Separations

17 pages, 2691 KiB

Open AccessArticle

Phytochemical Profile Screening and Selected Bioactivity of Myrtus communis Berries Extracts Obtained from Ultrasound-Assisted and Supercritical Fluid Extraction

by Ilir Mërtiri, Gigi Coman, Mihaela Cotârlet, Mihaela Turturică, Nicoleta Balan, Gabriela Râpeanu, Nicoleta Stănciuc and Liliana Mihalcea

Separations 2025, 12(1), 8; https://doi.org/10.3390/separations12010008 - 3 Jan 2025

Abstract

This research paper investigates the phytochemical profile, antioxidant activity, antidiabetic potential, and antibacterial activity of Myrtus communis berries. Two extraction methods were employed to obtain the extracts: solid–liquid ultrasound-assisted extraction (UAE) and supercritical fluid extraction (SFE). The extracts were characterized using spectrophotometric methods [...] Read more.

This research paper investigates the phytochemical profile, antioxidant activity, antidiabetic potential, and antibacterial activity of Myrtus communis berries. Two extraction methods were employed to obtain the extracts: solid–liquid ultrasound-assisted extraction (UAE) and supercritical fluid extraction (SFE). The extracts were characterized using spectrophotometric methods and Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC). The UAE extract exhibited higher total flavonoid and anthocyanin content, while the SFE extract prevailed in total phenolic content and antioxidant activity in the DPPH radical screening assay. RP-HPLC characterization identified and quantified several polyphenolic compounds. In the UAE extract, epigallocatechin was found in a concentration of 2656.24 ± 28.15 µg/g dry weight (DW). In the SFE extract, cafestol was the identified compound with the highest content at a level of 29.65 ± 0.03 µg/g DW. Both extracts contained several anthocyanin compounds, including cyanidin 3-O-glucoside chloride, cyanidin-3-O-rutinoside chloride, malvidin-3-O-glucoside chloride, pelargonidin 3-O-glucoside chloride, peonidin 3-O-glucoside chloride, and peonidin-3-O-rutinoside chloride. The antidiabetic potential was evaluated in vitro by measuring the inhibition of α-amylase from porcine pancreas (type I-A). The results highlighted the ability of myrtle berry extracts to inhibit α-amylase enzymatic activity, suggesting its potential as an alternative for controlling postprandial hyperglycemia. The UAE extract showed the lowest IC50 value among the two extracts, with an average of 8.37 ± 0.52 µg/mL DW. The antibacterial activity of the extracts was assessed in vitro against Bacillus spp., Escherichia coli, and Staphylococcus aureus using the disk diffusion method. Both myrtle berry extracts exhibited similar antibacterial activity against the tested bacterial strains. The results support further investigation of myrtle berries extracts as a potential ingredient in functional food formulation, particularly due to its antioxidant, antidiabetic, and antibacterial properties. Full article

(This article belongs to the Special Issue Green Extraction Techniques of Bioactive Compounds from Natural Sources)

► Show Figures

Figure 1

17 pages, 5169 KiB

Open AccessArticle

Research on the Flotation Mechanism of Microemulsion Collector Enhanced Removal of Dyeing Impurities from Phosphogypsum

by Xiaosheng Yu, Lijun Deng, Changpan Shen, Huiyong Li, Jingchao Li, Yijun Cao, Guoli Zhou and Guosheng Li

Separations 2025, 12(1), 7; https://doi.org/10.3390/separations12010007 - 31 Dec 2024

Abstract

Phosphogypsum is an industrial byproduct that is limited in its high-value application due to the presence of dyeing impurities (such as organic matter and carbon black). The flotation method has been verified to be effective in separating these dyeing impurities from gypsum. In [...] Read more.

Phosphogypsum is an industrial byproduct that is limited in its high-value application due to the presence of dyeing impurities (such as organic matter and carbon black). The flotation method has been verified to be effective in separating these dyeing impurities from gypsum. In this study, microemulsion was used as the collector method of dyeing impurities for their separation from gypsum. The results of flotation tests showed that the microemulsion collector exhibited excellent collection capability and selectivity under natural pH conditions (pH = 1.5). With a microemulsion collector consumption of 400 g/t, purified gypsum of 65.1% whiteness, 95.74% yield, and 97.01% recovery was obtained. The purified gypsum of 65.1% whiteness, 95.74% yield, 97.01 recovery obtained by a used microemulsion collector amount of 400 g/t was better than using the same dosage of kerosene collector. The dispersion behavior of the microemulsion collector was studied by low-temperature transmission electron microscopy. The microemulsion collector demonstrated superior dispersibility, as it forms nano-oil droplets with an average size of 176.83 nm in the pulp, resolving issues associated with poor dispersibility observed in traditional kerosene collectors. Additionally, the nano-oil droplets effectively adsorbed onto the surface of dyeing impurities through hydrogen bonding, enhancing their hydrophobicity. Therefore, the microemulsion collector holds great potential for application in flotation whitening processes involving phosphogypsum. Full article

(This article belongs to the Special Issue Separation and Extraction Technology in Mineral Processing)

► Show Figures

Figure 1

15 pages, 2061 KiB

Open AccessArticle

Kinetics of Supercritical CO₂ Extraction from Burrito (Aloysia polystachya) Leaves and Sucupira-Preta (Bowdichia virgilioides) Seeds

by Gabrielle Vaz Vieira, Michel Rubens dos Reis Souza, Carlos Toshiyuki Hiranobe, José Eduardo Goncalves, Cristiane Mengue Feniman Moritz, Otávio Akira Sakai, Leila Maria Sotocorno e Silva, Michael Jones da Silva, Erivaldo Antônio da Silva, Renivaldo José dos Santos, Edson Antônio da Silva, Lucio Cardozo-Filho and Leandro Ferreira-Pinto

Separations 2025, 12(1), 6; https://doi.org/10.3390/separations12010006 - 31 Dec 2024

Abstract

This study investigated the application of supercritical carbon dioxide (CO₂) for the extraction of essential oils from plant materials with anxiolytic potential, focusing on the leaves of burrito (Aloysia polystachya) and the seeds of sucupira-preta (Bowdichia virgilioides). [...] Read more.

