| The global water pollution problem has attracted more and more attention,and developing a simple and effective method to control water pollution is an urgent problem for human beings.Among all treatment methods,photocatalytic treatment of organic pollutants has gradually become one of the current international hot research fields due to its advantages of low cost,non-toxicity,energy saving and high efficiency.Metal-organic frameworks(MOFs)have the advantages of high specific surface area,high porosity,and good thermal stability,and their physical and chemical properties can be tuned by using different organic ligands or metal ions,resulting in MOFs in photocatalytic degradation.It has become a class of porous materials with potential application prospects.However,the rapid recombination of electrons and holes is still an important factor limiting the development of MOFs.The electronic structure of Bi--based materials is composed of O2 p and Bi6 s orbital hybridization,and has a suitable band gap,which can use visible light to generate reactive oxygen radicals and initiate redox reactions.However,Bi-based materials have the disadvantages of low utilization of visible light energy,small specific surface area,and insufficient active sites.In order to solve the above problems,various forms of heterojunctions are used to change the forbidden band width,improve the photon quantum yield,and promote the effective separation of photogenerated electrons and holes.Therefore,in this work,a bimetallic metalorganic framework(NH2-MIL-125(Ti-Zr),bimetallic MOFs)was synthesized,and the bimetallic MOFs was composited with Bi-based materials to develop the new method for preparation of Bi OCl@NH2-MIL-125(Ti-Zr)and Bi OClx I(1-x)@NH2-MIL-125(Ti-Zr)composite photocatalyst with a heterojunction structure,which was applied to photocatalytic degradation of organic pollutants in water,and obtained high degradation efficiency,the mechanism of the photocatalytic degradation was discussed in detail.The main research contents of this paper are as follows:Chapter 1: The removal methods of water pollutants,the synthesis and application of MOFs and Ti-MOFs and composite photocatalysts,as well as the photocatalytic degradation mechanism and the photocatalytic degradation of bismuth-based materials are briefly described.Chapter 2: A preparation method of bimetallic organic frameworks was developed and the mechanism of photocatalytic degradation of rhodamine B(Rh B)was investigated by solvothermal method.2-Aminoterephthalic acid was used as ligand,isopropyl titanate and zirconium n-butoxide were used as coordination metal ion precursors,and NH2-MIL-125(TiZr)was synthesized by solvothermal method.The effect of the amount of zirconium nbutoxide on the photocatalytic degradation performance was investigated.When the doping amount of Zr ions is 15%,the pseudo-first-order kinetic constant of its photocatalytic degradation is three times that of NH2-MIL-125(Ti),and it showed excellent stability in repeated experiments.After being recycled for 4 times,the degradation rate of 81% is still maintained.The experimental results shows that compared with NH2-MIL-125(Ti),NH2-MIL-125(Ti-Zr)has better photocatalytic degradation effect on Rh B.The free radical quenching experiment shows that the photocatalytic degradation of Rh B mainly depends on ·O2-.Chapter 3: NH2-MIL-125(Ti-Zr)was added to the Bi OCl reaction system,and Bi OCl was synthesized by in-situ synthesis to prepare Bi OCl@NH2-MIL-125(Ti-Zr)composites.An excellent photocatalyst with a heterojunction structure was obtained,and its photocatalytic performance for the degradation of acid red B(ARB)was studied.Compared with pure NH2-MIL-125(Ti-Zr)and Bi OCl,the composites have the best photocatalytic activity.The effect of the amount of MOFs on the photocatalytic degradation performance of the composites was studied in detail.When the doping amount of MOFs was 6%,the photocatalytic performance of the composites was the best,and the photocatalytic degradation rates of the composites were 2.7 times and 5.9 times that of MOFs and Bi OCl,respectively.In repeated experiments,excellent stability was shown.After being recycled for 3 times,the degradation rate of more than 70% is still maintained.Radical quenching experiments showed that photo-generated holes(h+)play a major role in the photocatalytic degradation of ARB,and a possible photocatalytic degradation mechanism was proposed.Chapter 4: In order to further enhance the absorption of visible light,during the synthesis of Bi OCl@NH2-MIL-125(Ti-Zr),the Bi OClx I(1-x)@NH2-MIL-125(Ti-Zr)composite photocatalyst with Bi OI was synthesized by adding KI.The effect of the amount of Bi OI on the photocatalytic degradation performance was investigated.The experimental results show that when the content of Bi OI is 0.2,the photocatalytic performance is the best.After 90 min of visible light irradiation,the photocatalytic degradation rate of ARB is 94.6%,which is much higher than Bi OCl@NH2-MIL-125(Ti-Zr).Moreover,in repeated experiments,it showed excellent stability,and the degradation rate remained above 90% after repeated use for three times.The quenching experiment of the main active substances was carried out.The experimental results showed that the h+ played a leading role,and a possible photocatalytic degradation mechanism was proposed.Chapter 5: The photocatalytic degradation of organic pollutants in water was prospected,and the synthesis methods and related problems in practical application of photocatalysts were proposed. |
PDF Full Text Request