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.

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its ozonation product, 6PPD-quinone (6PPD-Q), are contaminants of global concern due to their widespread occurrence and acute toxicity to aquatic organisms. Conventional treatment methods often fail to its complete removal in water. Peroxyacetic acid is extensively employed in advanced oxidation processes; however, it relies generally on ultraviolet light irradiation to generate reactive radical species. Here, we demonstrate for the first time that the target pollutant 6PPD-Q reacted with peroxyacetic acid to promote radical amplification and induced its own degradation without external energy input. Batch experiments were conducted under with and without ultraviolet irradiation at nearly neutral pH with varying peroxyacetic acid concentrations. The reaction of 6PPD-Q with peroxyacetic acid promoted radical amplification via electron transfer and semiquinone radicals formation, enabling 6PPD-Q degradation with more than 70

Persistent free radicals (PFRs) derived from the abiotic transformation of polycyclic aromatic hydrocarbons (PAHs) have been well documented as emerging contaminants, yet the formation and the role of PFRs in biodegradation process is unknown. Herein, the potential generation of PFRs and reactive oxygen species like O2•-, H2O2, and •OH, as well as their possible effects in the biodegradation of anthracene by Ochrobactrum sp. strain B01 were investigated systematically. Results unexpectedly showed that PFRs were formed in amounts rising from 1 to 3 d and reaching an equilibrium, consistent with the biodegradation trend of anthracene. Meanwhile, PFRs induced the formation of O2•- and H2O2, rather than •OH, enhanced antioxidant enzyme activities, and inhibited microbial abundance, inducing cytotoxic effects. Scavenger trapping experiments revealed that the cytotoxicity was mainly due to the ROS, which injured the cell wall and cause the inactivation of bacteria, thus inhibiting the biodegradation of anthracene by Ochrobactrum. Overall, these findings uncovered that the intrinsic mechanism of the difficulty in PAHs microbial biodegradation may be due to the production of PFRs, which is helpful in designing and optimizing more effective bioremediation technologies to remediate PAHs in soils.

CH4 emissions from agricultural activities in response to anticipated climate changes, such as elevated temperature (warming) and elevated CO2 levels (eCO2), remain highly uncertain. In this study, warming, eCO2, and their combined effects were simulated using open-top chambers to elucidate the underlying mechanisms regulating CH4 emission potential from paddy soils. We found that single or combined warming and eCO2 uniformly reduced CH4 emission potential, decreased by 17.0 to 32.7%. A suite of complementary analyses, including carbon isotopic tracing, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and microbial metagenomic and metabolomic profiling, were conducted to uncover the underlying mechanisms. We discovered only a marginal change of microbial community, metabolism and dead residuals (microbial necromass carbon). In comparison, CH4 production was primarily mediated by shift in dissolved organic matter (DOM) molecular composition. An increase of lignin-like compounds combined with a decrease of carbohydrate explained the changes in CH4 production. Variance partition analysis and structural equation model also evidenced the importance of DOM molecular composition rather than microbial traits on regulating CH4 production. This study highlights an important role of DOM chemical stability in regulating CH4 emissions in a changing world.

Just turning off the tap does not empty the bathtub, the bottom plug has to be opened. Similarly, just switching slowly from fossil to renewable energies will not stop in time the accumulation of huge amounts of greenhouse gases in the atmosphere. Among these gases, carbon dioxide will impact adversely all society and the planet. Indeed, natural processes are able to store carbon in terrestrial and marine environments, yet at a too slow rate compared to carbon dioxide emissions, promoting carbon dioxide accumulation in the atmosphere. Therefore, there is an urgent need to accelerate natural carbon storage to maintain the planet temperature 1.5–2.0 °C above the pre-industrial era. Thus, negative emission technologies should be developed and tested quickly. While these interventions are still debated due to possible negative effects, humans will not have another choice to avoid unprecedented changes in the Earth system. Here, we discuss ocean iron fertilization as a feasible, large-scale technique to increase atmospheric CO2 capture and sequester carbon in the deep sea from decades to thousands of years.