This study investigated the application of supercritical carbon dioxide (CO₂) for the extraction of essential oils from plant materials with anxiolytic potential, focusing on the leaves of burrito (Aloysia polystachya) and the seeds of sucupira-preta (Bowdichia virgilioides). The supercritical extraction technique was chosen for its ability to produce high-purity extracts without residual solvents and to reduce the environmental impact. This study evaluated the influence of temperature (40 °C, 50 °C, and 60 °C) and pressure (22 MPa, 25 MPa, and 28 MPa) on extraction efficiency using a 2² factorial design with triplicates at the central point. The maximum yields were 1.2% for burrito leaves and 4.2% for sucupira-preta seeds. Despite their relatively low yields, the extracts contained a diverse range of chemical compounds, including fatty acids (oleic, linoleic, and palmitic acids), squalene, β-carotene, vitamin E, and other bioactive molecules with antioxidant, anti-inflammatory, and immunomodulatory properties. Statistical analysis demonstrated that pressure was the most influential factor affecting yield, whereas temperature played a secondary role. The Sovová kinetic model provided a good fit for the extraction curves, with determination coefficients (R²) above 0.95, thus validating the efficiency of the method. These results highlight the pharmaceutical potential of these extracts, particularly for therapeutic and anxiolytic purposes. Full article

► Show Figures

Figure 1

17 pages, 5353 KiB

Open AccessArticle

A Compact Instrument for Temperature-Programming-Assisted Capillary–Nanoliquid Chromatography

by Lincon Coutinho Marins, Alessandra Maffei Monteiro, Vivane Lopes Leal, Deyber Arley Vargas Medina, Edwin Martin Cardenas and Fernando Mauro Lanças

Separations 2025, 12(1), 5; https://doi.org/10.3390/separations12010005 - 30 Dec 2024

Abstract

The miniaturization of liquid chromatography (LC) columns to capillary and nanoscales allows temperature programming to be an effective alternative to solvent gradients for modulating eluotropic strength. This approach simplifies instrument design and operation, as a single pump can suffice to achieve efficient separations. [...] Read more.

The miniaturization of liquid chromatography (LC) columns to capillary and nanoscales allows temperature programming to be an effective alternative to solvent gradients for modulating eluotropic strength. This approach simplifies instrument design and operation, as a single pump can suffice to achieve efficient separations. This study presents the development and application of a compact, lab-built high-pressure system for temperature-programmed capillary and nanoLC separations. The instrument includes a high-pressure capillary–nanoflow syringe pump, a time-based nanoliter injection system, a programmable capillary column oven for controlled temperature gradients, and a UV-Vis detection system with a custom nanoliter-scale detection cell. Each system component was designed and built in-house, with rigorous calibration to ensure accuracy and operational reliability. Experimental data confirm the system’s capability to deliver precise, reproducible temperature, and flow rates. Functionality was validated through temperature-programmed separations on packed and open tubular capillary columns. The results demonstrated that the developed instrument offers enhanced separation efficiency and reduced analysis time compared to isothermal methods, underscoring its potential for advanced applications in miniaturized liquid chromatography. Full article

(This article belongs to the Special Issue Separation Techniques on a Miniaturized Scale)

► Show Figures

Figure 1

22 pages, 2361 KiB

Open AccessReview

Advances in Recycling Technologies of Critical Metals and Resources from Cathodes and Anodes in Spent Lithium-Ion Batteries

by Shuwen Wang, Yanrong Lai, Jingran Yang, Jiaxue Zhao, Yushan Zhang, Miaoling Chen, Jinfeng Tang, Junhua Xu and Minhua Su

Separations 2025, 12(1), 4; https://doi.org/10.3390/separations12010004 - 30 Dec 2024

Abstract

With the rapid economic development and the continuous growth in the demand for new energy vehicles and energy storage systems, a significant number of waste lithium-ion batteries are expected to enter the market in the future. Effectively managing the processing and recycling of [...] Read more.

With the rapid economic development and the continuous growth in the demand for new energy vehicles and energy storage systems, a significant number of waste lithium-ion batteries are expected to enter the market in the future. Effectively managing the processing and recycling of these batteries to minimize environmental pollution is a major challenge currently facing the lithium-ion battery industry. This paper analyzes and compares the recycling strategies for different components of lithium-ion batteries, providing a summary of the main types of batteries, existing technologies at various pre-treatment stages, and recycling techniques for valuable resources such as heavy metals and graphite. Currently, pyrometallurgy and hydrometallurgy processes have matured; however, their high energy consumption and pollution levels conflict with the principles of the current green economy. As a result, innovative technologies have emerged, aiming to reduce energy consumption while achieving high recovery rates and minimizing the environmental impact. Nevertheless, most of these technologies are currently limited to the laboratory scale and are not yet suitable for large-scale application. Full article

(This article belongs to the Section Purification Technology)

► Show Figures

Figure 1

12 pages, 1644 KiB

Open AccessArticle

CO₂/CH₄ and CO₂/CO Selective Pebax-1657 Based Composite Hollow Fiber Membranes Prepared by a Novel Dip-Coating Technique

by Dionysios S. Karousos, George V. Theodorakopoulos, Francesco Chiesa, Stéphan Barbe, Mirtat Bouroushian and Evangelos P. Favvas

Separations 2025, 12(1), 3; https://doi.org/10.3390/separations12010003 - 29 Dec 2024

Abstract

A novel and innovative method was developed to fabricate defect-free composite hollow fiber (HF) membranes using drop-casting under continuous flow. The synthesized Pebax-1657—based membranes were examined for gas separation processes, focusing on the separation of CO₂ from CH₄ and CO gases. [...] Read more.

