Exploiting copper–silica–zirconia cooperative interactions for the stabilization of tetragonal zirconia catalysts and enhancement of the visible-light photodegradation of bisphenol A

Silica-doped tetragonal mesoporous zirconia nanoparticles, SiO₂/ZrO₂ (SZ), were successfully prepared by a simple microwave-assisted method, and the subsequent incorporation of copper (1–10 wt%) via an electrochemical method gave CuO/SiO₂/ZrO₂ (CSZ) catalysts. The SiO₂ stabilized the ZrO₂ completely in the tetragonal phase, but that the added copper occupied oxygen vacancies in the SZ lattice to perturb the catalysts and partially reintroduce the monoclinic phase. However, CuO enhanced the photoactivity of CSZ catalysts by lowering the band gap energy (from 4.35 eV to 2.70 eV) and acting as an electron trapper to suppress the recombination of electron–hole pairs. The activity of the catalysts in the photodegradation of bisphenol A was ranked in the following order: 5 CSZ (82%) > 1 CSZ (65%) > 10 CSZ (60%) > SZ (58%). The silica–copper–zirconia cooperative interactions affected the numbers of oxygen vacancies, defect sites, Zr–O–Si and Zr–O–Cu bonds, which consequently influenced the stabilization of ZrO₂ as well as the photoactivity of each catalyst. A kinetic study demonstrated that the photodegradation followed the pseudo-first-order Langmuir–Hinshelwood model.