Flexible regulation of persulfate activation mechanisms through tuning Cu valence in CuBTC-derived copper oxide catalysts for improved pollutant degradation

Radical and nonradical dominated persulfate activation processes have pros and cons in the degradation of pollutants. It is challenging to flexibly tune the contribution ratios of radicals and nonradicals in a persulfate activation process for improved pollutant degradation. Herein, we successfully synthesize copper oxide catalysts derived from metal-organic frameworks. By varying the annealing temperature, valence states of copper can be regulated in the catalyst, thereby enabling the switching between radical and nonradical mechanisms for persulfate activation. Copper oxides annealed at 300 degrees C (CuBTC-300) demonstrate high performance in peroxydisulfate (PDS) activation for the degradation of bisphenol A (BPA), with the synergy of radical and nonradical mechanisms. The surface activated PDS-catalyst complex and (OH)-O-center dot are identified as the reactive oxidative species involved in this process. On one hand, PDS undergoes a one-electron transfer reaction with Cu(I) sites in Cu2O, generating SO4 center dot-, which subsequently converts into (OH)-O-center dot for BPA degradation. On the other hand, the combination of PDS molecules with CuO forms surface-activated complexes, depriving electrons from BPA. The increased content of Cu(II) in the catalyst gradually directs PDS activation towards the nonradical pathway. As the annealing temperature increases from 300 degrees C to 500 degrees C, the contribution of nonradical oxidation to BPA degradation increases from 58.65 % to 100 %. This work provides new insights into flexibly regulating persulfate activation mechanisms via rational catalysts design.