A novel and innovative method was developed to fabricate defect-free composite hollow fiber (HF) membranes using drop-casting under continuous flow. The synthesized Pebax-1657—based membranes were examined for gas separation processes, focusing on the separation of CO₂ from CH₄ and CO gases. The separation performance of the membranes was rigorously assessed under realistic binary gas mixture conditions to evaluate their selectivity and performance. The effect of pressure on separation performance was systematically investigated, with transmembrane pressures up to 10 bar being applied at a temperature of 298 K. Remarkable CO₂/CH₄ selectivities of up to 110 and CO₂/CO selectivities of up to 48 were achieved, demonstrating the robustness and effectiveness of these composite HF membranes, suggesting their suitability for high-performance gas separation processes under varying operational conditions. Overall, this study introduces a novel approach for scaling up the fabrication of HF membranes and provides valuable insights into their application in CO₂ separation technologies, offering the potential for advancements in areas such as natural gas processing and carbon capture from CO-containing streams. Full article

(This article belongs to the Special Issue 10th Anniversary Special Issues: Membrane Separation Processes)

► Show Figures

Figure 1

21 pages, 5817 KiB

Open AccessArticle

Application of Magnetic Aquatic Plant Biochar for Efficient Removal of Antimony from Water: Adsorption Properties and Mechanism

by Luyi Nan, Yuting Zhang, Min Liu, Liangyuan Zhao, Yuxuan Zhu and Xun Zhang

Separations 2025, 12(1), 2; https://doi.org/10.3390/separations12010002 - 28 Dec 2024

Abstract

Antimony (Sb) pollution in natural water bodies can cause significant harm to aquatic ecosystems. Currently, the utilization of chemicals in water bodies presents disadvantages, such as the hardship in collecting dispersed flocs and the incomplete elimination of pollutants. In the present research, a [...] Read more.

Antimony (Sb) pollution in natural water bodies can cause significant harm to aquatic ecosystems. Currently, the utilization of chemicals in water bodies presents disadvantages, such as the hardship in collecting dispersed flocs and the incomplete elimination of pollutants. In the present research, a novel type of efficient adsorbent material for the magnetic recovery of Sb was proposed: the magnetic aquatic plant biochar. Its adsorption characteristics and mechanism were deeply investigated. The results demonstrated that, among the three types of aquatic plants, the magnetic biochar of Arundo donax magnetic biochar (LMBC) displayed the most superior adsorption effect on Sb. Under optimal adsorption conditions (pyrolysis temperature of 300 °C, dosage of 100 mg, pH of 8), the removal rate of Sb by LMBC exceeded 97%. The adsorption rate of Sb by LMBC was relatively rapid, and the kinetics of adsorption conformed to a pseudo-second-order kinetic model. The adsorption isotherm was consistent with the Langmuir and Freundlich models, and the maximum adsorption capacity of Sb reached 26.07 mg/g, suggesting that the adsorption process pertained to the adsorption of multi-molecular layers. The influence of coexisting ions on the adsorption effect of LMBC was insignificant. The SEM characterization results revealed that LMBC mainly consisted of the elements C and O. The BET characterization results demonstrated that the magnetization modification augmented the specific surface area by approximately 30 times to reach 89.14 m²/g, and the pore volume increased by twofold to 0.18 cm³/g, creating a favorable condition for Sb adsorption. The FTIR, XRD, and XPS results indicated that the surface of LMBC was rich in carboxyl and hydroxyl groups and was successfully loaded with Fe₂O₃ and Fe₃O₄. LMBC not only facilitates the resourceful utilization of aquatic plant waste but also effectively removes antimony (Sb) pollution through its magnetic properties. This dual functionality presents promising application prospects for the efficient adsorption and removal of Sb from water. Full article

(This article belongs to the Special Issue Adsorption of Emerging Water Pollutants by Advanced Materials)

► Show Figures

Figure 1

18 pages, 8445 KiB

Open AccessArticle

Irradiated Gao Miao Zi Bentonite for Uranium Retention: Performance and Mechanism

by Yushan Zhang, Gang Song, Yujie Mo, Shuwen Wang, Diyun Chen and Minhua Su

Separations 2025, 12(1), 1; https://doi.org/10.3390/separations12010001 - 26 Dec 2024

Abstract

Bentonite has been considered as backfill material in the long-term deep geological disposal sites for radioactive waste. The performance of raw and irradiated bentonite based on the retention of radioactive nuclides, such as U(VI), is a critical factor for its application. Herein, the [...] Read more.

Bentonite has been considered as backfill material in the long-term deep geological disposal sites for radioactive waste. The performance of raw and irradiated bentonite based on the retention of radioactive nuclides, such as U(VI), is a critical factor for its application. Herein, the intrinsic features and adsorption behavior of Gao Miao Zi (GMZ) bentonite based on uranyl ions was investigated. In aqueous solutions, bentonite can achieve an adsorption rate of up to 100% for U(VI). The primary mechanism of U(VI) adsorption by GMZ bentonite is ion exchange, supplemented by surface complexation. Strong irradiation can introduce slight structural changes and framework fractures in bentonite, reducing its adsorption capacity for U(VI). This study provides an in-depth analysis of the adverse effects of high doses of radiation (100 kGy) on the microstructure and adsorption properties of bentonite, offering important insights for the safe storage of radioactive waste. Full article

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

► Show Figures

Graphical abstract

19 pages, 3282 KiB

Open AccessArticle

The Effect of Plasma Pretreatment on the Flotation of Lithium Aluminate and Gehlenite Using Light-Switchable Collectors

by Ali Zgheib, Maximilian Hans Fischer, Stéphanie Mireille Tsanang, Iliass El Hraoui, Shukang Zhang, Annett Wollmann, Alfred P. Weber, Ursula E. A. Fittschen, Thomas Schirmer and Andreas Schmidt

Separations 2024, 11(12), 362; https://doi.org/10.3390/separations11120362 - 23 Dec 2024

Abstract

The pyridinium phenolate punicine is a switchable molecule from Punica granatum. Depending on the pH, punicine exists as a cation, neutral molecule, anion, or dianion. In addition, punicine reacts to light, under the influence of which it forms radical species. We report [...] Read more.

