Morphology-dependent activation of hydrogen peroxide with Cu₂O for tetracycline hydrochloride degradation in...

The design of efficient heterogeneous catalysts in bicarbonate-activated hydrogen peroxide systems (BAP) is a hot topic in wastewater treatment. In this work, Cu₂O nanoparticles with different morphologies including cubic shape (c-Cu₂O), octahedron shape (o-Cu₂O) and spherical shape (s-Cu₂O), were applied in BAP for the first time to degrade tetracycline hydrochloride (TC). Compared with Cu²⁺ ions and CuO, TC degradation was boosted in the presence of Cu₂O in the BAP system, with the degradation rate following the order c-Cu₂O > o-Cu₂O > s-Cu₂O. The morphology-dependent effects could be linearly correlated with the ratio of surface oxygen species (O_S), but not with the surface area or Cu(I) ratio. The c-Cu₂O catalyst with exposure of (100) facets contained 76.6% O_S as the active site for H₂O₂ adsorption and activation, while the value was much lower for o-Cu₂O and s-Cu₂O with dominant (111) facets. The presence of HCO₃^- enhanced the interactions among Cu₂O, H₂O₂ and TC, leading to facile oxidation of Cu(I) to Cu(II) by H₂O₂, and the formation of various reactive species such as hydroxyl radicals and Cu(III) contributed to TC degradation. This work provides a new method for enhancing H₂O₂ activation with heterogeneous catalysts by crystal facet engineering.