Development And Degradation Efficiency Of Advanced Oxidation Processes Based On Piezocatalysis Of Bi₂Fe₄O₉

Piezocatalytic oxidation based on piezoelectric effect,which can separate carriers by harvesting natural vibration energy to produce active species for degrading organic pollutants in water,is a very promising advanced oxidation technology and has attracted extensive attention of scholars.However,the poor carrier separation limits the potential development and application of piezocatalytic oxidation technology.In order to solve the above problem,using Bi₂Fe₄O₉nanosheets as model piezocatalyst in this paper,sodium persulfate（PDS）and light were introduced into the piezocatalysis to construct the piezocatalytic activated PDS and piezo-photocatalytic systems to promote carrier separation for improving degradation efficiency.Finally,the mechanism of enhanced degradation efficiency was explored and revealed.Firstly,the Bi₂Fe₄O₉nanosheets were prepared by hydrothermal method and used as piezocatalysts for the degradation of sulfamethoxazole（SMX）and bisphenol A（BPA）.The piezocatalytic degradation experiments showed that 98.2%of SMX and 46.1%of BPA could be removed in 80 minutes.Cl^-,Ca²⁺,Mg²⁺and HA in water all inhibited the piezocatalytic degradation efficiency of Bi₂Fe₄O₉ nanosheets partly.The main active species for the degradation of SMX in the piezocatalytic system were holes and O₂^·-generated via the reduction of molecular oxygen.During the activation process of molecular oxygen,it would be preferentially adsorbed by Fe sites of Bi₂Fe₄O₉ nanosheets,and then Fe²⁺sites act as active centers to activate molecular oxygen to generate O₂^·-by donating electrons,and the piezo-electrons could reduce Fe³⁺to Fe²⁺.To solve the problem of low carrier separation efficiency in piezocatalysis of Bi₂Fe₄O₉ nanosheets,the piezocatalytic activated PDS system with Bi₂Fe₄O₉ nanosheets was proposed.The degradation experiment showed that the piezocatalytic activated PDS system could not only remove BPA but also degrade SMX effectively.Within 30 minutes,the removal efficiency of BPA by the piezocatalytic activated PDS system reached to 98%.The SO₄^·-and·OH produced by piezocatalytic activation of PDS system were the main reactive oxygen species for BPA degradation.The reaction energy barrier for the activation of PDS was as low as 0.425e V.During the activation of PDS by Bi₂Fe₄O₉,the Fe sites in Bi₂Fe₄O₉ first adsorbed PDS,and Fe²⁺provided electrons to activate PDS to form SO₄^·-,accompanied by the oxidation of Fe²⁺to Fe³⁺.On the one hand,the electrons generated by piezoelectric effect can reduce Fe³⁺and accelerate the regeneration of Fe²⁺;on the other hand,PDS can promote the separation of carriers by accepting electrons from Fe²⁺,thereby synergistically improving the degradation efficiency.To further improve the degradation performance of BPA by piezocatalysis,the introduction of visible light into piezocatalysis was proposed to construct a piezo-photocatalysis system.The degradation experiments show that the piezo-photocatalytic system of Bi₂Fe₄O₉nanosheets can degrade 98.3%of BPA within 40 minutes,and the degradation rate is as high as 0.0987 min^-1,which is significantly better than that of piezocatalytic syetem(15.2%,0.0043 min^-1).It is also higher than the degradation performance of BPA by piezocatalytic activated PDS system(0.0604 min^-1),indicating that the introduction of light into the piezocatalysis can significantly improve the piezocatalytic activity for the degradation of BPA.The dominant active species for the degradation of BPA in the piezo-photocatalytic system were holes and O₂^·-generated via the reduction of molecular oxygen by the electrons.In the process of activating molecular oxygen,electrons are first transferred to the Fe site through the oxygen atom in the Fe O₆ octahedron layer,and then transferred to the molecular oxygen through the Fe³⁺/Fe²⁺cycle to generate O₂^·-.The excellent degradation efficiency of piezo-photocatalytic system benefits from two aspects:first,light can accelerate the migration of carriers and inhibit the rapid recombination of charges;second,piezoelectric field can adjust the energy band structure of Bi₂Fe₄O₉to enhance the reduction ability of electrons,promote the reduction reaction of generating O₂^·-,thereby synergistically enhancing the degradation efficiency.