Innovative wastewater treatment based on electrodeposited thin film: Systematic studies of interfacial processes between birnessite 2 and Mn(II) for a better efficiency

International audienceElectrodeposited birnessite thin films have remarkable properties for spontaneous degradation of organic pollutants until mineralization via a complex mechanism of charge transfer reactions. But, birnessite may be transformed into passivated material by reaction with Mn(II) species generated during the reduction of birnessite due to oxidation of organic pollutants. Such modification could imply a possible inhibition of the degradation process, a depreciated condition for future applications. This paper focuses on the determination of the real robustness of electrodeposited birnessite thin films and their quality for innovative wastewater treatment. Systematical studies were performed with solutions containing different Mn(II) concentrations in presence and in absence of oxygen to have unfavorable conditions. Samples were characterized at macroscopic scales (SEM and XRD) in addition to a focused study on the chemical modification at the extreme near surface by XPS. Open circuit potential (OCP) was also followed to complete the study. Similar characterizations were performed after interaction with organic pollutants solutions. As a result, nature and structure of the bulk and the near surface of birnessite stay unchanged after long times even in absence of oxygen or in presence of organic pollutants at high concentrations, proving their very good robustness and real interests for future applications

Evolution of Cu(In,Ga)Se2 surfaces under water immersion monitored by X-ray photoelectron spectroscopy

Proceedings of the 18th European Conference on Applications of Surface and Interface Analysis (ECASIA '19), Dresden, Germany, September 15-20, 2019International audienceCu(In,Ga)Se2 absorbers were immerged in deionized water for different times, and specific chemical evolutions were monitored thanks to X-ray photoemission spectroscopy. Cu(In,Ga)Se2 related dissolution products were studied in water through induced coupled plasma optical emission spectroscopy. From those analyses, specific surface network disorganization was observed, with Cu migration towards the surface, leading to different kinetics of oxidation and dissolution for each element that could be quantified

Stoichiometry loss induced by ionic bombardment of InP surfaces: A challenge for electrochemistry combined with XPS

International audienceIndium phosphide (InP) surfaces are greatly affected by ionic bombardment. We investigate the resulting surface perturbation through the use of the complementary analytical techniques of electrochemistry and X-ray photoelectron spectroscopy (XPS). Following bombardment, modifications to the surface were identified by a reduction in the dark open circuit potential in comparison to the pristine state. Through XPS studies, it was found that the sputtered surface was enriched with a metallic-like In contribution, which oxidized upon exposure to air. Cyclic voltammetry measurements confirmed this observation, with initial cathodic features related to an oxidized metallic In-enriched layer on the InP surface. Repeated cyclic voltammetry experiments resulted in the formation of a more In-rich overlayer due to a specific oxidation/reduction phenomenon. This behavior is very similar to that obtained by cathodic decomposition on InP surfaces

A general route to nanostructured M[V3O8] and M-x[V6O16] (x=1 and 2) and their first evaluation for building enzymatic biosensors

International audienceIn order to develop novel electroactive hosts for biosensor design, the possibility to use nanostructured vanadate phases as alternatives to well-known V2O5 gels was studied. For this purpose, the formation of M[V3O8] and M-x[V6O16] (x = 1 and 2) oxides by the sol-gel process has been studied over a wide range of cations (M+ = Li+, Na+, K+, Cs+, and NH4+; M2+ = Ca2+, Mg2+ and Ba2+). By a combination of XRD, V-51 NMR and SEM studies, it was possible to evidence the influence of the nature and hydration state of cations on the size and morphology of the resulting particles as well as on the kinetics of their formation. On this basis, K-2[V6O16] was evaluated for glucose oxidase encapsulation, either via impregnation or co-precipitation methods. When compared to V2O5, these novel bioelectrodes exhibit higher stability under pH conditions of optimum enzymatic activity, as well as better sensitivity, and reproducibility for glucose detection via amperometric titration

The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers

International audiencePerovskite materials have already proven their ability to reach photo-electric power conversion efficiencies higher than 22% in appropriate devices. If their instability against time could be solved, they could quickly compete with silicon since they benefit from low-cost manufacturing processes. Our work is dedicated to this stability study using the benefit of X-ray Photoelectron Spectroscopy (XPS) as a main tool, and coupled with XRD and SEM-EDX analysis. Using XPS, it is possible to track the surface (10 nm) changes the perovskite undergoes, in terms of both composition and chemical environments, and is therefore efficient towards understanding the first steps of the degradation process. At first, samples of spin-coated thin-film perovskite without capping on the top (glass/ITO/PEDOT:PSS/MAPI), were aged in different conditions (light with air and vacuum respectively), and analyzed using XPS at different times. The figure below presents the survey spectrum obtained for a fresh sample, and shows that all the expected elements can be identified with this spectrometry method. Starting from an initial known composition, the results obtained reveal interesting changes the material undergoes during the ageing. For example, it was observed that both nitrogen and iodine gradually escape the surface, and also, that metallic lead is observed in the final stages of the degradation process. Then, other currently ongoing experiments are designed to highlight the influence of oxygen and light as previously mentioned , but also to disentangle the influence of the bottom layers on the ageing. This will certainly provide other innovative results on the mechanisms governing the perovskite degradation

The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers

International audiencePerovskite materials have already proven their ability to reach photo-electric power conversion efficiencies higher than 22% in appropriate devices. If their instability against time could be solved, they could quickly compete with silicon since they benefit from low-cost manufacturing processes. Our work is dedicated to this stability study using the benefit of X-ray Photoelectron Spectroscopy (XPS) as a main tool, and coupled with XRD and SEM-EDX analysis. Using XPS, it is possible to track the surface (10 nm) changes the perovskite undergoes, in terms of both composition and chemical environments, and is therefore efficient towards understanding the first steps of the degradation process. At first, samples of spin-coated thin-film perovskite without capping on the top (glass/ITO/PEDOT:PSS/MAPI), were aged in different conditions (light with air and vacuum respectively), and analyzed using XPS at different times. The figure below presents the survey spectrum obtained for a fresh sample, and shows that all the expected elements can be identified with this spectrometry method. Starting from an initial known composition, the results obtained reveal interesting changes the material undergoes during the ageing. For example, it was observed that both nitrogen and iodine gradually escape the surface, and also, that metallic lead is observed in the final stages of the degradation process. Then, other currently ongoing experiments are designed to highlight the influence of oxygen and light as previously mentioned , but also to disentangle the influence of the bottom layers on the ageing. This will certainly provide other innovative results on the mechanisms governing the perovskite degradation