Studies On Controllable Construction Of Sodium Niobate Based Nanomaterials And External Field Enhanced Photocatalytic Properties

Photocatalysis technology has been widely recognized as one of the important technical ways to solve the problems of environmental pollution and energy shortage.The improvement of efficiency is the core problem to be solved urgently in this technical field.Currently,researchers improve the efficiency by developing new materials and promoting the carrier separation efficiency.Based on this,NaNbO₃ materials with both piezoelectricity and photocatalysis were selected as the research objects in this paper,and the simple and effective preparation methods for their composite with various materials were explored.The H₂ evolution performance of double-field catalysis（piezo-photocatalysis）and triple-field catalysis（piezo-magnetic-photocatalysis）under external field enhancement,and the mechanism of external field enhancement was discussed.Specifically include the following:1.Preparation of NaNbO₃@ZIF-8 and the double-field catalytic performance.NaNbO₃nanorods and ZIF-8 nanoparticles were composited through hydrothermal method and in situ growth method,and the bitter gourd-like NaNbO₃@ZIF-8 piezo-photocatalyst was synthesized by adjusting the ratio of reactants.The composition and structure of the catalyst were studied by means of X-ray diffraction（XRD）,transmission electron microscopy（TEM）and other characterization methods,and the activity of the catalyst was evaluated by the H₂ evolution performance.It was found that under double-field catalysis,the H₂ evolution rate of NaNbO₃@ZIF-8 reached 1.16 mmol g^-1 h^-1,which was significantly higher than that of 0.61mmol g^-1 h^-1 under single photocatalytic condition,with an increase of about 90%.The improved performance was attributed to the enhanced carrier migration by the built-in electric field generated by the piezoelectric effect.2.Preparation of NaNbO₃@g-C₃N₄ material and the double-field catalytic performance.The core-shell NaNbO₃@g-C₃N₄ material was prepared through a facile hydrothermal method and calcination method,and the morphology and structure of the catalyst were studied by scanning electron microscopy（SEM）and X-ray photoelectron spectroscopy（XPS）,and H₂evolution performance in double-field catalytic process was investigated.The results showed that the H₂ evolution rate of NaNbO₃@g-C₃N₄ was 1.02 mmol g^-1 h^-1 under double-field catalysis,which was 2.08 times that of photocatalytic condition,indicating that double-field catalysis could greatly promote the carrier separation efficiency of NaNbO₃@g-C₃N₄heterojunction materials in the photocatalytic process,inhibitted the recombination of photogenerated electrons and holes,and improved the photocatalytic performance.3.Preparation of NaNbO₃@rGO and the triple-field catalytic performance.The core-scroll structure NaNbO₃@rGO catalyst was prepared based on electrostatic self-assembly method and ultrasonic composite method.The morphology and structure of the catalyst were obtained by XRD,TEM and other characterization methods.On the basis of the double-field catalytic,a magnetic field was introduced as an external field enhancement,and the reactivity in the triple-field catalysis was investigated.It was found that the H₂ evolution rate of NaNbO₃@rGO was0.32 mmol g^-1 h^-1 under photocatalytic conditions,and the efficiency was improved to 0.65mmol g^-1 h^-1 under dual-field catalysis.Under the triple-field catalytic conditions,the H₂evolution rate reached the maximum value of 0.85 mmol g^-1 h^-1,which had an increase of 165%compared with the photocatalytic condition.The enhancement might be that the piezoelectric field generated by the piezoelectric effect in NaNbO₃@rGO and the micro-potential generated by the electromagnetic induction of rGO jointly accelerate the carrier migration and improve the catalytic activity.