Investigating crystal plane effect of Co3O4 with various morphologies on catalytic activation of monopersulfate for degradation of phenol in water

As phenol represents as the most typical persistent organic pollutants in wastewater, SO4•−-involved chemical oxidation techniques using monopersulfate (MPS) have been regarded as a promising method to eliminate phenol. Since Co3O4 is the benchmark heterogeneous catalyst for activating MPS, it is highly critical to investigate shape-varied Co3O4 catalysts with well-defined crystal planes for activating MPS to degrade phenol. Thus, the aim of this study is to elucidate how different Co3O4 catalysts with various well-defined planes would influence catalytic activities for MPS activation. Specifically, three Co3O4 nanocrystals are fabricated: nanoplate (NP), nanobundle (NB), and nanocube (NC) with different dominant exposed facets of {1 1 2}, {1 1 0}, and {1 0 0}, respectively. As the facets of {1 1 2} and {1 1 0} consist of more abundant Co2+/Co3+, Co3O4-NP and Co3O4-NB exhibit noticeably higher catalytic activities then Co3O4-NC for activating MPS to degrade phenol. Nevertheless, since Co3O4-NP shows a much higher surface area than Co3O4-NB, Co3O4-NP could exhibit a relatively high catalytic activity in comparison to Co3O4-NB. In addition, Co3O4-NP also exhibits much faster degradation kinetics with a rate constant of 0.061 min−1 at 30 °C, and more resistance towards pH variation, with much stable reaction stoichiometric efficiencies (RSE) ranging from 0.034 to 0.039 at pH = 3 ~ 9, than the other two Co3O4 nanocrystals, making Co3O4-NP with the {1 1 2} facet a more outstanding Co3O4 for activating MPS to degrade phenol.