Multivariate Bayesian Optimization of CoO Nanoparticles for CO2 Hydrogenation Catalysis.

The hydrogenation of CO2 holds promise for transforming the production of renewable fuels and chemicals. However, the challenge lies in developing robust and selective catalysts for this process. Transition metal oxide catalysts, particularly cobalt oxide, have shown potential for CO2 hydrogenation, with performance heavily reliant on crystal phase and morphology. Achieving precise control over these catalyst attributes through colloidal nanoparticle synthesis could pave the way for catalyst and process advancement. Yet, navigating the complexities of colloidal nanoparticle syntheses, governed by numerous input variables, poses a significant challenge in systematically controlling resultant catalyst features. We present a multivariate Bayesian optimization, coupled with a data-driven classifier, to map the synthetic design space for colloidal CoO nanoparticles and simultaneously optimize them for multiple catalytically relevant features within a target crystalline phase. The optimized experimental conditions yielded small, phase-pure rock salt CoO nanoparticles of uniform size and shape. These optimized nanoparticles were then supported on SiO2 and assessed for thermocatalytic CO2 hydrogenation against larger, polydisperse CoO nanoparticles on SiO2 and a conventionally prepared catalyst. The optimized CoO/SiO2 catalyst consistently exhibited higher activity and CH4 selectivity (ca. 98%) across various pretreatment reduction temperatures as compared to the other catalysts. This remarkable performance was attributed to particle stability and consistent H* surface coverage, even after undergoing the highest temperature reduction, achieving a more stable catalytic species that resists sintering and carbon occlusion.

The surface chemistry of ionic liquid-treated CsPbBr3 quantum dots.

The power conversion efficiencies of lead halide perovskite thin film solar cells have surged in the short time since their inception. Compounds, such as ionic liquids (ILs), have been explored as chemical additives and interface modifiers in perovskite solar cells, contributing to the rapid increase in cell efficiencies. However, due to the small surface area-to-volume ratio of the large grained polycrystalline halide perovskite films, an atomistic understanding of the interaction between ILs and perovskite surfaces is limited. Here, we use quantum dots (QDs) to study the coordinative surface interaction between phosphonium-based ILs and CsPbBr3. When native oleylammonium oleate ligands are exchanged off the QD surface with the phosphonium cation as well as the IL anion, a threefold increase in photoluminescent quantum yield of as-synthesized QDs is observed. The CsPbBr3 QD structure, shape, and size remain unchanged after ligand exchange, indicating only a surface ligand interaction at approximately equimolar additions of the IL. Increased concentrations of the IL lead to a disadvantageous phase change and a concomitant decrease in photoluminescent quantum yields. Valuable information regarding the coordinative interaction between certain ILs and lead halide perovskites has been elucidated and can be used for informed pairing of beneficial combinations of IL cations and anions.

Formation Pathway of Wurtzite-like Cu2ZnSnSe4 Nanocrystals.

Cu2ZnSnSe4 is a direct band gap semiconductor composed of earth-abundant elements, making it an attractive material for thin-film photovoltaic technologies. Cu2ZnSnSe4 crystallizes in the kesterite structure type as a bulk material, but it can also crystallize in a metastable wurtzite-like crystal structure when synthesized on the nanoscale. The wurtzite-like polymorph introduces unique and useful properties to Cu2ZnSnSe4 materials, including widely tunable band gaps and superior compositional flexibility as compared to kesterite Cu2ZnSnSe4. Here, we investigate the formation pathway of colloidally prepared wurtzite-like Cu2ZnSnSe4 nanocrystals. We show that this quaternary material forms through a chain of reactions, starting with binary Cu3Se2 nanocrystals that, due to both kinetic and thermodynamic reasons, preferentially react with tin to yield hexagonal copper tin selenide intermediates. These ternary intermediates then react with zinc to form the resulting wurtzite-like Cu2ZnSnSe4 nanocrystals. Based on this formation pathway, we suggest synthetic methods that may prevent the formation of unwanted impurity phases that are known to hamper the efficiency of Cu2ZnSnSe4-based optoelectronic devices.

