these antimicrobial drugs. Once verified the applicability of a direct detection, different sensor configurations were tested mainly focusing on: – the selection and validation of aptamers to be used as bioreceptors in the development of β-lactam biosensors; – the design of biomimetic receptors, particularly molecularly imprinted polymers, and other synthetic electrode modifiers compatible with a direct detection strategy. The selection of novel aptamers was performed following both a traditional FluMag SELEX protocol and a novel variant based on graphene oxide (GO). First results with the modified GO-SELEX are promising but more work still needs to be done to validate this novel approach. The few aptamers for β-lactam antibiotics, already reported in literature by other groups, were poorly characterized up to now. For this reason, a multi-analytical characterization protocol for aptamer binding studies was optimized and validated by focusing on aptamer AMP17 against ampicillin. The protocol combines ITC, nESI-MS and 1H-NMR. Very striking was the fact that the aptamer sequence did not show any sign of specific binding for its target, even if it was used in many other studies in the past. This thesis now offers a validated protocol for testing the affinity and binding capabilities of aptamer sequences. In parallel, the functionalization of the electrode surface with polymer modifiers was studied. In particular we optimized a MIP electrochemical sensor based on 4-aminobenzoic acid for the direct electrochemical detection of CFQ. Another approach was tested based on the intrinsic affinity of NAF for an oPD electropolymerized film on the electrode surface. Both sensors were found to be sensitive and selective for the detection of CFQ and NAF at MRLs in buffer solutions. The proposed protocols are robust and promising for technological transfer. Lastly, the research activity was directed towards milk sample analysis following two parallel routes: the development of a pre-treatment protocol for raw milk, based on solvent addition (ACN or ISO), and the study of β-lactam antibiotics electrochemistry in undiluted raw milk with addition of KNO3 as supporting electrolyte. Both approaches gave encouraging results and the detection of NAF, CFQ and CFU in the micromolar range was achieved, with the second approach in undiluted raw milk.

Abstract: Dislocations are always observed during crystal growth, and it is usually desirable to reduce the dislocation density in high-quality crystals. Here, the annihilation process of the 30 degrees Shockley partial dislocation pairs in CdTe is studied by first-principles calculations. We found that the dislocations can glide relatively easily due to the weak local bonding. Our systematic study of the slipping mechanism of the dislocations suggests that the energy barrier for the annihilation process is low. Band structure calculations reveal that the band bending caused by the charge transfer between the two dislocation cores depends on the core-core distance. A simple linear model is proposed to describe the mechanism of formation of the dislocation pair. More importantly, we demonstrate that hole injection can affect the core structure, increase the mobility, and eventually trigger a spontaneous mutual annihilation, which could be employed as a possible facile way to reduce the dislocation density.

Abstract: The painting 'Two fisherboys' has long caused confusion among experts. A close comparison of the painting with a forgery by Han van Meegeren and Frans Hals's `Fisherboy' solves the conundrum and provides valuable insights into the merits and drawbacks of modern analytical techniques.

Abstract: We investigate the effect of the temperature dependence of many-body correlations on hole-hole Coulomb drag in strongly coupled GaAs/GaAlAs double quantum wells. For arbitrary temperatures, we obtained the correlations using the classical-map hypernetted-chain approach. We compare the temperature dependence of the resulting drag resistivities rho D(T) at different densities with rho D(T) calculated assuming correlations fixed at zero temperature. Comparing the results with those when correlations are completely neglected, we confirm that correlations significantly increase the drag. We find that the drag becomes sensitive to the temperature dependence of T greater than or similar to 2TF, twice the Fermi temperature. Our results show excellent agreement with available experimental data. Published under license by AIP Publishing.

Abstract: We theoretically investigate, through Ginzburg?Landau simulations, the possibility to induce an open circuit voltage in absence of applied current, by dragging superconducting vortices with a dynamic pinning array as for instance that created by a nearby sliding vortex lattice or moving laser spots. Different dynamic regimes, such as synchronous vortex motion or dynamic vortex chains consisting of laggard vortices, can be observed by varying the velocity of the sliding pinning potential and the applied magnetic field. Additionally, due to the edge barrier, significantly different induced voltage is found depending on whether the vortices are dragged along the superconducting strip or perpendicular to the lateral edges. The output voltage in the proposed mesoscopic superconducting dynamo can be tuned by varying size, density and directions of the sliding pinning potential.

