Search Results (672)

Here, we report a comparative scanning tunneling microscopy study of two brominated dibenzo[c,g]carbazole derivatives on Ag(111): 5,9-dibromo-7H-dibenzo[c,g]carbazole (DBC) and 5,9,7-tribromo-7-(4-bromobutyl)-7H-dibenzo[c,g]carbazole (BrBu-DBC). At room temperature (RT), DBC forms ordered paired-row supramolecular assemblies, whereas annealing to 470 K induces the formation of butterfly-like dimers that further organize into periodic arrays, consistent with adatom-mediated N–Ag–N coordination. In contrast, BrBu-DBC shows disordered adsorption at RT but transforms at 490 K into dumbbell-shaped dimers coupled selectively at the terminal side chains, consistent with C–C linkage formation. We demonstrate how subtle functional modification modulates the competition between supramolecular assembly and surface-mediated transformation pathways. Full article

Direct air capture (DAC) of CO₂ via temperature-swing adsorption (TSA) can support sustainable carbon dioxide removal, but only if sorbents regenerate with low energy demand and maintain performance under humid ambient air. In this paper, we evaluate three commercial molecular sieves (JLPM3, 13X, and 4A) in packed-bed tests using humid ambient air. We compared 40 g samples as received with 200 g samples conditioned for 12 days at 100 °C to emulate prolonged exposure to regeneration temperature (the cumulative effect of many heating/desorption cycles); all cycle-stabilized uptake values are reported from the conditioned materials. JLPM3 delivered the highest stabilized CO₂ uptake (0.24 ± 0.01 mmol·g⁻¹), consistent with a combined physisorption/chemisorption mechanism. Its higher total porosity (26.190%) and smaller mesopores (7.569 nm width) promoted rapid mass transfer and site accessibility, while slightly greater micropore area (710.285 m²·g⁻¹) and volume (0.267 cm³·g⁻¹) than 13X supported its marginally higher capacity. Evidence of partial structural degradation under mechanical and thermal stress indicates that minimizing strain during cycling will be important for scale-up and for reducing sorbent replacement. Conditioning at 100 °C activated additional chemisorption sites across all sieves but reduced physisorption capacity. Importantly, a ~100 °C desorption step fully regenerated physisorbed CO₂ while purging moisture from zeolite pores, indicating that low-temperature TSA (compatible with low-grade or waste heat) can replace harsher 300 °C regeneration and lower energy demand. CO₂–H₂O competition experiments confirmed substantial site occupancy by water vapor, which limits capture under humid conditions and motivates water management strategies. Overall, maximizing DAC performance requires tailoring pore structure and operating conditions while preserving sorbent integrity; JLPM3 emerges as a promising candidate for more energy- and resource-efficient DAC. Full article

Elemental sulfur deposition in sulfur-bearing gas fields can disrupt gas well production and create safety risks, making it essential to understand its deposition mechanisms. While previous studies have examined sulfur adsorption on single minerals, the behavior in carbonate mixed minerals remains unclear. This study uses molecular simulations to investigate elemental sulfur adsorption in calcite–dolomite mixed slit models. Results show that, at the same slit size, sulfur adsorption increases with pressure and temperature, with adsorption amounts ranging from 5.95 × 10⁻⁵ to 1.08 × 10⁻² mg/m². Pressure has little effect on adsorption heat, whereas higher temperatures reduce it. At equilibrium, sulfur molecules preferentially adsorb on calcite. Increasing pressure raises sulfur adsorption on calcite, while higher temperatures enhance adsorption on both mineral surfaces. Compared with single-mineral slits, competitive adsorption in mixed systems leads to a less uniform sulfur distribution on calcite. These findings provide theoretical insights into sulfur deposition mechanisms and prevention strategies for high-sulfur gas reservoirs. Full article

