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A special issue of Separations (ISSN 2297-8739). This special issue belongs to the section "Materials in Separation Science".

Deadline for manuscript submissions: closed (20 August 2023) | Viewed by 17040

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Prof. Dr. Xinhua Qi

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College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
Interests: synthesis of value-added chemicals and materials from lignocellulosic biomass; biomass-derived porous carbons for catalysis; adsorption and energy storage
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Dear Colleagues,

Porous materials are a variety of materials that have a porous structure, large surface area, rich porosity, and rich functional groups. They have attracted more and more attention from numerous researchers and have been widely used in adsorbents for pollutant removal, the storage of CO₂ and H₂, medicine extraction, and enrichment due to their unique pore characteristics. With the development of material synthesis, more and more porous materials have been developed, including molecular sieves, porous carbons, metal-organic frameworks, porous resins, covalent organic frameworks, porous metal oxides, and porous composites, and so on.

This Special Issue of Separations, “Applications of Porous Materials in Adsorption”, is focused on the most recent advances made and studies carried out in the past few years on the synthesis and characterization of various porous materials and their applications in adsorption for different pollutants and gas storage. Research works, review documents, or communications that cover these new concepts, current challenges, and strategies for the synthesis of various porous materials in adsorption applications are welcome. We encourage you to contribute to this scientific program by submitting your papers for this Special Issue of Separations entitled “Applications of Porous Materials in Adsorption”.

Prof. Dr. Xinhua Qi
Guest Editor

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Keywords

porous materials
porous carbons
adsorption
pollutants
CO₂ storage
MOFs
molecular sieves
mesoporous silicon
aerogel

Published Papers (9 papers)

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Research

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15 pages, 13314 KiB

Open AccessArticle

Composites Based on CaCl₂-CaBr₂ Salt System for Adsorption Applications: Designing the Optimal Sorbent for Gas Drying and Air Conditioning

by Alexandra Grekova, Marina Solovyeva, Anastasiia Cherpakova and Mikhail Tokarev

Separations 2023, 10(9), 473; https://doi.org/10.3390/separations10090473 - 28 Aug 2023

Viewed by 749

Abstract

The different adsorption applications require the development of sorbents with predetermined properties. One of the ways for fine tuning the adsorption properties of the material is using a binary salt system as an active sorbing component. The aim of this work is to conduct a precision investigation of thermodynamic data on the sorption equilibrium of composite sorbents “(CaCl₂ + CaBr₂) confined to the silica gel pores” with water vapour. The isotherms and isosteres (at an uptake of N = 1.5 and 3.6 mole/mole) of water sorption on the composites were measured. It was shown that at a fixed temperature, the composites based on solid solutions of CaCl₂ in CaBr₂ form complexes with water at a pressure that is dependent on the CaCl₂/CaBr₂ molar ratio. The isosteric enthalpy and entropy of water sorption (ΔH = −48 ± 3 kJ/mol ΔS = −108 ± 2 J/(mol·K)) at N = 3.6 mole/mole were midway between the same parameters for composites on the base of the pure salts CaCl₂ and CaBr₂. The novelty of this work is in the design of sorbents optimized for air conditioning in hot climates and air drying cycles. It was shown that the use of the binary CaCl₂ + CaBr₂ system confined to the silica pores can be an effective tool for designing innovative materials with predetermined properties. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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16 pages, 4185 KiB

Open AccessFeature PaperArticle

Removal of Indium Ions from Aqueous Solutions Using Hydroxyapatite and Its Two Modifications

by Inga Zinicovscaia, Nikita Yushin, Doina Humelnicu, Maria Ignat, Ionel Humelnicu, Dmitrii Grozdov and Tatyana Vershinina

Separations 2023, 10(7), 401; https://doi.org/10.3390/separations10070401 - 12 Jul 2023

Cited by 2 | Viewed by 1037

Abstract

Hydroxyapatite (HAP) coupled with its two modifications HAP P123 and HAP F127 were applied for indium removal from aqueous solutions. Adsorbents’ abilities to remove indium ions were assessed in relation to pH, time of contact, indium concentration, temperature, and presence of co-existing ions. Adsorption was discovered to be pH-dependent for all sorbents, with maximum indium ion removal at pH 4.0. Both the Langmuir and the Freundlich isotherm models were used to explain the experimental results. For all adsorbents, the Freundlich isotherm provided a better description of the equilibrium of the sorption. The sorption capacity computed from the Langmuir model changed from 10,799 mg/g for HAP F127 to 11071 mg/g for HAP. A number of models were used to describe the adsorption’s kinetics. The adsorption of indium on HAP was better described by the pseudo-second-order model, on HAP P123 by the pseudo-first-order model, and on HAP F127 by the Elovich model. Thermodynamic parameters showed that indium ions’ adsorption onto HAP adsorbents was a feasible, spontaneous, and exothermic process. The effectiveness of indium removal by the examined adsorbents was unaffected by the presence of other metal ions in the solutions. ORCA quantum chemistry software was used to theoretically examine the interactions between the surfaces of adsorbents and the indium ions. High desorption efficiency showed that the applied adsorbents can be used for manifold wastewater treatment. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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12 pages, 5986 KiB

