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Separations
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Development of Mesoporous Materials for Adsorption and Recovery of Metals
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Development of Mesoporous Materials for Adsorption and Recovery of Metals

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

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 9696

Special Issue Editors

Prof. Dr. Eduardo Díez

E-Mail Website
Guest Editor
Department of Chemical and Materials Engineering (CyPS Research Group), Universidad Complutense de Madrid, 28040 Madrid, Spain
Interests: adsorption; wastewater treatment; strategic metals; solution thermodynamics; mesoporous materials; carbonaceous materials; zeolites
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Araceli Rodríguez

E-Mail Website
Guest Editor
Department of Chemical and Materials Engineering (CyPS Research Group), Universidad Complutense de Madrid, 28040 Madrid, Spain
Interests: adsorption; wastewater treatment; catalysis; carbonaceous materials; zeolites
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Nowadays, the increase in industrial activity has increased metal concentrations in water, which is considered a menace for both the environment and society. Among these metals present in water, those known as strategic metals are especially important due to their high market value, their scarcity in the Earth’s crust and their difficult extraction when employing conventional methods.

In the actual context of the circular economy, the possibility of the recovery of strategic metals from wastewaters is gaining importance. Therefore, it would be possible to fulfill SDG 6—clean water and sanitation; 12—responsible consumption and production; and 13—climate action. Among the techniques aiming to attain these goals, adsorption is particularly adequate, usually due to these metals being present in wastewaters at trace levels. Among the solids employed as adsorbents, mesoporous materials are especially interesting, as their porous structure can hinder diffusion problems.

This Special Issue aims to collect studies that show the progress in the synthesis, characterization and applications in the metal recovery of mesoporous materials. The expected contributions (original research papers and review articles) include the development of new materials, as well as their applications in the separation and recovery of metals from wastewater. Fixed-bed studies are especially welcomed, due to their higher TRL, along with selectivity studies, as these metals are usually present in complex matrices.

Prof. Dr. Eduardo Díez
Prof. Dr. Araceli Rodríguez
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Separations is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • strategic metal
  • synthesis
  • characterization
  • adsorption
  • recycling
  • metal recovery
  • fixed-bed

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Published Papers (4 papers)

