Separations

16 pages, 3021 KiB

Open AccessArticle

Repurposing Portable Gas Chromatograph–Mass Spectrometers for Detecting Volatile Organic Compound Biomarkers in Urine Headspace

by Mark Woollam, Serenidy Eckerle, Eray Schulz, Sahanaa Nishkaran, Sara Button and Mangilal Agarwal

Separations 2025, 12(5), 118; https://doi.org/10.3390/separations12050118 - 7 May 2025

Abstract

Volatile organic compounds (VOCs) in urine headspace are potential biomarkers for different medical conditions, as canines can detect human diseases simply by smelling VOCs. Because dogs can detect disease-specific VOCs, gas chromatography–mass spectrometry (GC–MS) systems may be able to differentiate medical conditions with [...] Read more.

Volatile organic compounds (VOCs) in urine headspace are potential biomarkers for different medical conditions, as canines can detect human diseases simply by smelling VOCs. Because dogs can detect disease-specific VOCs, gas chromatography–mass spectrometry (GC–MS) systems may be able to differentiate medical conditions with enhanced accuracy and precision, given they have unprecedented efficiency in separating, quantifying, and identifying VOCs in urine. Advancements in instrumentation have permitted the development of portable GC–MS systems that analyze VOCs at the point of care, but these are designed for environmental monitoring, emergency response, and manufacturing/processing. The purpose of this study is to repurpose the HAPSITE^® ER portable GC–MS for identifying urinary VOC biomarkers. Method development focused on optimizing sample preparation, off-column conditions, and instrumental parameters that may affect performance. Once standardized, the method was used to analyze a urine standard (n = 10) to characterize intra-day reproducibility. To characterize inter-day performance, n = 3 samples each from three volunteers (and the standard) were analyzed each day for a total of four days (n = 48 samples). Results showed the method could detect VOC signals with adequate reproducibility and distinguish VOC profiles from different volunteers with 100% accuracy. Full article

(This article belongs to the Special Issue Chromatographic Analysis of Biomarkers)

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25 pages, 5272 KiB

Open AccessArticle

Synthesis of Magnetic Iron Oxide Heat-Activated Termite Mound Composite for Adsorption of Basic Blue 41 Dye from Textile Wastewater: Characterization and Box–Behnken Optimization

by Amare Melaku, Esayas Alemayehu, Abebe Worku and Bernd Lennartz

Separations 2025, 12(5), 117; https://doi.org/10.3390/separations12050117 - 6 May 2025

Abstract

The discharge of textile effluents containing dyes poses severe environmental risks. This study aimed to develop a

m a g n e t i c i r o n o x i d e

–HTM (magnetite–heat-activated termite mound) composite via the [...] Read more.

The discharge of textile effluents containing dyes poses severe environmental risks. This study aimed to develop a

m a g n e t i c i r o n o x i d e

–HTM (magnetite–heat-activated termite mound) composite via the coprecipitation method for the adsorption of Basic Blue 41 (BB41) dye from textile wastewater under batch conditions. The

m a g n e t i c i r o n o x i d e

–HTM composite was characterized using BET (surface area), XRD (crystalline structure), FTIR (functional groups), and SEM (microstructure) analyses, confirming the successful synthesis of

m a g n e t i c i r o n o x i d e

–HTM. Comprising 80% HTM by mass, the composite demonstrates economic viability. Using batch experiments and a Box–Behnken design, the adsorption performance of

m a g n e t i c i r o n o x i d e

–HTM for BB41 dye removal from aqueous solutions was evaluated. Optimization of the sorption process revealed that a dosage of 2.6 g/L, a contact time of 47.5 min, a temperature of 60 °C, and an initial dye concentration of 100 mg/L resulted in a BB41 dye removal efficiency of 98%. Additionally,

m a g n e t i c

–HTM effectively removed BB41 dye from real wastewater samples, achieving a removal efficiency exceeding 80%, highlighting the improved sorption properties of the modified termite mound. The spent

m a g n e t i c

–HTM was easily separated from the treated solution using an external magnet and successfully recovered. Its reusability demonstrated a dye removal efficiency of 78% after four cycles, without compromising its magnetic properties. Overall, the magnetically separable

m a g n e t i c i r o n o x i d e

–HTM composite shows significant potential for the treatment of textile wastewater. Full article

(This article belongs to the Section Purification Technology)

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22 pages, 2918 KiB

Open AccessArticle

Comparative Evaluation of UV-C-Activated Peroxide and Peroxydisulfate for Degradation of a Selected Herbicide

by Jelena Mitrović, Miljana Radović Vučić, Miloš Kostić, Milica Petrović, Nena Velinov, Slobodan Najdanović and Aleksandar Bojić

Separations 2025, 12(5), 116; https://doi.org/10.3390/separations12050116 - 3 May 2025

Abstract

Extensive utilization of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has resulted in contamination of the aquatic environment; this situation requires effective treatment technology. Ultraviolet-based advanced oxidation processes (UV-AOPs) are widely employed for the removal of organic contaminants from water. This study’s aim was to [...] Read more.

