Magnetic Field Assisted Photocatalytic Organic Pollutant Degradation With Simultaneous Hydrogen Production By Dual Z-scheme Photocatalyst Composite Film

With the development of society,modern medical science and technology is in continuous progress and innovation.Various drugs are widely used to treat multifarious diseases.Among them,antibiotics,as a class of drugs with excellent antibacterial performance,have been widely concerned by human beings.The reason is that antibiotics can be used to remedy a variety of diseases caused by bacterial infection,so the dosage of antibiotics is increasing year by year.Inevitably,more and more wastewater will be generated in the produced process of antibiotics.If these wastewater without treatment is discharged randomly,it will pollute the environment,which in turn will harm the health of organisms.Therefore,before discharging wastewater,organic pollutants in it need to be removed or mineralized into water,carbon dioxide and inorganic ions and other pollution-free substances.In the process of seeking effective methods to treat wastewater,it is generally believed that the photocatalytic technology has the low cost,clean,pollution-free characteristics and strong mineralization ability,so it has been widely used in disinfection,air purification,wastewater treatment and other aspects.In recent years,some scholars have tried to introduce an external magnetic field into the photocatalytic reaction process to enhance photocatalytic activity.However,all the photocatalysts used in the study are in powder state,and there are some shortcomings in the use process,such as difficult recovery,complex treating processes and low recycling utilization.Especially,under the condition of using external magnetic field,the nanoparticles of pulverous photocatalyst stirred by magnetic force are usually in the free dispersion state in solution and the direction of electron transfer in the photocatalyst is not uniform.Therefore,the introduction of magnetic field may facilitate the separation of photo-generated carriers of one part of nanoparticles in pulverous photocatalyst,while may suppress the separation of photo-generated carriers of the other part nanoparticles in pulverous photocatalyst.Thus,the two effects may be canceled each other out.Obviously,it is very necessary to design a kind of immobilized photocatalyst that the electron transfer can be accelerated and separation efficiency of carriers can be improved due to the application of external magnetic field.In view of the above ideas,in the first part of the work,CuO and Cu₂O were grown on the copper foil as a carrier by in situ growth and the chemical oxidation methods,respectively.After that,TiO₂ was coated on the surface of CuO and Cu₂O by sol-gel and high temperature calcination methods to construct a dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film.Then,XRD,XPS,EDX and EDS mapping spectrometers were adopted to analyze the phase structure,element species and chemical valence of the as-prepared samples.Afterwards,the surface morphologies of the samples were analyzed by SEM and TEM,respectively.In addition,PL,TPR and EIS tests were used to systematically analyze the recombination of photo-generated electrons and holes in the samples under photoexcitation.Furtherly,in the second part of the work,under the simulated sunlight irradiation,the photocatalytic activity of dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film was evaluated by photocatalytic norfloxacin degradation with simultaneous hydrogen production.Additionally,a rotational magnetic field with a fixed direction was introduced into photocatalytic norfloxacin degradation with simultaneous hydrogen production reaction.The photocatalytic performance of dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film was enhanced due to assistance of magnetic field.In detail,the effects of magnetic field types,magnetic field intensities and rotational speeds on photocatalytic degradation with simultaneous hydrogen production were studied.When the fixed external magnetic field and the dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film rotated relatively in clockwise direction,the inductive electromotive force was generated on the photocatalyst to accelerate the flow of photo-generated electrons,which effectively enhanced the separation efficiency of electrons and holes.According to the experimental results,when the magnetic poles were all N poles,magnetic field intensity was 0.3 T and rotational speed was 1500 rpm under simulated solar light irradiation for 180 min,the norfloxacin photocatalytic degradation ratio of dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film was 87.46%,which was10.89%higher than that without magnetic field（78.87%）.The biggest hydrogen production amount can reach 418.53μmol/dm~2,increased by 25.00%than when no magnetic field（334.82μmol/dm~2）.In addition,four cycling experiments proved that the prepared dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film possessed high stability,convenient recycling and repeated utilisation.In the meanwhile,the possible mechanism of magnetic field assisted photocatalytic norfloxacin degradation with simultaneous hydrogen production performed by dual Z-scheme Cu|Cu₂O/TiO₂/CuO photocatalyst composite film was also put forward.It is hoped that the photocatalyst composite film proposed in this study can play a positive role in today that environmental pollution and energy shortage have become a difficult problem for all mankind.