![]() ![]() 7,8 The discovery of subcritical drying for aerogels was reported by Deshpande, Smith and Brinker in a patent (US5565142A) granted in 1996. 1), which is certainly justified by the unpaired aerogel characteristics, i.e., a fine nanostructured 3D network composed of clusters of interlinked nanoparticles, with porosity usually above 90% (mainly in the mesopores range), that results in a high surface area, ultra-lightweight solid. The growth of works under this topic has been exponential since then ( Fig. In the following decades, the works found on aerogels are very scarce (not many years have more than one article during that period), and only started to raise in the 1980s due to the increasing interest in the application of aerogels as Cherenkov counters and catalysts. 15 mW m −1 K −1) was since the beginning one of its most noticed features. 4–6 The thermal conductivity of the latter ( ca. The work of Kistler continued with the application of the developed procedure to obtain thoria aerogel catalysts 2,3 and with the characterization of the structure and properties of the very new silica aerogel. This protocol, currently called supercritical drying, consisted in replacing the liquid (alcohol) inside the pores of a silica gel by a gas, with little or no shrinkage, which was accomplished by turning the solvent in a supercritical fluid, thus avoiding the capillary forces existent during evaporative drying. Introduction In 1930, Samuel Stephens Kistler developed a systematized procedure to produce a new material that he designated as “aerogel” (published in Nature in 1931 1). Our paper also contributes to a more informed and sustainable development of nanomaterials, in particular silica aerogels and amorphous silica nanoparticles in general. No similar paper is published in the literature, consequently most of the information we present is fragmented in the open literature and not easily widespread. Based on the published literature, in our paper we conclude about the health effects and ecotoxicity of these nano silicas and present the best available information/recommendations regarding safe handling and disposal. These types of amorphous silica nanostructured materials are very common despite the lack of knowledge about their effects, safe handling and disposal. In the current paper, we review, analyse, and discuss the toxicity, ecotoxicity, workplace exposure, handling practices and alternatives of disposal of silica aerogels and nanoparticles. However, there is a clear lack of knowledge on the health and environmental effects of such substances and, information on their handling and disposal is also frequently incomplete. Environmental significance Currently, many nanoforms are used in commercial products and their research is widespread. Furthermore, relevant safety practices for handling these materials are discussed and strategies used to recycle and dispose them are summarized. In this work, the knowledge on toxicity of amorphous silica nanostructures and suitable regulations are reviewed. Amorphous silica is known to be less toxic than its crystalline form, but toxicity studies, regulatory aspects and handling practices are still scarce. Nevertheless, the health effects of amorphous silica materials are not fully understood, as occurs with many other nanoforms. These are commercialized as aerogels or as nanoparticles, which can feature many similarities, not only in the synthesis process but also because clusters of nanoparticles are commonly released from aerogels. Farmacología, Farmacia y Tecnología Farmacéutica, I+D Farma group (GI-1645), Faculty of Pharmacy and Health Research Institute of Santiago de Compostela (IDIS), Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain c University of Coimbra, CQC, Department of Chemistry, Rua Larga, 3004-535 Coimbra, Portugal d Immunology Group, CINBIO, Universidade de Vigo, 36310 Vigo, Spain e Instituto de Investigación Sanitaria Galicia Sur, Hospital Álvaro Cunqueiro, 31310 Vigo, Spain f Department of Mineral Building Materials, Materials Testing Institute University of Stuttgart (Otto-Graf-Institute), Pfaffenwaldring 4c, 70569 Stuttgart, GermanyĪmorphous forms of silica have always raised a lot of interest by the scientific community and are nowadays rapidly growing in commercial applications. ![]() * a a University of Coimbra, CIEPQPF, Department of Chemical Engineering, Rua Sílvio Lima, 3030-790 Coimbra, Portugal. Sci.: Nano, 2021, 8, 1177-1195 Insights on toxicity, safe handling and disposal of silica aerogels and amorphous nanoparticles ![]()
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