Extensive utilization of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has resulted in contamination of the aquatic environment; this situation requires effective treatment technology. Ultraviolet-based advanced oxidation processes (UV-AOPs) are widely employed for the removal of organic contaminants from water. This study’s aim was to compare the degradation of the pesticide 2,4-D in UV-C-activated peroxide and peroxydisulfate systems. UV-C irradiation alone exhibited a negligible effect on pesticide degradation, whereas the addition of oxidants significantly enhanced the degradation efficiency relative to 2,4-D. Complete pesticide removal was achieved after 15 min of UV/H₂O₂ treatment, while twice as much time was required with the UV/S₂O₈²⁻ process. COD decreased by 74% and 28% for UV-C-activated peroxide and peroxydisulfate, respectively. Both investigated systems demonstrated good performance for 2,4-D dechlorination. Pesticide degradation rates increased with increasing dosages of the applied oxidants. Acidic conditions were more favorable for degradation of 2,4-D, compared to neutral and basic conditions, for both systems studied. The degradation efficiency relative to 2,4-D decreased in the presence of HA, Cl⁻ and HCO₃⁻ in water matrices. The predominant radical for the UV-C-activated peroxydisulfate was determined to be a sulfate radical. These findings are of fundamental and practical significance in understanding UV-C-activated 2,4-D degradation, paving the way for the selection of preferred processes for the optimal removal of pesticides from various aqueous matrices. Full article

(This article belongs to the Special Issue Adsorption/Degradation Methods for Water and Wastewater Treatment)

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20 pages, 4455 KiB

Open AccessArticle

Chemical Composition, Chemometric Analysis, and Sensory Profile of Santolina chamaecyparissus L. (Asteraceae) Essential Oil: Insights from a Case Study in Serbia and Literature-Based Review

by Biljana Lončar, Mirjana Cvetković, Milica Rat, Jovana Stanković Jeremić, Jelena Filipović, Lato Pezo and Milica Aćimović

Separations 2025, 12(5), 115; https://doi.org/10.3390/separations12050115 - 2 May 2025

Abstract

The flowers of Santolina chamaecyparissus have a distinct aroma and taste, with a wide range of applications in medicine, food, and packaging. Its essential oil offers numerous health benefits, including antioxidant, hepatoprotective, anticancer, antidiabetic, spasmolytic, anti-inflammatory, immunomodulatory, antimicrobial, and antiparasitic properties. Additionally, it [...] Read more.

The flowers of Santolina chamaecyparissus have a distinct aroma and taste, with a wide range of applications in medicine, food, and packaging. Its essential oil offers numerous health benefits, including antioxidant, hepatoprotective, anticancer, antidiabetic, spasmolytic, anti-inflammatory, immunomodulatory, antimicrobial, and antiparasitic properties. Additionally, it is used as a flavoring agent in food and beverages and as a natural preservative in edible coatings for food packaging. This study investigates the chemical composition and sensory properties of the S. chamaecyparissus essential oil from Serbia, obtained via hydrodistillation, and includes a literature-based analysis of the existing profiles. Gas Chromatography–Mass Spectrometry (GC–MS) was employed for identifying the essential oil composition, while chemometric techniques like the genetic algorithm (GA), quantitative structure–retention relationship (QSRR) analysis, artificial neural network (ANN), and molecular descriptors were applied to ensure accurate and reliable results for authenticating the oil. Among the 47 identified compounds, oxygenated monoterpenes, especially artemisia ketone (36.11%), and oxygenated sesquiterpenes, notably vulgarone B (22.13%), were the primary constituents. Chemometric analysis proved effective in predicting the oil’s composition, and sensory evaluation revealed a herbal aroma with earthy, woody, and camphoraceous notes. A literature review highlighted the variability in oil composition due to geographical, environmental, and extraction factors, underscoring its chemical diversity, bioactivity, and potential applications. Full article

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17 pages, 2019 KiB

Open AccessArticle

Free Fatty Acid Determination in Alcoholic and Non-Alcoholic Beers via Liquid Chromatography–High-Resolution Mass Spectrometry Analysis

by Christiana Mantzourani and Maroula G. Kokotou

Separations 2025, 12(5), 114; https://doi.org/10.3390/separations12050114 - 1 May 2025

Abstract

In recent years, non-alcoholic beers have been gaining popularity. Among the various components that affect the flavor and sensory characteristics of beers, free fatty acids (FFAs) are minor components. However, due to their involvement in beer quality, fast and simple methods for analyzing [...] Read more.