Energy transformation requires the development of distributed renewable energy, in which heat and electricity are produced by small units or production facilities for local needs. One favorable development direction is the thermal conversion of biomass, which is classified as a renewable energy source. Due to the variability of its physicochemical properties, gasification technology offers a flexible and competitive alternative to combustion processes. One of the key challenges associated with biomass gasification is the relatively high concentration of contaminants in the raw producer gas. This article presents the results of pilot studies on producer gas purification using activated carbon fixed-bed adsorption. The pilot studies focused on assessing the effectiveness of this technology in the context of purifying producer gas from biomass gasification installations. During the conducted experimental study, approximately 2.2 kg of contaminants were adsorbed. The calculated unit mass of adsorbed contaminants per unit volume of producer gas was 11.7 g/Nm³. The removal efficiency of contaminants was 61.5% for tar compounds and 83.6% for volatile organic compounds. A 100% removal efficiency was achieved for the analyzed sulfur compounds (H₂S, COS, and CH₃SH). The research showed positive effects of adsorption for final producer gas purification, supporting further experimental research. Full article

In recent years, Metal–Biomass Carbon (M–BC) hybrids have been widely studied as promising, cost-effective, and sustainable catalysts for persulfate activation in the degradation of emerging organic contaminants. M–BC systems offer advantages such as good performance and the sustainable use of biomass waste. Despite the considerable attention they have received, significant uncertainty remains regarding their precise catalytic mechanisms. A primary concern is the inherent complexity of biomass precursors, which frequently render the resulting catalytic structures ill-defined or akin to a “black box”. To address this challenge, this review critically evaluates the current state of mechanistic research, focusing on the debate between radical and non-radical pathways. In this paper, five fundamental challenges to clear mechanistic understanding are identified, including interference of inherent inorganic species, lack of precursors standardization and inherent heterogeneity, ambiguous overlapping active sites, methodological limitations in chemical quenching due to competitive adsorption, and conductivity-related constraints on non-radical pathways. Among these, the interference from inherent inorganic species is of primary concern, as the available evidence suggests it frequently confounds reported synergistic effects. Additionally, the future research directions for improving the experimental standardization and mechanistic understanding of M–BC catalysts are proposed. This review enriches the field by providing a clear path toward rigorous mechanistic understanding and the rational design of M–BC catalysts for water remediation. Full article

This work is devoted to the synthesis and comprehensive study of activated carbons (ACs) obtained from agricultural wastes—specifically corn cob (C) and onion (O)—for the effective removal of paracetamol (PCM) and sulfamethoxazole (SMX) from aqueous media. The synthesis was carried out by chemical activation using H₃PO₄, HNO₃, and NaOH as activating agents, which made it possible to obtain materials with a clearly defined microporous structure (microporous fraction V_micro/V_total = 0.75–0.81) and specific surface chemistry. Particular attention was paid to studying the kinetics and equilibrium of adsorption in both single-component and binary (two-pollutant) systems. It was established that the equilibrium time is 8 h, and the experimental data are best described by a pseudo-second-order kinetic model. During binary adsorption tests, the competitive behavior was observed for certain materials, such as the corn-derived carbon activated with HNO₃ (AC-CN) and the onion-derived carbon activated with HNO₃ (AC-ON), where molecules compete for active sites. Conversely, synergistic effects were identified in other systems, controlled by specific surface-functional groups and hydration effects. The maximum adsorption capacity was found to be 29.4 mg∙g⁻¹ for PCM on the AC-CN sample. Adsorption mechanisms, including multilayer isotherm profiles and the competition between pollutant and water molecules, were interpreted using quantum chemical calculations within the framework of Density Functional Theory (DFT). These calculations revealed that partial deprotonation and intense solvation of SMX molecules at natural pH reduce their adsorption capacity. In contrast, the PCM structure favors π-π interactions and the formation of strong hydrogen bonds with oxygen-containing groups on the carbon surface. These results demonstrate the high potential of using agro-industrial waste to create a new generation of selective adsorbents with tailored surface properties. 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

