Environmental Chemistry Letters最新文献

Aviation is a major contributor to greenhouse gas emissions, and thus developing renewable alternatives such as lignin-derived biofuels is critical. Current catalytic routes for hydrodeoxygenation of bio-oil model compounds, such as isoeugenol, fail to produce the desired aromatics to cycloalkane ratios required for aviation fuels. We hypothesized that tailoring metal-support interactions in a nickel aluminate spinel catalyst can enable selective formation of hydrocarbon blends meeting fuel specifications. Hydrodeoxygenation of isoeugenol was conducted in a batch reactor using a nickel aluminate spinel catalyst synthesized via a one-pot sol-gel method. Reactions were conducted at 250–300 °C and 20–40 bar hydrogen pressure, and products were analyzed by gas chromatography-mass spectrometry to determine yields of aromatics, cycloalkanes, and intermediates. Catalyst structure and surface properties were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and electron microscopy to establish structure–performance relationships. Under optimized conditions of 275 °C at 20 bar H₂, aromatic and cycloalkane yields reached 16 wt% and 30 wt%, respectively. Reaction trends showed that elevated temperatures favor cycloalkane formation while hydrogen pressure controls intermediate conversion. The moderate Lewis acidity combined with medium-sized Ni⁰ crystallites promote selective hydrogenation and deoxygenation while minimizing over-hydrogenation. This catalytic system produces fuel-grade hydrocarbon mixtures in a single step, exceeding previously reported performance. These findings provide a practical route for lignin valorization and the production of renewable aviation fuels with reduced greenhouse gas emissions.

The carbon dioxide radical anion, CO₂^●−, is a highly reactive radical species involved in the reduction of the CO₂ greenhouse gas, organic synthesis, atmospheric aerosol chemistry, and treatment of halogenated compounds. In recent years, CO₂^●− has emerged as a strong reductant, or single electron donor. Here we present techniques used to generate CO₂^●− and we discuss applications to degrading pollutants such as halogenated alkanes. The potential occurrence of such reductions in water and aqueous aerosols is discussed, notably for the degradation of perfluoroalkyl substances. In the laboratory, CO₂^●− is directly generated by either direct electrochemical reduction of CO₂ or hydrogen atom transfer of either formate salts with and without catalysts or ferrioxalate through photochemical or radiolytic processes. The CO₂^●− has an ultraviolet spectrum, and CO₂^●− vibration modes are characterized by fast kinetics using infrared and Raman spectroscopy. The second-order rate constants of the reactions of CO₂^●− with halogenated alkanes, of -1.84 ± 0.22 V, are generally slower than that of the hydrated electron, of -2.87 V, and give a negative linear relationship with energy of lower unoccupied molecular orbital, suggesting single electron transfer mechanism in reducing the halogenated compounds.

Per- and polyfluoroalkyl substances, often named ‘forever pollutants’ due to their persistence and very low biodegradability, are contaminating many water sources worldwide, and represent a major health issue because most water treatment plants are not designed to remove these pollutants. Here we review the advantages and disadvantages of removal methods, and we explain how to choose an optimal method. We also compare contamination of drinking water sources and industrial effluents. Removal methods include carbon adsorption, ion-exchange, and reverse osmosis. Filtration-adsorption on granular activated carbon appears as a cheap and efficient method, yet short-chain per- and polyfluoroalkyl substances are little or no retained by the adsorbent. Ion exchange is efficient, and the resins can be regenerated, yet this method highly depends on water composition because the efficiency may be decreased by adsorption competition with other substances. Reverse osmosis is the most effective treatment, yet it is energy intensive. The three methods display other problems such as the disposal of the waste produced.

Antimicrobial resistance caused by antibiotic contamination is a major health issue, yet the mechanisms of antibiotic diffusion are poorly known, notably in the presence of colloids. Here we studied the movement of norfloxacin mixed with pyrogenic carbon colloids through sand columns with 50 v% or 100 v% water saturation, at acidic pH of 4.2, neutral pH of 7.4, and alkaline pH of 10.5, using batch adsorption, column transport, and colloid stability analyses based on particle size and zeta potential. Prior to injection, pyrogenic carbon colloids were pre-equilibrated with 1 and 15 mg/L norfloxacin solutions. Results show that, at acidic pH, norfloxacin and pyrogenic carbon colloids were retained in the column, possibly by colloid aggregation due to reduced surface charge. At neutral pH and 1 mg/L norfloxacin, all norfloxacin passed through the column in the form of colloid-bound norfloxacin, with a mass recovery of 102.0 w% norfloxacin in the effluent. By contrast, at 15 mg/L norfloxacin, most colloid-bound norfloxacin was retained in the column, and only 1.9 w% of norfloxacin was recovered in the effluent. At alkaline pH, carbon colloids and norfloxacin were co-transported, as a possible result of electrostatic repulsion. Water saturation had no effect on the transport behavior.