In recent years, non-alcoholic beers have been gaining popularity. Among the various components that affect the flavor and sensory characteristics of beers, free fatty acids (FFAs) are minor components. However, due to their involvement in beer quality, fast and simple methods for analyzing FFAs in beers are of importance. In this work, we present a liquid chromatography–high-resolution mass spectrometry (LC-HRMS) method for the rapid determination of FFAs in beers, avoiding a tedious sample preparation and derivatization and allowing the simultaneous study of a large set of FAs, including medium-chain, long-chain, saturated, monounsaturated and polyunsaturated FAs. The method was applied in the analysis of twelve non-alcoholic and nine alcoholic beer samples from the local market, permitting the comparison of their FFA profiling. Among the 37 FAs studied, 29 were quantified, and palmitic, stearic, oleic and myristic acids were identified as the predominant FAs in both alcoholic and non-alcoholic beers. The majority of the predominant long-chain FAs, including palmitic, stearic and myristic acids, were found in decreased amounts in non-alcoholic beers, compared to the alcoholic ones, with the marked exception of oleic acid, which was increased in non-alcoholic beers. Among the medium-chain FAs, octanoic acid was found at lower concentrations in non-alcoholic beers, comparing to regular beers, while lauric acid was slightly increased. Principal component analysis (PCA) suggested the correlation of FFAs with the type of beer (alcoholic or non-alcoholic beer). Full article

(This article belongs to the Special Issue Chromatography/Mass Spectrometry for the Determination of Food Authenticity and Food Analysis)

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19 pages, 3465 KiB

Open AccessArticle

Metabolic Profiling and Pharmacokinetics Characterization of Yinhua Pinggan Granules with High-Performance Liquid Chromatography Combined with High-Resolution Mass Spectrometry

by Ningning Gu, Haofang Wan, Imranjan Yalkun, Yu He, Yihang Lu, Chang Li and Haitong Wan

Separations 2025, 12(5), 113; https://doi.org/10.3390/separations12050113 - 28 Apr 2025

Abstract

Yinhua Pinggan Granules (YPG) is a patented traditional Chinese medicine (TCM) compound prescription, with wide clinical application against cold, cough, and relevant diseases. However, the chemical profiles of YPG in vivo are still unknown, hindering further pharmacological and quality control (QC) researches. This [...] Read more.

Yinhua Pinggan Granules (YPG) is a patented traditional Chinese medicine (TCM) compound prescription, with wide clinical application against cold, cough, and relevant diseases. However, the chemical profiles of YPG in vivo are still unknown, hindering further pharmacological and quality control (QC) researches. This study presents an ultra-high-performance liquid chromatography coupled with high-resolution orbitrap mass spectrometry (UHPLC-MS)-based method. Using the Compound Discoverer platform and a self-built ‘in-house’ compound database, the metabolic profiles and pharmacokinetics characters of YPG were investigated. Consequently, a total of 230 compounds (including 39 prototype components and 191 metabolites) were tentatively identified, in which the parent compounds were mainly flavonoids, alkaloids, and terpenoids, and the main metabolic pathways of metabolites include hydration, dehydration, and oxidation. The serum concentration of seven major representative compounds, including quinic acid, chlorogenic acid, amygdalin, 3′-methoxypuerarin, puerarin, glycyrrhizic acid, and polydatin, were also measured, to elucidate their pharmacokinetics behaviors in vivo. The pharmacokinetic study showed that the seven representative compounds were quantified in rat plasma within 5 min post-administration, with T_max of less than 2 h, followed by a gradual decline in concentration over a 10 h period. The method demonstrated excellent linearity (R² > 0.998), precision, and recovery (RSD < 15%). As the first systematic characterization of YPG’ s in vivo components and metabolites using UHPLC-MS, this study may contribute to comprehensively elucidate the metabolic profiles of the major components in YPG, and provide a critical foundation for further investigation on the QC and bioactivity research of YPG. Full article

(This article belongs to the Special Issue Determination and Quantification of Pharmaceuticals Using Chromatography Methods)

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14 pages, 3695 KiB

Open AccessArticle

Synergistic Effects of SDS and Non-Ionic Surfactants on Ceramic Membrane Cleaning Performance Under Acidic Conditions

by Yang Deng, Mengkui Tian, Hai Liu, Yan An, Mingkun Wu and Hongpeng Lu

Separations 2025, 12(5), 112; https://doi.org/10.3390/separations12050112 - 28 Apr 2025

Abstract

To reinforce the cleaning agent’s wetting and cleaning capabilities on ceramic microfiltration membranes in acidic environments, the wetting properties of sodium dodecyl sulfate (SDS) in combination with multiple nonionic surfactants were examined in a systematic manner. The research findings suggested that there was [...] Read more.

To reinforce the cleaning agent’s wetting and cleaning capabilities on ceramic microfiltration membranes in acidic environments, the wetting properties of sodium dodecyl sulfate (SDS) in combination with multiple nonionic surfactants were examined in a systematic manner. The research findings suggested that there was a potential synergistic effect among SDS, isooctyl alcohol polyoxyethylene ether (JFC), and fatty alcohol polyoxyethylene ether (AEO-7). Moreover, atomic force microscopy (AFM) and infrared spectroscopy were utilized to assess the pre- and post-cleaning contamination levels. The research findings also demonstrated that using a compound cleaning agent conspicuously regenerated the structure and elevated the hydrophilicity of the ceramic membrane surface. The synergistic mechanism between JFC and SDS can be explained by the fact that the inclusion of JFC can lessen the electrostatic repulsion between the ionic groups of SDS and heighten their hydrogen bonding effect, which in turn enhances the dispersion of contaminants and lowers the surface tension of composite solution. Full article

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13 pages, 3847 KiB

Open AccessArticle

Construction of Z-Scheme Heterojunction BiOCl/Bi₂WO₆ for Visible-Light Photocatalytic Degradation of Tetracycline Hydrochloride

by Hetian Zhang, Zengying Zhu, Yajie Huang, Jiaxing Yu and Ming Li

Separations 2025, 12(5), 111; https://doi.org/10.3390/separations12050111 - 28 Apr 2025

Abstract

Tetracycline hydrochloride pollution poses a serious environmental threat; however, it is difficult to deal with by conventional methods. In this study, the Z-scheme BiOCl/Bi₂WO₆ composite was hydrothermally synthesized and evaluated for its ability to decompose tetracycline hydrochloride under visible light. [...] Read more.

