Preparation And Photocatalytic Degradation Of Organic Pollutents By Bi₂WO₆/TiO₂ Nanotube Arrays

The rapid development of industrialization has caused severe energy and environmental problems,seriously threatening the human health.Solar light is abundant with the advantages of environmental friendliness and sustainability,has been widely concerned.Solar light based photocatalytic technology can effectively solve the resource and energy problems.Titanium dioxide（TiO₂）is considered as a universal photocatalytic material,with the merits of high reserves,low toxicity and high catalytic activity,which has stimulated the promotion of photocatalysis field in the past few decades.TiO₂ is normally used as nanoparticles with difficult recycle and reuse,which may cause high cost or secondary pollution for solid-liquid separation process.Meanwhile,the wide band gap of TiO₂（～3.2 e V）decreases the light utilization and low electron-hole separation efficiency reduces the catalytic efficiency.To solve the above issues,the fixed TiO₂nanotube arrays was prepared in this thesis to effectively recycle,followed by the decoration of Bi-based material to improve the photocatalytic performance.The specific research contents are as follows:Titanium dioxide nanotube array（TNTAs）was successfully prepared by anodic oxidation method with Ti mesh as anode and platinum plate as cathode.The structures and morphology of TNTAs were characterized by XRD and SEM images.The energy gap was calculated to be 3.21 e V.The results of inner diameter,length and wall thickness of the nanotubes were taken to determine the optimal conditions:the oxidation voltage to be40 V,the volume fraction of glycerol to be 80%,the mass fraction of NH₄F to be 0.5 wt%,and the oxidation time to be 2 h.Under the optimal condition,the inner diameter,length and wall thickness were 153 nm,2μm and 20 nm,respectively.In order to select the appropriate specifications of titanium mesh,the prepared TNTAs with 10 mesh,20 mesh,30 mesh and 100 mesh were used to degrade the tetracycline under UV light.Among all the Ti mesh,the TNTAs with 30 mesh achieved the highest degradation efficiency of83.5%in 80 min.Compared with the TiO₂ powders,TNTAs can recycle the catalyst with little loss.The Ⅱ-type heterojunction Bi₂WO₆/TiO₂ nanocomposites（BWO/TNTAs）with different Bi₂WO₆ loading contents were synthesized by a hydrothermal method.The SEM,XRD and XPS characterization confirmed the successful decoration of Bi₂WO₆.The photoelectrochemical results showed that the coupling of Bi₂WO₆ with TNTAs expanded the light absorption range of TiO₂ and promote the charge separation,thus enhancing the photocatalytic performance.All samples were applied for photocatalytic degradation of tetracycline.0.2 BWO/TNTAs exhibited the supreme photocalysitic degradation performance with degrading rate of 92.2%within 180 min under visible light,as well as the superior stability and activity after 5th recycle.Radical capture experiment indicated that·OH was the main active species to dominate the degradation of tetracycline.The possible decomposition mechanism of tetracycline by mass spectra was proposed by gradual loss of hydroxyl groups and C-ring cleavage.