Traditional urea production methods, primarily the Haber-Bosch and Bosch-Meiser processes, consume substantial amounts of energy and have significant environmental impacts, calling for more sustainable alternatives. Alternatively, photoelectrocatalytic (PEC) urea synthesis utilizes sunlight and electrochemistry to facilitate C-N coupling reactions under mild, environmentally friendly conditions. This review focuses on the recent progress in electrocatalytic, photocatalytic, and photoelectrocatalytic urea synthesis, with a focus on methodology, technological constraints and innovations. Key limitations include low Faradaic efficiencies, restricted catalytic selectivity and mechanistic understanding, and suboptimal charge-transfer processes. We discuss the potential of several photo-electroactive constructions, and quantification methodologies, highlighting a need for standardized testing protocols. Economic aspects of the technology are also discussed, with focus on the industrial feasibility of green urea production. Although PEC synthesis offers notable benefits over conventional methods, it still faces challenges, including catalyst durability, high energy consumption, and limited scalability. This review provides strategies to overcome these challenges and advance PEC urea synthesis toward real-world implementation in sustainable fertilizer manufacturing.

Photocatalysis research has evolved towards increasingly sophisticated structural regulation and material design. The synergistic enhancement of photocatalysis by multi-component semiconductors and biochar warrants detailed investigation. This study introduces an innovative biochar-based g-C3N4/Bi2WO6/Ag3PO4 nanocomposite (CN/Bi/Ag@ACB), which was applied to the efficient removal of antibiotic pollutants represented by tetracycline (TC). Findings reveal that CN/Bi/Ag@ACB forms a double Z-scheme heterojunction, significantly reducing photogenerated carrier recombination. It absorbs light in the 200-800 nm range, with a band gap of 1.91 eV. Under 120 min of illumination, the composite nearly completely removed 50 mg·L-1 of TC, achieving a removal rate of 0.0351 min-1, which is 8.56-13.50 times higher than that of the individual semiconductors. In real wastewater, TC removal exceeded 85.95%, with concurrent removal of other antibiotics, and achieved 99% sterilization of E. coli and S. aureus within 48 hours. The catalytic system was predominantly driven by ·O2-, h+, and ·OH radicals. The unique structure and surface characteristics of the composite, along with the incorporation of heteroatoms, substantially enhance photocatalytic activity. The TC degradation process is associated with the conversion of fulvic and humic acids, with three potential degradation pathways proposed. This study elucidates the synergistic mechanisms of photocatalysis enhancement by multi-component semiconductors and biochar.

Wetlands are essential carbon (C) reservoirs, crucial for climate change mitigation, but their hydrological regimes are increasingly threatened by climate change. Inundation depth, a key hydrological factor in wetlands, influences Soil Organic Carbon (SOC) storage and stability, yet its effects on SOC fractions and stability, especially in subsoils, remain critically underexplored. This study investigated the impact of inundation depth on SOC in the topsoil (0-20 cm) and subsoil (20-40 cm) over a 6-year field experiment. As the inundation depth increased from 0 cm to 40 cm, SOC content increased significantly by 62% in the topsoil and by 222% in the subsoil. Particulate Organic C (POC) and Mineral-Associated Organic C (MAOC) responded differently across soil layers, with topsoil POC driven by plant inputs and MAOC by microbial turnover, while subsoil POC and MAOC were influenced by nutrient availability and mineral protection, respectively. Inundation depth increased the subsoil SOC stability but did not affect topsoil stability, where key mineral protection capacity (i.e., clay and free/amorphous Fe/Al oxides) remained unaltered. In the subsoil, both microbial biomass and mineral protection jointly enhanced SOC stability. We identified 20 cm inundation depth as an operational benchmark where SOC accumulation reaches a saturation plateau. This suggests that, within hydrologically managed restoration settings in the Yellow River Delta, maintaining moderate inundation around this depth may help maximize SOC storage, whereas deeper inundation did not provide additional SOC gains. Collectively, these findings advance our mechanistic understanding of depth-dependent carbon dynamics and provide a practical reference for sitelevel hydrological regulation, although the applicability of this threshold to other wetlands requires further validation.