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Research

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14 pages, 2974 KiB  
Article
A Prominent Streptomyces sp. Biomass-Based Biosorption of Zinc (II) and Lead (II) from Aqueous Solutions: Isotherm and Kinetic
by Sheetal Kumari, Nitin Kumar Agrawal, Animesh Agarwal, Anil Kumar, Neeraj Malik, Dinesh Goyal, Vishnu D. Rajput, Tatiana Minkina, Pinki Sharma and Manoj Chandra Garg
Separations 2023, 10(7), 393; https://doi.org/10.3390/separations10070393 - 4 Jul 2023
Cited by 11 | Viewed by 1537
Abstract
Traditional freshwater sources have been over-abstracted in the worldwide crisis of water scarcity. Effluents have extremely high amounts of Zn2+ and Pb2+, according to an investigation of wastewater samples taken from several industrial zones. However, these heavy metals are among [...] Read more.
Traditional freshwater sources have been over-abstracted in the worldwide crisis of water scarcity. Effluents have extremely high amounts of Zn2+ and Pb2+, according to an investigation of wastewater samples taken from several industrial zones. However, these heavy metals are among the most harmful to both humans and wildlife that are currently known. Streptomyces sp. is utilized in this study as a biosorbent to biosorb Zn2+ and Pb2+ from single and binary aqueous solutions. Several factors, such as biomass concentration (0.25–4 g), metal solution concentration (5–50 mg L−1), solution pH (2–5), and contact time were standardized. Streptomyces sp. biomass was able to extract 93% Pb2+ and 91% Zn2+ from a single and 95% Pb2+ and 97% Zn2+ from a binary metal aqueous solution containing 25 mg L−1 and pH 4. The highest adsorption capacity in both single and binary sorption experiments was determined to be shared by Zn2+ and Pb2+. The biosorbent’s metal adsorption increased from 0.48 to 4.56 mg g−1 for Pb2+ and from 0.21 mg g−1 to 4.65 mg g−1 for Zn2+ when the metals were present singly, and from 0.44 to 4.18 mg g−1 for Pb2+ and from 0.41 mg g−1 to 5.67 mg g−1 for Zn2+ when the metals were present in binary form. The amount of metal ions was raised from 5 to 50 mg L−1. Correlation coefficient (R2) values indicate that the adsorption pattern for Zn2+ and Pb2+ followed Freundlich isotherm R2 > 0.9543 for single and 0.9582 for binary sorption system. In order to remove Zn2+ and Pb2+ from an aqueous solution, Streptomyces sp. is a potential and different source of adsorbents. Full article
(This article belongs to the Special Issue Development of Mesoporous Materials for Adsorption and Recovery of Metals)
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22 pages, 6162 KiB  
Article
Assessment of Two Materials as Adsorbents for the Effective Removal and Further Pre-Concentration of Gallium from Aqueous Solutions: Mesoporous Carbon vs. Clinoptilolite
by Patricia Sáez, Ignacio Bernabé, José Mª. Gómez, Eduardo Díez, Cristina Fraile, Noelia García and Araceli Rodríguez
Separations 2023, 10(6), 349; https://doi.org/10.3390/separations10060349 - 9 Jun 2023
Cited by 2 | Viewed by 1484
Abstract
In this research, the adsorption of gallium onto natural zeolite (clinoptilolite) and two mesoporous-activated carbons were compared and evaluated. The clinoptilolite was treated with HCl (HCPL), while mesoporous-activated carbons (MCSG60A and MCO1) were synthesized by replica method, using sucrose as the carbon precursor [...] Read more.
In this research, the adsorption of gallium onto natural zeolite (clinoptilolite) and two mesoporous-activated carbons were compared and evaluated. The clinoptilolite was treated with HCl (HCPL), while mesoporous-activated carbons (MCSG60A and MCO1) were synthesized by replica method, using sucrose as the carbon precursor and silica gel as the template. These carbonaceous materials showed large pore sizes and mesoporous surface, as well as a suitable surface chemistry for cation adsorption, which promotes a high negative charge density. On the other hand, zeolites have narrower pore sizes, which hinders the material diffusion inside the particle; however, its strength is their ion exchange capacity. Regarding the gallium kinetic studies, it is described by Pseudo-second order model for both sorts of adsorbents. MCO1 is the best carbonaceous adsorbent studied, with a capacity of 4.58 mg/g. As for zeolites, between the two zeolites studied, HCPL showed the best results, with a gallium adsorption capacity of 3.1 mg/g. The gallium adsorption mechanism onto MCO1 material is based on physisorption, while HCPL is mainly retained due to an ion-exchange process. Regarding the Giles classification, MCO1 isotherm described an H-4 pattern of high affinity and characteristic of multilayer adsorption. The Double-Langmuir model fits properly within these experimental results. In the case of zeolites, HCPL adsorption isotherm followed an L-2 pattern, typical of monolayer adsorption—the Sips model is the one that better describes the adsorption of gallium onto the zeolite. Full article
(This article belongs to the Special Issue Development of Mesoporous Materials for Adsorption and Recovery of Metals)
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19 pages, 7836 KiB  
Article
Application of Walnut Shell Biowaste as an Inexpensive Adsorbent for Methylene Blue Dye: Isotherms, Kinetics, Thermodynamics, and Modeling
by Sabrina Farch, Madiha Melha Yahoum, Selma Toumi, Hichem Tahraoui, Sonia Lefnaoui, Mohammed Kebir, Meriem Zamouche, Abdeltif Amrane, Jie Zhang, Amina Hadadi and Lotfi Mouni
Separations 2023, 10(1), 60; https://doi.org/10.3390/separations10010060 - 16 Jan 2023
Cited by 28 | Viewed by 3245
Abstract
This research aimed to assess the adsorption properties of raw walnut shell powder (WNSp) for the elimination of methylene blue (MB) from an aqueous medium. The initial MB concentration (2–50 mg/L), the mass of the biomaterial (0.1–1 g/L), the contact time (10–120 min), [...] Read more.
This research aimed to assess the adsorption properties of raw walnut shell powder (WNSp) for the elimination of methylene blue (MB) from an aqueous medium. The initial MB concentration (2–50 mg/L), the mass of the biomaterial (0.1–1 g/L), the contact time (10–120 min), the medium’s pH (2–12), and the temperature (25–55 °C) were optimized as experimental conditions. A maximum adsorption capacity of 19.99 mg/g was obtained at an MB concentration of 50 mg/L, a medium pH of 6.93 and a temperature of 25 °C, using 0.2 g/L of WNSp. These conditions showed that the MB dye elimination process occurred spontaneously. Different analytical approaches were used to characterize the WNSp biomaterial, including functional groups involved in MB adsorption, the surface characteristics and morphological features of the WNSp before and after MB uptake, and identification of WNSp based on their diffraction pattern. The experimental isotherm data were analyzed by the Langmuir and Freundlich models for the adsorption of MB dye. The corresponding values of parameter RL of Langmuir were between 0.51 and 0.172, which confirmed the WNSp’s favorable MB dye adsorption. The experimental kinetic data were examined, and the pseudo-second-order model was shown to be more suitable for describing the adsorption process, with an excellent determination coefficient (R2 = 0.999). The exchanged standard enthalpy (H° = −22.456 KJ.mol−1) was calculated using the van ‘t Hoff equation, and it was proven that the adsorption process was exothermic. The spontaneous nature and feasibility of the MB dye adsorption process on WNSp were validated by negative standard enthalpy values (G°) ranging from −2.580 to −0.469 at different temperatures. It was established that WNSp may be employed as a novel, effective, low-cost adsorbent for the elimination of methylene blue in aqueous solutions. Full article
(This article belongs to the Special Issue Development of Mesoporous Materials for Adsorption and Recovery of Metals)
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Review