Tetracycline hydrochloride pollution poses a serious environmental threat; however, it is difficult to deal with by conventional methods. In this study, the Z-scheme BiOCl/Bi₂WO₆ composite was hydrothermally synthesized and evaluated for its ability to decompose tetracycline hydrochloride under visible light. The composite material was systematically characterized by XRD, SEM, TEM/HRTEM, XPS, FTIR, BET, PL, UV-Vis DRS, and EPR to analyze its structure, morphology, and optical/electrochemical properties. Characterization revealed that the composite featured a flower-ball structure with broader light absorption and higher solar energy efficiency. A narrow bandgap further facilitated charge separation, boosting photocatalytic performance. Among the synthesized materials, the 20% BiOCl/Bi₂WO₆ composite exhibited the best performance, removing 94% of tetracycline hydrochloride in 60 min, which was 5.2 times and 1.4 times higher than pure BiOCl and Bi₂WO₆, respectively. The rate constant was 10.8 times and 2.5 times higher than that of pure BiOCl and Bi₂WO₆. After five cycles, it maintained the 88.7% removal rate, with X-ray diffraction analysis confirming its structural stability and well mechanical properties. Electron paramagnetic resonance and radical scavenging experiments identified photogenerated holes (h⁺) and superoxide radicals (·O₂⁻) as the primary active species. This work highlights the fact that the prepared Z-scheme BiOCl/Bi₂WO₆ composite exhibited excellent photocatalytic performance in the degradation of tetracycline hydrochloride, demonstrating promising potential for practical applications. Full article

(This article belongs to the Special Issue Photocatalytic Degradation of Organic Pollutant in Wastewater)

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15 pages, 3815 KiB

Open AccessArticle

Study of Bacterial Elution from High-Efficiency Glass Fiber Filters

by Le Rong, Yun Liang, Zhaoqian Li, Desheng Wang, Hao Wang, Lingyun Wang and Min Tang

Separations 2025, 12(5), 110; https://doi.org/10.3390/separations12050110 - 25 Apr 2025

Abstract

Antibacterial filter materials have been effectively utilized for controlling biological contaminants and purifying indoor air, with the market for such materials experiencing continuous expansion. Currently, textile antibacterial testing standards are widely adopted to evaluate the antimicrobial efficacy of filter materials, yet no dedicated [...] Read more.

Antibacterial filter materials have been effectively utilized for controlling biological contaminants and purifying indoor air, with the market for such materials experiencing continuous expansion. Currently, textile antibacterial testing standards are widely adopted to evaluate the antimicrobial efficacy of filter materials, yet no dedicated assessment protocols specifically tailored for filtration media have been established. This study aims to investigate the applicability of textile antibacterial testing methods to high-efficiency glass fiber filter materials (filtration efficiency > 99.9%), as well as to explore the factors that affect the rate of bacterial elution from high-efficiency glass fiber filter materials. By referencing the textile antibacterial testing standard (absorption method), significant discrepancies in bacterial recovery counts were observed between the high-efficiency glass fiber materials and the various textile control samples, with the former exhibiting a markedly lower recovery rate (approximately 10%). Pore structure and wettability analyses revealed the underlying causes of these differences. To ensure the accuracy of the antibacterial evaluation results, the effects of oscillation elution parameters (time and intensity) and material incubation conditions (duration, sealing and humidity) on bacterial recovery rates in glass fiber filter materials were systematically investigated to optimize the elution methodology. The results indicate that specimen type, size, elution method, incubation duration (4 h or 24 h), sealing conditions, and environmental humidity (10% or 30%, 60% and 95% RH) collectively influence bacterial recovery efficiency. The highest recovery efficiency (55%) was achieved when the filter materials were incubated in a sealed environment with humidity maintained at ≥60% RH. These findings emphasize the critical need to establish clear and specialized antibacterial performance testing standards for filter materials. The study provides essential guidance for developing material-specific evaluation protocols to ensure a reliable and standardized assessment of antimicrobial efficacy in high-efficiency filtration systems. Full article

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14 pages, 680 KiB

Open AccessArticle

Ultrasound-Assisted Extraction of Phenolic Compounds and Flavonoids from Banana Inflorescence and Characterization of Its Fibrous Residue

by Fábio Dias Bertoco Júnior, Érica Marusa Pergo Coelho, Mirian Cristina Feiten and Beatriz Cervejeira Bolanho Barros

Separations 2025, 12(5), 109; https://doi.org/10.3390/separations12050109 - 25 Apr 2025

Abstract

The banana inflorescence (BI) is a rich source of antioxidants and dietary fiber, making it a valuable by-product of banana harvesting. This study aimed to maximize the ultrasound-assisted extraction (UAE) of antioxidant compounds from BI and analyze the residue’s composition and functional properties. [...] Read more.

