Search Results (279)

Electrocatalytic CO₂ reduction reaction (CO₂RR) to ethylene (C₂H₄) has emerged as a promising approach for converting CO₂ into valuable chemicals while utilizing renewable electricity. To facilitate the commercialization of this technology, a process-level techno-economic assessment (TEA) is constructed for a plant producing 100 tons/day of C₂H₄ from coal-power flue gas CO₂ using a membrane electrode assembly (MEA) electrolyzer and downstream gas separations. The model integrates (i) flue gas CO₂ capture by chemical absorption, (ii) CO₂RR to C₂H₄ with H₂ as the only co-product, and (iii) cathode off-gas separation by pressure swing adsorption (PSA) plus anode off-gas CO₂ recovery and recycle. A Cu₁₀–Sn catalyst measured in an H-cell is projected to MEA operation by scaling current density by 10×, yielding a “Case Study in This Article” scenario of j = 246 mA·cm⁻² and FE(C₂H₄) = 48.74%. Under this scenario, the total cost is 592.61 thousand USD/day (5926 USD/ton), dominated by electricity (39.8%). Scenario analysis shows that the total cost can decrease to 76,755.0 USD/day (767.6 USD/ton) under a future-outlook case with improved electrolyzer performance and low-cost power, enabling a net profit of 19,945.0 USD/day at an ethylene selling price of 967 USD/ton. Sensitivity analysis identifies FE(C₂H₄), full-cell voltage, and electricity price as the most influential variables. The results translate laboratory catalyst metrics into industrial cost drivers and clarify quantitative performance targets for commercialization. Full article

Coagulation-based technologies are increasingly recognized as key for controlling fluoride and hexavalent chromium in urban water and wastewater. Combined geogenic and industrial sources often drive chronic exposure and create an underrecognized public health burden. This review synthesizes current knowledge on the occurrence, speciation, and toxicology of F⁻ and Cr(VI) in urban systems, links regulatory targets to health outcomes, and critically examines conventional, advanced, and electrochemical coagulation processes for their removal under realistic water-quality conditions. Mechanistic sections describe how aluminum-, iron-, magnesium- and zirconium-based coagulants, including pre-polymerized and composite formulations (e.g., IPC-type coagulants, PSiFAC-Mg, ZrCl₄), remove fluoride via Al–F complexation, Al–F–OH co-precipitation, ion exchange, and sweep flocculation, while Cr(VI) control relies on Fe(II)-mediated reduction to Cr(III), followed by adsorption and co-precipitation with metal hydroxides. The review assesses how water chemistry and operating conditions affect single- and multi-contaminant removal, highlighting competition among fluoride, Cr(VI), nutrients, and other oxyanions. Performance data from bench-, pilot-, and selected full-scale studies show that optimized coagulation and electrocoagulation can substantially reduce fluoride and Cr(VI) (to drinking-water-relevant levels) in diverse urban waters, but also reveal persistent issues of sludge generation and stability, residual metals, process robustness, and cost. The review identifies priorities, including long-term urban-scale assessments, low-toxicity green coagulants, life-cycle and health impact assessments, and real-time coagulation control for fluoride and Cr(VI). Full article