Interspecific and environment-induced variation in hypoxia tolerance in sunfish.

Hypoxia tolerance is a plastic trait, and can vary between species. We compared hypoxia tolerance (hypoxic loss of equilibrium, LOE, and critical O2 tension, Pcrit) and traits that dictate O2 transport and metabolism in pumpkinseed (Lepomis gibbosus), bluegill (L. macrochirus), and the naturally occurring hybrid in different acclimation environments (wild versus lab-acclimated fish) and at different temperatures. Wild fish generally had lower Pcrit and lower PO2 at LOE in progressive hypoxia than lab-acclimated fish, but time to LOE in sustained hypoxia (PO2 of 2kPa) did not vary between environments. Wild fish also had greater gill surface area and higher haematocrit, suggesting that increased O2 transport capacity underlies the environmental variation in Pcrit. Metabolic (lactate dehydrogenase, LDH; pyruvate kinase, PK; citrate synthase; cytochrome c oxidase) and antioxidant (catalase and superoxide dismutase) enzyme activities varied appreciably between environments. Wild fish had higher protein contents across tissues and higher activities of LDH in heart, PK in brain, and catalase in brain, liver, and skeletal muscle. Otherwise, wild fish had lower activities for most enzymes. Warming temperature from 15 to 25°C increased O2 consumption rate, Pcrit, PO2 at LOE, and haemoglobin-O2 affinity, and decreased time to LOE, but pumpkinseed had ≥2-fold longer time to LOE than bluegill and hybrids across this temperature range. This was associated with higher LDH activities in the heart and muscle, and lower or similar antioxidant enzyme activities in several tissues. However, the greater hypoxia tolerance of pumpkinseed collapsed at 28°C, demonstrating that the interactive effects of hypoxia and warming temperature can differ between species. Overall, distinct mechanisms appear to underpin interspecific and environment-induced variation in hypoxia tolerance in sunfish.

Physiological tradeoffs may underlie the evolution of hypoxia tolerance and exercise performance in sunfish (Centrarchidae).

Tradeoffs between hypoxia tolerance and aerobic exercise performance appear to exist in some fish taxa, even though both of these traits are often associated with a high O2 transport capacity. We examined the physiological basis for this potential tradeoff in four species of sunfish from the family Centrarchidae. Hypoxia tolerance was greatest in rock bass, intermediate in pumpkinseed and bluegill and lowest in largemouth bass, based on measurements of critical O2 tension (Pcrit) and O2 tension at loss of equilibrium (PO2 at LOE). Consistent with there being a tradeoff between hypoxia tolerance and aerobic exercise capacity, the least hypoxia-tolerant species had the highest critical swimming speed (Ucrit) during normoxia and suffered the greatest decrease in Ucrit in hypoxia. There was also a positive correlation between Ucrit in normoxia and PO2 at LOE, which remained significant after accounting for phylogeny using phylogenetically independent contrasts. Several sub-organismal traits appeared to contribute to both hypoxia tolerance and aerobic exercise capacity (reflected by traits that were highest in both rock bass and largemouth bass), such as the gas-exchange surface area of the gills, the pH sensitivity of haemoglobin-O2 affinity, and the activities of lactate dehydrogenase and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase in the liver. Some other sub-organismal traits were uniquely associated with either hypoxia tolerance (low sensitivity of haemoglobin-O2 affinity to organic phosphates, high pyruvate kinase and lactate dehydrogenase activities in the heart) or aerobic exercise capacity (capillarity and fibre size of the axial swimming muscle). Therefore, the cumulative influence of a variety of respiratory and metabolic traits can result in physiological tradeoffs associated with the evolution of hypoxia tolerance and aerobic exercise performance in fish.