Design And Photocatalytic Properties Of Bismuth Molybdate Based Photocatalytic Material

Bismuth molybdate based photocatalyst,as an important visible light responsive photocatalyst of Aurivillius type,has attracted more and more attention.However,the bismuth molybdate photocatalyst has some disadvantages,such as weak visible light absorption ability,slow photogenerated carrier migration rate and high recombination rate,which lead to its poor photocatalytic activity.Researchers have solved these problems through methods such as constructing composite heterojunctions,metal deposition and ferroelectric polarization.In this paper,the method of depositing metal Bi on the surface of layeredO6 microspheres,constructing flower-likeO9 heterojunction photocatalyst by one-step solvothermal method and a method of ferroelectric polarization onO6 are designed to improve the photocatalytic performance of bismuth molybdate materials.Firstly,O6 microspheres were synthesized by solvothermal method.O6 heterojunction photocatalyst was constructed by in-situ depositing metal Bi onto the surface ofO6 microspheres.The degradation efficiency of pureO6 to Rhodamine B（Rh B）solution and bisphenol A（BPA）solution was only30.5%and 31.2%under visible light illumination for 40 min,but the photocatalytic activity ofO6 heterojunction photocatalyst was significantly improved.When the loading of Bi was 15%（the catalyst was denoted as Bi-Mo-2）,the composite has the highest photocatalytic activity,and the degradation rates of Rh B and BPA could reach 97.8%and 92%.The degradation rate constants of Rh B and BPA by Bi-Mo-2 were 10.8 and 6.9 times higher than those ofO6,respectively.The enhanced photocatalytic activity of the composite may be attributed to the decrease of the photogenerated electron-hole recombination rate at the interface,the increase of the specific surface area,and the broadening of the light absorption range.The degradation process of BPA was studied and its degradation path was analyzed.The fluorescence intensity of Bi-Mo-2 composite is lower than that of pureO6and metallic Bi,indicating that the formation ofO6 composite inhibits the recombination of electrons and holes.Photoelectrochemical impedance and transient photocurrent response tests also show rapid transfer and separation of photogenerated carriers.Capture experiments showed that holes were the main active species,and hydroxyl radicals and superoxide radicals also played a role.The enhanced photocatalytic activity of the composite may be attributed to the faster electron-hole separation efficiency and enhanced light absorption capacity caused by the plasma surface resonance（SPR）effect of metal Bi.Based on this,a possible photocatalytic mechanism was proposed by combining DRS with Mott-Schottky.Secondly,flower-likeO9 heterojunction photocatalyst was constructed by one-step solvothermal method.The synthesis method is green and simple.Due to the weak oxidation ability ofO9,the photocatalytic degradation of the antibiotic ciprofloxacin（CIP）solution was improved by introducing a wide bandgapO5.The effect of molybdenum source on the synthesis of the composite was discussed in depth.The experimental results show that whenO4 is used as molybdenum source（the catalyst is denoted as S-1）,the synthesized composite has the best morphology,crystal form and the best photocatalytic degradation activity.The degradation efficiency ofO5 andO9 on CIP solution was only 54.3%and 41.4%under 40 min light irradiation.However,after the construction ofO9 heterojunction,the photocatalytic degradation activity of S-1 to CIP reached 95.7%.The degradation rate constant of S-1 to CIP is 0.0699 min^-1,which is4.13 and 5.68 times higher than that ofO5 andO9,respectively.Based on practical application,the influence of coexisting inorganic salt ions in CIP on the degradation activity of the composite was studied.The results showed that Na,and Nahad less effect on the degradation of CIP solution by the composite.In addition,the effect of initial CIP solubility on the degradation activity of the composite was studied.The results showed that the degradation of CIP by the catalyst decreased gradually with the increase of the concentration of CIP solution.When the concentration of CIP increased to 40 mg/L,the degradation efficiency of the composite could still reach 63.1%.Finally,recycling experiments demonstrated that the complex had high stability.XRD,SEM,TEM,XPS and EDS mapping characterizations demonstrated thatO9 nanoparticles were tightly immobilized on the surface ofO5 layered nanosheets to form heterojunctions.The enhanced photocatalytic activity ofO9 composite may be attributed to the faster separation and migration rate of photogenerated carriers between heterojunctions,increased specific surface area,and enhanced light absorption capacity.Based on this,a possible photocatalytic mechanism is proposed by combining density functional theory calculation,Mott-Schottky and DRS characterization.Finally,the effect of ferroelectric polarization on the activity enhancement ofO6 photocatalyst was explored by applying ferroelectric field polarization to organic-inorganic composite film materials constructed by ferroelectric photocatalystO6 and polymethyl methacrylate（PMMA）.The efficiency of unpolarizedO6 degradation of Rh B was 57.6%under 40 min light irradiation,and the degradation efficiency of BPA was 33.4%under 150 min light irradiation.The photocatalytic activity ofO6 material polarized for 1.5 h at 15 V voltages（the catalyst is denoted as BMO-2）was greatly enhanced,and the degradation efficiency of Rh B and BPA under the same conditions reached 98.1%and 79.2%,respectively.The reason for the enhancement of photocatalytic activity is attributed to the enhancement of the internal electric field.The ferroelectric domains of the internal electric field of unpolarizedO6 are disordered and unevenly distributed,and photogenerated carriers are very prone to recombination.When the applied electric field polarizesO6,the ferroelectric domains ofO6 tend to be ordered,and the polarization direction tends to be the same.Positive charges are generated on one side of the surface（C⁺region）and negative charges are generated on the other side（C^-region）.The polarized electric field from C^-region to C⁺region drives therespectively.This process promotes the rapid migration of photogenerated charge carriers from the interior to the surface,improves and prolongs the separation efficiency and lifetime of photogenerated carriers,leading to the enhancement of photocatalytic activity.