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Engineered Gels for Environmental Applications
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Engineered Gels for Environmental Applications

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Applied Chemistry".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 30212

Special Issue Editors

Dr. Luísa Durães

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Guest Editor
Chemical Process Engineering and Forest Products Research Centre, Department of Chemical Engineering, University of Coimbra, 3000-370 Coimbra, Portugal
Interests: aerogels; nanoparticles; sol-gel; soft-solution synthesis; functional nanomaterials; environmental remediation; thermal insulation
Special Issues, Collections and Topics in MDPI journals
Dr. Artur Valente

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Guest Editor
Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
Interests: transport phenomena; surfactants; biopolymers; polysaccharides; supramolecular chemistry
Special Issues, Collections and Topics in MDPI journals
Dr. Ioannis Anastopoulos

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Guest Editor
Department of Agriculture, University of Ioannina, UoI Kostakii Campus, 47100 Arta, Greece
Interests: wastewater treatment; adsorption; soil pollution; heavy metals; dyes; pharmaceuticals; climate change; composting
Special Issues, Collections and Topics in MDPI journals
Dr. Nicolas Brun

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Guest Editor
Universite de Montpellier, ENSCM, UMR CNRS 5253, Inst Charles Gerhardt, Pl Eugene Bataillon, F-34095 Montpellier 05, France
Interests: porous carbons; functional carbon nanocomposites; biosourced materials; valorization of agrowastes; surface modification; environmental remediation; CO2 capture and conversion; adsorption; energy storage; electrocatalysis; heterogeneous biocatalysis; enzymatic and microbial electrosynthesis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The United Nations established seventeen Sustainable Development Goals to be achieved in the next decade, which address several current global challenges. Part of these goals is linked to reversing climate change and environmental degradation through approaches that avoid wasting water, generate clean energy, stimulate the recycling of materials, and reduce global warming and the incidence of pollutants and wastes.

The design of new advanced materials may greatly contribute to innovative technological solutions that will aid the accomplishment of the referred goals. On a global scale, there are many materials that are applied for environmental applications, such as agricultural biomass/waste, carbonaceous and mineral-based materials, nanomaterials, metal and carbon organic frameworks (MOFs and COFs, respectively), etc. Gels are another significant category, which are chemically versatile materials in terms of their composition and show high interface areas. The latter can be excellent platforms for intensification of interactions between compounds. Moreover, the possibility of adding/mixing new phases that will be retained either by simple physical entrapment or by the formation of chemical bonds opens new possibilities to tailor the final material properties to specific environmental-inspired applications and unusual performance targets. These end-uses can include membranes, catalysts, adsorbents, and superinsulators, among others.

Gels may be used in wet state, as in the case of hydrogels, or be dried by several strategies to remove the swelling agents, still retaining their porous structure. Supercritical drying or freeze-thawing are the most prominent examples of methods that allow the drying of gels, often maintaining intact the pore size distribution of the solid network. Very singular mesoporous materials, such as aerogels and cryogels, can be prepared by these methods. Nonetheless, the use of green routes and sustainable precursors for the synthesis of these materials cannot be disregarded, nor can the possibility to reuse them several times or to reintroduce them in their own synthesis.

Considering all the above, this Special Issue targets the latest trends and advances on engineered gels for environmental applications, including energy storage and/or conversion, clean energy production, thermal and acoustic insulation, water and soil remediation, agriculture, soil erosion, and recycling of materials and/or wastes. Emphasis will be given to the utilization of new gel formulations fabricated with an eco-friendly (green) way.

This Special Issue is an initiative of the AERoGELS (CA18125—Advanced Engineering and Research of aeroGels for Environment and Life Sciences) Action (https://cost-aerogels.eu) by COST (European Cooperation in Science and Technology) that aims to boost the development of aerogels for biomedical and environmental applications by setting up a multidisciplinary knowledge-based network from technological, scientific, and market points of view.

Prof. Dr. Luísa Durães
Prof. Dr. Artur J.M. Valente
Dr. Ioannis Anastopoulos
Dr. Nicolas Brun
Guest Editors

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Published Papers (7 papers)

