Construction Of Novel Bismuth-based Visible Light Composite Photocatalytic System And Its Application For E.coli Disinfection

Pollution originated from pathogenic microbes has posed a tremendously threat to ecology environment and human's health in recent years.The industrial application of conventional chemical and physic technologies for waterborne pathogenic microorganisms purification were usually constricted due to the versatile defects such as high-cost,tedious operation and disinfection by-products?DBPs?generation during their operation process.Therefore,developing a novel,high-efficiency and environmental friendly technology for waterborne pathogenic microorganisms removal is urgently needed.Since 1985 Matsunaga et al.revealed that the TiO₂ could inactivate the E.coli effectively under ultraviolet light illumination,the technology of photocatalytic bactericidal was widely popular due to its high-efficient,without secondary pollution generation and stability.Unfortunately,the traditional semiconductor photocatalysts?eg.TiO₂,ZnO?were far less meet the requirement for the industrial application because of their relatively wide band gap and high recombination rate of photogenerated charge carriers.Hence,development of an innovative,high-efficient visible light response semiconductor photocatalyst for dealing with the question of waterborne pathogenic microbes pollution appears particularly urgently.In this context,the two novel visible light response semiconductors SnIn₄S₈ and Bi₂MoO₆ were selected as the main research subjects to construct several different heterojunctions to ameliorate their photocatalytic property of inactivation against E.coli under visible light irradiation through various strategies including:Bi₂S₃/SnIn₄S₈ Z-scheme heterojunction,ternary Ag QDs/Bi₂S₃/SnIn₄S₈ Z-scheme heterojunction,Bi₂O₃/Bi₂MoO₆ Z-scheme heterojunction and CuBi₂O₄/Bi₂MoO₆ p-n heterojunction.Besides,the theory and technology of molecular biology was employed to investigate the bactericidal mechanism of the above as-prepared four heterojunctions photo-catalysts.The main research contents and results of this work are as follows:1.The Bi₂S₃/SnIn₄S₈ Z-scheme heterojunction was fabricated through the facile one-step solvothermal method and its photocatalytic performance and mechanism of inactivating E.coli under visible light irradiation???>?420?nm?was investigated.The results indicated that the construction of the Bi₂S₃/SnIn₄S₈ composites could enhance the light trapping ability of SnIn₄S₈ and improve the separation and transfer efficiency of photoinduced charge carriers effectively in the interface of catalyst.When the loading mole ratio of Bi₂S₃ to SnIn₄S₈ was2.5%,namely,2.5%-BS/SIS composite possessed the strongest disinfection property which could completely inactivate the 2.5×10⁷ cfu/mL within 5 h visible light illumination.Moreover,the results uncovered that the free radical h⁺,e^-and?O₂^-were the main active species in the photocatalytic inactivation Z-scheme system of Bi₂S3/SnIn₄S₈,which could destroy the cell membrane of bacteria and induce the leakage and degradation of cellular content such as genetic material DNA.Finally,completely inactivated the pathogenic microbes.2.Based on the last chapter,the two-steps solvothermal methods were used to prepare the ternary Ag QDs/Bi₂S₃/SnIn₄S₈ Z-scheme heterojunction and the photocatalytic performance and mechanism of inactivating E.coli of Ag QDs/Bi₂S₃/SnIn₄S₈ Z-scheme heterojunction under visible light irradiation???>?420?nm?was evaluated.The results showed that the Ag QDs were distribution homogeneously in the ternary composite system,and the introduction of Ag QDs into Bi₂S3/SnIn₄S₈ system could further elevate the light trapping capacity of SnIn₄S₈,facilitated the separation and transfer rate of photoinduced charge carriers over the interface of catalysts,which give the Ag QDs/Bi₂S₃/SnIn₄S₈ ternary compound system stronger photocatalytic activity of inactivation to pure SnIn₄S₈ and 2.5%-BS/SIS hybrid.When the loading mole ratio of Bi₂S3 to SnIn₄S₈ was 2.5%and the volume of Ag QDs suspension was 200?L,namely,200 Ag QDs/Bi₂S3/SnIn₄S₈ composite owned the highest inactivation ability of E.coli,which could absolutely deactivate the 2.5×10⁷ cfu/m L within 4h visible light illumination.Furthermore,the results uncovered that the reactive species h⁺,e^-and?O₂^-play the leading role in the process of photocatalytic disinfection reaction initiated by this ternary compound system,which could destroy the cell membrane of bacteria and induce the leakage and decomposition of cellular content such as protein and DNA.Ultimately,completely killed the pathogenic microbes.Additionally,the Ag QDs played versatile roles in this ternary system to further improve the photocatalytic disinfection performance,including served as the electron injector and acceptor to facilitate the separation and transfer rate of photogenerated electron-hole pairs,and enhanced the light absorption ability by the surface plasmon resonance?SPR?effect.3.The Bi₂O₃/Bi₂MoO₆ Z-scheme heterojunction was synthesized through the in-situ solvothermal-calcination method and its photocatalytic performance and mechanism of inactivating E.coli under visible light irradiation???>?420?nm?was researched.The results from SEM,TEM and other characterization indicated that the plate-like Bi₂O₃ were tightly grew on the surface of Bi₂MoO₆ in the Bi₂O₃/Bi₂MoO₆ composite,which improve the light trapping ability of Bi₂MoO₆ and enhanced the separation and transfer efficiency of photoinduced charge carriers effectively.The optimal mass ratio of Bi₂O₃ to Bi₂MoO₆ was30%,namely,30%BO/BMO hybrid exhibited the strongest inactivation property again E.coli,which could completely inactivate the 1×10⁷ cfu/mL within 5 h visible light illumination.The results of free radical trapping and identification experiments suggested that the transfer pathway of the photoinduced electrons and holes obey by the Z-scheme mechanism over the Bi₂O₃/Bi₂MoO₆ composite.Additionally,the h⁺,e^-and?OH were the major reactive species lead to the disruption of the cell membrane of bacteria,leakage and decomposition of cellular content such as protein and DNA in this compound system.The enhanced photocatalytic activity of the Bi₂O₃/Bi₂MoO₆ hybrid mainly be ascribed to the recombination rate of photogeneration charge carries was drastically inhibited by the tightly touch between the Bi₂O₃ and Bi₂MoO₆ and the strengthened utilization efficiency of visible light.4.The solvothermal methods were used to prepare the CuBi₂O₄/Bi₂MoO₆ p-n heterojunction and the photocatalytic performance and mechanism of inactivating E.coli of CuBi₂O₄/Bi₂MoO₆ p-n heterojunction under visible light irradiation???>?420?nm?was studied for the first time.Comparing with the pure Bi₂MoO₆,the establishment of the CuBi₂O4/Bi₂MoO₆ composites possessed the stronger visible light trapping capacity and higher separation and transfer rate of photoinduced charge carriers and bactericidal performance.Among them,When the 0.5 wt%CuBi₂O₄ loaded on the Bi₂MoO₆,namely,CBO/BMO-0.5 composite displayed the highest inactivation ability of E.coli,which could absolutely inactivate the 1×10⁷ cfu/mL within 4 h visible light illumination.In this composite,the reactive species h⁺,e^-and?O₂^-played the important role in destroying the cell membrane of bacteria,inducing the leakage and decomposition of cellular content such as protein and DNA,and making the irreversible death of E.coli.The enhanced photocatalytic inactivation property of CuBi₂O₄/Bi₂MoO₆ p-n heterojunction mainly be attributed to the promoted visible light trapping ability,high-efficient separation and migration of the photoproduced electrons and holes under the driven of built-in electric field and more generation of?O₂^-.