Arsenic (As) contamination in groundwater represents a critical global environmental health issue. The reductive dissolution of arsenic-bearing iron oxides by dissimilatory metal-reducing bacteria (DMRB) is a key biogeochemical process driving arsenic mobilization and release in groundwater. However, the mechanism of exogenous electron shuttles in this process remains poorly understood. This study investigated the impact of the quinone-based electron shuttle anthraquinone-2,6-disulfonate (AQDS) on the reductive dissolution of arsenic-loaded goethite by the model DMRB Shewanella putrefaciens CN32 (S.P CN32). The mobilization and transformation behaviors of arsenic and iron were compared under different pH conditions and using different arsenic-loading methods (coprecipitation vs. adsorption). Results demonstrated that AQDS acted as an electron transfer mediator. It significantly enhanced the reductive dissolution of Fe(III). It also significantly enhanced the reduction of As(V). These actions collectively accelerated arsenic release and mobilization. The study also revealed a competitive preferential order in microbial reduction, where the thermodynamically more favorable Fe(III) reduction preceded As(V) reduction. Environmental pH co-regulated this process. Its influence worked through microbial activity and mineral surface properties. A neutral pH was most conducive to the AQDS-mediated bioreduction of arsenic and iron. This study elucidates the critical role of electron shuttles in the biogeochemical cycling of arsenic in contaminated sites, providing a scientific basis for a deeper understanding of the formation mechanisms and risk assessment of high-arsenic groundwater. Full article

To further understand redox mechanisms occurring in wine, caffeic acid (CAF, 150 mg/L) and/or glutathione (GSH, 150 mg/L) were added to a model wine solution, followed by ferric iron (2 mg/L Fe(III), added as 10 mg/L Fe(III) chloride hexahydrate), while monitoring the oxidation–reduction potential (ORP, redox potential). Caffeic acid produced only modest ORP changes. In contrast, glutathione and caffeic acid + glutathione additions dropped the ORP from 243 mV and 238 mV, respectively, to the same post-addition value of 189 mV, suggesting that glutathione dictated the ORP, while caffeic acid showed no effect. The quinone of caffeic acid (assumed as changes in AU at 420 nm), was not detected, suggesting caffeic acid did not participate in oxidation reactions under wine conditions under superfluous amounts of dissolved oxygen (DO). After the addition of Fe(III), ORP increased to similar values across all treatments: 266 mV (FE), 269 mV (CAF), 284 mV (GSH), and 242 mV (CAF + GSH), suggesting that the Fe(II)/Fe(III) redox couple dominated the ORP electrode response. CAF + GSH produced the steepest ORP decline after the addition of Fe(III) chloride hexahydrate (β (slope of the ORP) = −0.7082), significantly steeper than FE (β = −0.3051; p = 0.0032) and GSH (β = −0.4643; p = 0.0496), suggesting synergistic radical quenching and metal redox cycling. Photo-Fenton-like reactions likely contributed to slight decreases in the ORP over time. In conclusion, glutathione strongly lowered the ORP, Fe(III) increased the ORP across treatments, and caffeic acid had minimal impact on the ORP under model wine conditions. Full article

Fenton-based processes are widely used advanced oxidation methods that are known for degrading persistent pollutants. However, these techniques often generate significant amounts of iron-containing sludge, which poses environmental disposal challenges due to its complex composition. Furthermore, the sludge produced by the Fenton process contains a high content of Fe(III) compounds, which can serve as an iron source to stimulate dissimilatory iron reduction (DIR), enhancing the performance of anaerobic digestion. Based on the characterization results from a previous study, this work investigated the use of the ferrous precipitate generated by the electrochemical peroxidation process applied to tannery wastewater treatment as an additive to enhance volatile fatty acids (VFAs) production during dark fermentation. The performance of ferrous precipitate (R-Fe₃O₄) was compared to that of conventional magnetite (Fe₃O₄) during dark fermentation under high organic loading conditions, emphasizing their potential to enhance hydrolysis efficiency and VFAs production yields, while promoting sustainable resource recovery and reuse within a circular bioeconomy framework. The results showed that the addition of both Fe₃O₄ and R-Fe₃O₄ significantly increased the VFAs yields, with a predominance of long-chain fatty acids. The presence of CaCO₃ in the ferrous precipitate contributed to maintaining a stable pH environment, supporting microbial activity and enhancing the hydrolysis of soluble compounds. Moreover, the availability of essential micronutrients within the ferrous precipitate favored greater microbial diversity. Consequently, the addition of R-Fe₃O₄ promoted VFAs production, even at higher organic loading rates, suggesting a promising application of Fenton-based by-products as functional additives to improve the economic and environmental performance of the dark fermentation process. Full article

