Design And Application Of PVDF Ultra-filtration Membrane For Oil-Water Separation And Conversion

With the rapid development of industry,the demand for oil is increasing.However,due to the imperfection of various technologies and inadequate management,a large number of oils enter the water body,endangering the environment and human health.The traditional separation methods include chemical separation,microwave separation and heating separation.Although the above disposal methods can achieve the desired results,there are some shortcomings,such as large energy consumption,high operating cost,secondary pollution and so on.Therefore,there is an urgent need to find an economic,efficient and rapid treatment method for oily wastewater.Ultrafiltration membrane technology,as a new technology,has a bright application prospect in water treatment.PVDF ultrafiltration membranes are popular because of their excellent performance and good mechanical strength.However,membrane fouling has always been the main reason for limiting the development of membrane technology.Photocatalysis has attracted much attention because of its advantages of using green energy,environmental protection and safety.However,because photocatalytic materials are mainly nano-materials,the particle size is very small,it is difficult to separate and recover after treatment,which results in a lot of waste and increases the operation cost.In recent years,many attentions have been paid to the process of photocatalyst-membrane composite.An integrated photocatalytic-membrane separation composite technology can not only effectively separate and enrich reactants and reaction products by using membrane separation performance,but also improve the photocatalytic reaction efficiency.At the same time,it solves the problem of difficult recycling of photocatalytic materials.At the same time,the pollutants will be degraded under the irradiation of light,which can effectively alleviate the membrane surface pollution and operation pressure,prolong the service life of the membrane,improve the efficiency of wastewater treatment and economic applicability.In this paper,photocatalyst ZIF-8/GO was used to modify PVDF ultrafiltration membranes to improve the anti-fouling ability of membranes and catalyze the conversion of toluene through photocatalysis,and increase the membrane flux.The main contents and results of this paper are as follows:(1)ZIF-8/GO loaded ultrafiltration membranes were prepared by layer-by-layer self-assembly(LbL),and characterized by SEM and XPS.It was proved that ZIF-8/GO composites were successfully loaded on the surface of PVDF membranes.The reduction of surface roughness of modified membranes was not conducive to reducing the interaction between pollutants and membrane surface.The contact angle of the four modified membranes with different loadings decreased gradually,indicating that the hydrophilicity of the membranes increased gradually.At the same time,the flux of four modified membranes and the separation efficiency of dyes and heavy metal ions were tested.Considering comprehensively,ZIF-8/GO-1.5 PVDF ultrafiltration membrane was selected for oil-water separation and conversion experiments.(2)The oil-water emulsion of toluene/water was separated by ZIF-8/GO ultrafiltration membrane,and the photocatalytic reaction of toluene under illumination was carried out to degrade toluene.The filtrate was characterized by microscope,UV-VIS,GC-MS and dynamic light scattering.The regeneration performance of the membrane material was tested to explore the anti-fouling performance of the membrane material.Microscopic analysis of the filtrate shows that there is a distinct difference between the filtrate and the original.For the filtered emulsion,the droplet size is about 200 nm and the droplet covers the whole field of vision.The presence of droplets was not observed in the filtrate images,which meant that toluene in the water had been successfully removed.In addition,it can be seen from the digital photos that the filtered emulsion is milky white,while the filtered filtrate is clear and transparent.This also indicates the removal of toluene.The results of UV-VIS and GC-MS showed that toluene in the filtrate could be completely removed,which indicated that the membrane material had excellent removal performance for toluene.(3)After simulated solar irradiation,the results showed that ZIF-8/GO ultrafiltration membrane had photocatalytic activity.The main products of toluene decomposition are benzyl alcohol and benz aldehyde.The results of dynamic light scattering show that the particle size of the emulsion is between 8 and 250 nm.After separation by blank membrane,the particle size of the filter is between 50 and 125 nm.In the absence of light,the size of the filtrate of ZIF-8/GO-1.5 ultrafiltration membrane is less than 30nm,indicating that the modified ZIF-8/GO-1.5 ultrafiltration membrane can efficiently separate the emulsion with particle size greater than 30nm.During the illumination process,the droplet size distribution did not change significantly.In the process of illumination,the increase of the same amount of membrane is mainly due to the enhancement of hydrophilicity and oleophobic of membrane,resulting in a significant increase in membrane flux.The cycle performance test showed that ZIF-8/GO modified ultrafiltration membrane showed good anti-pollution performance in the photocatalytic process,and with the increase of cycle times,the advantages of ZIF-8/GO ultrafiltration membrane gradually became obvious.