Abstract: Nickel-containing N-doped carbons were synthesized for the electrochemical reduction of CO2 to CO, which is a promising approach to reduce the atmospheric CO2 levels and its negative impact on the environment. Unfortunately, poor performance (activity, selectivity and/or stability) is still a major hurdle for the economical implementation of this type of materials. The electrocatalysts were prepared through an easily up-scalable and easily tunable method based on the pyrolysis of Ni-containing N-doped carbons. Ni–N–AC–B1 synthesized with a high relative amount of nitrogen and nickel with respect to carbon, was identified as the most promising candidate for this reaction based on its partial CO current density (4.2 mA cm−2), its overpotential (0.57 V) and its faradaic efficiency to CO (>99%). This results in unprecedented values for the current density per g active sites (690 A g−1 active sites). Combined with its decent stability and its high performance in an actual electrolyzer setup, this makes it a promising candidate for the electrochemical reduction of CO2 to CO on a larger scale. Finally, the evaluation of this kind of material in a flow-cell setup has been limited and to the best of our knowledge never included an evaluation of several crucial parameters (e.g. electrolyte type, anode composition and membrane type) and is an essential investigation in the move towards up-scaling and ultimately industrial application of this technique. This study resulted in an optimal cell configuration, consisting of Pt as an anode, Fumatech® as the membrane and 1 M KHCO3 and 2 M KOH as catholyte and anolyte, respectively. In conclusion, this research offers a unique combination of electrocatalyst development and reactor optimization.

Abstract: The present work investigates the challenges accompanied by the electrochemical cocaine detection in physiological conditions (pH 7) in the presence of chlorpromazine, promethazine, procaine, and dextromethorphan, frequently used cutting agents in cocaine street samples. The problem translates into the absence of the cocaine oxidation signal (signal suppression) when in a mixture with one of these compounds, leading to false negative results. Although a solution to this problem was provided through earlier experiments of our group, the mechanisms behind the suppression are now fundamentally investigated via electrochemical and liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS) strategies. The latter was used to confirm the passivation of the electrodes due to their interaction with promethazine and chlorpromazine. Electron transfer mechanisms were further identified via linear sweep voltammetry. Next, adsorption experiments were performed on the graphite screen printed electrodes both with and without potential assistance in order to confirm if the suppression of the cocaine signals is due to passivation induced by the cutting agents or their oxidized products. The proposed strategies allowed us to identify the mechanisms of cocaine suppression for each cutting agent mentioned. Suppression due to procaine and dextromethorphan is caused by fouling of the electrode surface by their oxidized forms, while for chlorpromazine and promethazine the suppression of the cocaine signal is related to the strong adsorption of these (nonoxidized) cutting agents onto the graphite electrode surface. These findings provide fundamental insights in possible suppression and other interfering mechanisms using electrochemistry in general not only in the drug detection sector.

Abstract: When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moire pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moire patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moire pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moire super cell.

Abstract: As landfill mining (LFM) gains public attention, systematic assessment of its economic potential is deemed necessary. The aim of this review is to critically analyze the usefulness and validity of previous economic assessments of LFM. Following the life cycle costing (LCC) framework, (i) the employed methods based on goal and scope, technical parameters and data inventory, and modelling choices were contrasted with respect to (ii) the synthesized main findings based on net profitability and economic performance drivers. Results showed that the selected studies (n=15) are mostly case study-specific and concluded that LFM has a weak economic potential, hinting at the importance of favorable market and regulation settings. However, several method issues are apparent as costs and revenues are accounted at different levels of aggregation, scope and scale-from process to sub-process level, from private to societal economics, and from laboratory to pilot-scale, respectively. Moreover, despite the inherent large uncertainties, more than half of the studies did not perform any uncertainty or sensitivity analyses posing validity issues. Consequently, this also limits the usefulness of results as individual case studies and as a collective, towards a generic understanding of LFM economics. Irrespective of case study-specific or generic aims, this review recommends that future assessments should be learning-oriented. That is, uncovering granular information about what builds up the net profitability of LFM, to be able to systematically determine promising paths for the development of cost-efficient projects.

Abstract: Transmission electron microscopy (TEM) is carried out in vacuum to minimize the interaction of the imaging electrons with gas molecules while passing through the microscope column. Nevertheless, in typical devices, the pressure remains at 10(-7) mbar or above, providing a large number of gas molecules for the electron beam to crack, which can lead to structural changes in the sample. Here, we describe experiments carried out in a modified scanning TEM (STEM) instrument, based on the Nion UltraSTEM 100. In this instrument, the base pressure at the sample is around 2 x 10(-10 )mbar, and can be varied up to 10(-6) mbar through introduction of gases directly into the objective area while maintaining atomic resolution imaging conditions. We show that air leaked into the microscope column during the experiment is efficient in cleaning graphene samples from contamination, but ineffective in damaging the pristine lattice. Our experiments also show that exposure to O(2 )and H2O lead to a similar result, oxygen providing an etching effect nearly twice as efficient as water, presumably due to the two 0 atoms per molecule. H(2 )and N-2 environments have no influence on etching. These results show that the residual gas environment in typical TEM instruments can have a large influence on the observations, and show that chemical etching of carbon-based structures can be effectively carried out with oxygen.