Polymer-Assisted Modification of Metal-Organic Framework MIL-96 (Al): Influence on Particle Size, Crystal Morphology and Perfluorooctanoic Acid (PFOA) Removal

Abstract

<div><b>Abstract</b></div><div>A new synthesis method was developed to prepare an aluminum-based metal organic framework (MIL-96) with a larger particle size and different crystal habits. A low cost and water-soluble polymer, hydrolyzed polyacrylamide (HPAM), was added in varying quantities into the synthesis reaction to achieve >200% particle size enlargement with controlled crystal morphology. The modified adsorbent, MIL-96-RHPAM2, was systematically characterized by SEM, XRD, FTIR, BET and TGA-MS. Using activated carbon (AC) as a reference adsorbent, the effectiveness of MIL-96-RHPAM2 for perfluorooctanoic acid (PFOA) removal from water was examined. The study confirms stable morphology of hydrated MIL-96-RHPAM2 particles as well as a superior PFOA adsorption capacity (340 mg/g) despite its lower surface area, relative to standard MIL-96. MIL-96-RHPAM2 suffers from slow adsorption kinetics as the modification significantly blocks pore access. The strong adsorption of PFOA by MIL-96-RHPAM2 was associated with the formation of electrostatic bonds between the anionic carboxylate of PFOA and the amine functionality present in the HPAM backbone. Thus, the strongly held PFOA molecules in the pores of MIL-96-RHPAM2 were not easily desorbed even after eluted with a high ionic strength solvent (500 mM NaCl). Nevertheless, this simple HPAM addition strategy can still chart promising pathways to impart judicious control over adsorbent particle size and crystal shapes while the introduction of amine functionality onto the surface chemistry is simultaneously useful for enhanced PFOA removal from contaminated aqueous systems.<br></div>

Occurrence and removal of poly/perfluoroalkyl substances (PFAS) in municipal and industrial wastewater treatment plants

“…It has been reported that the sorption capacity of chromium analog MOF was higher as compared to iron analog MOF due to stronger interaction between the metal node and sulfur moieties of PFOS molecule (Barpaga et al 2019). Another study developed an aluminum-based MOF for PFOA uptake from water at a laboratory scale and sorbent performance was compared with AC (Hakim Mohd Azmi et al 2020). The much stronger adsorption capacity of PFOA (340 mg/g) compared to AC (120 mg/g) was observed, and which was attributed to the electrostatic bonds formed between the anionic functional group of PFOA and the aluminum-based MOF.…”