Continuous generation of hydroxyl radicals for highly efficient elimination of chlorophenols and phenols catalyzed by heterogeneous Fenton-like catalysts yolk/shell Pd@Fe3O4@metal organic frameworks

Abstract

Core/shell Fe3O4-decorated Pd nanoparticles (NPs) hybrids (Pd@Fe3O4) are prepared through a “green”, and one-pot chemical process. The Pd@Fe3O4 hybrids consisted of faceted quasi-spherical Pd nanoparticles (NPs) cores (∼20 nm) surrounded by close-packed Fe3O4 NPs (∼7 nm). To improve the stability and avoid aggregation of Pd@Fe3O4 hybrids in water, hollow Fe-metal organic frameworks (Fe-MOFs) were applied to enwrap Pd@Fe3O4 to obtain yolk/shell structured composites. Sub-10 nm Fe3O4 and Pd NPs close to each other were distributed evenly in the MOFs shell of Pd@Fe3O4@MOFs. The yolk/shell Pd@Fe3O4@MOFs can catalyze the oxidative degradation of chlorophenols and phenols by hydroxyl radicals (OH) decomposed from H2O2. With low molar ratio of H2O2/pollutants, the pollutants are degraded and mineralized efficiently and rapidly. The outstanding catalytic efficiency of Pd@Fe3O4@MOFs is contributed by the fast and continuous generation of OH radicals in Pd@Fe3O4@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 (HO2/O2−) in the Pd@Fe3O4@MOFs-H2O2 system might suggest that the production of OH radicals results from the electron transferring from Pd to Fe3O4 component both in the inner Pd@Fe3O4 and MOF shell, which facilitates fast Fe(III)/Fe(II) redox cycle.