Highly efficient persulfate oxidation process activated with NiO nanosheets with dominantly exposed {110} reactive facets for degradation of RhB

In this study, we developed a facile mechanochemical method to prepare ultrafine nickel oxide nanosheets with preferential high energy {1 1 0}-facets, an ultrathin thickness of 2 nm and a platelet size of 2-20 nm. These ultrafine nanosheets were synthesized by hand grinding hydrated copper nitrate salt with solid NaOH, while spherical nanoparticles with no preferential facets were obtained using Na2CO3 as base instead. The ultrafine NiO nanosheets exhibited a catalytic efficiency as high as 98.3% at 30 min for degrading RhB by activating persulfate (PS) at a handful of catalyst (0.3 g/L) and oxidant (0.3 g/L), much higher than the 64.6% efficiency of the Na2CO3-obtained NiO nanoparticles. The superior catalyzing ability of the ultrafine NiO nanosheet was attributed to its high proportion of the high-energy NiO {1 1 0}-facets, although its specific surface area (64.74 m(2)/g) was lower than that of the Na2CO3-obtained NiO (84.08 m(2)/g). The effects of NiO nanosheet dosage, PS concentration, initial pH and anions on RhB degradation were systematically investigated. The ultrafine nanosheets also exhibit low metal leaching and good recyclability. Furthermore, the mechanism for PS activation by NiO nanosheets was elucidated by Electron spin resonance (ESR) spectra, scavenger experiments and X-ray photoelectron spectroscopy (XPS) analysis. The results revealed that surface-bound radicals were the primary active species in the NiO nanosheet/PS system. This work offers a quick, simple, cheap, facile and scalable way to prepare highly efficient catalysts for advanced catalytic oxidation.