Preparation Of Carbon Based Photocatalytic Semiconductor Materials And Their Application In Hotocatalysis

Resource and environmental problems in today’s world are the most important aspects affecting social development.On the one hand,with the development of social productivity,energy demand will also increase;on the other hand,chemical and chemical production is limited by by-products and filtration and separation technology.If it is not perfect,a large amount of organic waste water will be discharged into the environment,which will cause problems such as environmental pollution and ecological imbalance.People are actively seeking solutions to energy and environmental problems,including transforming energy utilization,especially developing new energy,such as solar photocatalysis.Among them,photocatalysis utilizes solar energy to efficiently treat organic wastewater,which has become a hot research topic.Carbon-based photocatalytic materials have the advantages of good stability and wide source of raw materials.As a structural element,carbon exists in various carbon-based organics.Metal-organic frameworks（MOFs）are carbon-based materials composed of metal nodes and organic ligands.The MOF material is combined with common photocatalytic materials such as TiO2 by means of modification,which can enhance the photocatalytic activity of TiO2 while exerting the structural advantages of carbon-based materials.In this paper,based on the research of carbon-based photocatalytic materials,the composite with metal oxide TiO₂ photocatalyst was explored and modified.The TiO₂prepared by the hydrolysis hydrothermal method and the synthesized Carbon-based MOF material were composited under solvothermal conditions to prepare the MOF-74-TiO₂,Ti₄Zn₁-MOF-5 composite material.Colored dyes such as methylene blue（MB）and rhodamine B（RhB）were used as models to test their photocatalytic activity and electrochemical performance.In addition,we also designed a novel Ag@Fe₂O₃nanoparticle cathode multifunctional dual-chamber photocatalytic fuel cell based on previous research work,which can degrade dyes and reduce toxic substances while generating electricity only under the irradiation of light.The main work is as follows:（1）The heterostructured MOF-74-TiO2 nanomaterials were synthesized by a two-step hydrolysis-hydrothermal method.It was found by SEM and elemental analysis that MOF-74 and TiO₂ NPs are tightly connected.According to the nitrogen adsorption and desorption experiments,we can obtain the information related to the specific surface area of MOF-74-TiO₂ NPs.Through analysis,we found that the larger specific surface area of MOF-74 provides TiO₂ nanospheres attachment sites on the one hand,and on the other hand can Provide more sites for dye adsorption.In addition,it can be found by DRS analysis that the low content of MOF-74 in TiO₂ has little effect on the energy band structure,and the photo-induced carrier recombination can be effectively suppressed.Compared with pure TiO₂,adding an appropriate amount of MOF-74 to the composite can greatly promote the photocatalytic reaction.For example,when 2 mg of MOF-74was added to the TiO₂ precursor in the hydrothermal reaction,the kapp value was the highest(0.021 min^-1),which was 2.76 times higher than that of pure TiO₂(0.0076 min^-1).Different quenching reactions were tested to study the main oxide species and elucidate the mechanism of the improved performance of MOF-74-TiO₂.It turns out that holes（h⁺）are the key radicals for the degradation of RhB in the MOF-74-TiO₂ system.The experimental results of 4 consecutive cycles show that the MOF-74-TiO₂photocatalyst is stable and reusable.It can be concluded that MOF-74 can be used as a good porous support matrix,and play a synergistic effect with TiO₂ to improve its photocatalytic performance,which broadens the application of MOF materials in the field of photocatalysis.（2）By adding Tiprecursor in the synthesis and preparation of Zn-MOF-5,TiO₂particles were successfully attached to the MOF-5 rod structure using an in-situ growth strategy and interacted with ZnO to form a Ti₄Zn₁-MOF-5 composite photocatalyst.It was used for photocatalytic degradation of RhB,showing excellent photocatalytic activity.The properties of Ti₄Zn₁-MOF-5 were analyzed by XRD,SEM,UV-ViS,BET and XPS to elucidate its excellent photocatalytic performance.Through experimental characterization and theoretical analysis,we believe that its good photocatalyst is mainly due to the following aspects,（ⅰ）large specific surface area and suitable pore size distribution,which can be obtained from BET analysis,in which Zn-MOF-The specific surface area of MOF-5 is as high as 552.45 m~2g^-1,which is 22 times and 4.7 times that of Ti-MOF-5 and Ti₄Zn₁-MOF-5,respectively.Using MOF-5 organic porous framework structure,its porous structure is not only TiO₂.The growing crystals provide good sites and also provide active sites for the adsorption of organic dyes.（ⅱ）The electron transfer properties of Ti₄Zn₁-MOF-5 were analyzed by XPS spectroscopy,we found that in the composite samples,the binding energy of Tielement decreased,and there may be Ti³⁺to prove the lack of oxygen and crystal defects in the heterostructure of ZnO and TiO₂.（ⅲ）Five consecutive cycle experiments were performed,and the results showed that the Ti₄Zn₁-MOF-5 photocatalyst was stable and reusable.It can be concluded that Ti₄Zn₁-MOF-5 is a novel environmentally friendly composite photocatalyst for degrading colored wastewater in the environment.This facile synthesis method provides a new idea for the application of MOF materials in the field of photocatalysis.（3）Ag@Fe₂O₃ core-shell nanoparticles were synthesized by a mild condensation reflux method and used as the cathode material of a novel PFC device containing two separate chambers.Under illumination,the photocatalytic decolorization of the organic dye X3B and the reduction of heavy metal Cr（Ⅵ）were achieved at the anode and cathode,respectively,accompanied by a photoelectric energy conversion process.In addition,the addition of H₂O₂ in the anode compartment can significantly improve the overall performance of the PFC,especially the cathodic reduction performance of Cr（Ⅵ）.It is inferred from this that H₂O₂ can consume h⁺and even e^-to generate some oxidative radicals,thereby decomposing the dye,thereby greatly enhancing the generation of photo-induced carriers（h⁺and e^-）.However,excess H₂O₂ inhibits the degradation of X3B because it competes with the dye for h⁺.Meanwhile,various types of materials,including commercial electrodes（platinum foil and bare FTO substrate）and home-made Ag or Fe₂O₃ NPs were used as cathodes for comparison.Therefore,Ag@Fe₂O₃ shows the best catalytic performance for the reduction of Cr（Ⅵ）due to its low resistance to TiO₂,valence change,and lower conduction band.At present,although the wastewater purification or energy conversion ability of PFC is inferior to that of individual photocatalytic,fuel cell or photovoltaic systems,it still has great potential for practical comprehensive application under mild conditions.