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Research

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11 pages, 2380 KiB  
Article
Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification
by Atheer Al Khudhair, Karim Bouchmella, Pierre Hubert Mutin, Vasile Hulea, Olinda Gimello and Ahmad Mehdi
Molecules 2022, 27(8), 2534; https://doi.org/10.3390/molecules27082534 - 14 Apr 2022
Viewed by 1919
Abstract
The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO2-Al2O3 mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and [...] Read more.
The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO2-Al2O3 mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N2-physisorption, powder XRD, 29Si, 27Al MAS-NMR, and NH3-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to 27Al and 29Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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20 pages, 2531 KiB  
Article
Poly(β-cyclodextrin)-Activated Carbon Gel Composites for Removal of Pesticides from Water
by Gianluca Utzeri, Luis Verissimo, Dina Murtinho, Alberto A. C. C. Pais, F. Xavier Perrin, Fabio Ziarelli, Tanta-Verona Iordache, Andrei Sarbu and Artur J. M. Valente
Molecules 2021, 26(5), 1426; https://doi.org/10.3390/molecules26051426 - 6 Mar 2021
Cited by 26 | Viewed by 3354
Abstract
Pesticides are widely used in agriculture to increase and protect crop production. A substantial percentage of the active substances applied is retained in the soil or flows into water courses, constituting a very relevant environmental problem. There are several methods for the removal [...] Read more.
Pesticides are widely used in agriculture to increase and protect crop production. A substantial percentage of the active substances applied is retained in the soil or flows into water courses, constituting a very relevant environmental problem. There are several methods for the removal of pesticides from soils and water; however, their efficiency is still a challenge. An alternative to current methods relies on the use of effective adsorbents in removing pesticides which are, simultaneously, capable of releasing pesticides into the soil when needed. This reduces costs related to their application and waste treatments and, thus, overall environmental costs. In this paper, we describe the synthesis and preparation of activated carbon-containing poly(β-cyclodextrin) composites. The composites were characterized by different techniques and their ability to absorb pesticides was assessed by using two active substances: cymoxanil and imidacloprid. Composites with 5 and 10 wt% of activated carbon showed very good stability, high removal efficiencies (>75%) and pesticide sorption capacity up to ca. 50 mg g−1. The effect of additives (NaCl and urea) was also evaluated. The composites were able to release around 30% of the initial sorbed amount of pesticide without losing the capacity to keep the maximum removal efficiency in sorption/desorption cycles. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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15 pages, 1765 KiB  
Article
Effective Removal of Cyanide and Heavy Metals from an Industrial Electroplating Stream Using Calcium Alginate Hydrogels
by Benita Pérez-Cid, Sergio Calvar, Ana Belén Moldes and Jose Manuel Cruz
Molecules 2020, 25(21), 5183; https://doi.org/10.3390/molecules25215183 - 7 Nov 2020
Cited by 8 | Viewed by 3440
Abstract
A real electroplating wastewater, containing 51,190 mg/L of free cyanide (CNf), 4899 mg/L of Ni and 1904 mg/L of Cu, was treated with calcium alginate hydrogel beads (CAB), pure or impregnated with biodegraded grape marc (EBGM) or activated carbon (EAC) in [...] Read more.
A real electroplating wastewater, containing 51,190 mg/L of free cyanide (CNf), 4899 mg/L of Ni and 1904 mg/L of Cu, was treated with calcium alginate hydrogel beads (CAB), pure or impregnated with biodegraded grape marc (EBGM) or activated carbon (EAC) in order to reduce the elevated load of toxic pollutants below the regulatory limits. It was evaluated the effect of increasing the amount of bioadsorbent as well as the influence of two successive adsorption cycles in the removal efficiency of pollutants. The most favourable sorption conditions onto CAB provided removal percentages of 85.02% for CNf and between 93.40–98.21% for heavy metals regarding the raw wastewater. The adsorption capacity of each pollutant onto CAB was considerably increased during the first 30 min of contact time, but after achieving the equilibrium, the following sorption capacities were obtained: 1177, 107.3, 39.5 and 1.52 mg/g for CNf, Ni, Cu and Zn, respectively. The kinetic adsorption of pollutants onto the CAB was adjusted to different kinetic models, observing that kinetic data agreed with the pseudo-second-order model. The information about intraparticle diffusion mechanisms in the bioadsorption process was also interpreted. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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13 pages, 3102 KiB  
Article
Removal of Pharmaceuticals from Water by Free and Imobilised Microalgae
by Telma Encarnação, Cátia Palito, Alberto A. C. C. Pais, Artur J. M. Valente and Hugh D. Burrows
Molecules 2020, 25(16), 3639; https://doi.org/10.3390/molecules25163639 - 10 Aug 2020
Cited by 35 | Viewed by 4134
Abstract
Pharmaceuticals and their metabolites are released into the environment by domestic, hospital, and pharmaceutical industry wastewaters. Conventional wastewater treatment technology does not guarantee effluents of high quality, and apparently clean water may be loaded with pollutants. In this study, we assess the performance [...] Read more.
Pharmaceuticals and their metabolites are released into the environment by domestic, hospital, and pharmaceutical industry wastewaters. Conventional wastewater treatment technology does not guarantee effluents of high quality, and apparently clean water may be loaded with pollutants. In this study, we assess the performance and efficiency of free and immobilised cells of microalgae Nannochloropsis sp. in removing four pharmaceuticals, chosen for their occurrence or persistence in the environment. These are paracetamol, ibuprofen, olanzapine and simvastatin. The results showed that free microalgae cells remain alive for a longer time than the immobilised ones, suggesting the inhibition of cell proliferation by the polymeric matrix polyvinyl alcohol. Both cells, free and immobilised, respond differently to each pharmaceutical. The removal of paracetamol and ibuprofen by Nannochloropsis sp., after 24 h of culture, was significantly higher in immobilised cells. Free cells removed a significantly higher concentration of olanzapine than immobilised ones, suggesting a higher affinity to this molecule than to paracetamol and ibuprofen. The results demonstrate the effectiveness of Nannochloropsis sp. free cells for removing olanzapine and Nannochloropsis sp. immobilised cells for removing paracetamol and ibuprofen. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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19 pages, 3330 KiB  
Article
Silica Aerogels/Xerogels Modified with Nitrogen-Containing Groups for Heavy Metal Adsorption
by João P. Vareda, Artur J. M. Valente and Luisa Durães
Molecules 2020, 25(12), 2788; https://doi.org/10.3390/molecules25122788 - 17 Jun 2020
Cited by 21 | Viewed by 3764
Abstract
Heavy metals are common inorganic pollutants found in the environment that have to be removed from wastewaters and drinking waters. In this work, silica-derived aerogels and xerogels were modified via a co-precursor method to obtain functional adsorbents for metal cations. A total of [...] Read more.
Heavy metals are common inorganic pollutants found in the environment that have to be removed from wastewaters and drinking waters. In this work, silica-derived aerogels and xerogels were modified via a co-precursor method to obtain functional adsorbents for metal cations. A total of six formulations based upon four different functional precursors were prepared. The materials′ structural characterization revealed a decreased porosity and surface area on modified samples, more prominent in xerogel counterparts. Preliminary tests were conducted, and the prepared samples were also compared to activated carbon. Three samples were selected for in-depth studies. Isotherm studies revealed that the pre-selected samples remove well copper, lead, cadmium and nickel, and with similar types of interactions, following a Langmuir trend. The adsorption kinetics starts very fast and either equilibrium is reached quickly or slowly, in a two-stage process attributed to the existence of different types of active sites. Based on the previous tests, the best sample, prepared by mixing different functional co-precursors, was selected and its behavior was studied under different temperatures. For this material, the adsorption performance at 20 °C is dependent on the cation, ranging from 56 mg·g−1 for copper to 172 mg·g−1 for lead. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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Review