The banana inflorescence (BI) is a rich source of antioxidants and dietary fiber, making it a valuable by-product of banana harvesting. This study aimed to maximize the ultrasound-assisted extraction (UAE) of antioxidant compounds from BI and analyze the residue’s composition and functional properties. The Box–Behnken Design was applied to test different ultrasound powers, temperatures, and sample-to-solvent ratios on the total phenolic content (TPC) and total flavonoid content (TFC). The UAE conducted at 350 W, 55 °C, 1:30 (g/mL) ratio for 30 min resulted in the highest TPC (1637.12 mg/100 g) and TFC (22.97 mg/100 g). Isovanillin, caffeine, naringin, sinapaldehyde, nicotinic acid, quinic acid, malic acid, and fumaric acids were reported for the first time for BI. The extract obtained by UAE showed a higher content of these compounds and higher antioxidant activity than that obtained through conventional extraction (orbital shaking). The residue obtained after UAE presented dietary fiber as the main component (71.91 g/100 g) and a higher oil absorption index (5.78 g/g) than untreated BI. Therefore, BI is a source of bioactive compounds, and both the extract and residue can be used in the pharmaceutical, food, and cosmetic industries, enabling the productive sector to move closer to the circular economy. Full article

(This article belongs to the Special Issue Application of Sustainable Separation Techniques in Food Processing)

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14 pages, 1759 KiB

Open AccessArticle

Electrochemical Precipitation of Struvite from Wastewater: A Sustainable Approach for Nitrogen Recovery

by Rúbia Mores, Anildo Cunha Junior, Fabiane Goldschmidt Antes, Marco Di Luccio, Carolina E. Demaman Oro, Marcus V. Tres, Clarice Steffens, Juliana Steffens, Airton Kunz and Rogério Marcos Dallago

Separations 2025, 12(5), 108; https://doi.org/10.3390/separations12050108 - 25 Apr 2025

Abstract

This study evaluates the feasibility of nitrogen recovery from wastewater via electrochemical methods as an alternative nutrient source for agricultural applications. Ammonium nitrogen (NH₄⁺-N) and phosphate (PO₄³⁻-P) contamination poses significant environmental risks and challenges water resource management [...] Read more.

This study evaluates the feasibility of nitrogen recovery from wastewater via electrochemical methods as an alternative nutrient source for agricultural applications. Ammonium nitrogen (NH₄⁺-N) and phosphate (PO₄³⁻-P) contamination poses significant environmental risks and challenges water resource management globally. The electrochemical precipitation of struvite (MgNH₄PO₄·6H₂O) offers a promising solution for nutrient recovery, with potential applications as a slow-release fertilizer. Experimental results demonstrate that increased current density (from 2.5 to 7.5 mA/cm²) and reduced electrode distance (1 cm) significantly enhance NH₄⁺ and PO₄³⁻ consumption and struvite precipitation. Increasing the amperage from 2.5 to 7.5 mA·cm⁻² at a 1 cm electrode distance raised the ammoniacal nitrogen incorporation from 1.59 to 5.34 g/100 g, signifying greater struvite production. The Mg and P concentrations were 15.44 and 12.60 g/100 g, respectively, for this higher amperage, although lower than the concentrations seen with 2.5 mA·cm⁻² (22.16 and 14.52 g/100 g). The majority of Mg (60%) and P (93.6%) were, however, incorporated within struvite. Additionally, this study reveals that Mg is primarily incorporated as struvite when using higher current densities, while lower current densities yield greater Mg incorporation in non-struvite forms, such as magnesium carbonate. Findings suggest that optimizing current density and electrode distance can improve nitrogen and phosphorus recovery efficiencies, making electrochemical struvite production a viable, sustainable approach for nutrient recycling. This method not only reduces dependence on synthetic fertilizers but also supports sustainable agricultural practices by transforming wastewater contaminants into valuable resources. Full article

(This article belongs to the Special Issue Application of Sustainable Separation Techniques in Food Processing)

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17 pages, 3618 KiB

Open AccessArticle

Polymer-Coated Nickel Nanoparticles for CO₂ Capture in Seawater

by Abhishek, Abhishek Ratanpara, Adib Mahmoodi Nasrabadi and Myeongsub Kim

Separations 2025, 12(5), 107; https://doi.org/10.3390/separations12050107 - 24 Apr 2025

Abstract

Carbon capture and storage (CCS) technologies are employed to mitigate global warming by removing carbon from the atmosphere. To enhance carbon capture efficiency, nanoparticles have gained considerable attention as catalysts due to their large surface area, tunable properties, regeneration, and enhanced reactivity. However, [...] Read more.

