Hydrothermally synthesized Ti/Zr bimetallic MOFs derived N self-doped TiO₂/ZrO₂ composite catalysts with enhanced photocatalytic degradation of methylene blue

The nitrogen-rich Ti/Zr bimetallic metal organic framework (MOF) precursors were synthesized by a facile one-step hydrothermal method. By pyrolyzing the MOF precursors at 600 °C, the N self-doped TiO₂/ZrO₂ composites were obtained, and the morphology of the MOF precursor was well preserved. The powder X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) indicated the highly crystalline polycrystallization of mix-phase TiO₂ and tetragonal ZrO₂ in the composites. The X-ray photoelectron spectroscopy (XPS) and elemental mapping image demonstrated the successful uniform doping of N. The scanning electron microscopy (SEM) proved that the bimetal oxides retained the thin disk morphology of the MOF precursor. The photoluminescence (PL) spectroscopic analysis proved that the N-doped TiO₂/ZrO₂ composites have a lower photogenerated electron and hole pair recombination rate than single metal oxides. Mott-Schottky analysis confirmed that the N-doped TiO₂/ZrO₂ composites belonged to the n-n heterojunction. The N doped TiO₂/ZrO₂ composites exhibited the outstanding performance of methylene blue (MB) photodegradation under UV light illumination with an efficiency of 93.2% after 80 min. In addition, the degradation rate of N-doped TiO₂/ZrO₂ for tetracycline and phenol and was 86.3% and 72.4% after 120 min, respectively. The quenching test demonstrated that the •OH was the main active radicals, and the electron spin resonance (ESR) confirmed the existence of •OH radicals. The stability and reusability of the composites were confirmed by cyclic experiments, and the possible photocatalytic mechanism was discussed. Overall, N-doped TiO₂/ZrO₂ composites have the considerable application prospect for photocatalysis of organic pollutants in the polluted water.