Synthesis Of Molybdate-based Photocatalytic Materials And The Enhancement Photocatalytic Performance

Molybdates containing metal elements are a class of semiconductor materials with good optical properties and have been widely developed and applied in the field of photocatalysis.The structure of metal molybdate is composed of metal ions and molybdate groups.Unfortunately,a single molybdate photocatalyst has defects such as limited light absorption range,low light conversion efficiency and fast photo-generated charge recombination rate,which leads to its unsatisfactory photocatalytic performance.Researchers solve these problems through modification strategies such as the construction of semiconductor heterojunctions,oxygen vacancy engineering,precious metal deposition,and ferroelectric polarization effects.In this paper,molybdate is used as the matrix to design and synthesize Bi₂MoO₆/Co MoO₄ type II heterojunction,Bi OCl/Zn MoO₄ heterojunction with oxygen vacancy structure and C/Bi/Bi₂MoO₆polarization material with ferroelectric properties to improve molybdenum Photocatalytic performance of acid salt monomer.Firstly,the Bi₂MoO₆/Co MoO₄ composite photocatalyst was prepared by a one-step hydrothermal method.Taking the chemical dye methylene blue（MB）and the medical antibiotic ceftriaxone sodium as the degradation targets,the photocatalytic activity of the synthesized materials under visible light was evaluated.After 60 min of light,the degradation efficiencies of pure Bi₂MoO₆ and Co MoO₄ on MB were only28.4%and 62.0%,but after the construction of Bi₂MoO₆/Co MoO₄ heterojunction,the photocatalytic performance of the composite material was significantly improved.When the mass fraction of Bi₂MoO₆ is 30%（the material is denoted as BCMO-30）,the composite exhibits the highest photocatalytic activity.It can degrade 85%of MB in 60minutes and 78%of ceftriaxone sodium in 120 minutes.After five cycles of experiments,the degradation rate of BCMO-30 only lost 8%,indicating that the material showed high stability.The results of ultraviolet-visible diffuse reflectance spectroscopy show that the light absorption range of BCMO-30 has been broadened.Photoluminescence spectroscopy,electrochemical impedance spectroscopy and transient photoresponse current tests confirmed that the photogenerated carrier separation rate of the composite material was significantly improved.The experimental analysis of free radical capture shows that holes are the main active substance in the photocatalytic degradation process,and superoxide anions and hydroxyl radicals only play a certain role.Therefore,the enhanced photocatalytic activity of the composite can be attributed to the type II heterojunction formed between Bi₂MoO₆ and Co MoO₄,which broadens the photoresponse range and promotes the separation of photo-generated charges,thereby improving the overall photocatalytic performance.Based on this theory,we proposed the possible photocatalytic mechanism of the Bi₂MoO₆/Co MoO₄ composite system.Secondly,using ethylene glycol as a reducing agent,a two-step method was used to synthesize a Bi OCl/Zn MoO₄ composite material with an oxygen vacancy structure（OV）.Due to the unsatisfactory catalytic activity of Bi OCl and Zn MoO₄ monomers,the introduction of oxygen vacancies and the construction of a composite heterojunction promoted the improvement of photocatalytic performance.The target pollutants used in the performance study were the dye rhodamine B（Rh B）and the antibiotic norfloxacin（NOR）.The photocatalytic degradation rates of pure Bi OCl and Zn MoO₄and Bi OCl with oxygen vacancy structure（OV-Bi OCl）are all within 60%.After combining pure Zn MoO₄ and OV-Bi OCl,the photocatalytic activity of the material is significantly improved.After irradiating under visible light for 40 min and 100 min,the degradation efficiency of OBZM-5（representing 30%OV-Bi OCl）compound on Rh B and NOR was 99%and 88%,respectively.Starting from the actual application,the stability and recyclability of the material were studied.After OBZM-5 undergoes 5cycles of experiments,the loss of degradation rate is controlled within 10%,indicating that it has good stability and recyclability.The optical properties of the composite materials were analyzed by ultraviolet-visible diffuse reflectance spectroscopy.The results showed that the light absorption intensity of OBZM-5 was significantly higher than that of pure Bi OCl,Zn MoO₄ and OV-Bi OCl.In addition,photoluminescence spectroscopy,electrical impedance spectroscopy,and photoresponse current characterization and analysis of the charge transfer and recombination process of the prepared catalyst were also performed.The results show that the separation rate of photogenerated carriers of OBZM-5 is significantly higher than that of pure Bi OCl,Zn MoO₄ and OV-Bi OCl.The results of free radical trapping experiments confirmed that holes and superoxide anions play an important role in photocatalytic degradation.Combined with the experimental results,the possible photocatalytic mechanism is proposed.Finally,the C/Bi/Bi₂MoO₆ polarized material was synthesized by solvothermal method and nondestructive electric polarization method.The first step is to prepare C/Bi/Bi₂MoO₆ composite material with EDTA-Bi as the precursor.The second step is to use polymethyl methacrylate（PMMA）as an auxiliary body to form an organic-inorganic composite film with a catalyst,and conduct a polarization experiment under the action of a DC voltage to study the effect of ferroelectric polarization on the photocatalysis of the composite material performance impact.The degradation targets are the endocrine interferon bisphenol A（BPA）and the antibiotic ciprofloxacin（CIP）.Pure Bi₂MoO₆ can only degrade 32%of BPA and 30%of CIP respectively within 120minutes,and the degradation efficiency of CBMO-5（EDTA-Bi mass fraction is 5%）composite material for BPA and CIP respectively rises to 50%and 45%within 120minutes,indicating that the use of traditional modification methods（carbon layer and metal Bi introduction）can improve the photocatalytic degradation activity of Bi₂MoO₆monomer to a certain extent.After CBMO-5 was polarized at a voltage of 30 V for 1 h（denoted as PCBMO-5）,it showed higher photocatalytic performance,and the degradation efficiency of BPA and CIP reached 90%within 120 minutes.The enhancement of photocatalytic activity can be attributed to the enhancement of the interface charge transfer and transport efficiency,the increase of the specific surface area and the broadening of the photoresponse range.In order to explore the role of the iron polarization effect,a piezoelectric mechanical microscope was used to characterize the PCBMO-5 polarization material.The results show that PCBMO-5 has ferroelectric properties and polarization switching signals.In addition,the degradation pathways and reaction intermediates of PCBMO-5 were also analyzed through research literature.Based on experimental analysis,we believe that the traditional modification method can only promote the separation of the surface charge of the semiconductor,the photogenerated carriers will recombine rapidly in the body,and the ferroelectric polarization effect can simultaneously promote the separation of the surface and internal charges of the catalyst,and it can also promote The orderly arrangement of ferroelectric domains is conducive to the enhancement of semiconductor photocatalytic performance.