Auto-Assembled Pd–Rh Nanoalloys Catalyzed Faster and Deeper Hydrodefluorination of Perfluorooctanoic Acid (PFOA) in Environmental Conditions
Min Long, Chen Zhou, Welman C. Elias, Hunter P. Jacobs, Kimberly N. Heck, Michael S. Wong, Bruce E. Rittmann
Abstract
Perfluoroalkyl substances (PFASs) are drawing attention because of their widespread contamination in waters and their risks to human and ecosystem health at low concentrations. We evaluated auto-assembled palladium (Pd) plus rhodium (Rh) nanoalloys for H 2 -induced catalytic hydrodefluorination for one of the most prominent PFASs, perfluorooctanoic acid (PFOA), at neutral pH and ambient temperature. Nanoalloys of Pd and Rh displayed enhanced hydrodefluorination capacity compared to Pd and Rh mononanoparticles. Compared to Rh, Pd–Rh retained the similar specific hydrodefluorination ratio but yielded a 5-fold higher hydrodefluorination efficiency due to the stronger adsorption capacity from Pd. Compared to Pd, Pd–Rh showed a slower PFOA removal rate, but its hydrodefluorination capacity was enhanced 12-fold due to the presence of Rh in the alloy. Correspondingly, the completely defluorinated product, octanoic acid, became the dominant product of hydrodefluorination with the Pd–Rh alloy. In continuous-flow tests at pH 7, the bimetallic Pd–Rh catalysts exhibited better and longer-lasting PFOA removal and hydrodefluorination compared to mono-Pd and -Rh catalysts. Atom-scale modeling using density functional theory (DFT) explained the synergistic effect of nanoalloys in adsorbing and C–F dissociation of PFOA at neutral pH. The experimental results and thermodynamic modeling support that Pd–Rh nanoalloys have promise for detoxifying PFOA in environmentally relevant conditions.