Arsenic (As) is a ubiquitous and highly toxic metalloid with well-established carcinogenicity. Its accumulation and secondary release from lake sediments pose potential risks to lake ecosystem integrity and human health. Meanwhile, the ongoing intensification of lake eutrophication at the global scale has altered the sources, composition, and environmental behavior of internally derived dissolved organic matter (DOM). These changes have profoundly influenced As mobilization and transformation at the sediment-water interface (SWI). To advance understanding of the regulatory roles and underlying mechanisms of algal dissolved organic matter (ADOM) and submerged macrophyte dissolved organic matter (SMDOM) in As biogeochemical cycling under lake ecosystem regime shifts, extensive findings from the international literature were synthesized. The characteristic properties and environmental behaviors of ADOM and SMDOM were systematically compared, and their distinct regulatory pathways in lacustrine systems were further summarized. Results indicate that ADOM is typically characterized by low molecular weight, weak aromaticity, and high bioavailability. It can enhance As dissolution and mobilization from sediments through direct complexation, competition for adsorption sites, and stimulation of microbial metabolism and Fe(III) reduction. In contrast, SMDOM exhibits higher molecular weight, greater aromaticity, and a higher degree of humification. It tends to form stable complexes with mineral phases. Under the influence of radial oxygen loss (ROL) from submerged macrophyte roots during the growth phase, its capacity to promote mineral reduction is relatively limited. This process favors stable As retention in sediments. The regulatory effects of ADOM and SMDOM on As behavior are strongly modulated by environmental factors such as pH, redox potential (Eh), temperature, and light conditions, as well as by microbial communities. ADOM is more sensitive to reducing environments and photochemical processes. SMDOM, in contrast, exerts more persistent control under oxidizing conditions and at mineral-water interfaces. In addition, ADOM more readily drives microbial community shifts toward assemblages with enhanced capacities for Fe(III) reduction and As reduction or methylation. SMDOM is less likely to trigger strongly reducing processes. Based on these mechanisms, the outbreak and decay phases in algal-dominated lakes often correspond to critical periods of enhanced As mobilization and elevated ecological risk. In submerged macrophyte-dominated lakes, the decay phase may represent an important window for sedimentary As release. Finally, a conceptual framework describing the differential regulation of As biogeochemical cycling by ADOM and SMDOM is proposed. This framework provides a theoretical basis for As risk identification, the determination of critical risk periods, and the development of management strategies across lakes with different trophic states. Full article

Background/Objectives: The widespread use of mupirocin and fusidic acid for the treatment and decolonization of Staphylococcus aureus (SA) skin infections has led to a rapid emergence of resistant strains, limiting the effectiveness of the few topical agents currently available for clinical use. Methods: In this study, we evaluate Fe(tropo)₃, a neutral and lipophilic iron(III)–tropolone complex, as a non-antibiotic topical antimicrobial candidate for the management of drug-resistant SA skin and soft tissue infections. Results: Fe(tropo)₃ exhibits potent in vitro activity against methicillin-susceptible SA, methicillin-resistant SA (MRSA), vancomycin-intermediate SA, and strains with high-level resistance to mupirocin and fusidate, with minimum inhibitory concentrations of 2 µg/mL across all tested isolates. The compound effectively penetrates bacterial cells, induces intracellular iron accumulation, and triggers dose-dependent reactive oxygen species generation, resulting in rapid bacterial killing and significant antibiofilm activity. Importantly, Fe(tropo)₃ shows a slower development of resistance compared with ciprofloxacin and displays synergistic activity with oxacillin against MRSA. When formulated as a 1% topical ointment, Fe(tropo)₃ significantly reduces bacterial burden in a murine excisional wound infection model, achieving a 98% ± 1% reduction in SA load without detectable hemolysis or skin irritation. Conclusions: These pilot study results support Fe(tropo)₃ as a clinically relevant, mechanism-distinct topical antimicrobial with potential utility in settings where resistance to existing topical antibiotics compromises standard care. Full article

