Continuous generation of hydroxyl radicals for highly efficient elimination of chlorophenols and phenols catalyzed by heterogeneous Fenton-like catalysts yolk/shell Pd@FeO@metal organic frameworks.

Core/shell FeO-decorated Pd nanoparticles (NPs) hybrids (Pd@FeO) are prepared through a "green", and one-pot chemical process. The Pd@FeO hybrids consisted of faceted quasi-spherical Pd nanoparticles (NPs) cores (∼20 nm) surrounded by close-packed FeO NPs (∼7 nm). To improve the stability and avoid aggregation of Pd@FeO hybrids in water, hollow Fe-metal organic frameworks (Fe-MOFs) were applied to enwrap Pd@FeO to obtain yolk/shell structured composites. Sub-10 nm FeO and Pd NPs close to each other were distributed evenly in the MOFs shell of Pd@FeO@MOFs. The yolk/shell Pd@FeO@MOFs can catalyze the oxidative degradation of chlorophenols and phenols by hydroxyl radicals (OH) decomposed from HO. With low molar ratio of HO/pollutants, the pollutants are degraded and mineralized efficiently and rapidly. The outstanding catalytic efficiency of Pd@FeO@MOFs is contributed by the fast and continuous generation of OH radicals in Pd@FeO@MOFs suspension which is detected with the electron spin resonance spin-trap technique and a continuous-flow chemiluminescence system. Lack of consumption of hydroperoxyl radicals/superoxide radicals (HO/O) in the Pd@FeO@MOFs-HO system might suggest that the production of OH radicals results from the electron transferring from Pd to FeO component both in the inner Pd@FeO and MOF shell, which facilitates fast Fe(III)/Fe(II) redox cycle.