The present paper investigates the adsorption performance of pinewood-derived biochars produced at two pyrolysis temperatures (850 °C, PW-A; 1000 °C, PW-B), including sieved fractions (PW-A1 and PW-A2) and a functionalized variant (PW-C), for the removal of five short- and intermediate-chain PFASs (PFBA, PFBS, PFHxA, PFHxS, and GenX) from water under continuous-flow conditions. Adsorption behavior was evaluated using Freundlich and Hill isotherm models. The Hill model provided a superior fit for most PFAS–adsorbent systems, highlighting the importance of cooperativity effects, particularly for short-chain PFASs. In single-compound experiments, PFBS and GenX showed the highest adsorption capacities (up to 82.3 and 68.5 mg g⁻¹), while PFBA and PFHxA exhibited the lowest. Among the tested materials, biochar produced at 1000 °C (PW-B) consistently demonstrated the highest adsorption efficiency. Compared to activated carbon, PW-B showed comparable performance for PFBA, PFBS, PFHxA and PFHxS and significantly better performance for GenX. In mixed-PFAS systems, competitive effects reduced adsorption capacity and cooperativity. Sulfonic PFASs showed higher affinity than carboxylic PFASs, following the trend PFHxS > PFBS > PFHxA > PFBA. Overall, the results demonstrate that waste-derived biochar represents a low-cost and sustainable alternative for PFAS removal in realistic water-treatment scenarios, supporting scalable solutions aligned with global environmental goals. Full article

To achieve efficient development of medium-depth and shallow high-rank coalbed methane in the Qinshui Basin of Shanxi Province, the authors focused on the microscopic methane release mechanism. Through scanning electron microscopy, nuclear magnetic resonance, and isothermal adsorption experiments, the pore structure, distribution patterns, and influence of hydration effects in this type of coal were revealed. It was clarified that the ineffective utilization of “bound-state” methane within nanopores is the key factor leading to low productivity and efficiency in coalbed methane development. Further, based on molecular simulations, the competitive adsorption characteristics between water and methane molecules were quantified, indicating that about 78% of the methane in the internal pores of 4 nm coal molecular clusters cannot be desorbed through pressure reduction. Meanwhile, the production enhancement mechanism of hydraulic fracturing on coal seam depressurization, permeability enhancement, reduction in low-speed diffusion distance, and enhancement of high-speed linear flow was clarified. Through large-scale pad water injection and stepwise slow production increase, the coal seam can be fully communicated, the reservoir effectively stimulated, and the adsorbed methane sufficiently released. This paper establishes a “channeled” fracturing concept and its supporting technological system for medium-depth and shallow high-rank coal, which has been successfully applied in field operations. The pilot well group achieved stable daily production exceeding 50,000 cubic meters per day, laying a solid foundation for the continuous and stable production increase in medium-depth and shallow high-rank coalbed methane in the Qinshui Basin. Full article

In the present study, we evaluate the CO₂ uptake capacities of four activated carbons (ACs) obtained from olive stones. Two of the samples were generated using a chemical process utilizing phosphoric acid, thereafter undergoing carbonization in a nitrogen steam, yielding both granular and pellet forms, designated CH-ACG-410 and CH-ACP-410, respectively. The third sample, labeled CO-ACG-390, was produced by carbonization under a steam-nitrogen flow, while the fourth sample, designated PH-ACG-850, was prepared by a physical process involving water vapor at 850 °C. The carbon materials obtained in granular and pellet form were subjected to textural characterization using N₂ and CO₂ adsorption isotherms at 77 K and 273 K, respectively. Additionally, surface chemistry was analyzed using FTIR, Boehm titration, and TPD-MS. The materials were also assessed for CO₂ adsorption in a binary mixture consisting of 10% CO₂ and 90% N₂ at two temperatures, 25 and 50 °C. The results demonstrated that all prepared adsorbents exhibited competitive CO₂ capture performance, with the CH-ACP-410 sample (pellet form), showing the highest adsorption capacities, achieving approximately 4.6 wt. % at 25 °C and 2.2 wt. % at 50 °C. This superior behavior can be attributed to the conditioning methods applied to this material, which significantly influenced its textural properties and, consequently, its CO₂ adsorption capability. Full article

