| As a by-product of industrial production,oily wastewater comes from a wide range of sources,including the oil and gas,food and beverage,shipping and maritime,tanning,textile,metal and mechanical processing industries.If not properly treated,it will have adverse effects on the environment and cause huge economic losses.Membrane separation technology is an economical and effective method to separate emulsified oil and water.However,the traditional membrane technology has inherent disadvantages,such as the membrane fouling caused by the deposition of oil droplets on the membrane surface,resulting in the decrease of membrane flux and service life,energy loss and maintenance cost.Photocatalyst can make use of the inexhaustible solar energy,and has been widely used in many fields.It plays the role of degrading organic matter and disinfecting and sterilizing in the fields of environmental purification,health care,deodorization and deodorization.However,the suspended photocatalyst powder in the reactor is difficult to be separated from the treated water and reused,which may cause secondary pollution.The combination of photocatalytic technology and membrane technology can degrade organic pollutants while separating oil from water,reduce pore diameter blockage,prevent formation of oil layer,and thus improve membrane flux and service life.It also solves the problem of photocatalyst recovery.In this paper,the composite semiconductor photocatalyst g-C3N4/TiO2 was used to modify the PVDF ultrafiltration membrane and the photoresponse capability of the composite material was used to construct the superhydrophilic/underwater superhydrophobic interface,so as to achieve the purpose of oil/water separation.The main research contents and results of this paper are as follows:(1)g-C3N4/TiO2 composite semiconductor photocatalyst was prepared by sol-gel method and characterized by XRD,UV-VIS and other methods.It was proved that g-C3N4 successfully combined with TiO2 and the photoresponse capacity of composite material was improved.Then,g-C3N4/TiO2 was modified on the surface of PVDF membrane by biological adhesion method,and the morphological structure and physicochemical properties of the membrane were analyzed and characterized.The results showed that the composite was successfully loaded on the membrane surface,and the roughness of the membrane surface was reduced,porosity was increased,and the hydrophilicity of the membrane surface was significantly increased.More importantly,the film surface obtained super hydrophilic/underwater super hydrophobic properties under optical drive,showing potential permeability,retention and anti-pollution properties.Using kerosene,toluene,soybean oil,hexane and petroleum ether as simulated pollutants,the oil-water separation,pollution resistance and regeneration performance of g-C3N4/TiO2-PVDF film driven by visible light were investigated.The results showed that the properties of the composite film could be improved significantly by light assistance,and the pure water flux could be increased by 2.2 times compared with that under dark conditions.The filtration efficiency can be increased to over 97.7%.The filtration flux can be increased to more than 371LMH.In the 12-hour separation experiment,the flux loss rate was only 28.7%.The recovery rate of membrane flux after light regeneration is close to 100%and the retention efficiency is always above 99%.The efficient separation,pollution resistance and regeneration performance of composite film benefit from the ·OH generated on the surface of composite material under photocatalysis.The presence of ·OH is conducive to the construction of super hydrophilic/underwater super hydrophobic interface.In the process of oil-water separation,this interface can form a layer of water film on the surface of the film,which can isolate the invasion of oil droplets and allow water to pass through smoothly.In addition,in the process of membrane regeneration,·OH plays a certain role in degradation of organic pollutants,making the membrane regenerate rapidly.(2)TiO2 photocatalysts with different crystal types were prepared by hydrothermal method and compounded with g-C3N4.The crystal plane spacing of the TiO2 was consistent with that of the TiO2(001)type.The g-C3N4/TiO2 composite material was modified on the PVDF basement membrane by vacuum filtration and the film thickness was optimized.When the supported material quality was 0.61mg/cm2,the separation effect was the best.At the same time,compared with g-C3N4/TiO2(101)-PVDF film,the surface hydrophilicity of the film was further improved and the time required for photo-induced superhydrophilicity/underwater superhydrophobic was only 20 minutes,which meant that the optical response ability of the composite film was improved.Using the same five kinds of emulsified oil water as simulated pollutants,the oil/water separation performance,anti-pollution performance and regeneration performance of g-C3N4/TiO2(101)-PVDF film driven by visible light were investigated.The pure water flux of the composite membrane driven by visible light can reach 2003LMH.With high filtration efficiency(over 99%),the filtration flux can reach 665LMH.After 6 hours of continuous separation experiment,the composite membrane still has the filtration flux of 264LMH.During the 8 cycles,the composite membrane always maintained high filtration flux and efficiency.Compared with g-C3N4/TiO2(101)-PVDF film,g-C3N4/TiO2(001)-PVDF film has obvious advantages in terms of optical response ability,retention efficiency and filtration flux.Different composite materials loaded on PVDF films play a key role.g-C3N4/TiO2(001)has larger specific surface area and smaller particle size,higher photocurrent density and charge transfer rate,which means that the increase of reactive sites and the enhancement of reactive activity make it have more excellent optical response ability.Under the same conditions,g-C3N4/TiO2(001)can produce more ·OH. |