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22 pages, 7059 KiB  
Review
Fluoride Removal from Water Sources by Adsorption on MOFs
by Athanasia K. Tolkou and Anastasios I. Zouboulis
Separations 2023, 10(9), 467; https://doi.org/10.3390/separations10090467 - 24 Aug 2023
Cited by 10 | Viewed by 2845
Abstract
Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum permissible concentration limit of 1.5 mg/L (according [...] Read more.
Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum permissible concentration limit of 1.5 mg/L (according to WHO). Among the numerous technologies for removing fluoride from waters, metal–organic framework (MOF) materials are considered to be promising adsorbents due to their advantages of high porosity, high specific surface area, diverse functions and easy modification. In this study, the synthesis of MOFs and the progress of their application to the removal of fluoride from contaminated water, as published in the recent literature mainly over the past five years, are reviewed. The adsorption mechanism(s) and its main characteristics, such as effect of initial fluoride concentration, adsorbent dosage, solution pH, contact time, adsorption capacity, thermodynamic and regeneration studies, etc., for the removal of fluoride with the addition of different MOFs are compared. According to these comparisons, the hydrothermal/solvothermal synthesis method is most commonly used for the preparation of MOFs, whereas higher BET surface areas are shown by specific MOFs based on aluminum metal ions. The main fluoride adsorption mechanisms were found to be electrostatic attraction and/or complexation. The most common pH for conducting experiments was 7.0, but several examined materials were found to be effective over a wide pH range. Four to six regeneration cycles were successfully applied on average, regarding the MOFs under review, whereas in the majority of these cases, the sorption process was found to be endothermic. Full article
(This article belongs to the Special Issue Development of Mesoporous Materials for Adsorption and Recovery of Metals)
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