Macroporous adsorption resins (MARs) are widely used for preparative-scale flavonoid purification, yet rational resin selection remains difficult because flavonoids differ substantially in hydrophobicity, hydrogen-bonding capacity, molecular size, and planarity. This review reorganizes the available literature into a structure-guided and data-supported selection aid rather than a fully predictive model. A systematic search of Web of Science, Scopus, PubMed, and CNKI (January 2000 to February 2026) identified 55 studies for qualitative synthesis. Because many reports describe total flavonoids or mixed extracts rather than explicit single-compound adsorption data, only the subset with sufficiently clear compound-level or narrowly interpretable adsorption information was used for cautious comparative interpretation. Across the compiled evidence, non-polar resins generally favored less polar aglycones and methoxylated flavonoids, whereas medium-polar and polar resins more often performed well for glycosylated or more hydrophilic targets. On this basis, flavonoids were organized into four operational classes linked to recommended resin polarity, indicative adsorption capacity ranges, and typical ethanol-elution windows. A retrospective comparison with independent literature cases suggests practical value for initial resin prioritization, but the framework should be interpreted primarily as a heuristic, trend-based guide rather than as a strictly predictive model, because mixed-matrix effects, pore accessibility, and competitive adsorption can override simple polarity matching. A generalized operating window for adsorption and desorption is also summarized. Overall, this review provides a mechanism-informed starting point for resin screening while making explicit the conditions under which case-specific experiments remain necessary. Full article

Arsenic (As) contamination of soils is a critical environmental and geochemical concern, with its mobility and bioavailability largely controlled by molecular-scale interactions with soil minerals. This study investigates the adsorption behavior of arsenate [As(V)] and arsenious acid [As(III)] on major clay minerals to elucidate fundamental controls on As retention in soil and sediment systems. Molecular modeling approaches were employed to investigate these interactions. Density functional theory (DFT) calculations were performed on cluster models of illite, chlorite, montmorillonite, and kaolinite to evaluate adsorption configurations and binding energies of arsenate and arsenious acid. In addition, semiempirical (PM6) and classical force-field (UFF) methods were used to examine the influence of vermicompost-derived organic matter on arsenate-mineral interactions. Multiple adsorption configurations, including atop atom, bridge, three-fold filled, and three-fold hollow sites, were evaluated, and binding energies were calculated with correction for basis set superposition error. The results indicate that three-fold hollow sites are the most favorable, with As(V) binding energies of 60–65 kcal mol⁻¹ on illite, chlorite, and montmorillonite, reaching 75 kcal mol⁻¹ on kaolinite at a surface distance of 2.7 Å. In contrast, As(III) shows weaker and energetically flatter adsorption, with binding energies of 28–54 kcal mol⁻¹ and larger equilibrium distances of 3.2–4.0 Å. Modeling of vermicompost addition suggests a substantial reduction in arsenate binding on most clay minerals, except illite, indicating competitive or disruptive interactions at mineral surfaces. These findings provide quantitative, atomistic insight into mineral- and amendment-specific controls on As stabilization and mobility in soil and sediment systems. Full article