Carbon capture and storage (CCS) technologies are employed to mitigate global warming by removing carbon from the atmosphere. To enhance carbon capture efficiency, nanoparticles have gained considerable attention as catalysts due to their large surface area, tunable properties, regeneration, and enhanced reactivity. However, it poses some challenges, such as nanoparticle aggregation and reduced effectiveness in sustainable solvents like seawater. To address these limitations and promote an environmentally sustainable method for carbon capture, this study evaluates the CO₂ capture efficiency of seawater using nickel nanoparticles (NiNPs) coated with polyvinylpyrrolidone (PVP) as a catalyst. We examined the time-dependent size variations of CO₂ bubbles in a flow-focusing microchannel using high-speed bubble-based microfluidics, directly associated with transitory CO₂ dissolution into the surrounding solution. We hypothesized that smaller polymer-coated NiNPs, due to their higher surface-to-volume ratio, can enhance CO₂ solubility and capture rates under identical environmental conditions. To verify this, polymer-coated NiNPs of three different sizes—5 nm, 10 nm, and 20 nm—were synthesized and tested. The experiments revealed that 5 nm NiNPs achieved a CO₂ dissolution rate of 77%, in contrast to 71% for 10 nm and 43% for 20 nm particles. These findings validate the hypothesis, demonstrating that smaller nanoparticles facilitate more effective CO₂ capture using equivalent material quantities, thereby potentially improving the overall efficiency of CO₂ reduction. This innovative approach contributes to advancing NiNP-based catalysts for saltwater-based CO₂ capture. Full article

(This article belongs to the Special Issue Application of Advanced Materials and Technologies in the Separation and Adsorption)

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15 pages, 2586 KiB

Open AccessArticle

Enhanced Selective Separation of Pu(IV) and U(VI) Using Novel Diethylene Glycolamide Ligand

by Xiaoyun Guo, Junli Wang, Yao Liu, Haojun Zhao, Hui Wang, Wentao Wang, Baole Li and Taihong Yan

Separations 2025, 12(5), 106; https://doi.org/10.3390/separations12050106 - 23 Apr 2025

Abstract

Developing a new efficient separation ligand based on the “CHON” principle to address the limitations of phosphorus containing extractants in nuclear fuel reprocessing can help further simplify the process flow and reduce the amount of secondary waste. Building upon this critical need, a [...] Read more.

Developing a new efficient separation ligand based on the “CHON” principle to address the limitations of phosphorus containing extractants in nuclear fuel reprocessing can help further simplify the process flow and reduce the amount of secondary waste. Building upon this critical need, a novel ligand was developed through a strategic application of the Hard and Soft Acids and Bases (HSAB) theory, integrating a soft donor nitrogen atom into the linear architecture of bis-diglycolamide. This groundbreaking ligand, named N,N′-bis[2-(2-(N,N-dioctylcarbamoyl)ethoxy)ethylacetamido]-N″-diethylenetriamine (TOMDEA-BisDGA), has demonstrated remarkable potential in the extraction of Pu(IV). The study unveils that the ligand demonstrates remarkable selectivity and separation efficiency towards Pu(IV) ions while maintaining an exceptionally low extraction capacity for U(VI) across a wide acidity spectrum of 0.1~6 mol/L. To explain the structure properties of complex formed by the ligand and Pu(IV), a systematic analysis was performed, including slope analysis, proton nuclear magnetic resonance (NMR) titration, and Fourier-transform infrared (FT-IR) spectroscopy. This study explores the coordination and separation behavior of diglycolamide ligands with actinide. This work is expected to provide important information and theoretical bases upon which advanced design and optimization of ligands for high-performance processes for the separation of plutonium might be carried out. Such findings will contribute to the understanding of actinide chemistry and further the design of improved separation methods for nuclear applications. Full article

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6 pages, 761 KiB

Open AccessTechnical Note

Optimizing Liquid Electron Ionization Interface to Boost LC-MS Instrumental Efficiency

by Tommaso Grazioso, Genny Grasselli, Adriana Arigò, Giorgio Famiglini and Achille Cappiello

Separations 2025, 12(5), 105; https://doi.org/10.3390/separations12050105 - 23 Apr 2025

Abstract

Liquid Electron Ionization (LEI) is a powerful and robust interface for the qualitative and quantitative analysis of medium-low-molecular-weight compounds, including numerous environmental pollutants and toxicological substances. Although the robustness and performance of this interface have already been demonstrated, research on its optimization can [...] Read more.

Liquid Electron Ionization (LEI) is a powerful and robust interface for the qualitative and quantitative analysis of medium-low-molecular-weight compounds, including numerous environmental pollutants and toxicological substances. Although the robustness and performance of this interface have already been demonstrated, research on its optimization can still improve instrumental performance in terms of detectability. In this study, different setups of the interface’s vaporization micro-channel (VMC) made using different capillaries and various sizes were tested to evaluate the correspondent instrumental performance. The results show that a new combination of capillaries in the interface set up significantly improves instrumental detectability, reaching LOD values almost five times lower than those of the previous setup. Full article

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13 pages, 2822 KiB

Open AccessArticle

A Two-Dimensional Thiotitanate Ion Exchanger with High Cs⁺ Removal Performance

by Chang Wei, Shaoqing Jia, Yingying Zhao, Jiating Liu, Haiyan Sun, Meiling Feng and Xiaoying Huang

Separations 2025, 12(5), 104; https://doi.org/10.3390/separations12050104 - 22 Apr 2025

Abstract

¹³⁷Cs is a persistent β/γ-emitter (t_1/2 = 30.1 years) generated from ²³⁵U and ²³⁹Pu fission. It is a critical challenge to efficiently capture ¹³⁷Cs⁺ for nuclear waste management due to its high solubility, [...] Read more.