The pyridinium phenolate punicine is a switchable molecule from Punica granatum. Depending on the pH, punicine exists as a cation, neutral molecule, anion, or dianion. In addition, punicine reacts to light, under the influence of which it forms radical species. We report on three punicine derivatives that possess an adamantyl, 2-methylnonyl, or heptadecyl substituent and on their performance in the flotation of lithium aluminate, an engineered artificial mineral (EnAM) for the recycling of lithium, e.g., from lithium-ion batteries. By optimizing the parameters: pH and light conditions (daylight, darkness), recovery rates of 92% of LiAlO₂ are achieved. In all cases, the flotation of the gangue material gehlenite (Ca₂Al[AlSiO₇]) is suppressed. IR, the contact angle, zeta potential measurements, TG-MS, and PXRD confirm that the punicines interact with the surface of LiAlO₂, which is covered by LiAl₂(OH)₇ after contact to water, resulting in a hydrophobization of the particle. The plasma pretreatment of the lithium aluminate has a significant influence on the flotation results and increases the recovery rates of lithium aluminate in blank tests by 58%. The oxidative plasma leads to a partial dehydratisation of the LiAl₂(OH)₇ and thus to a hydrophobization of the particles, while a reductive plasma causes a more hydrophilic particle surface. Full article

(This article belongs to the Special Issue Green Separation and Purification Technology)

► Show Figures

Graphical abstract

18 pages, 2967 KiB

Open AccessArticle

Modified Biochar Adsorption Combined with Alkaline Solution Absorption for Sulfur-Containing Odor Gases Removal from Domestic Waste Transfer Stations

by Wei Wei, Ningjie Wang and Xiaolei Zhang

Separations 2024, 11(12), 361; https://doi.org/10.3390/separations11120361 - 23 Dec 2024

Abstract

Odor emission has become a major issue in waste transfer stations. Hydrogen sulfide, methyl mercaptan (MM), and dimethyl disulfide (DMDS) are the main odorous gases. They have a low odor threshold and are difficult to remove. In this study, pine bark biochar was [...] Read more.

Odor emission has become a major issue in waste transfer stations. Hydrogen sulfide, methyl mercaptan (MM), and dimethyl disulfide (DMDS) are the main odorous gases. They have a low odor threshold and are difficult to remove. In this study, pine bark biochar was produced and modified with metal ions, including Ni²⁺, Ti²⁺, Mn²⁺, Zn²⁺, Mg²⁺, and Cu²⁺. It was then used for the removal of hydrogen sulfide, methyl mercaptan, and dimethyl disulfide. Among all modifications, the Cu²⁺ modified biochar showed the best sorption capacity, and the maximum sorption amounts were 20.50 mg/g for H₂S, 36.50 mg/g for MM, and 57.98 mg/g for DMDS. To understand the adsorption, BET, SEM, and XPS of the original and modified biochar were performed. This illustrated that modification with Cu²⁺ increased the surface area and porosity, thus enhancing the adsorption capacity. In the alkaline absorption study, it was found that the removal of the three odor gases increased with the pH increase. Based on the results, a combined process called absorption–adsorption was established to treat the odor gas generated in a local waste transfer station. Thirty-one gas components were detected in the odor gas of the waste transfer station. The process proceeded for 30 days, and these gas components were not found in the effluent during treatment. Regarding H₂S, MM, and DMDS, they were not detected even after 90 days. This indicates the high adsorption capacity of the modified biochar toward the three odor gases. In addition, the process is simple and easy to operate. This suggests that it is suitable for treating odor in places where there is no technician, and the odor needs efficient treatment. The study provides a feasible alternative for domestic waste transfer stations to control the odor problem. Full article

(This article belongs to the Topic Advances in Separation Engineering)

► Show Figures

Figure 1

22 pages, 5851 KiB

Open AccessArticle

Ion Activity Coefficient of Sodium Halides in Anion-Exchange Polymers: Empirical Model Based on Manning’s Counterion Condensation Theory

by Guiming Liu and Dandan Gao

Separations 2024, 11(12), 360; https://doi.org/10.3390/separations11120360 - 23 Dec 2024

Abstract

The theory of electrolyte solution provides a precise description of the thermodynamic state and non-ideality of electrolyte solutions, allowing for the accurate prediction of the crystallization separation process of Salt Lake brine. Analogously, we attempt to describe the non-ideality of ions in ion-exchange [...] Read more.