Arsenic (As) pollution has become a global concern, and the search for effective and sustainable As remediation methods has attracted much attention. Sustainable and cost-effective technologies for As remediation are essential to protect public health. This study aligns with the United Nations Sustainable Development Goals (SDGs), specifically SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production), by transforming agricultural waste into value-added biochar for environmental remediation. Currently, studies on the remediation of As pollution using iron-modified biochar (Fe-BC) and cerium-modified biochar (Ce-BC) have demonstrated promising application potential. Although there is an established research foundation regarding their remediation performance and mechanisms, comparative studies evaluating their performance and mechanisms under unified experimental conditions remain limited. As in this study, Fe-BC and Ce-BC were prepared and systematically investigated. The As remediation performance and mechanisms of the two biochars were compared and analyzed through material characterization, aqueous adsorption experiments, and soil remediation assessments. The results showed that the specific surface areas of Fe-BC and Ce-BC were 94.380 m²·g⁻¹ and 36.388 m²·g⁻¹, respectively, both higher than that of the original biochar (BC). The Langmuir and Freundlich models adequately fitted the As adsorption processes of all three materials. Fe-BC and Ce-BC exhibited a tendency toward monolayer adsorption for As(III). The Freundlich distribution coefficient K_F of Fe-BC was 0.1604, which was higher than that of BC and Ce-BC, indicating superior adsorption performance for As(III). In the pot experiment, when Fe-BC and Ce-BC were applied at 5%, the As content in ryegrass decreased by 78.38% and 77.15%, respectively. Fe-BC reduced the available As content in soil by 63.1% and decreased As accumulation in ryegrass by 78.38%. The reduction in available As content achieved by Fe-BC was greater than that achieved by Ce-BC. Fe(III) oxides supported on Fe-BC immobilized As through complexation and precipitation mechanisms. Fe⁰ and Fe₃O₄ in the materials altered the redox potential of the local microenvironment, affecting the transformation and stabilization of As species. Ce-BC primarily oxidized As(III) to As(V), and Ce⁴⁺ facilitated the formation of CeAsO₄ precipitates due to its high redox potential. Full article

Loading dissolved organic matter (DOM) onto iron–manganese oxides (FeMnOx) was a promising strategy for enhancing the hexavalent chromium (Cr(VI)) removal from wastewater. To optimize this process and gain deeper mechanistic insight, this study systematically investigated the DOM loading characteristics onto FeMnOx and its subsequent effect on Cr(VI) adsorption. DOM loading onto FeMnOx was significantly affected by the initial concentration of DOM and pH, with optimal loading conditions identified as a DOM concentration of 75 mg/L, pH of 4, ionic strength of 0.005 mol/L, temperature of 50 °C, and contact time of 4 h. During loading, FeMnOx preferentially adsorbed low-molecular-weight/low-aromaticity components such as tryptophan-like (C1) and fulvic acid-like (C2) substances. The adsorption process followed a non-uniform monolayer surface adsorption and involved multiple stages dominated by chemical interactions. DOM coating on FeMnOx significantly enhanced the Cr(VI) removal, and the maximum adsorption capacity under optimal loading conditions increased from 18.46 mg/g to 23.26 mg/g. Characterization by SEM-EDS, BET, ICP-MS, XPS, FTIR, and CV revealed that a moderate DOM loading (55–75 mg/L) enhanced the material’s surface reducibility and mesoporous structure. This improvement was attributed to the reduction of surface Mn(IV) to more-reactive Mn(III) by reductive functional groups in DOM, thereby promoting Cr(VI) adsorption and reduction. In contrast, excessive DOM loading (105 mg/L) formed a dense organic layer that masked active sites and hindered electron transfer, ultimately compromising the long-term reductive capability. These findings elucidate the concentration-dependent regulatory role of DOM in modifying FeMnOx properties, providing a theoretical foundation for the rational design of efficient DOM–metal oxide composites for heavy metal remediation in aquatic environments. Full article

