Preparation Of Sodium Molybdote-based Piezoelectric Materials And Properties And Mechanisms Of Piezoelectric-catalyzed Degradation Of Sildenafil

In recent years,sildenafil has been detected in large quantities in the aqueous environment,raising widespread concern about this new contaminant.Sildenafil has certain ecotoxicity and is difficult to be treated by wastewater plants and some traditional advanced oxidation techniques,so it is quite harmful to the environment.In this experiment,we prepared Y³⁺ion-doped and interfacially polarized new piezoelectric catalytic materials,sodium bismuth molybdate（NaBi（Mo O₄）₂）（NBMO）and multi-phase（1T,2H and 1T-2H）MoS₂ composite modified sodium bismuth molybdate,respectively,and systematically investigated the environmental cleanup efficacy of the synthesized piezoelectric catalytic materials in degrading sildenafil,and The mechanism of sildenafil degradation by piezo-catalytic oxidation was investigated using computational analysis of the piezo-catalytic degradation process of sildenafil based on quantum chemical frontier molecular orbital（FMO）theory.A QSAR toxicological analysis of the ecotoxicity of the by-products during the piezo-catalytic oxidative degradation was performed.NBMO and 1.5Y-NBMO piezoelectric catalytic materials were successfully synthesized and characterized for their crystal structure,microscopic morphology and piezoelectric properties.The experimental degradation of sildenafil by piezoelectric catalysis demonstrated that 1.5Y-NBMO has stronger piezoelectric catalytic degradation efficiency than NBMO.Under the optimal experimental conditions,i.e.,1.5Y-NBMO dosing amount of 0.25 g/L,p H of 6.0,and rotor speed of 720 RPM,the degradation rate of sildenafil could reach 98.5%in 150 min.The free radical experiments showed that the order of the strong and weak effects of free radicals on the degradation of sildenafil was cavity>superoxide radical>hydroxyl radical>singlet oxygen.In this experiment,three different heterojunction piezoelectric catalytic materials,1T MS/NBMO,1T-2H MS/NBMO,and 2H MS/NBMO,were constructed by interfacial polarization engineering.The experiments of piezoelectric catalytic degradation of sildenafil showed that 1T MS/NBMO has the best piezoelectric catalytic degradation efficiency.Under the optimal experimental conditions（i.e.,1T MS/NBMO dosing of 0.20 g/L,p H of 6.0,and rotor speed of 900 RPM）for 60 min,99.8%of sildenafil could be degraded.The degradation of sildenafil into small molecular fragments was effectively demonstrated by HPLC-MS,and the results were consistent with the prediction of molecular polarity by quantum chemical ESP.And the QSAR results analysis proved that the toxicity of sildenafil was decreasing during the degradation process.Mechanistic analysis showed that by forming Bi-S-Mo and Mo（IV）-S-Mo（VI）electron transfer channels,followed by the decomposition of H₂O₂into undifferentiated aggressive-OH via Mo（IV）and Mo（VI）conversion,1T MS/NBMO formed S-type piezoelectric heterojunctions for efficient polarized electron transfer and migration,as well as the accumulation of highly reactive holes.The indirect generation of holes,superoxide radicals,hydroxyl radicals and singlet oxygen through diverse channels improves the degradation efficiency of sildenafil during piezoelectric catalysis.The results of this thesis will provide theoretical basis and technical support for the piezoelectric catalysis based on sodium molybdate-based composite piezoelectric materials for the purification of sildenafil-like refractory organic compounds.