Open AccessArticle

Microporous Carbons Obtained via Solvent-Free Mechanochemical Processing, Carbonization and Activation with Potassium Citrate and Zinc Chloride for CO₂ Adsorption

by Amonrada Saning, Rabindra Dubadi, Laemthong Chuenchom, Decha Dechtrirat and Mietek Jaroniec

Separations 2023, 10(5), 304; https://doi.org/10.3390/separations10050304 - 10 May 2023

Cited by 4 | Viewed by 1631

Abstract

In this study, the facile and sustainable synthesis of highly microporous carbons is explored to reduce the extensive use of harsh activating agents and solvents. The role of potassium citrate (PC) as a greener activating agent in addition to the conventional ZnCl₂ is investigated in the mechanochemical solvent-free preparation of highly microporous carbon materials from chestnut tannin (CT), a biomass-type carbon precursor. A small amount of potassium citrate as a chemical activator coupled with CO₂ activation at 700 °C afforded carbons with higher specific surface area (1256 m² g⁻¹) and larger micropore volume (0.54 cm³ g⁻¹) as compared to the carbons activated with both PC and ZnCl₂. The high microporosity of the PC-activated carbon materials, significantly enlarged after CO₂ activation from micropore volume of 0.16 to 0.54 cm³ g⁻¹, makes them favorable for CO₂ adsorption, as evidenced by high adsorption capacity of 3.55 mmol g⁻¹ at ambient conditions (25 °C, 1 bar). This study shows that the solvent-free mechanochemical processing of tannin in the presence of PC is a promising method for obtaining highly microporous carbon materials. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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18 pages, 5932 KiB

Open AccessEditor’s ChoiceArticle

Green-Engineered Barrier Creams with Montmorillonite-Chlorophyll Clays as Adsorbents for Benzene, Toluene, and Xylene

by Meichen Wang and Timothy D. Phillips

Separations 2023, 10(4), 237; https://doi.org/10.3390/separations10040237 - 04 Apr 2023

Cited by 6 | Viewed by 2083

Abstract

Dermal exposures to hazardous environmental chemicals in water can significantly affect the morphology and integrity of skin structure, leading to enhanced and deeper penetration. Organic solvents, such as benzene, toluene, and xylene (BTX), have been detected in humans following skin exposure. In this study, novel barrier cream formulations (EVB^TM) engineered with either montmorillonite (CM and SM) or chlorophyll-amended montmorillonite (CMCH and SMCH) clays were tested for their binding efficacy for BTX mixtures in water. The physicochemical properties of all sorbents and barrier creams were characterized and were shown to be suitable for topical application. In vitro adsorption results indicated that EVB-SMCH was the most effective and favorable barrier for BTX, as supported by the high binding percentage (29–59% at 0.05 g and 0.1 g), stable binding at equilibrium, low desorption rates, and high binding affinity. Pseudo-second-order and the Freundlich models best fit the adsorption kinetics and isotherms, and the adsorption was an exothermic reaction. Ecotoxicological models using L. minor and H. vulgaris that were submersed in aqueous culture media showed that the inclusion of 0.05% and 0.2% EVB-SMCH reduced BTX concentration. This result was further supported by the significant and dose-dependent increase in multiple growth endpoints, including plant frond number, surface area, chlorophyll content, growth rate, inhibition rate, and hydra morphology. The in vitro adsorption results and in vivo plant and animal models indicated that green-engineered EVB-SMCH can be used as an effective barrier to bind BTX mixtures and interrupt their diffusion and dermal contact. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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19 pages, 6115 KiB

Open AccessArticle

Mesoporous Activated Carbon from Bamboo Waste via Microwave-Assisted K₂CO₃ Activation: Adsorption Optimization and Mechanism for Methylene Blue Dye

by Khaizuran Fyrdaus Azlan Zahari, Uttam Kumar Sahu, Tumirah Khadiran, Siti Norasmah Surip, Zeid A. ALOthman and Ali H. Jawad

