Review and Perspectives on the Sustainability of Organic Aerogels

Abstract

Aerogels are exceptionally lightweight materials characterized by their high open porosity and remarkable specific surface area, currently used across a wide array of industrial sectors from construction to energy storage and have great potential for expanding their applicability and unlocking new market opportunities. Driven by global economic growth and an intensifying environmental crisis, there is a growing demand for engineering innovations that prioritize sustainability. Aerogels are well-positioned to support these sustainability efforts. Their unique properties make them ideal for energy-saving solutions, environmental remediation, and more efficient use of resources. As the demand for eco-conscious technologies rises, aerogels are poised to contribute significantly to the development of greener, more efficient products and processes across multiple industries. The sustainability of aerogel technology is crucial for the mid-to-long-term future, yet its current status has been scarcely reviewed in the literature. This Perspective explores and critically reviews significant advances on organic and hybrid aerogels in the current socioeconomic scenario, with selected case studies endorsing their contribution to the UN Sustainable Development Goals. It also identifies research gaps while proposing innovative strategies to enhance the sustainability of aerogel production through the application of circular economy principles. Key strategies discussed involve the fabrication of aerogels using eco-friendly sources, such as biopolymers derived from biorefinery processes or from waste materials. Additionally, this Perspective examines the development of methods for the reuse, recycling, and end-of-life management of aerogels, along with the implementation of more efficient processing routes. Ultimately, this work highlights the need for comprehensive assessments of aerogel sustainability through life cycle assessment (LCA) and evaluations of safety and toxicity. By addressing these critical aspects, the potential of aerogels to contribute to a more sustainable future appears highly favorable from both commercial and research perspectives, paving the way for a circular aerogel economy and providing a lasting impact to the society in which we live.

Keywords: aerogel recycling; bioaerogels; circular technologies; sustainable production; waste upcycling.

1

Outlook of the most remarkable contributions of aerogels to the UN sustainable development goals.

2

Implementation of biorefinery approaches in aerogel production: (a) Lignocellulosic biomass chemical composition. Adapted with permission from ref . Copyright 2017, Elsevier. (b) Lignin-based aerogel for wastewater remediation. Adapted with permission from ref . Copyright 2022, Elsevier. (c) Aerogel preparation from lignin derived from wheat straw. Reprinted with permission from ref . Copyright 2014, Elsevier.

3

Aerogels prepared from waste textile ((a) rayon, (b, c) viscose) in the shape of monoliths (bulk density 0.1 g/cm³; specific surface area 330 m²/g; porosity >90%) and beads (roundness 0.97–0.98, density 0.08 g/cm³; specific surface area 400 m²/g; porosity 97%); (d, e) their internal morphology, at different scales and similar for all aerogels, is imaged by scanning electron microscopy. , Adapted with permission from ref . Copyright 2024, Springer Nature.

4

Transmetalation of Fe@C aerogels to M@C aerogels (M: Au, Pt, Pd, Ni, and Rh) leading to reusable catalysts. Adapted from ref . Copyright 2016, American Chemical Society. (The figure has been edited from its original version, where the authors had used the term “recycle”; in the context of the current understanding of the terminology, “recycle” is replaced with “reuse”).

5

(a) Reusability of X-alginate aerogels for adsorption of Hg­(II) (C _initial = 100 ppb), after reprocessing that includes washing with an aqueous solution of Na₂EDTA and water. (b) Three consecutive cycles of water vapor uptake between a high (99%) and a low (10%) relative humidity environment by β-CDPU-aerogels. (c) Ten consecutive cycles of water vapor uptake monitored every 24 h for α-CDPU- and β-CDPU-aerogels (xx: %w/w concentration of monomers in the sol). (b, c) Adapted from ref . Copyright 2019, American Chemical Society.

6

Illustration of the (a) closed-loop recycling and upcycling scheme; (b) closed-loop recycling scheme for polyimine aerogels; (c) closed-loop recycling and upcycling scheme for polyimine-cyanurate aerogels.

7

Conventional steps in the preparation of an aerogel (left). Integration of 3D-printing technology into aerogel production with selected examples (right). (a) Microgel-directed suspended printing setup: (i) printing of a Kevlar nanofiber in a microgel matrix using such method; (ii) cellulose, (iii) alginate, and (iv) chitosan aerogels (and their corresponding SEM images) obtained by using microgel-directed suspended printing. Reprinted from ref . Copyright 2022, American Chemical Society. (b) (i) Drop-on-demand printing process setup on a superhydrophobic surface, (ii) low and (iii) high magnifications of SEM images of antibiotic-loaded alginate aerogels microspheres printed by drop on demand. Reprinted with permission from ref . Copyright 2022, MDPI AG. (c) (i) Extrusion-based 3D-printing setup, (ii) visual appearance of 3D-printed alginate aerogels, (iii) 3D pattern observed on the hydrogel-based scaffolds. SEM images at (iv) low and (v) high magnifications of upconversion nanoparticle decorated alginate aerogels. Reprinted with permission from ref . Copyright 2024, Elsevier.