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21 pages, 4410 KiB  
Review
The Importance of Precursors and Modification Groups of Aerogels in CO2 Capture
by Leila Keshavarz, Mohammad Reza Ghaani and Niall J. English
Molecules 2021, 26(16), 5023; https://doi.org/10.3390/molecules26165023 - 19 Aug 2021
Cited by 15 | Viewed by 4504
Abstract
The rapid growth of CO2 emissions in the atmosphere has attracted great attention due to the influence of the greenhouse effect. Aerogels’ application for capturing CO2 is quite promising owing to their numerous advantages, such as high porosity (~95%); these are [...] Read more.
The rapid growth of CO2 emissions in the atmosphere has attracted great attention due to the influence of the greenhouse effect. Aerogels’ application for capturing CO2 is quite promising owing to their numerous advantages, such as high porosity (~95%); these are predominantly mesoporous (20–50 nm) materials with very high surface area (>800 m2∙g−1). To increase the CO2 level of aerogels’ uptake capacity and selectivity, active materials have been investigated, such as potassium carbonate, K2CO3, amines, and ionic-liquid amino-acid moieties loaded onto the surface of aerogels. The flexibility of the composition and surface chemistry of aerogels can be modified intentionally—indeed, manipulated—for CO2 capture. Up to now, most research has focused mainly on the synthesis of amine-modified silica aerogels and the evaluation of their CO2-sorption properties. However, there is no comprehensive study focusing on the effect of different types of aerogels and modification groups on the adsorption of CO2. In this review, we present, in broad terms, the use of different precursors, as well as modification of synthesis parameters. The present review aims to consider which kind of precursors and modification groups can serve as potentially attractive molecular-design characteristics in promising materials for capturing CO2. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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35 pages, 1296 KiB  
Review
Porous Aerogels and Adsorption of Pollutants from Water and Air: A Review
by Paola Franco, Stefano Cardea, Antonio Tabernero and Iolanda De Marco
Molecules 2021, 26(15), 4440; https://doi.org/10.3390/molecules26154440 - 23 Jul 2021
Cited by 62 | Viewed by 7378
Abstract
Aerogels are open, three-dimensional, porous materials characterized by outstanding properties, such as low density, high porosity, and high surface area. They have been used in various fields as adsorbents, catalysts, materials for thermal insulation, or matrices for drug delivery. Aerogels have been successfully [...] Read more.
Aerogels are open, three-dimensional, porous materials characterized by outstanding properties, such as low density, high porosity, and high surface area. They have been used in various fields as adsorbents, catalysts, materials for thermal insulation, or matrices for drug delivery. Aerogels have been successfully used for environmental applications to eliminate toxic and harmful substances—such as metal ions or organic dyes—contained in wastewater, and pollutants—including aromatic or oxygenated volatile organic compounds (VOCs)—contained in the air. This updated review on the use of different aerogels—for instance, graphene oxide-, cellulose-, chitosan-, and silica-based aerogels—provides information on their various applications in removing pollutants, the results obtained, and potential future developments. Full article
(This article belongs to the Special Issue Engineered Gels for Environmental Applications)
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