Separations 2022, 9(12), 390; https://doi.org/10.3390/separations9120390 - 23 Nov 2022

Cited by 10 | Viewed by 1749

Abstract

Bamboo waste (BW) was activated with a K₂CO₃ precursor in a microwave process for the adsorption of MB dye from an aqueous solution. The prepared bamboo-waste-activated carbon (BWAC) was analyzed by instrumental techniques such as FTIR, SEM, and BET analysis. The surface of the BWAC was mesoporous with a surface area of 107.148 m²/g. The MB dye removal was optimized with the three variables of adsorbent dose, pH, and contact time using the Box–Behnken design (BBD) model. Up to 87% of MB was removed in the optimized conditions of adsorbent dose of 0.08 g/100 mL, pH of 7.62, time of 8 min, and concentration of 50 mg/L. Here, the most effective parameter for MB removal was found to be adsorbent dose with an F-value of 121.70, while time and pH showed a smaller effect. The maximum adsorption capacity of BWAC in the optimized conditions was found to be 85.6 mg/g. The adsorption of MB on BWAC’s surface was through chemisorption and a spontaneous process. The adsorption mechanism study showed that three types of interactions are responsible for the removal of MB dye from aqueous solutions by BWAC, i.e., electrostatic interactions, H-bonding, and pi–pi interactions. Hence, BWAC can be considered a highly efficient adsorbent for MB removal from wastewater. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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18 pages, 4480 KiB

Open AccessArticle

Polyaniline/Glauconite Nanocomposite Adsorbent for Congo Red Dye from Textile Wastewater

by Doaa Salah, Ahmed Hamd, N. K. Soliman, Ali M. Elzanaty, Abdulaziz M. Alanazi, Mohamed Shaban, Refat El-Sayed and Sayed A. Ahmed

Separations 2022, 9(11), 384; https://doi.org/10.3390/separations9110384 - 21 Nov 2022

Cited by 8 | Viewed by 2388

Abstract

Glauconite (Gl), a naturally occurring clay material, was utilized as an affordable and ecologically friendly adsorbent to explore its capturing capacity towards Congo red (CR) dye from textile industrial waste effluent. To improve adsorption and removal effectiveness, a modification technique utilizing polyaniline (PAN) was investigated. An X-ray diffractometer (XRD), a scanning electron microscope (SEM), and Fourier transformer infrared (FTI-R) were applied as strong familiar characterization techniques for all used adsorbents. The effects of starting concentration, contact duration, adsorbent dose, pH, and temperature on the adsorption process were also studied. The reusability of the adsorbent was studied over four adsorption cycles. The results show that PAN modification of Gl enhances the effectiveness of CR elimination. The clearance efficiency of raw and modified glauconite at 25 °C and pH 7 was 77% and 91%, respectively. The kinetics and isotherms of Congo red dye adsorption were investigated using batch studies to determine the impacts of various experimental conditions. The maximum adsorption capacity of the glauconite/polyaniline (Gl/PAN) nanocomposite rose from 11.9 mg/g for Gl to 14.1 mg/g in accordance with the isotherm analysis, which shows that the Langmuir isotherm properly characterizes the experimental data. The pseudo-second-order model (R² = 0.998) properly expresses the experimental data. The reusability research proved that the adsorbents may be reused effectively. The overall results suggest that the modified Gl by PAN might be used as a low-cost, natural adsorbent for eliminating CR color from textile effluent. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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13 pages, 2032 KiB

Open AccessArticle

Development of Novel Formaldehyde-Free Melamine Resin for Retanning of Leather and Reduced Effluent Discharge in Water

by Muhammad Naveed Ashraf, Azhar Ali, Muhammad Bilal Shakoor, Sajid Rashid Ahmad, Fida Hussain and Sang-Eun Oh

Separations 2022, 9(11), 368; https://doi.org/10.3390/separations9110368 - 13 Nov 2022

