Studies On The Preparations And The Photocatalytic Properties Of MOFs-based Composites

It is an effective strategy to solve future energy and environmental problems by using of photocatalytic technology to degrade environmental organic pollutants.Many of the attentions from the researchers all over the world have been concentrated on it.To date,lots of semiconductor photocatalytic materials have been designed to fulfill these researches.However,most of these photocatalysts show unsatisfied photocatalytic activities when applications.One of the main reasons is that the migration rate and separation efficiency of photo-generated carriers in these photocatalysts are not so efficient,which restricts its applications.In recent years,MOFs have caught more and more attentions attribute to their distinctive crystal structures.Based on this,it has become the most important way to prepare new photocatalysts using MOFs,which always bear various morphologies and structures,as templates to design and prepare a series of porous derivable materials with adjustable morphology?such as nano-porous metal oxides and metal sulfides?.The reason is that the obtained MOFs derivatives can not only retain the structural characteristics of the original MOFs,but also overcome the shortcomings of low photo-generated carrier separation efficiency and poor visible light response.From the point of view of higher visible light response,in this thesis,we have designed three new types of MOFs derivative photocatalysts by means of doping with rare earth elements,constructing effective heterojunctions structures as well as direct sulfurization of two-dimensional MOFs.The as-prepared photocatalysts were then applied to the photocatalytic degradation of organic dye,tetracycline,and phenol under visible light irradiation.The possible reaction mechanisms were also discussed.The thesis consists of three subsections as follows:1.A hierarchical nanorod photocatalyst of Ce/Fe₃O₄@C was firstly prepared using Ce-doped MIL-88A?Fe?as template through a one-step hydrothermal method and a heat treatment process.FT-IR,XRD,XPS,SEM,TEM,UV-vis DRS,BET and other characterization methods was employed to reveal the crystal structure,the morphology,the atomic and surface functional group composition,the magnetic as well as the optical properties of the prepared Ce/Fe₃O₄@C hierarchical nanorods.Then the photocatalyst was used to the visible light-induced degradation of RhB and tetracycline.The results showed that Ce/Fe₃O₄@C hierarchical nanorod photocatalyst has a faster photocatalytic degradation rate for the photo-degradation of RhB and tetracycline.RhB was almost completely degraded in 15 minutes,and the degradation rate of tetracycline reached90%in 40 minutes.The band gap structure and possible mechanism of the catalyst for the degradations were also discussed in depth by electrochemical means and free radical capture experiments.2.On the basis of subsection one,MIL-88A?Fe?was used as template and was calcinated to form Fe₂O₃@C nanotubes.Subsequently,ZnIn₂S₄ nanosheets were epitaxially grown on the surface of Fe₂O₃@C nanotubes through a via in-situ oil bath reaction to synthesize Fe₂O₃@C/ZnIn₂S₄ nanocomposite with hierarchical structures.The synthesized Fe₂O₃@C/ZnIn₂S₄ nanocomposite has much better photocatalytic degradation efficiency for the visible light-induced degradation of phenol and tetracycline than that of the single Fe₂O₃@C or ZnIn₂S₄ catalysts.3.In order to solve the problem of difficulties in the preparation of 2D MOFs derivatives,in this part,we firstly synthesized the 2D ZIF-67 nanosheets by a simple in situ synthesis method,then different sulfur sources was used to vulcanize 2D ZIF-67nanosheets through solvothermal reaction to prepare Co₃S₄ nanosheets with different morphologies.Finally,it was applied to the photocatalytic degradation of RhB under visible light conditions.The experimental results showed that the photocatalytic degradation performance of metal sulfides with different sulfur sources was also different.The ultra-thin Co₃S₄?TAA?nanosheets prepared with thioacetamide as sulfur source have the best degradation performance for RhB.The degradation rate reached 99.9%in 15 minutes.