Large quantities of wastewater (OMW) are generated by the olive oil industry, requiring sustainable management to mitigate environmental impacts. The main goal of this work is to evaluate the possibility of using the homogeneous Fenton process as a pretreatment of OMW, as well as the iron (Fe (II) and Fe (III)) addition to improve the methane production through AD. The Fenton process achieved chemical oxygen demand (COD) and total phenolic compound (TPh) removals of 17–47% and 75–94%, respectively. However, methane production did not improve compared with untreated OMW, which yielded about 82 NmL CH₄/ g COD_i. The increase in H₂S production from about 2 mL in raw OMW to more than 8 mL in treated OMW may justify the inhibition of AD. Supplementing AD with 2 mg/L of Fe (III) increased methane production by 65% and significantly reduced H₂S due to FeS precipitation. The addition of 1 and 2 mg/L of Fe (II) also increased methane production by 82 and 59%, respectively, but no reduction in H₂S was observed. Therefore, although the Fenton pretreatment effectively reduces recalcitrant organic matter, it does not necessarily enhance methane production. A balance must be achieved between improving OMW characteristics and minimizing adverse impacts on AD performance. Full article

The redox activity of natural organic matter (NOM) is crucial for contaminants transformation in soils. Soil micropores (<2.5 nm) have limited accessibility for microorganisms and large NOM molecules; therefore, insoluble organic pollutants and heavy metals trapped in these micropores are usually reached by low molecular weight fractions (LMWF) of NOM. However, the mechanism of spatial electron transfer via electron shuttle of LMWF remains unclear. In this study, we separated low molecular weight fractions (LMWF < 3500 Da and LMWF < 14,000 Da) of Leonardite humic acids (LHA) and measured its acceleration of microbial ferrihydrite reduction. The results show that LMWF, as an electron shuttle, significantly accelerates the reduction in Fe (III), among which 3500-LMWF is the main fraction contributing to the acceleration. Additionally, 3D-EEM shows that quinone content was positively correlated with reduction efficiency, supporting its role as the key functional group. Based on the accelerating experiments, we determined an electron shuttling critical distance of 117.2 nm for LMWF LHA. These findings establish LMWFs as effective natural electron shuttles, providing a theoretical basis for understanding pollutant dynamics in soil micropores. Full article

Modification of zeolitic structures through the incorporation of transition metal oxides has proven to be a promising approach for heterogeneous catalysis. In the present study, *BEA zeolite was modified using the incipient wetness impregnation method with varying amounts (10, 20, and 40 wt.%) of iron(III) oxide to investigate its structural and physicochemical properties. Characterization techniques such as XRD, UV–Vis DRS, FT–IR, Raman spectroscopy, SEM/EDS, TEM/EDS, and SAED, as well as textural and thermal analyses, were employed to assess the main changes. Different iron species were detected, including isolated iron(III) and well-dispersed Fe₂O₃ nanoparticles coating the zeolite surface. Under the synthesis conditions, increased Fe₂O₃ loading promoted hematite nanocrystal growth and the formation of the α-Fe₂O₃ phase, as demonstrated by XRD, Raman, and SAED analyses. Key observations included the preservation of the zeolite framework, high relative crystallinity (ranging from 70% to 85%), and a band gap of approximately 2.0 eV. Furthermore, a general increase in mesoporosity and external surface area was observed, along with a reduction in the number of acidic sites. This decrease may be attributed to restricted accessibility of the probe molecule (pyridine) to Brønsted sites due to micropore blockage in *BEA. These results demonstrate that the adopted synthesis method effectively produced α-Fe₂O₃/BEA catalysts, with no other crystalline phases of iron(III) oxide detected. Full article