The theory of electrolyte solution provides a precise description of the thermodynamic state and non-ideality of electrolyte solutions, allowing for the accurate prediction of the crystallization separation process of Salt Lake brine. Analogously, we attempt to describe the non-ideality of ions in ion-exchange polymers based on Manning’s Counterion Condensation Theory, which was originally used to describe the thermodynamics of polyelectrolyte solutions, has amply proven the potential to extend to ion-exchange polymers. In this article, equilibrium solvent and solute concentrations in aminated cross-linked polystyrene AEM were determined experimentally as a function of external NaCl concentration, and ion activity coefficients in the membranes were obtained via a thermodynamic treatment. With the recombination and empirical parameters added to Manning’s model, the ion activity coefficient of NaCl and NaBr in the aminated cross-linked polystyrene AEM can be accurately described in concentration ranges of 0.01 mol·kg⁻¹~3 mol·kg⁻¹. Compared with the original model, the Coefficient of Determination between the improved model and the experimental data was increased from 0.65 to 0.95. The Residual Sum of Squares is reduced by about one order of magnitude, significantly improving the Manning model’s adaptability when applied to AEM. Full article

(This article belongs to the Special Issue Green and Efficient Separation and Extraction of Salt Lake Resources)

► Show Figures

Figure 1

13 pages, 3767 KiB

Open AccessArticle

Unveiling the Floral Scent Dynamics of Calamondin (Citrus × microcarpa) Across Developmental Stages

by Yiwei Chen, Zhiqing Liang, Shiyu Chen, Fulong Yan, Jingjuan He, Yiwei Zhou and Ting Gao

Separations 2024, 11(12), 359; https://doi.org/10.3390/separations11120359 - 23 Dec 2024

Abstract

The calamondin (Citrus × microcarpa) is highly valued for its ornamental appeal and rich aromatic compounds, making it suitable for therapeutic gardens and widely applicable in the cosmetics, food, pharmaceutical, and perfume industries. Despite its importance, there is a lack of [...] Read more.

The calamondin (Citrus × microcarpa) is highly valued for its ornamental appeal and rich aromatic compounds, making it suitable for therapeutic gardens and widely applicable in the cosmetics, food, pharmaceutical, and perfume industries. Despite its importance, there is a lack of research on its floral volatiles. This study utilized headspace solid-phase microextraction gas chromatography–mass spectrometry (HS–SPME–GC–MS) to detect the volatile organic compounds (VOCs) of calamondin at different floral developmental stages: bud (BS), half-open (HS), full bloom (FS), and senescence (SS). Multivariate statistical analysis was employed to elucidate the aromatic characteristics. The results identified 67 VOCs across the four stages, including forty-eight terpenoids, six esters, five aromatics, four aldehydes, one olefin, one alcohol, and two others. Thirty-three VOCs were common across all stages, while BS, HS, FS, and SS had three, three, four, and nine unique VOCs, respectively. The total VOC content increased initially and then decreased as the flowers developed, with terpenoids being the predominant compounds, accounting for over 90% of the total emissions at all stages. Principal component analysis and hierarchical cluster analysis confirmed significant differences in VOC profiles at different stages. Partial least squares discriminant analysis identified five VOCs with variable importance in projection (VIP) values greater than one, including limonene, linalool, β-pinene, germacrene D, and β-ocimene, indicating their varying emission levels across stages. These findings enhance our understanding of the VOC characteristics of calamondin flowers and provide a scientific basis for further ornamental and industrial applications. Full article

(This article belongs to the Special Issue Research Progress for Isolation of Plant Active Compounds)

► Show Figures

Figure 1

Figure 1
Total Ion Chromatograms (TIC) of calamondin’s floral scent at four different developmental stages detected by HS-SPME-GC-MS. The highlighted numbers indicate the main identified peak areas. 1: β-Pinene; 2: Limonene; 3: β-Ocimene; 4: Linalool; 5: Methyl anthranilate; 6: α-Farnesene. IS: Internal standard, ethyl caproate. Full article ">Figure 2
Identification of the number of different categories of VOCs at four developmental stages. (A) Number of different VOC categories in floral scents at four developmental stages; (B) Composition of 67 VOCs by compound category; (C) Venn diagram analysis of unique and common VOCs in floral scents at different stages. Full article ">Figure 3
Comparative analysis of the relative total VOC content and the percentage of different VOC categories at four different flowering stages. (A) Comparative analysis of total VOC content. Different lowercase letters indicate significant differences at the p < 0.05 level. (B–E) Relative content percentages of different VOC categories at BS, HS, FS, and SS stages, respectively. Full article ">Figure 4
PCA analysis based on the relative content of 67 VOCs. Full article ">Figure 5
HCA heatmap analysis based on the relative content of 67 VOCs. Full article ">Figure 6
K-means analysis based on the relative content of 67 VOCs. The black line elucidates the trend in the relative content of the specific VOCs across four floral development stages. Simultaneously, the colored lines represent the variation in the relative abundance of diverse VOCs within different groups, spanning four floral development stages. Full article ">Figure 7
Top 10 VOCs with the highest VIP values based on PLS-DA analysis. The pink color means the compound’s value of VIP greater than 1, and the blue color means the compound’s value of VIP less than 1. Full article ">

22 pages, 6794 KiB

Open AccessArticle

Metal Sulfide Nanoparticles as Sphalerite Surface Activators to Improve Zinc Recovery Through Flotation Process

by Delia Monserrat Ávila-Márquez, Alien Blanco-Flores, Helen Paola Toledo-Jaldin, Maribel González Torres, Alfredo Rafael Vilchis-Nestor, Iván Alejandro Reyes Domínguez and Ramiro de Aquino García

Separations 2024, 11(12), 358; https://doi.org/10.3390/separations11120358 - 22 Dec 2024

Abstract

CuS nanoparticles (Np) were synthesized and deposited on synthetic sphalerite (S_P) using two different methods. Two nanoparticle products were obtained on the surface of S_P, Np1 and Np2, resulting in two active materials (Np1-S [...] Read more.

