| With the continuous progress of global industrialization,more and more industrial wastewater carrying a large number of refractory organic pollutants is discharged out of control,which has caused serious pollution to the scarce natural water environment and intensified the further shortage of fresh water resources.In view of above reasons,water treatment workers urgently need to seek all kinds of economic adaptation,advanced,efficient water and wastewater treatment methods in order to effectively treat all kinds of refractory wastewater.As a kind of photocatalyst with safety,high efficiency,innocuity,wide source,low cost and simple preparation.Ti02 can be used to degrade sewage by light source.Since it was used in the field of environment in 1972.TiO2 is considered to be one of the most promising photocatalysts.However,TiO2 has some inherent shortcomings,such as narrow spectral response range,high photogenerated electron-hole recombination rate,difficult to recycle and so on.All of these limits the pace of TiO2 towards industrialization in varying degrees.Therefore,using different methods to modify TiO2,including broaden its spectral response range,change its morphology,and improve the utilization of its photocarriers,which were the direction that most researchers have been working hard.Based on the above reasons,in this paper,we developed a series of TiO2 fibers modified by Bi-based materials over semiconductor coupling method,and successfully synthesized all-solid-state Z-scheme heterojunction including Ag-Bi1217C12/TiO2 fibers and Ultrathin-Bii2O17C12/Ag/TiO2 fibers,direct Z-scheme heterojunction including BiOBr/TiO2 fibers and BiO1/TiO2 fibers.The specific research contents are as follows:(1)All-solid-state Z-scheme heterojunction Ag-Bi12O17Cl2/TiO2 fibers were prepared by solvothermal method and photo-deposition method.In the preparation process,Cl-,the byproduct of TiO2 synthesis,was used as the raw material to realize self-production and self-marketing.Ag NPs were selectively deposited at the interface between Bi12O17Cl2 and TiO2 and on the surface of Bii2O17Cl12.Ag NPs at different positions played the role of electron-hole medium and surface plasmon resonance(SPR),respectively.The former changes the flow direction of photogenerated electrons and holes,increases the separation and transfer of photogenerated carriers,while the latter increases the absorption of visible light and provides more photogenerated electrons,which improve the photocatalytic performance of semiconductors,synergistically.In addition,the catalysts were characterized by XRD,SEM,TEM,XPS,EIS and Transient photocurrent density,which proved the good combination of the synthesized catalysts.The mechanism of photocatalysis was discussed by using capture experiment and ESR.It was proved that the Ag-Bi12O17Cl2/TiO2 fibers was all-solid-state Z-scheme heterojunction semiconductor.Finally,the photocatalytic performance of Ag-Bi12O17Cl2/TiO2 was evaluated by degradation of azo dye X-3B under visible light.The degradation rate of Ag-Bii2O17Cl2/TiO2 reached 98%in 90 min,which was 5.4 and 1.4 times of the degradation rate of TiO2 and Bi12O17Cl2,respectively.And the recycle test proved that it had good stability.(2)Based on the phenomenon of selective deposition of Ag NPs on the surface of Bi12O17Cl2,the "improved ion intercalation exfoliated method" was developed to synthesis Ultrathin-Bii2O17Cl2 nanosheet.And TiO2 fiber was modified by this method to synthesis Ultrathin-Bi12O17Cl2/Ag/TiO2 fiber.The "improved ion intercalation exfoliated method" is based on the special[Bi12O17]2+-[Cl]2-layered structure of Bi12O17Cl2.The free Cl-of Bi12O17Cl2 could be able to combine Ag+ in AgNO3 solution to generate AgCl precipitate,and then reduce Ag+ to Ag NPs by photo-deposition,so that the Ag NPs can enter the Bi12O17Cl2 layer to realize exfoliation.The BET analysis showed that the specific surface area increased 57.4%to 19.2 m2/g,and the total pore volume increased 106.2%to 0.033 cm3/g.Combined with TEM analysis,we have obtained Ag intercalated Bi12O17Cl2 nano-tablets with an average thickness of 4-8 nm,which shows that we have successfully exfoliate Bi12O17Cl2 and exposed more active sites.In addition,PL analysis shows that the Ultrathin-Bi12O17Cl2/Ag/TiO2 fibers can significantly inhibit the recombination of photogenerated carriers and improve the utilization of photogenerated electrons and holes.Finally,the photocatalytic activity of Ultrathin-Bi12O17Cl2/Ag/TiO2 was evaluated by its degradation of azo dye X-3B under visible light,which was 5.5 and 1.4 times higher than that of TiO2 and Bi12O17Cl2,respectively.The recycle test showed that Ultrathin-Bi12O17Cl2/Ag/TiO2 had good stability.(3)Based on the synthesis of all-solid-state Z-scheme heterojunction in the first two parts,direct Z-scheme heterojunction was synthesized,which in order to further optimize the visible capture ability of TiO2 fiber,shorten the synthesis process and save the cost of materials.In this chapter,the direct Z-scheme heterojunction BiOBr/TiO2 fiber and BiOI/TiO2 fiber were synthesized by solvothermal method using hexadecyl trimethyl ammonium bromide and potassium iodide as Br and I source,respectively And the noble metal Ag NPs was abandoned.In this chapter,Ti02 fibers are modified by p-type semiconductor BiOBr and BiOI to increase the binding force,respectively,between semiconductors by coupling different semiconductors.In addition,due to the difference of Fermi levels of semiconductors,the energy band will bend after coupling,which is the fundamental reason for the formation of direct Z-scheme heterojunction Through SEM TEM and EDX analysis,we have successfully synthesized BiOBr/TiO2 fibers with good morphology.By DRS and Mott-Schottky analysis,the forbidden band gap,the position of the conduction band and the valence band of TiO2 and BiOBr were measured.Then,the positions of the Fermi energy levels of TiO2 and BiOBr were determined by band-XPS,which were+0.28 eV and+1.15 eV,respectively.In addition,the degradation rate of azo dye reactive brilliant red X-3B in visible light was used to evaluate its photocatalytic effect.The degradation rate of BiOBr/Ti02 fibers reached 93%in 60 min.which degradation efficiency was 7.2 and 1.8 times of pure TiO2 and BiOBr,respectively.However,the catalytic effect of BiOI/TiO2 fibers is not satisfactory,which provides a direction for us to further optimize the design and explore the synthesis process.At last,the mechanism of photocatalysis is discussed by trapping experiment and ESR analysis,which proves that we have successfully synthesized the direct Z-scheme heterojunction. |
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