Heavy metal adsorption by mercapto and amine functionalized silica aerogel-like materials

The pollution by heavy metals is a serious problem of today’s world. Both soils and water courses are affected by this issue as the two are very intertwined. In both media, heavy metals exist as cations in solution, the most... [ view full abstract ]

The pollution by heavy metals is a serious problem of today’s world. Both soils and water courses are affected by this issue as the two are very intertwined. In both media, heavy metals exist as cations in solution, the most dangerous form of these chemical elements, and adsorption appears as an adequate process to remove these contaminants. Silica based aerogels are incredible nanostructured materials that feature many interesting properties. Amongst them is the ability to tailor their surface chemistry, that allows the development of tailored new adsorbents for the removal of heavy metals from contaminated media. Using triethoxymethylsilane, tetraethyl orthosilicate, (3-aminopropyl) trimethoxysilane and/or (3-mercaptopropyl)trimethoxysilane the new adsorbents were prepared (Fig. 1) using sol-gel chemistry to remove the heavy metals most significant for Iberian soils. Because silica is a natural compound that exists in large amounts and forms in the environment, these new adsorbents are not armful in this context. The new adsorbents were ground into fine powders, sieved and assessed via batch sorption equilibrium and kinetic tests with Ni(II), Zn(II), Cd(II) and Cr(III) in single-metal solutions. The equilibrium tests reveal that the adsorbents show affinity towards these cations and that the removal of the contaminants via sorption is very efficient, achieving high values (results for metal uptake ranges from ~40 mg/g up to ~130 mg/g at an initial concentration of 500 ppm of cation with 0.09 g of adsorbent). The adoption process is very fast, being the equilibrium concentration achieved up to one hour for some metals and in about two hours for the remaining ones. Cation mixtures of these metals were also tested with these adsorbents.

Acknowledgment: Work developed under the project “AeroMCatch – Silica Aerogels for Remediation of Soils Contaminated with Heavy Metals” (Process No 141735), by João Vareda and University of Coimbra, funded by Fundação Calouste Gulbenkian (Portugal), through the “Programa de Estímulo à Investigação 2015”.

Keywords: Heavy metal; Aerogel-like materials; Adsorption; Organically-modified silica; Iberian Peninsula pollutants