Cited by 1 | Viewed by 2104

Abstract

The objective of this study was to develop a novel melamine-based resin suitable for producing formaldehyde-free leather with improved retanning properties. The resin was prepared by optimized condensation of melamine, glyoxal and metanilic acid. The novel resin was compared with a commercial resin against different parameters. Functional group analysis of the polymer structure and the route of synthesis was verified with the help of FT-IR spectroscopy. A Leica metallurgical microscope coupled with a CCD camera was used for SEM analysis. The results revealed that the mechanical and organoleptic properties of the novel resin were better than those of the commercial melamine resin. Tensile strength, tear strength and percentage elongation of leather were increased by 17.43%, 10.41% and 8.62%, respectively, in the direction parallel to the backbone, while the increases in these parameters were 15.17%, 9.79% and 6.0%, respectively, in the direction perpendicular to the backbone at the same dose. We observed a 100% reduction in free formaldehyde content in retanned leather as well as in effluent produced by the novel melamine resin. Pollution load study of effluent showed reductions in chemical oxygen demand, total suspended solids and total dissolved solids by 9.21%, 5.60% and 6.97%, respectively, for the novel melamine resin, reflecting its improved exhaustion. The fiber structure of the leather produced by the novel melamine resin was more orderly arranged, showing its improved retanning. These results prove that the novel melamine resin is an effective retanning agent suitable for producing formaldehyde-free leather with a reduction in effluent pollution load. This work introduces an alternative to formaldehyde for amino resins to address its carcinogenic effects. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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15 pages, 1688 KiB

Open AccessArticle

The Potential of Biochar as N Carrier to Recover N from Wastewater for Reuse in Planting Soil: Adsorption Capacity and Bioavailability Analysis

by Yingliang Yu, Bei Yang, Evangelos Petropoulos, Jingjing Duan, Linzhang Yang and Lihong Xue

Separations 2022, 9(11), 337; https://doi.org/10.3390/separations9110337 - 02 Nov 2022

Cited by 2 | Viewed by 1244

Abstract

Recovering nitrogen (N) from agricultural wastewater for reuse in planting fields is a more sustainable and economical strategy to limit N pollution than using conventional treatments. Hereby, regular biochar produced by wheat straw pyrolysis and Mg-modified biochar were used as the N carriers to assess inorganic-N adsorption from simulated agricultural wastewater and the potential for reuse of the carried N in a planting system. The results showed that biochar materials have different affinities towards inorganic-N types. The amount of biochar carried-N increased with the increase in inorganic-N concentration and reached 4.44 mg/g as the maximum. The biochar carried ~4 mg/g of inorganic N substituting nearly 40% of N fertilizer following a 1% w/w addition rate for vegetable planting. After a trial season, 34.7–42.7% of the carried N from biochar was assimilated by the plant, 45.9–53.7% was retained by the soil, and only about 10% was lost. In comparison to the condition with all N inputs from chemical fertilizer, the addition of part of N by the N–biochar matrix significantly reduced the N loss by improving the plant N uptake or increasing the N content in the soil. This study demonstrates that biochar materials could be used as N carriers to recover N from wastewater for reuse in soil, carrier stability, and bioavailability preservation. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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32 pages, 3193 KiB

Open AccessEditor’s ChoiceReview

Application of Hydrogen-Bonded Organic Frameworks in Environmental Remediation: Recent Advances and Future Trends

by Yu Zhang, Mengfei Tian, Zahid Majeed, Yuxin Xie, Kaili Zheng, Zidan Luo, Chunying Li and Chunjian Zhao

Separations 2023, 10(3), 196; https://doi.org/10.3390/separations10030196 - 13 Mar 2023

Cited by 4 | Viewed by 3215

Abstract

The hydrogen-bonded organic frameworks (HOFs) are a class of porous materials with crystalline frame structures, which are self-assembled from organic structures by hydrogen bonding in non-covalent bonds π-π packing and van der Waals force interaction. HOFs are widely used in environmental remediation due to their high specific surface area, ordered pore structure, pore modifiability, and post-synthesis adjustability of various physical and chemical forms. This work summarizes some rules for constructing stable HOFs and the synthesis of HOF-based materials (synthesis of HOFs, metallized HOFs, and HOF-derived materials). In addition, the applications of HOF-based materials in the field of environmental remediation are introduced, including adsorption and separation (NH₃, CO₂/CH₄ and CO₂/N₂, C₂H₂/C₂H_e and C_eH₆, C₂H₂/CO₂, Xe/Kr, etc.), heavy metal and radioactive metal adsorption, organic dye and pesticide adsorption, energy conversion (producing H₂ and CO₂ reduced to CO), organic dye degradation and pollutant sensing (metal ion, aniline, antibiotic, explosive steam, etc.). Finally, the current challenges and further studies of HOFs (such as functional modification, molecular simulation, application extension as remediation of contaminated soil, and cost assessment) are discussed. It is hoped that this work will help develop widespread applications for HOFs in removing a variety of pollutants from the environment. Full article

(This article belongs to the Special Issue Applications of Porous Materials in Adsorption)

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