Adsorption and recovery of perfluorinated compounds from synthetic wastewater using mesoporous silicates

Abstract

In this study, adsorption and recovery of Perfluorinated Compounds (PFCs), priority persistent chemical, from synthetic wastewater by using Hexagonal Mesoporous Silicate (HMSc) was investigated, comparing with microporous zeolite (NaY and HY) and powdered activated carbon (PAC). Moreover, effects of surface functional groups (silanol groups, 3-aminopropyltriethoxy-, 3-mercaptopropyl-, and Octyldichloroethoxy-) including titanium substitution on PFCs adsorption and recovery efficiency were evaluated. Adsorption of Perfluorooctane Sulfonate (PFOS) was higher than Perfluorooctane Acid (PFOA). PAC showed the highest adsorption affinity of PFCs because of complexity of surface functional groups and large surface area. 3-aminopropyltriethoxy- grafted HMS gave higher adsorption capacity compared with other silicate adsorbents. Unless PFOA, adsorption capacities of PFOS on all adsorbents were not affected by decreasing of pH, except 3-aminopropyltriethoxy- grafted HMS. Hydrogen bonding and electrostatic interaction might play the important role for PFCs adsorption on silicate adsorbents. PFOS adsorbed on HMSs can be completely recovered by a mixture of alcohol and water at 5:5 ratios, which is more effective than PAC. Repeating of regeneration by solvent extraction did not affect the PFOS adsorption capacities of hydrophobic functional groups grafted HMS, significantly. Effect of hydrolysis by solvent-extraction process might decrease PFOS adsorption capacities of pristine HMS up to 30%. Adsorption capacity of reused PAC was decreased up to 21% compared with the virgin one.