Adsorption of perfluorooctanoic acid from water by pH-modulated Brönsted acid and base sites in mesoporous hafnium oxide ceramics

Fatima A Hussain; Samuel E Janisse; Marie C Heffern; Maureen Kinyua; Jesús M Velázquez

doi:10.1016/j.isci.2022.104138

Adsorption of perfluorooctanoic acid from water by pH-modulated Brönsted acid and base sites in mesoporous hafnium oxide ceramics

iScience. 2022 Mar 22;25(4):104138. doi: 10.1016/j.isci.2022.104138. eCollection 2022 Apr 15.

Authors

Fatima A Hussain¹, Samuel E Janisse¹, Marie C Heffern¹, Maureen Kinyua², Jesús M Velázquez¹

Affiliations

¹ Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616, USA.
² Department of Civil & Environmental Engineering, University of California, One Shields Avenue, Davis, CA 95616, USA.

Abstract

Per- and polyfluoroalkyl substances (PFAS) are increasingly appearing in drinking water sources globally. Our work focuses specifically on the adsorption of the legacy perfluorooctanoic acid (PFOA) using mesoporous hafnium oxide (MHO) ceramic synthesized via a sol-gel process. Experiments were performed at varying pH to determine the effect of surface charge on adsorption capacity of PFOA by MHO, and to postulate adsorption behavior. At pH 2.3, the adsorption capacity of PFOA on MHO was 20.9 mg/g, whereas at a higher pH of 6.3, it was much lower at 9.2 mg/g. This was due to increased coulombic attractions at lower pH between the positively charged conjugate acid active sites on MHO surface and negatively charged deprotonated PFOA anion in solution. After adsorption, the solid MHO was regenerated via calcination, reducing the amount of toxic solid waste to be disposed since the adsorbent is regenerated, and the PFOA is completely removed.

Keywords: Chemical Engineering; Environmental Chemistry; Materials Chemistry; Materials Science.