TY - JOUR A1 - Getenet, M. A1 - Otálora, F. A1 - Emmerling, Franziska A1 - Al-Sabbagh, Dominik A1 - García-Ruiz, J. M. T1 - Mineral precipitation and hydrochemical evolution through evaporitic processes in soda brines (East African Rift Valley) JF - Chemical geology N2 - Soda lakes of the East African Rift Valley are hyperalkaline, hypersaline lakes extremely enriched in Na+, K+, Cl−, CO32−, HCO3−, and SiO2. In this paper, we investigate the chemical evolution in these lakes and the production of chemical sediments by salt precipitation via evaporation. Water samples from tributary springs and three lakes (Magadi, Nasikie Engida and Natron) have been experimentally studied by in-situ X-ray diffraction during evaporation experiments to characterize the sequence of mineral precipitation. These data are complemented by ex-situ diffraction studies, chemical analyses and thermodynamic hydrochemical calculations producing detailed information on the activity of all solution species and the saturation state of all minerals potentially generated by the given composition. Major minerals precipitating from these samples are sodium carbonates/bicarbonates as well as halite. The CO3/HCO3 ratio, controlled by pH, is the main factor defining the Na‑carbonates precipitation sequence: in lake brines where CO3/HCO3 > 1, trona precipitates first whereas in hot springs, where CO3/HCO3 ≪ 1, nahcolite precipitates instead of trona, which forms later via partial dissolution of nahcolite. Precipitation of nahcolite is possible only at lower pH values (pCO2 higher than −2.7) explaining the distribution of trona and nahcolite in current lakes and the stratigraphic sequences. Later, during evaporation, thermonatrite precipitates, normally at the same time as halite, at a very high pH (>11.2) after significant depletion of HCO3− due to trona precipitation. The precipitation of these soluble minerals increases the pH of the brine and is the main factor contributing to the hyperalkaline and hypersaline character of the lakes. Villiaumite, sylvite, alkaline earth carbonates, fluorapatite and silica are also predicted to precipitate, but most of them have not been observed in evaporation experiments, either because of the small amount of precipitates produced, kinetic effects delaying the nucleation of some phases, or by biologically induced effects in the lake chemistry that are not considered in our calculations. Even in these cases, the chemical composition in the corresponding ions allows for discussion on their accumulation and the eventual precipitation of these phases. The coupling of in-situ and ex-situ experiments and geochemical modelling is key to understanding the hydrogeochemical and hydroclimatic conditions of soda lakes, evaporite settings, and potentially soda oceans of early Earth and other extraterrestrial bodies. KW - Crystallization sequence KW - Hydrochemical evolution KW - Alkaline brines KW - Sodium carbonate minerals KW - Soda lakes KW - Evaporite deposits PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-568431 DO - https://doi.org/10.1016/j.chemgeo.2022.121222 SN - 0009-2541 VL - 616 SP - 1 EP - 13 PB - Elsevier CY - New York, NY AN - OPUS4-56843 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pérez Blanes, H. A1 - Ghiasi, P. A1 - Sandkühler, J. A1 - Yesilcicek, Yasemin A1 - Pentzien, Simone A1 - Conradi, Andrea A1 - Prinz, Carsten A1 - Al-Sabbagh, Dominik A1 - Thünemann, Andreas A1 - Ozcan, Ozlem A1 - Witt, Julia T1 - High CO2 reduction activity on AlCrCoCuFeNi multi-principal element alloy nanoparticle electrocatalysts prepared by means of pulsed laser ablation JF - Journal of Materials Research and Technology N2 - Noble metal-free nanoparticles (NPs) based on multi-principal element alloys (MPEAs) were synthesized using a one-step pulsed laser ablation in liquids (PLALs) method for the electrochemical reduction of CO2. Laser ablation was performed in pure water or poly-(diallyldimethylammonium chloride) (PDADMAC)-containing an aqueous solution of Al8Cr17Co17Cu8Fe17Ni33 MPEA targets. Transmission electron microscopy (TEM) measurements combined with energy dispersive X-ray (EDX) mapping were used to characterize the structure and composition of the laser-generated MPEA nanoparticles (MPEA-NPs). These results confirmed the presence of a characteristic elemental distribution of a core-shell phase structure as the predominant NP species. The electrocatalytic performance of the laser-generated MPEA-NPs was characterized by linear sweep voltammetry (LSV) demonstrating an enhanced electrocatalytic CO2 activity for PDADMAC-stabilized NPs. The findings of these investigations indicate that MPEAs have great potential to replace conventional, expensive noble metal electrocatalysts. KW - Multi-principal element alloys KW - Chemically Complex Materials KW - CCMat KW - Electrocatalysis KW - Carbon dioxide reduction KW - Pulsed laser ablation PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-594018 DO - https://doi.org/10.1016/j.jmrt.2023.05.143 VL - 24 SP - 9434 EP - 9440 PB - Elsevier BV AN - OPUS4-59401 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pérez Blanes, H. A1 - Ghiasi, Pouria A1 - Sandkühler, J. A1 - Yesilcicek, Yasemin A1 - Pentzien, Simone A1 - Conradi, Andrea A1 - Prinz, Carsten A1 - Al-Sabbagh, Dominik A1 - Thünemann, Andreas A1 - Özcan Sandikcioglu, Özlem A1 - Witt, Julia T1 - High CO2 reduction activity on AlCrCoCuFeNi multi-principal element alloy nanoparticle electrocatalysts prepared by means of pulsed laser ablation JF - Journal of Materials Research and Technology N2 - Noble metal-free nanoparticles (NPs) based on multi-principal element alloys (MPEAs) were synthesized using a one-step pulsed laser ablation in liquids (PLALs) method for the electrochemical reduction of CO2. Laser ablation was performed in pure water or poly-(diallyldimethylammonium chloride) (PDADMAC)-containing an aqueous solution of Al8Cr17Co17Cu8Fe17Ni33 MPEA targets. Transmission electron microscopy (TEM) measurements combined with energy dispersive X-ray (EDX) mapping were used to characterize the structure and composition of the laser-generated MPEA nanoparticles (MPEA-NPs). These results confirmed the presence of a characteristic elemental distribution of a core-shell phase structure as the predominant NP species. The electrocatalytic performance of the laser-generated MPEA-NPs was characterized by linear sweep voltammetry (LSV) demonstrating an enhanced electrocatalytic CO2 activity for PDADMAC-stabilized NPs. The findings of these investigations indicate that MPEAs have great potential to replace conventional, expensive noble metal electrocatalysts. KW - Metals and Alloys KW - Surfaces KW - Biomaterials KW - Ceramics and Composites KW - Coatings and Films PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-588218 DO - https://doi.org/10.1016/j.jmrt.2023.05.143 SN - 2238-7854 VL - 24 SP - 9434 EP - 9440 PB - Elsevier B.V. AN - OPUS4-58821 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -