Study On Photocatalytic And Piezoelectric Catalytic Properties Of Bismuth Layered Ferroelectric Materials

With the rapid development of modern society,industrial waste water is inevitable,especially the dye pollutants,which seriously pollutes the fresh water resources.Semiconductor photocatalysis provides a low-cost and effective strategy for the large-scale decomposition of these pollutants.However,there are still several drawbacks of semiconductor photocatalysis:some semiconductors with a wider band gap reduce the utilization of solar energy for photocatalytic reactions;photocatalytic efficiency is invariably affected by the separation rate of electrons and holes;the product of the redox reaction will react twice with the original reactant.Therefore,it is necessary to explore a new material system that is sensitive to visible light as a photocatalyst to overcome the above shortcomings.Therefore,a series of novel bismuth layered M_0.5Bi_2.5Nb₂O₉（M=Li,Na,K）nanosheets were prepared by hydrothermal method.Moreover,these nanosheets show excellent photodegradation performance for various organic dyes with a concentration of up to 20mg/L.With the assist of ex-situ ultrasound,an internally polarized field is generated on the surface of the nanosheet.This internal polarization field induces charge-hole separation,which effectively increases the degradation rate constant of organic dyes.In situ ultrasound-induced piezoelectric catalysis has been used as a new type of catalysis method in the degradation of organic pollutants.However,ultrasonic excitation can directly achieve dye degradation through sonocatalysis.The effect of in situ ultrasound-induced sonocatalysis is generally neglected in most reports.Therefore,the performance of piezoelectric catalysis may be overestimated.In order to effectively distinguish between piezoelectric catalysis and acoustic catalysis,we explored the photocatalysis,piezoelectric catalysis and sono-piezo-photo synergistic catalysis performance of the layered powders M_0.5Bi_2.5Nb₂O₉（M=Li,Na,K）.It is found in experiments that the degradation rate of Rh B induced by sonocatalysis strongly depends on the speed of mechanical stirring.Under lower stirring speed and reaction time（<50 rpm and 2 h）,the cavitation effect is almost negligible,only piezocatalysis behavior occurs,which can be used as a key condition to distinguish the piezocatalysis and sonocatalysis.Na_0.5Bi_4.5Ti₄O₁₅ and Bi₄Ti₃O₁₂ are two typical bismuth layered ferroelectric materials with excellent photochromism.Photochromic property refers to the formation of color centers by defect trapping electrons when the material is stimulated by visible light.It necessary to explore whether the color center can effectively regulate the performance of catalytic degradation of organic dyes.These results prove that the bismuth layered material with photochromic properties can effectively improve the efficiency of photocatalytic and piezoelectric degradation.