Study On The In-situ Controllable Preparation And Properties Of Bi-based Thin Film Photocatalyst From Bi Plate

The semiconductor photocatalysis was discovered in 1972,in the past few decades,it has become a potential technology to address the urgent issues of energy crisis and environment pollution confronting by human society.Bi-based materials,such as BiOX?X=Cl,Br and I?,Bi₂O₂CO₃,Bi₂WO₆,Bi₂MoO₆,as a kind of 2D layered-structure photocatalysts,present a variety of promising applications in catalysis,energy storage and electronics.Besides,these layered-structure materials are element abundances,nontoxic,optically and chemically stable,and have suitable energy band structure,thus exhibiting excellent photocatalytic performance in environmental pollution remediation and energy conversion.Moreover,the layered structure of Bi-based materials can produce internal electric fields,which will boost the separation of photo-induced charges and enhance photocatalytic activity,all these intriguing qualities attract the attention of researchers from all over the world.In the process to have a good knowledge of inherent properties and reaction mechanism in photocatalyst,nanoparticle photocatalyst has always been used in the research area.However,some drawbacks of powder photocatalyst including easy agglomeration,hard separation and recycle limit its application.Hence,how to produce photocatalyst with a simple and green strategy and how to use photocatalyst effectively as well as avoid residual nanoparticle contaminate water system,have become the challenging obstacle to conquer.To resolve the emerging problems in photocatalyst usage,in this dissertation,we choose Bi-based photocatalyst as the main research subject,use metal Bi plate as starting Bi source,and employ electrochemical strategy to in-situ construct Bi-based thin film photocatalyst on Bi plate.We mainly fabricated porous Bi OBr thin film,double-layer BiOCl/BiPO₄ composite film and double-layer BiOCl_0.5Br_0.5/Bi PO₄ composite film.Moreover,the composition,morphology,formation process and photodegradation properties and mechanism of these Bi-based thin films have been investigated systematically.Besides,the preparation process of Bi₂O₂CO₃nanoplates and BiOCl/BiPO₄ composite powder photocatalysts provided experimental basis for one-pot electrochemical method to construct Bi-based composite films.The primary contents of this dissertation are concentrated on the following five parts:?1?One-pot electrochemical way to synthesize porous Bi OBr thin film and Bi nanopowder simultaneously.The metal Bi plate and Ti sheet were used as anode and cathode,the pH=8,100 mL 0.05 mol/L KBr and0.06 mol/L EDTA aqueous solution was used as electrolyte.After electrolyzing for 1 h under a 4 V DC stabilized powder supply,we obtained homogeneous,compact and porous BiOBr film on Bi plate,at the same time,a large amount of Bi nanopowder was collected around cathode Ti sheet.The as-prepared BiOBr film and Bi nanopowder all showed superior photocatalytic activity.The degradation efficiencies of Bi OBr film for MO and BPA reached 99.7%and 64.05%,respectively.Besides,Bi OBr film exhibited excellent photocatalytic stability,the MO degradation ratio can still remain 97.6%after being used for 4 times.Moreover,the NO removal rate of Bi nanopowder achieved 48.5%under simulated sunlight illumination.In the end,based on the experimental phenomenon and reacted production,we speculated the possible electrochemical reaction mechanism.?2?When we used Bi nanopowder to degrade MO solution,the black Bi nanopowder changed into white Bi₂O₂CO₃ after photocatalytic reaction.Based on this phenomenon,we chose Bi nanopowder as Bi source,CO₂ coming from atmosphere as carbon source and CTAB as surfactant.The Bi₂O₂CO₃ nanoplate was synthesized by hydrolysis method at 60?and exhibited outstanding photocatalytic performance.The NO conversion ratio of Bi₂O₂CO₃ nanoplate can achieved 58.4%under simulated sunlight irradiation,nearly 1.26 times more than that of Bi nanopowder.These results demonstrated that Bi nanopowder could be used as a direct plasmonic photocatalyst and also can be employed to synthesize Bi₂O₂CO₃ to extend its application.?3?An anion exchange strategy to synthesize BiOCl/Bi PO₄composite powder.By adding KH₂PO₄ to the BiOCl suspension liquid,weobtainedBiOCl/Bi PO₄composite photocatalystwith tight heterojunction interface structure at room temperature and made the conclusion that BiOCl could be transformed into BiPO₄ in the existence of KH₂PO₄.Furthermore,we analyzed the transformation process in detail.Besides,the photocatalytic performance of BiOCl/Bi PO₄composite was evaluated by the degradation of phenol,the results displayed that the photocatalyst composite exhibited higher degradation efficiency,especially,thephotocatalyticefficiencyofsample Bi OCl/BiPO₄-2 was 1.69 times more than that of pure BiOCl.The content in this part laid a foundation for one-pot electrochemical method to prepare Bi-based composite film.?4?In order to further improve the photocatalytic performance of single component photocatalyst film,using the transformation reaction from Bi OCl to BiPO₄,we constructed BiOCl/BiPO₄ composite film by one-pot electrochemical approach.In the preparation process,we still applied Bi plate and Ti sheet as anode and cathode,respectively.The 100mL 0.05 mol/L KCl and 0.05 mol/L KH₂PO₄ aqueous solution was used as electrolyte.After electrolyzing for 5 h under a 5 V DC stabilized powder supply,we obtained the double-layer film consisted of BiPO₄nanorods array at the bottom and BiOCl nanosheets on the top.The as-obtainedBiOCl/BiPO₄compositefilmdisplayedexcellent photocatalytic activity and stability,the degradation efficiency of phenol reached 98%under ultraviolet-light irradiation for 180 min and remained96%after being used for five times.The enhanced photocatalytic reactivity can be ascribed to the efficient separation of photo-induced electron-hole pairs excited on BiOCl nanosheets.Moreover,the scavenger test presented that the·O₂^-and·OH played a crucial role in the photodegradation process of phenol.?5?In this part,we introduced BiOBr to broaden the absorbance spectra range of Bi OCl/BiPO₄ composite film,and designed the double-layer thin film with BiPO₄ growing on the top layer to be excited by simulated solar light irradiation.By adjusting the experimental parameters of one-pot electrochemical method,we constructed Bi OCl_0.5Br_0.5/BiPO₄ composite film.In the preparation process,we still applied Bi plate and Ti sheet as anode and cathode,respectively.The 100mL 0.01 mol/L of KCl,0.01 mol/L of KBr and 0.01 mol/L KH₂PO₄aqueous solution was used as electrolyte.After electrolyzing for 2 h under a 8 V DC stabilized powder supply,we obtained the double-layer film consisted of BiOCl_0.5Br_0.5.5 solid solution at the bottom and BiPO₄nanoparticles layer at the top.The interface internal electric field of Bi OCl_0.5Br_0.5/BiPO₄ composite film leads the photo-induced electrons and holes to shift in the opposite direction,thus improving the photocatalytic performance of Bi OCl_0.5Br_0.5/BiPO₄ composite film.The results displayed that the photodegradation efficiency of phenol reached 99.97%under simulated sunlight irradiation for 120 min,which was nearly 1.69 times and 1.20 times more than that of BiOCl/BiPO₄ and BiOBr/Bi PO₄composite film,respectively.Besides,the h⁺and·OH played a crucial role in the photodegradation process of phenol.The improved photocatalytic performance of Bi OCl_0.5Br_0.5/BiPO₄ composite film can be ascribed to the broadened absorbance spectra range and efficient separation of photo-induced charge carriers.