Organophosphate pesticides (OPs) are widespread contaminants in agricultural and aquatic environments. Growing evidence indicates that even low-level, chronic exposure to OPs is associated with neurotoxic effects and long-term neurological risks. Over the past decade, substantial progress has been made in developing porous carbon materials capable of efficiently removing OPs from water, food systems, and other environmental matrices. However, adsorption studies have largely focused on equilibrium performance metrics rather than on conditions relevant to real exposure scenarios. This review introduces an exposure-oriented perspective for evaluating porous carbon materials for OP mitigation by linking adsorption science with exposure-driven neurotoxicity considerations. By analysing recent studies on OP adsorption, we demonstrate that equilibrium adsorption capacity alone is often a poor predictor of real-world exposure mitigation. Instead, adsorption kinetics at low concentrations, pore accessibility, and surface chemical heterogeneity emerge as key factors governing sustained OP sequestration. The review further highlights how hierarchical pore architectures and balanced surface functionalization can enhance adsorption efficiency under environmentally realistic conditions. By integrating environmental carbon research with exposure-relevant considerations, this work outlines design principles for carbon adsorbents to reduce long-term OP exposure and associated neurological risks. Full article

Reverse osmosis concentrate (ROC) contains relatively high levels of refractory organic pollutants, posing significant challenges due to its difficult treatment and high environmental risks. Therefore, efficient and convenient removal strategies are essential. In this study, a self-developed iron-modified activated carbon fiber (Fe-ACF) was employed as an adsorbent to remove organic pollutants from ROC. Additionally, response surface methodology (RSM) was applied to model the adsorption process, identify and evaluate key influencing parameters, and optimize operational conditions. The adsorption mechanisms and regeneration stability of Fe-ACF were also investigated. Kinetic analysis revealed that the adsorption process is predominantly governed by chemisorption, with intraparticle diffusion identified as the primary rate-limiting step. Isothermal adsorption studies demonstrated that the Langmuir–Freundlich model best describes the adsorption behavior, yielding a theoretical maximum adsorption capacity of 12.21 ± 0.80 mg/g. Thermodynamic analysis confirmed that the adsorption process is spontaneous, endothermic, and driven by an increase in entropy. The RSM optimization identified pH as the dominant factor. The optimal adsorption conditions were a pH of 4.18, a temperature of 34.63 °C, a stirring speed of 547.91 rpm, and an adsorbent dosage of 1.55 g/L. The adsorption mechanism involves hydrogen bonding, π–π interactions, surface complexation, and electrostatic forces. Fe-ACF exhibits competitive regeneration stability and structural integrity. In summary, Fe-ACF demonstrates significant potential as a treatment material for ROC. Full article

Polymeric microspheres synthesized via Pickering emulsion polymerization offer structural tunability, making them attractive platforms for dye adsorption. This study investigates the adsorption behavior of methylene blue onto two classes of polymeric microspheres—poly(methacrylic acid) crosslinked with ethylene glycol dimethacrylate (PM), containing both micro- and nanopores, and poly(methacrylic acid) crosslinked with divinylbenzene (PD), containing only nanopores. The adsorption kinetics were modeled using a dual-process approach that distinguishes between diffusion-controlled transport and surface-controlled kinetic adsorption. We quantified the relative contributions of these mechanisms and correlated them with particle architecture. In the PM particles, diffusion plays a significant role in smaller particles with larger macropores, enabling methylene blue to penetrate the interior. As the particle size increased and macroporosity decreased, adsorption becomes increasingly dominated by surface kinetics. In contrast, PD particles —which lack macropores—showed the opposite trend: smaller particles were primarily governed by fast surface adsorption, while in larger particles, diffusion through nanopores became increasingly relevant. Correlation analysis between adsorption rate constants and structural parameters such as particle diameter and pore sizes revealed strong, opposing trends. In PD particles, a near-perfect inverse correlation was observed between the diffusion and kinetic components, indicating competitive suppression, where the dominance of one mechanism limited the contribution of the other. These results demonstrated that internal pore architecture played a central role in controlling the adsorption mechanism. Tuning particle size and porosity allowed deliberate control over the balance between diffusion and surface kinetics, enabling the rational design of microparticle adsorbents with tailored uptake behavior for water purification and dye removal applications. Full article