Environmental Chemistry Letters最新文献

Abstract

The recovery of pure water and valuable substances from wastewater is a major challenge in the context of the circular economy, requiring advanced separation methods. However, actual membrane separation techniques such as forward osmosis are limited by membrane fouling and selectivity. Here, we synthesized composite membranes by crosslinking polyvinyl alcohol hydrogel, using both glutaraldehyde and borax as crosslinking agents, on top of cellulose ester membranes. We tested these composite membranes on model and real wastewater. Results show that the composite membranes retain ammonium effectively, maintain surface electroneutrality, and exhibit remarkable resistance to fouling by organic and biological contaminants. This is explained by the high hydrophilicity of the membrane surface after application of a hydrogel layer.

The global plastic production has steadily increased from 1.7 million tons in 1950 to over 400 million tons in 2022, with about 60% of plastic ultimately ending up in landfills and oceans. There is also growing evidence that microplastics exert negative effects on biota and ecosystems. Biodegradable plastics may represent a safe alternative, yet their potential adverse effects have not been comprehensively analyzed. Here, we reviewed biodegradable plastics, with focus on their conversion into microplastics, their interactions with pollutants, and their combined toxicity for aquatic biota. Biodegradable plastics include polylactic acid, polyhydroxyalkanoates, polybutylene succinate, poly(butylene adipate-co-terephthalate), and poly(ε-caprolactone). We found that some biobased plastics are hardly biodegradable. Some biobased plastics are compostable but require specific environmental conditions for their biodegradation. Biobased plastics can generate microplastics when released into the environment, which can impact biota. Contrary to the common public belief, biodegradable plastics may not only originate from biosources but can be synthesized from fossil fuels. Microplastics originating from biodegradable plastics can interact with pollutants, adsorbing and transporting these pollutants, resulting in synergistic or antagonistic effects on exposed organisms. Biofilm formation on microplastics impacts their degradation and pollutant interactions.

Metal oxides are used as catalysts in energy and environmental applications. For instance, ruthenium(IV) oxides are oxygen evolution reaction catalysts in water splitting that have been investigated under highly acidic or alkaline conditions. Still, their stability and activity are limited under such harsh conditions. High-valent ruthenium ligand (L) complexes Ru^IV-L and Ru^V-L have been extensively studied for oxygen evolution reaction in non-aqueous environments. The new approach used herein is the combination of two high-valent ruthenium(IV) oxide (Ru^IV) and iron(VI) (Fe^VIO₄²⁻, Fe^VI) that yielded efficient oxygen evolution reaction activity under mild alkaline aqueous conditions, at pH 8.2 and 9.0. The easily available ruthenium(III) ion (Ru^III) reacted with Fe^VI at a molar ratio of 0.25 ([Ru^III]:[Fe^VI]) to produce in situ Ru^IV and unconsumed Fe^VI mixture solution, which had an onset potential around 1.40 V with a shift in onset potential of 260 mV and 150 mV with respect to Ru^III and Fe^VI alone, respectively. The unique mixed solution of Ru^IV-Fe^VI had less resistance to perform the catalytic reaction. Here, we show that combining high-valent ruthenium(IV) oxide and iron(VI) under mild alkaline aqueous conditions exhibits superior performance for oxygen evolution reaction, making it a potential candidate for water splitting reaction.