Piezocatalytic degradation of organic pollutants by the synergy of Iron/cobalt/nickel-doped barium titanates and Peroxymonosulfate

The treatment of organic pollutants in the water environment is crucial to human health and sustainable development. The advanced oxidation process (AOP) exemplified by peroxymonosulfate holds the potential as an effective solution, and the emerging piezocatalytic technology may further promote the high-efficient degradation. This study employed a synergistic approach combining iron/cobalt/nickel-doped barium titanates and peroxymonosulfate to piezocatalytic degrade Rhodamine B solution. Firstly, cubic and tetragonal BaTiO3 calcined at different temperatures were systematically characterized. SEM was employed to demonstrate the micro-morphology of the materials, and X-ray diffraction (XRD) was used to verify the crystalline phase. Fourier Transform Infrared Spectrometer (FTIR) was applied to characterize the functional group on the surface of the materials. Piezoelectrical Force Microscope (PFM) was utilized to measure the piezoelectric performance of the materials. Then, different crystalline phases of iron/cobalt/nickel-doped BaTiO3 were prepared, and XRD was used to demonstrate the lattice distortion compared with pure BaTiO3. In the RhB piezocatalytic degradation experiments, metal-doped BaTiO3 performed better than pure BaTiO3. For iron/nickel-doped BaTiO3, 4% doping concentration was better than 8% because 8% doping exceeded the optimum doping concentration. Calcination at 900 °C was better than 600 °C because the piezoelectric performance improved by the transition from the cubic phase to the tetragonal phase through high temperature. Pure/iron/nickel-doped BaTiO3 can all achieve a degradation rate exceeding 97% for the RhB solution in 1.5 hours. For cobalt-doped BaTiO3, the degradation effect mainly depended on the activation of PMS by the Co element. 8% doping concentration was better than 4%, and calcination at 600 °C was better than 900 °C. This was due to the increased exposure of cobalt elements on the material's surface. 8% cobalt-doped BaTiO3 calcined at 600°C can achieve 99.8% degradation of RhB in three minutes. Ethanol, 1,4-Benzoquinone (BQ), and Tert- butyl alcohol (TPA) were used to capture the sulfate radical (·SO4-), the superoxide radical (·O2-) and the hydroxyl radical (·OH), respectively. Through the different free radical scavengers, it was verified that pure/iron/nickel-doped BaTiO3 depended on the piezocatalytic effect and the hydroxyl radical (·OH) dominated the degradation process, while cobalt-doped BaTiO3 depended on the activation of PMS by Co and the sulfate radical (·SO4-) dominated the degradation process. The activation of PMS by the specific transition metal element shows a significant effect on the degradation, while piezocatalysis shows a comparatively supportive effect. This work provides new insights and guidelines for the integration of the advanced oxidation process and piezocatalytic technology.