Synergetic Removal Of Heavy Metals And Phthalate Esters Mixed Pollutants On Bi₂WO₆/Mesoporous TiO₂ Nanotubes

Environmental pollution problems are brought by economic development inevitably.For water pollution problems,multi-factor pollution?e.g.heavy metals and refractory organics?rather than single component is formed,like Cr?VI?and dibutyl phthalate.The heavy metals and refractory organics are commonly treated separately.Therefore,it is important to develop an effective pathway to remove the heavy metals and organics simultaneously in the complex water.Due to its environmental friendliness and high mineralization rate,photocatalysis is a promising technology in the field of water purification.However,it is hard to neglect the disadvantages that limit the photocatalytic activity of TiO₂,namely the low light utilization and quantum yield.Constructing mesoporous TiO₂ nanotubes?TNTs?with multi-scale channels?i.e.mesopores in the tube wall and the openings of the tube?can greatly improve the mass transfer of guest molecules,increase the access of light to refract and reflect in the interior of the tube,and expose additional number of active sites.Furthermore,a heterostructure between Bi₂WO₆?BWO?and TiO₂ can improve the availability of visible light and the separation of electron-hole pairs.BWO was coupled with TNTs via a dual-template method and a solvothermal method to remove combined pollution heavy metal and refractory organic.Photocatalytic removal of hexavalent chromium and dibutyl phthalate?denoted as Cr?VI?-DBP?mixed pollutants under UV and visible light irradiation was chosen as model reactions.Bi₂WO₆/mesoporous TiO₂ nanotubes?BWO/TNTs?composite photocatalysts were successfully synthesized and were characterized by XRD,SEM,BET and XPS.The photoelectrochemical properties were investigated using UV-vis,EIS,photocurrent response and Mott-schottky plots well.Coupling TNTs with BWO greatly improved the activity in the photocatalytic removal of Cr?VI?and DBP from single or mixed pollution due to synergetic effects.On the one hand,this system can take full advantage of charge carriers and spatially separated reduction sites and oxidation sites of the photocatalysts.On the other hand,TNTs possess unique multiscale-channel structures that can improve the mass transfer and light utilization.These features result in a significantly superior photocatalytic activity.BWO/TNTs with different morphologies and band gap structures were prepared by hydro-/solvot-thermal method with different solvents?deionized water,ethylene glycol and propylene triol?.Cr?VI?-DBP combined contamination was treated under visible light as the model reaction to evaluate the photocatalytic activity of the catalysts.The results showed that both BWO?EG?/TNTs could improve the photocatalytic oxidation and reduction activities.While photocatalytic reduction activity of BWO?GL?/TNTs was significantly increased,the oxidation activity was only slightly increased.On the contrary,the photocatalytic activity of BWO?DI?/TNTs decreased.Therefore,the matching of morphology and band gap structure of two semiconductor materials should be considered when they are coupled.This work demonstrates a feasible manner to fabricate composite photocatalysts that can be applied in the simultaneous removal of heavy metals and refractory organics from contaminated water.