Posted by Nowadays, per- and polyfluoroalkyl substances (PFAS) are used in hundreds of thousands of industrial products, i.e. food packaging, paints, cosmetics, etc. and, due their high stability and water-solubility, PFAS occurrence in drinking water has been reported in several areas and their accumulation in different environmental compartments has become subject of global concern.
Their persistency in the environment and human bodies as well as their proved eco- and human toxicity is particularly risky because most of PFAS are not retained by actual water treatment technologies like the adsorption on granular activated carbon (GAC). In fact, GAC performances are strongly related to the carbon-chain length of PFAS and usually subject to a fast drop of initial adsorption performance from 100% to 20% for short chain PFAS in real water treatment plants.
This work relates to the synthesis of βCD modified graphene oxide (GO) nanosheets, displaying alkyl linkers of different lengths (GO-Cn-βCD). First of all, βCD was mono-functionalized with 1,2-ethylenediamine (C2), 1,6-hexamethylenediamine (C6), and 1,12-dodecanediamine (C12) in order to achieve a pending amino group on the primary side then used to graft them to GO nanosheets by epoxide ring opening reaction. As a reference, also monoamino βCD (C0) was linked to GO. Covalent binding was demonstrated by comparing ATR-FTIR, TGA, XPS and Elemental Analysis data and the degree of functionalization of GO with CD-derivatives was estimated in the range 12% – 36%.
Adsorption tests on perfluorobutanoic acid (PFBA), a particularly persistent PFAS selected as case study, revealed a strong influence of the alkyl linker length on the adsorption efficiency, with the hexyl linker derivative GO-C6-βCD outperforming both pristine GO and GAC at short contact time and well compares with the adsorption of GAC after 24h. Molecular dynamic simulations ascribed this evidence to the favourable orientation of the βCD unit on the surface of GO which enables a strong contaminant molecules retention. The adsorption synergy of GO and βCD was finally proved for a mixture of PFAS of different fluoroalkyl chain length. Long-chain PFAS were well adsorbed by GO and short-chain ones were retained by the CD unit, this revealing great potential of the presented approach for drinking water purification from emerging contaminants paving the way for the exploitation of GO-C6-βCD in more engineered technologies, such as membranes for PFAS removal under flow conditions.
Chemical Tailoring of β-Cyclodextrin-Graphene Oxide for Enhanced Per- and Polyfluoroalkyl Substances (PFAS) Adsorption from Drinking Water – F. Tunioli, T. D. Marforio, L. Favaretto, S. Mantovani, A. Pintus, A. Bianchi, A. Kovtun, M. Agnes, V. Palermo, M. Calvaresi, M. L. Navacchia and M. Melucci, Chem.Eur.J., 2023, 29, e20230185. DOI: https://doi.org/10.1002/chem.202301854