New insights into removal efficacy of perfluoroalkyl substances by layered double hydroxide and its composite materials

Abstract

Though the use of per-and polyfluoroalkyl substances (PFAS) is strictly restricted worldwide, PFAS have been increasingly detected in aqueous environment with high human exposure risk. Effective PFAS remediation requires the simultaneous concentration and decomposition of these compounds from dilute solutions, presenting a significant challenge. The present work evaluated the suitability of layered double hydroxide (LDH) materials, promising adsorbents for anionic pollutants, for the removal of long-chain and short-chain PFAS in micro-polluted water. Additionally, it explored their potential for PFAS degradation after modification. The results suggested that LDH adsorbents have limited ability to extract short-chain PFAS such as perfluorobutane sulfonate (PFBS) from water matrices, especially in dilute solutions. Although organic modification of LDHs could enhance their uptake efficacy on PFAS, it cannot improve the decomposition of PFAS. Innovatively, a composite featuring zero-valent iron (ZVI) particles coupled with LDH was developed, in which the nanoscale ZVI core is coated with LDH to adsorb and decompose perfluorooctanoic acid (PFOA) synergistically. Characterization of the composite showed that LDH coating not only hinders the aggregation of ZVI particles, but also reduces the passivation of ZVI. The PFOA removal efficacy of the composite can be further facilitated in acid environment. By-product analysis revealed that the composite decomposed PFOA mainly through decarboxylation and formation of unstable alcohol.