In most countries, arsenic (As) and antimony (Sb) are regulated pollutants, due to their significant impacts on the environment and human health. Iron-based (Fe) coagulants play a fundamental role in the removal of both elements from aqueous media. This study aims to investigate the competitive removal of As and Sb in relation to Fe solubility. Coagulation experiments were conducted in synthetic water under various pH and contaminant loading, using ferric chloride (FC) as a coagulant. In the single system, the pentavalent species significantly reduced the Fe solubility and thereby enhanced the mobility of As and Sb under these environmental conditions. The coexistence of pentavalent and trivalent species in the binary system considerably decreases the Fe solubility at acidic conditions while enhancing the dissolution under alkaline conditions, thus affecting the overall removal of both species. The presence of four redox species in the quaternary system decreases the Fe solubility remarkably over a wide pH range, with better Sb removal, as compared to As under similar conditions. The adsorption study of the single system showed a decrease in As(V) adsorption capacity at higher concentration, while in the binary system, the Sb(III) showed strong adsorption potential, compared to other species. In the quaternary system, the presence of all four redox species has a synergistic effect on total Sb adsorption, in comparison to the total As. Furthermore, the results of Fourier transform infrared (FT-IR) analysis of FC composite contaminant flocs confirm that the combined effect of charge neutralization and inner sphere complexation might be a possible removal mechanism. These findings may facilitate the fate, transport and comparative removal of redox species in the heterogeneous aquatic environment.

The Awash river basin has been the most extensively developed and used river basin in Ethiopia since modern agriculture was introduced. This paper investigated the annual precipitation, temperature, and river discharge variability using the innovative trend analysis method (ITAM), Mann–Kendall (MK) test, and Sen’s slope estimator test. The results showed that the trend of annual precipitation was significantly increasing in Fitche (Z = 0.82) and Gewane (Z = 0.80), whereas the trend in Bui (Z = 69) was slightly decreasing and the trend in Sekoru (Z = 0.45) was sharply decreasing. As far as temperature trends were concerned, a statistically significant increasing trend was observed in Fitche (Z = 3.77), Bui (Z = 4.84), and Gewane (Z = 5.59). However, the trend in Sekoru (Z = 1.37) was decreasing with statistical significance. The discharge in the study basin showed a decreasing trend during the study period. Generally, the increasing and decreasing levels of precipitation, temperature, and discharge across the stations in this study indicate the change in trends. The results of this study could help researchers, policymakers, and water resources managers to understand the variability of precipitation, temperature, and river discharge over the study basin.

The extensive emission of CO2 into the atmosphere due to the burning of fossil fuels has urged many countries to move toward decarbonized energy. Based on the concept of carbon neutrality, the European Union Emissions Trading System implemented the aviation carbon tax (ACT), which stimulated the rapid transformation in aviation fuels. To cope with the ACT and mitigate the CO2 emissions from the aviation industry, here, we present a promising route for the synthesis of precursors such as aromatics, alkyl benzenes, and naphthenes, which account for 40–50 vol % fraction of the kerosene-based aviation fuel, from waste CO2 or biomass-derived syngas. The ultra-high selectivity of single-ring aromatics (precursors for the kerosene-based aviation fuel) with a selective range of carbon chain numbers (C8–C12) was achieved (>80% in hydrocarbons at a reaction temperature of 275 °C) via the catalytic hydrogenation of CO2 or CO over a bifunctional catalyst (nano-sized ZnCr2O4/Sbx-H-ZSM-5). In situ diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, gas chromatography–mass spectrometry, and reaction analysis revealed that the product distribution was controlled by thermodynamics and the formation of the aromatics followed an “aldol–aromatic” mechanism. The high selectivity of aromatics at the low reaction temperature (i.e., 275 °C) was attributed to the catalyst topology, the closed carbon chain aromatization reaction, and the presence of highly active oxygenated species in the hydrocarbon pool. For the first time, an asymmetric desorption behavior between the active oxygenate species and aromatic hydrocarbons over the ZnCr2O4/Sbx-H-ZSM-5 catalyst is reported with the help of integrated differential phase contrast scanning transmission electron microscopy, which made the reaction highly selective toward aromatics. This strategy gives a carbon-neutral route for the synthesis of kerosene-based aviation fuel precursors and will reduce the burden of the carbon tax on the aviation industry.

The cobalt single atoms supported on N-doped carbon (Co SAs/ NC) were prepared by the direct pyrolysis of metal−organic framework (MOF) precursor. Compared with Co nanoparticle (NP) catalysts prepared by impregnation, the Co SAs/NC catalyst showed a much better performance in the selective hydrogenation of nitrobenzene, giving a specific activity 5.4 and 32.0 times higher than those of Co NPs supported on N-doped carbon and active carbon, respectively. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure (XAFS), X-ray photoelectron spectra (XPS), N 2 adsorption−desorption isotherms, and X-ray diffraction (XRD) characterizations revealed that the atomically dispersed Co species and doped nitrogen atoms in carbon support contributed to the high activity of Co SAs/NC. The reaction rate and aniline selectivity were further remarkably enhanced by introducing water into the reaction system. By adding 30% water to the solvent of ethanol, the activity was increased from 43.2 to 76.8 h −1 and the aniline selectivity was increased from 62.8 to 99.1%. Combining experimental results and density functional theory (DFT) calculations evidenced that the promoting effect of water addition was attributed to its differentiating ability in the competitive adsorption between nitrobenzene and aniline in the hydrogenation reaction. This catalytic system was highly efficient for the selective hydrogenation of various nitroarenes.

Selectivity control in the single-step conversion of syngas to a single aromatic product is a big challenge. Here, we report an aldol-aromatic mechanism composed of aldol, phenolic, and aromatic cycles, that gave high selectivity >70% of a single product, tetramethylbenzene (TeMB) in hydrocarbons, at a reaction temperature as low as 275 °C. We evidently found the existence of oxygenated-aromatic compounds in the carbon pool, which remained active throughout the reaction and acted as key intermediates for the formation of the aromatics. The physical contact of ZnCr 2 O 4 with H-ZSM-5 exhibited a strong coupling effect that promoted surface diffusion of C 1 oxygenates (i.e., formaldehyde and methanol) from ZnCr 2 O 4 into H-ZSM-5 and transformed into aromatics via an aldol-aromatic reaction pathway, thus overcoming the most difficult step for first carbon−carbon bond formation. In addition, ZnCr 2 O 4 promoted the aromatics desorption by lowering the desorption activation energy and prevented the oversaturation of carbon pool species. Furthermore, it was found that a combination of thermodynamic equilibrium, surface methylation, and static repulsion are the key factors for giving high selectivity of TeMB in both carbon pool and final aromatics. This aldol-aromatic mechanism will open an efficient reaction pathway to upscale the process for selective aromatic synthesis in high yield from syngas.