Bromate, a carcinogenic disinfection byproduct, threatens water safety due to its persistence and health risks. Although microbial reduction of bromate is a sustainable remediation approach, its efficiency is often hampered by the common co-contamination of nitrate. We addressed this issue by generating palladium nanoparticles (PdNPs) in situ within the biofilm matrix of a membrane biofilm reactor (MBfR), creating a Pd-MBfR. Co-reduction of bromate and nitrate by the Pd-MBfR was investigated in terms of bromate removal, reduction kinetics, and microbial functions. To evaluate the impact of catalytic hydrogenation, a non-palladized MBfR was operated in parallel. Continuous operation over 125 days demonstrated that the Pd-MBfR reduced bromate concentration (4 mg·L-1) up to 70 %, versus 30 % for the conventional MBfR under competitive nitrate or nitrite conditions. Kinetic modeling revealed that extracellular Pd-catalyzed bromate reduction diverted approximately18 % of bromate flux from intracellular NADH-dependent pathways, while biogenic PdNPs rapidly scavenged nitrite via catalytic hydrogenation, diverting 39 % of intracellular electron flux from denitrification to extracellular catalytic reduction. Under nitrate stress, biofilms in the Pd-MBfR maintained syntrophic interactions between bromate-reducing bacteria Dechloromonas and homoacetogens Acetobacterium, whereas the conventional MBfR favored autotrophic denitrifiers Hydrogenophaga and Rhodoblastus that prioritized nitrate reduction. Functional-gene profiling confirms that the intracellular electron flow from hydrogen to NADH-dependent denitrification reductases was displaced by extracellular Pd-catalyzed hydrogenation. This diversion of electron flow enhanced bromate reduction in biofilms coupled with PdNPs by minimizing competition for intracellular NADH.

About 10 million tons of waste rubber are generated annually in China, which has caused potential environmental pollution and resource waste due to improper disposal. In the circular economy context, there is a need for methods to make rubber waste into valuable carbon materials. Here, we report a simple acid-assisted hydrothermal process for the first time to convert nitrile gloves into value-added carbon quantum dots (CQDs), and their use in ink-writing hydrogels. The product yield of CQDs is 36 % under optimized conditions, surpassing previously reported results of CQDs derived from plastics. Moreover, the CQDs exhibit high fluorescence stability from pH 2-7, under ultraviolet irradiation during 3 h, and treated by H2O2 at concentrations of 0-500 mu mol/L. CQDs were near-spherical with an average particle size of 2.45 nm and the lattice fringe spacing measured at 0.21 nm. The oxygen-containing groups on the surface of CQDs endowed them high hydrophilicity and excitation-dependent fluorescence behavior with a quantum yield of 9.7 % and a lifetime of 6.94 ns. Given their favorable fluorescence and hydrophilic properties, the direct ink-writing hydrogels prepared with CQDs and polyvinyl alcohol display unique patterns on polyethylene terephthalate (PET) substrates, exhibiting high dimensional accuracy and the ability to show fluorescent colors.

Photocatalysis has been widely used to address the environmental issues and energy crises that threaten the future of planet Earth. One of the main drawbacks to developing photocatalysts for practical applications is the electron–hole recombination concept, which seriously hinders the photoreaction rate. To resolve this, heterojunctions with different patterns, including Z and S schemes, showed great potential to enhance photoactivity and thus attracted increasing attention. Herein, we concisely reviewed recent progress in various types of such systems, focusing on the mechanistic understanding of clean energy and environmental applications. The principles of constructions based on optoelectronic properties and semiconducting behavior are comprehensively discussed. The advantages and disadvantages of each system are also considered to make a logical conclusion and inspirational perspectives.