CuS nanoparticles (Np) were synthesized and deposited on synthetic sphalerite (S_P) using two different methods. Two nanoparticle products were obtained on the surface of S_P, Np1 and Np2, resulting in two active materials (Np1-S_P and Np2-S_P) with specific characteristics. Nanoparticles and active materials were characterized by TEM, XRD, SEM, and XPS. The collectors PAX and SIPX were adsorbed on Np1-S_P and Np2-S_P to determine the adsorption capacity. Method 1 provides a higher quantity of nanoparticles on S_P, which allows for the adsorption of a higher amount of SIPX. Method 1 was used to deposit nanoparticles on two natural sphalerites (S_N) with different iron contents. S_N, unlike S_P, can be used to test nanoparticle activation results in microflotation experiments. S_N was activated with nanoparticles (Np1-S_N) and using the traditional method (Cu-S_N). The recovery of 75% of zinc using the microflotation process suggests that the hydrophobicity of Np1-S_N is higher than that of Cu-S_N. Nanoparticles improve the hydrophobicity of S_N compared to the traditional activation used in the mining industry. These results suggest that using nanoparticles is an excellent option to activate minerals in flotation processes, decreasing the consumption of reagents and helping to mitigate negative impacts on the environment. Full article

(This article belongs to the Section Materials in Separation Science)

► Show Figures

Graphical abstract

14 pages, 1356 KiB

Open AccessArticle

Innovative Nafion- and Lignin-Based Cation Exchange Materials Against Standard Resins for the Removal of Heavy Metals During Water Treatment

by Sara Bergamasco, Luis Alexander Hein, Laura Silvestri, Robert Hartmann, Giampiero Menegatti, Alfonso Pozio and Antonio Rinaldi

Separations 2024, 11(12), 357; https://doi.org/10.3390/separations11120357 - 21 Dec 2024

Abstract

The contamination of water by heavy metals poses an escalating risk to human health and the environment, underscoring the critical need for efficient removal methods to secure safe water resources. This study evaluated the performance of four cationic exchange materials (labeled “PS—DVB”, “PA—DVB”, [...] Read more.

The contamination of water by heavy metals poses an escalating risk to human health and the environment, underscoring the critical need for efficient removal methods to secure safe water resources. This study evaluated the performance of four cationic exchange materials (labeled “PS—DVB”, “PA—DVB”, “TFSA”, and “OGL”) in removing or harvesting metals such as copper, silver, lead, cobalt, and nickel from aqueous solutions, several of which are precious and/or classified as Critical Raw Materials (CRMs) due to their economic importance and supply risk. The objective was to screen and benchmark the four ion exchange materials for water treatment applications by investigating their metal sequestration capacities. Experiments were conducted using synthetic solutions with controlled metal concentrations, analyzed through ICP-OES, and supported by kinetic modeling. The adsorption capacities (qe) obtained experimentally were compared with those predicted by pseudo-first-order and pseudo-second-order models. This methodology enables high precision and reproducibility, validating its applicability for assessing ion exchange performance. The results indicated that PS—DVB and PA—DVB resins proved to be of “wide range”, exhibiting high efficacy for most of the metals tested, including CRM-designated ones, and suggesting their suitability for water purification. Additionally, the second-life Nafion-based “TFSA” material demonstrated commendable performance, highlighting its potential as a viable and technologically advanced alternative in water treatment. Lastly, the lignin-based material, “OGL”, representing the most innovative and sustainability apt option, offered relevant performance only in selected cases. The significant differences in performance among the resins underscore the impact of structural and compositional factors on adsorption efficiency. This study offers valuable insights for investigating and selecting new sustainable materials for treating contaminated water, opening new pathways for targeted and optimized solutions in environmental remediation. Full article

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

► Show Figures

Figure 1

18 pages, 9422 KiB

Open AccessArticle

Activating Peroxymonosulfate by a NovelFe-MOF-C/N Catalyst to Effectively Degrade Sulfamethoxazole: Catalyst Performance and Its Mechanism

by Zhaowei Wu, Meiyi Hu, Pengfan Zhuo, Jie Wang and Shaoping Tong

Separations 2024, 11(12), 356; https://doi.org/10.3390/separations11120356 - 21 Dec 2024

Abstract

A composite Fe-MOF-C/N was prepared with Fe-MOF and g-C₃N₄ precursors, and its activation property of peroxymonosulfate (PMS) in the degradation of Sulfamethoxazole (SMX) was studied. XRD, SEM, and TEM analyses showed that Fe-MOF-C/N was porous and mainly composed of phases [...] Read more.

A composite Fe-MOF-C/N was prepared with Fe-MOF and g-C₃N₄ precursors, and its activation property of peroxymonosulfate (PMS) in the degradation of Sulfamethoxazole (SMX) was studied. XRD, SEM, and TEM analyses showed that Fe-MOF-C/N was porous and mainly composed of phases of Fe₃N, C_0.08Fe_1.92, and graphite. XPS indicated that Fe-MOF-C/N mainly had Fe, C, N, and O elements, among which Fe existed in the form of Fe²⁺ and Fe³⁺. Fe-MOF-C/N was used to activate PMS to degrade SMX, and the result showed that Fe-MOF-C/N had excellent catalytic performance and 84.17% of SMX could be removed in 8 min. Free radical quenching experiments showed that ¹O₂ was the main active species in Fe-MOF-C/N/PMS. The stability experiment showed that Fe-MOF-C/N had good stability, and the degradation rate of SMX only decreased by 5.8% after five times of use. Full article

► Show Figures

Figure 1

16 pages, 12963 KiB

Open AccessArticle

Evaluating Bioflocculation Harvesting of Freshwater and Marine Microalgae Using Exopolysaccharides (EPSs) from Klebsiella sp.

by Yicheng Yuan, Jingxuan Lu and Quan Wang

Separations 2024, 11(12), 355; https://doi.org/10.3390/separations11120355 - 19 Dec 2024

Abstract

The rising global energy demand and environmental concerns associated with fossil fuels have intensified interest in sustainable biofuel sources, with microalgae emerging as a viable candidate due to its high biomass yield and efficient CO₂ conversion. However, the economic feasibility of microalgal [...] Read more.