¹³⁷Cs is a persistent β/γ-emitter (t_1/2 = 30.1 years) generated from ²³⁵U and ²³⁹Pu fission. It is a critical challenge to efficiently capture ¹³⁷Cs⁺ for nuclear waste management due to its high solubility, environmental mobility, and propensity for biological accumulation. Herein, we prepare a two-dimensional (2D) thiotitanate Rb_0.32TiS₂·0.75H₂O (denoted Rb-TiS₂) using a special molten salt synthesis method, “Mg + RbCl”. Rb-TiS₂ can selectively capture Cs⁺ from aqueous solutions. Its structure features a flexible anionic thiotitanate layer with Rb⁺ as counter ions located at the interlayer spaces. As an ion exchanger, it possesses high adsorption capacity (q_m^Cs = 232.70 mg·g⁻¹), rapid kinetics (the removal rate R > 72% within 10 min), and a wide pH tolerance range (pH = 4–12) for Cs⁺ adsorption. Through a single-crystal X-ray structural analysis, we elucidated the mechanism of Cs⁺ capture, revealing the ion exchange pathways between Cs⁺ and Rb⁺ in Rb-TiS₂. This work not only provides an important reference for the synthesis of transition metal sulfides with alkali metal cations but also proves the application prospect of transition metal sulfides in radionuclide remediation. Full article

(This article belongs to the Special Issue Separation Technology for Metal Extraction and Removal)

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19 pages, 3171 KiB

Open AccessArticle

Nonylphenol Removal from Water and Wastewater with Alginate-Activated Carbon Beads

by Angelica A. Chacon, Elizabeth Noriega Landa, Sheng Yin, Ahsan Habib, Kiana L. Holbrook, Luis R. Duran Bojorquez, Sabur Badmos, Dino Villagrán and Wen-Yee Lee

Separations 2025, 12(5), 103; https://doi.org/10.3390/separations12050103 - 22 Apr 2025

Abstract

In this study, eco-friendly and sustainable alginate-activated carbon (Alg-C)-based beads were synthesized and characterized for the adsorption of nonylphenols (NPs) from aqueous environments under various conditions. The surface characterization, functional groups, and adsorption behavior were analyzed using multiple analytical techniques. The effect of [...] Read more.

In this study, eco-friendly and sustainable alginate-activated carbon (Alg-C)-based beads were synthesized and characterized for the adsorption of nonylphenols (NPs) from aqueous environments under various conditions. The surface characterization, functional groups, and adsorption behavior were analyzed using multiple analytical techniques. The effect of key parameters, including dosage, pH, temperature, and reusability, were evaluated. Isotherm and kinetic studies revealed that the adsorption process followed a pseudo-second-order kinetic model and aligned with the Freundlich isotherm, indicating a heterogeneous surface. The beads exhibited a high removal efficiency of 97% over five reuse cycles in a 50 mL solution of 10 mg L⁻¹ NPs under static conditions, demonstrating their recyclability. Thermodynamic analysis suggested potential electrostatic interactions, supported by positive Gibbs free energy values. The highest removal performance was achieved within 90 min, with adsorption capacities from 0.10 to 0.39 mg g⁻¹. Additionally, the performance of Alg-C beads remained stable across different pH levels, highlighting their robustness. When tested with wastewater samples, Alg-C beads maintained high removal efficiency, with no significant matrix effects observed. These results underscore Alg-C beads as a promising and sustainable solution for the elimination of NPs from contaminated water sources. Full article

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12 pages, 3159 KiB

Open AccessArticle

Effects of Lubricants and the Additives on the Foaming of Desulfurization Solvent

by Jiandong Zhang, Changchun Li, Yang Yang, Xiaolong Xu and Hui Sun

Separations 2025, 12(4), 102; https://doi.org/10.3390/separations12040102 - 21 Apr 2025

Abstract

Understanding the effects of industrial lubricating oil and additives on desulfurization solution foaming is very important to both engineers and academic researchers. In this study, the influences of lubricating oil and its additive components on the foaming performance of desulfurization solution were examined, [...] Read more.

Understanding the effects of industrial lubricating oil and additives on desulfurization solution foaming is very important to both engineers and academic researchers. In this study, the influences of lubricating oil and its additive components on the foaming performance of desulfurization solution were examined, and the empirical model was established to predict the foam height of desulfurization solution containing contaminants. It is established that the additives of dodecenyl succinic acid and zinc dialkyl dithiophosphate have more significant influence on the foaming performance of desulfurization solution than the lubricant base oil. In addition, the effect can be enlarged at lower temperatures. The prediction model of the foaming performance of desulfurization solution was established, and the prediction deviation of the foam height was no more than 7%. The predicted foam height increases with increasing apparent air velocity, solution surface tension, and viscosity, and decreases with increasing solution density and average bubble radius. Additionally, the foam height and defoaming time of the contaminated industrial solution were largely reduced by employing an adsorption purification process using activated carbon as an adsorbent. The present study highlights the quantitative relationship between contaminant contents and foam height, as well as defoaming time. Full article

(This article belongs to the Section Purification Technology)

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16 pages, 4992 KiB

Open AccessArticle

Degradation of Acid Orange II by FeOCl/Biochar-Catalyzed Heterogeneous Fenton Oxidation

by Jiren Yuan, Dongao Xie, Dan Li and Feigao Xu

Separations 2025, 12(4), 101; https://doi.org/10.3390/separations12040101 - 21 Apr 2025

Abstract

In recent years, the rapid development of industry has led to the discharge of large quantities of pollutants, including harmful dyes, into water sources, thereby posing potential threats to human health and the environment. FeOCl and biochar have their own shortcomings as a [...] Read more.

In recent years, the rapid development of industry has led to the discharge of large quantities of pollutants, including harmful dyes, into water sources, thereby posing potential threats to human health and the environment. FeOCl and biochar have their own shortcomings as a mediator in the heterogeneous Fenton process. To make both materials useful, FeOCl supported on bamboo biochar (FeOCl/BC) was prepared by calcination using FeCl₃·6H₂O and bamboo powder as raw materials, and the composite’s catalytic activities were explored with acid orange II (AO-II) as the target pollutant. The degradation efficiency of FeOCl/BC composites on AO-II was determined by testing the mass ratio of FeOCl and BC, initial pH, temperature, H₂O₂ concentration, catalyst addition, addition of coexisting inorganic anions, and natural organic matter. The addition of biochar to FeOCl increased the activation of H₂O₂ to generate •OH for the removal of AO-II and accelerated the cycle of Fe³⁺/Fe²⁺. The removal rate of AO-II by the Fe₁C_0.2 composite was 97.1% when the mass ratio of FeOCl and BC was 1:0.2 (Fe₁C_0.2), which was higher than that of the pure components (FeOCl or BC) at pH = 6.1. Moreover, after five reuses, the Fe₁C_0.2 composite still showed high degradation activity for AO-II, with 83.3% degradation and low activity loss. The capture experiments on the active material showed that the removal of AO-II by the Fe₁C_0.2 composite was mainly dominated by •OH; however, •O₂⁻ and h⁺ played minor roles. The synthesized Fe₁C_0.2 composite could be applied for organic contaminants such as AO-II with high removal efficiency. Full article

(This article belongs to the Special Issue Advances in Photocatalysis for Environmental Pollutant Removal)

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28 pages, 19278 KiB

Open AccessArticle

Synthesis and Application of Poly(N-isopropylacrylamide-co-methacrylic Acid) Hydrogels as Sorbent Materials for Wastewater Treatment

by Aleksandar Zdravković, Vesna Nikolić, Snežana Ilić-Stojanović, Sanja Stojanović, Ana Dinić, Maja Urošević, Ivana Gajić and Ljubiša Nikolić

Separations 2025, 12(4), 100; https://doi.org/10.3390/separations12040100 - 17 Apr 2025

Abstract

N-isopropylacrylamide and methacrylic acid were copolymerized by a free radical polymerized mechanism. The obtained hydrogel poly(N-isopropylacrylamide-co-methacrylic acid) hydrogels, poly(NIPAM-co-MAA), were utilized as sorbent material for removal Cr(VI), Mn(II), and Pb(II) ions from simulated aqueous solutions. Hydrogel [...] Read more.

N-isopropylacrylamide and methacrylic acid were copolymerized by a free radical polymerized mechanism. The obtained hydrogel poly(N-isopropylacrylamide-co-methacrylic acid) hydrogels, poly(NIPAM-co-MAA), were utilized as sorbent material for removal Cr(VI), Mn(II), and Pb(II) ions from simulated aqueous solutions. Hydrogel structures before and after heavy metal sorption are characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The swelling results indicate that poly(NIPAM-co-MAA) hydrogels are pH- and temperature-sensitive and have high swelling reversibility through three swelling/contraction cycles. The studied parameters of heavy metal sorption include the effect of pH, the initial concentration of heavy metal, the effect of temperature, and the desorption of metal ions. The maximum sorption capacities of poly(NIPAM-co-MAA) hydrogels were determined at pH 4.5 and 25 °C, and they are, for Cr(VI), Mn(II), and Pb(II) ions, 289.35 mg/g, 190.59 mg/g, and 349.71 mg/g, respectively. The pseudo-second-order model and the Langmuir adsorption isotherm best describe the sorption of heavy metal ions onto hydrogels. The removal of heavy metals is an exothermic reaction, and the interaction mechanism between the metal and the hydrogel is primarily physical in nature. Results of three sorption/desorption cycles show a good desorption ratio and sorption capacity of poly(NIPAM-co-MAA) hydrogels. Full article

(This article belongs to the Special Issue New and Modified Polymers for Detection and Removal of Pollutants from Water and Air)

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