Nutrient cycling has barely been studied in acidic environments and may have an important influence on the evolution of the microbial communities. In this research, we studied nutrient sources and fluxes in acidic metal-mine pit lakes to evaluate their relationship with the lakes’ microbial ecology. Nutrient concentrations (including phosphorus, nitrogen, and dissolved inorganic carbon) increase with depth in all the studied pit lakes. Phosphorus comes mainly from the leaching of the host rock and is rapidly scavenged from the aqueous phase in the oxygenic and Fe(III)-rich mixolimnion due to adsorption on ferric precipitates (schwertmannite, jarosite), which leads to an important P-limitation in the photic zone. Below the chemocline, however, the sum of phosphorus inputs (e.g., settling of algal biomass, desorption from the ferric compounds, microbial reduction of Fe(III)-sediments) sharply increases the concentration of this element in the anoxic monimolimnion. Nitrogen is very scarce in the host rocks, and only a limited input occurs via atmospheric deposition followed by N-uptake by algae, N-fixation by acidophilic microorganisms, sedimentation, and organic matter degradation in the sediments. The latter process releases ammonium to the anoxic monimolimnion and allows some nitrogen cycling in the chemocline. Soluble SiO₂ in the mixolimnion is abundant and does not represent a limiting nutrient for diatom growth. Differences in phytoplankton biomass and extent of bacterial sulfate reduction between relatively unproductive lakes (San Telmo) and the more fertile lakes (Cueva de la Mora) are likely caused by a P-limitation in the former due to the abundance of ferric iron colloids in the water column. Our results suggest that phosphorus amendment in the photic zone could be an efficient method to indirectly increase acidity-consuming and metal-sequestering bacterial metabolisms in these lakes. Full article

This study investigates the influence of sevoflurane and desflurane on the electrochemical behavior of the Fe(III)-acetylacetonate (Fe(acac)₃) complex. Using cyclic voltammetry (CV), we demonstrate that while Fe(acac)₃ exhibits reversible redox behavior in an oxygen-free environment, the presence of dissolved oxygen renders the system irreversible, leading to the formation of a thick, reddish film on the electrode surface upon potential cycling. Notably, the addition of sevoflurane and desflurane restores the electrochemical reversibility and dramatically inhibits this film formation. Raman spectroscopy of the resulting films confirmed structural changes which are consistent with this inhibiting action. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis reveals that the iron in the film remains predominantly in the Fe³⁺ oxidation state even after prolonged electrochemical reduction cycles. These findings suggest that the anesthetics act by inhibiting the interaction between the Fe(acac)₃ complex and oxygen, likely through a spin–decoherence mechanism. This work highlights the critical role of anesthetics in modifying the electrochemical behavior of metal-oxygen complexes, with potential implications for sensing, electrocatalysis, and bio-oriented systems. Full article

Fluoride is a crucial inorganic anion found in drinking water, which may pose serious health hazards to human health if consumed in excess amounts. The quantification of fluoride in drinking water with high sensitivity, selectivity, and cross-sensitivity is critical. Given these factors, the present work proposes a spectroelectrochemical sensing platform for fluoride sensing using 5,10,15,20-tetraphenyl-21H,23H-porphine iron (III) chloride (FeTPP), and tetrabutylammonium perchlorate (TBAP) as the electrolyte. The proposed spectroelectrochemistry (SEC) is a hybrid platform that concurrently provides spectroscopic and electrochemical information about a system susceptible to oxidation and reduction. An ensemble–based multivariate prediction model was developed to simultaneously analyze electrochemical and spectroscopic data to predict fluoride concentration with enhanced reliability and precision. The prediction model provided promising results with a coefficient of determination of 0.9923 ± 0.0063 and a MSE of 0.369 ± 0.0596. These encouraging results demonstrate the promising performance of the proposed spectroelectrochemical platform in complex real-world applications. Full article