The rising global energy demand and environmental concerns associated with fossil fuels have intensified interest in sustainable biofuel sources, with microalgae emerging as a viable candidate due to its high biomass yield and efficient CO₂ conversion. However, the economic feasibility of microalgal biofuels is currently challenged by costly harvesting processes. This study investigates the use of exopolysaccharides (EPSs) derived from Klebsiella sp. as an environmentally friendly bioflocculant for harvesting two microalgae species: Raphidocelis subcapitata and Dunaliella salina. Comparative flocculation experiments revealed that Klebsiella EPS promotes efficient aggregation in R. subcapitata, achieving over 90% flocculation efficiency, while performance with D. salina was impacted by high salinity, which reduced charge neutralization and bridging effects. Structural analyses using FTIR, 3D-EEM, CLSM, and XPS elucidated the EPS composition, underscoring the roles of polysaccharides and proteins in facilitating microalgal aggregation. The findings indicate that Klebsiella EPS offers a sustainable alternative to chemical flocculants, supporting eco-friendly biofuel production and potential applications in wastewater treatment. This approach provides insights into optimizing EPS-based flocculation for diverse environmental conditions, paving the way for more sustainable biomass recovery practices. Full article

(This article belongs to the Special Issue Separation Technology for Solid Waste Treatment and Recycling)

► Show Figures

Figure 1

Figure 1
Harvesting efficiency of (a) directly added Klebsiella sp. suspensions, (b) EPS extracted from Klebsiella sp. on two microalgae species. Full article ">Figure 2
Floc structures of (a) RS15-K4, (b) RS15-K8, (c) 90EPS-RS, (d) DS15-K4, (e) DS15-K8, and (f) 90EPS-DS under 20× optical microscopy. Full article ">Figure 3
SEM imaging of floc structures: (a) RS15-K4, (b) RS15-K8, (c) 90EPS-RS, (d) DS15-K4, (e) DS15-K8, and (f) 90EPS-DS. Full article ">Figure 4
Particle size distributions of floc structures: (a) R. subcapitata, (b) D. salina, and (c) zeta-potential change after the addition of Klebsiella sp. broth. Full article ">Figure 5
(a) FTIR spectra detailing the chemical composition of EPS. (b1–b3) The 3D-EEM spectra for S-EPS, LB-EPS, and TB-EPS. (c1–c5) CLSM images of Klebsiella: general cellular staining (c1), specific red staining for lipids (c2), blue staining for proteins (c3), green staining for polysaccharides (c4), and a composite overlay of all stains (c5). (d) Pie chart showing the composition ratios of S-EPS, LB-EPS, and TB-EPS in EPS. Full article ">Figure 6
XPS spectra for total EPS and S-EPS: (a1,b1,c1) represent the C1s, O1s, and N1s spectra for total EPS, respectively, while (a2,b2,c2) show the high-resolution C1s, O1s, and N1s spectra for S-EPS. Full article ">

22 pages, 8084 KiB

Open AccessArticle

Optimization of Extraction of Luteolin from Schisandra chinensis by Ionic Liquid–Enzyme Complex System and Antioxidant Study Analysis

by Jingwei Hao, Nan Dong, Yifan Sun, Xiaoxia Lu, Yingying Pei, Yi Zhou, Xiangkun Zhou and Heming Liu

Separations 2024, 11(12), 354; https://doi.org/10.3390/separations11120354 - 19 Dec 2024

Abstract

The luteolin in Schisandra chinensis [Schisandraceae Schisandra (Turcz.) Baill.] were extracted by ultrasonic extraction assisted by an ionic liquid–enzyme composite system, and the content of luteolins was determined using high-performance liquid chromatography (HPLC). This process was initially conducted through a one-factor experiment and [...] Read more.

The luteolin in Schisandra chinensis [Schisandraceae Schisandra (Turcz.) Baill.] were extracted by ultrasonic extraction assisted by an ionic liquid–enzyme composite system, and the content of luteolins was determined using high-performance liquid chromatography (HPLC). This process was initially conducted through a one-factor experiment and a Box–Behnken combinatorial design of response surface method. The extraction process was optimized, and the results demonstrated that the optimal extraction conditions were 13.31% enzyme addition, 0.53 mol/L ionic liquid concentration, 173.47 min ultrasonic shaking, and 0.2266 mg/g, which was 4.88 times higher than that of the traditional reflux extraction. Secondly, the antioxidant function of luteolins was studied based on network pharmacology. For the study of the antioxidant mechanism of luteolin, the herb group identification database, SwissTargetPrediction on luteolins target prediction, and GeneCards database to achieve the antioxidant target were used. For the analysis of the intersection of the target protein interactions, GO bioanalysis and KEGG signaling pathway enrichment analysis were used. There were 57 overlapping targets of luteolin and antioxidants, including AKT1, MMP9, ESR1, EGFR, and SRC. GO function and KEGG pathway enrichment analysis showed that luteolin antioxidants were related to zoerythromycin metabolic process, adriamycin metabolic process, negative regulation of apoptotic process, endocrine resistance and oxidoreductase. The key targets in the pathways, such as luteolin AKT1 and MMP9, exert antioxidant effects. The antioxidant activity of luteolins was investigated by determining the scavenging ability of luteolins against two types of free radicals: 2,2-bipyridine-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt (ABTS+) free radicals and 1,1-diphenyl-2-trinitrophenylhydrazine free radicals (DPPH-). The results of the antioxidant test demonstrated that the ABTS radical scavenging rate was 87.26%, and the DPPH radical scavenging rate was 93.85% when the quality concentration of Schisandra luteolins was 0.1 mg/g, indicating the potential of this natural antioxidant. This method of extracting Schisandra chinensis luteolins is highly productive, environmentally friendly, and practical, and it facilitates the development and utilization of industrial Schisandra chinensis. Full article

