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Tannins: Prospectives and Actual Industrial Applications
Open AccessReview

Tannin Gels and Their Carbon Derivatives: A Review

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Centre Technologique des Résidus Industriels (CTRI, Technology Center for Industrial Waste), Cégep de l’Abitibi-Témiscamingue (College of Abitibi-Témiscamingue), 425 Boul. du Collège, Rouyn-Noranda, QC J9X 5E5, Canada
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Department of Metallurgical and Materials Engineering PMT-USP, University of São Paulo, Avenida Mello Moraes, 2463, Cidade Universitária, São Paulo CEP 05508-030, Brazil
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Centre des Matériaux des Mines d’Alès (C2MA), IMT Mines d’Alès, Université de Montpellier, 6 Avenue de Clavières, 30319 Alès CEDEX, France
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LERMAB-ENSTIB, University of Lorraine, 27 rue du Merle Blanc, BP 1041, 88051 Epinal, France
*
Author to whom correspondence should be addressed.
Biomolecules 2019, 9(10), 587; https://doi.org/10.3390/biom9100587
Received: 21 August 2019 / Revised: 29 September 2019 / Accepted: 5 October 2019 / Published: 8 October 2019
(This article belongs to the Special Issue Perspectives on Tannins)
Tannins are one of the most natural, non-toxic, and highly reactive aromatic biomolecules classified as polyphenols. The reactive phenolic compounds present in their chemical structure can be an alternative precursor for the preparation of several polymeric materials for applications in distinct industries: adhesives and coatings, leather tanning, wood protection, wine manufacture, animal feed industries, and recently also in the production of new porous materials (i.e., foams and gels). Among these new polymeric materials synthesized with tannins, organic and carbon gels have shown remarkable textural and physicochemical properties. Thus, this review presents and discusses the available studies on organic and carbon gels produced from tannin feedstock and how their properties are related to the different operating conditions, hence causing their cross-linking reaction mechanisms. Moreover, the steps during tannin gels preparation, such as the gelation and curing processes (under normal or hydrothermal conditions), solvent extraction, and gel drying approaches (i.e., supercritical, subcritical, and freeze-drying) as well as the methods available for their carbonization (i.e., pyrolysis and activation) are presented and discussed. Findings from organic and carbon tannin gels features demonstrate that their physicochemical and textural properties can vary greatly depending on the synthesis parameters, drying conditions, and carbonization methods. Research is still ongoing on the improvement of tannin gels synthesis and properties, but the review evaluates the application of these highly porous materials in multidisciplinary areas of science and engineering, including thermal insulation, contaminant sorption in drinking water and wastewater, and electrochemistry. Finally, the substitution of phenolic materials (i.e., phenol and resorcinol) by tannin in the production of gels could be beneficial to both the bioeconomy and the environment due to its low-cost, bio-based, non-toxic, and non-carcinogenic characteristics. View Full-Text
Keywords: tannin; polyphenolic molecules; sol-gel; organic gel; carbon gel; hydrothermal carbonization; porous materials; pore structure; biopolymer; low-cost tannin; polyphenolic molecules; sol-gel; organic gel; carbon gel; hydrothermal carbonization; porous materials; pore structure; biopolymer; low-cost
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MDPI and ACS Style

Braghiroli, F.L.; Amaral-Labat, G.; Boss, A.F.N.; Lacoste, C.; Pizzi, A. Tannin Gels and Their Carbon Derivatives: A Review. Biomolecules 2019, 9, 587.

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