► Show Figures

Figure 1

17 pages, 2035 KiB

Open AccessReview

The Removal of Organic Pollutants and Ammonia Nitrogen from High-Salt Wastewater by the Electro-Chlorination Process and Its Mechanism

by Yujun Zhou, Tangrui Hou and Bo Zhou

Separations 2024, 11(12), 353; https://doi.org/10.3390/separations11120353 - 18 Dec 2024

Abstract

Electro-chlorination (E-Cl) is an emerging and promising electrochemical advanced oxidation technology for wastewater treatment with the advantages of high efficiency, deep mineralization, a green process, and easy operation. It was found that the mechanism of pollutant removal by electro-chlorination mainly involves an indirect [...] Read more.

Electro-chlorination (E-Cl) is an emerging and promising electrochemical advanced oxidation technology for wastewater treatment with the advantages of high efficiency, deep mineralization, a green process, and easy operation. It was found that the mechanism of pollutant removal by electro-chlorination mainly involves an indirect oxidation process, in which pollutant removal is mainly driven by the intermediate active species, especially RCS and chlorine radicals, with a strong oxidization ability produced at the anodes. In this work, we summarized the principles and pathways of the removal/degradation of pollutants (organic pollutants and ammonia nitrogen) by E-Cl and the major affecting factors including the applied current density, voltage, electrolyte concentration, initial pH value, etc. In the E-Cl system, the DSA and BDD electrodes were the most widely used electrode materials. The flow-through electrode reactor was considered to be the most promising reactor since it had a high porosity and large pore size, which could effectively improve the mass transfer efficiency and electron transfer efficiency of the reaction. Of the many detection methods for chlorine radicals and RCS, electron paramagnetic resonance (EPR) and spectrophotometry with N, N-diethyl-1,4-phenylenediamine sulfate (DPD) as the chromogenic agent were the two most widely used methods. Overall, the E-Cl process had excellent performance and prospects in treating salt-containing wastewater. Full article

(This article belongs to the Special Issue Design and Preparation of Environmental Functional Materials for Pollutant Removal)

► Show Figures

Figure 1

Figure 1
Comparison of voltammetric currents associated with the evolution of chlorine for five electrode materials [<a href="#B49-separations-11-00353" class="html-bibr">49</a>]. Full article ">Figure 2
Configuration of flow-through reactor [<a href="#B53-separations-11-00353" class="html-bibr">53</a>]. Full article ">Figure 3
Mechanism of ECl process for ammonia nitrogen removal [<a href="#B14-separations-11-00353" class="html-bibr">14</a>]. Full article ">Figure 4
Mechanism of E-Cl process for ofloxacin removal [<a href="#B76-separations-11-00353" class="html-bibr">76</a>]. Full article ">Figure 5
EPR scan result of DMPO-X [<a href="#B28-separations-11-00353" class="html-bibr">28</a>]. Full article ">Figure 6
Quenching experiments for RCS determination in E-Cl system. Na2S2O3 = MeOH = TBA = 50 mmol/L, NB = 1000 mg/L [<a href="#B10-separations-11-00353" class="html-bibr">10</a>]. Full article ">Figure 7
Ammonia nitrogen loading efficiency and removal efficiency (a), Nitrite concentration of influent and removal/accumulation of nitrite (b) in MEBR and MBR [<a href="#B101-separations-11-00353" class="html-bibr">101</a>]. Full article ">

16 pages, 2546 KiB

Open AccessArticle

Volatile Organic Compounds in Honey: Tandem Mass Spectrometry as Tool to Quantitate Priority VOCs

by Evangelia N. Tzanetou, Efstathia Vousaxaki, Kyriaki Machera, Jozef van der Steen and Konstantinos M. Kasiotis

Separations 2024, 11(12), 352; https://doi.org/10.3390/separations11120352 - 17 Dec 2024

Abstract

A headspace gas chromatographic tandem mass spectrometric (HS-GC-MS/MS) method was developed and fully validated, aiming for the simultaneous determination of 25 volatile organic compounds (VOCs, some of them previously unreported in honey bee studies) in 52 selected honey samples from Greece. The HS [...] Read more.

A headspace gas chromatographic tandem mass spectrometric (HS-GC-MS/MS) method was developed and fully validated, aiming for the simultaneous determination of 25 volatile organic compounds (VOCs, some of them previously unreported in honey bee studies) in 52 selected honey samples from Greece. The HS conditions were optimized, and method validation criteria were extensively investigated. The existence impact of the matrix effect was assessed, and matrix-matched calibration curves were developed for quantification purposes. The limits of quantification of the 25 analytes ranged from 0.2 ng g⁻¹ to 0.6 ng g⁻¹. Isoprene was the most commonly detected VOC, followed by octane and styrene. Other detected VOCs include benzene, n-hexane, trimethylbenzenes, xylenes, toluene, and p-dichlorobenzene. Concentrations fluctuated from 0.5 ng g⁻¹ for isoprene and toluene, as well as 1,2,4-trimethylbenzene, to 22.6 ng g⁻¹ for isoprene. Despite VOCs not being at the forefront of honey’s potential contamination, their prevalence in honey can provide significant data for human health risk assessment, considering their undisputable widespread consumption and the documented potential toxicity of VOCs in humans. In this sense, risk assessment for adults and children, as depicted in the hazard quotient and index and carcinogenic risk determination, did not disclose any potential threat after consumption of the investigated honey samples. Full article

(This article belongs to the Special Issue Chemical and Contaminant Residue Analysis via Chromatography)

► Show Figures

Figure 1

Journal Description

Separations

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI