| As a kind of frequently-used membrane materials in membrane separation technology for water treatment,polyvinylidene fluoride?PVDF?has been widely used in many separation processes.However,PVDF is a kind of material with strong hydrophobicity,which results in serious fouling of membrane component in actual operation process.The application of PVDF has been limited significantly because of membrane fouling phenomenon.The preparation and properties characterization of composite membrane modified by inorganic nano-particles has become research hotspot currently,so the synthesis of novel additive appeals to many scholars all the time.In this paper,composite membranes modified respectively by silicon dioxide?SiO2?,graphene oxide?GO?and SiO2-GO nano-hybrid particles were prepared.Fourier transform infrared spectroscopy?FTIR?was employed to achieve the detection of functional group on the composite membrane surface,and the structure of cross-section was easily observed by scanning electron microscope?SEM?.The analysis of adsorption process and transformation of adsorption layer of the foulant on composite membranes will come true easily from adsorption kinetics and micro-acting-force point by the coupling technique of quartz crystal microbalance?QCM-D?and atomic force microscopy?AFM?.The experimental results are ultimately as follows:Different composite membranes were prepared by controlling the content of nano-particles,and the additive were SiO2 and polyvinylpyrrolidone?PVP?.The adsorption behavior of effluent organic matter?EfOM?on the modified ultrafiltration membranes had been investigated,and the EfOM as raw water derived from Xi 'an fourth sewage plant.The results showed that the roughness on the surface of composite membranes would decline with the increase of content of nano-particles.The results suggested that the adsorption curves of EfOM could be divided into two stages according to the slope.In the first stage,dissipation and frequency presented linear correlation clearly.Meanwhile,it was found that the accumulation speed of EfOM on the surface of coating film wafers was quiet fast,because of the intense interaction force between membranes surface and organic moleculars of EfOM.However,in the second stage,the slope of EfOM adsorption curves appeared variation,because of the complete cover on the surface of coating film wafers by the contaminant.Comparing with the first stage,the adsorption of contaminant on the surface of composite membranes approximately trended to be stable,but the dissipation still increased.AFM was employed to observe the micro-acting-force between EfOM and the surface of composite membranes or Ef OM in the experiment.The results showed that the adhesion force is 0.211 mN/m between EfOM and the surface of membranes,but the adhesion force between EfOM declined with the increase of adsorbance.Adhesion force between EfOM decreased to 0.115 mN/m after the filtration of 800 m L raw water.Obviously,the interaction force between EfOM and the surface of membranes was stronger than between EfOM,and the properties of composite membranes had a serious influence on the interaction force between EfOM in some degree.The combination of interaction force and QCM-D results could easily explain that the adsorption layer during initial stage was looser than in the later period.Adhesion force between EfOM and PVP/PVDF membrane was 0.373 mN/m,and it would gradually decline with the increase of the content of SiO2 nano-particles.The value of adhesion force would decline to 0.150 mN/m when the content of SiO2 is 0.5wt%.Therefore,the affinity between EfOM and PVP/PVDF membranes was stronger than the others,and compact adsorption layer could easily generate on the surface of the composite membranes.However,the adhesion force between EfOM and the composite membranes modified by nano-particles was weaker,and the structure of adsorption layer was looser,which could be easily washed out by hydraulic scouring effect.It was found that the addition of SiO2-GO nanohybrid particles could significantly enhance the properties of composite membranes during the investigation of the characteristic of SiO2-GO/PVDF composite membrane.The interaction force between albuminoidal substances and composite membranes was tested by AFM,and BSA acted as the typical foulant.The results showed that the adhesion force between BSA and PVP/PVDF membrane or SiO2-GO/PVP/PVDF membrane were 0.78 mN/m and 0.37 mN/m,respectively.Obviously,the adsorption process of albuminoidal substances on the surface of composite membranes was restrained effectively after the addition of SiO2-GO nanohybrid particles.However,through the comparison for the adhesion curves of BSA to PVP/PVDF membrane,GO/PVP/PVDF membrane,SiO2/PVP/PVDF membrane and SiO2-GO/PVP/PVDF membrane,it was found that the adhesion force between BSA and SiO2-GO/PVP/PVDF membrane was a little bit higher than SiO2/PVP/PVDF membrane.The phenomenon could be easily explained,because the modification effect of SiO2 was a little bit better than GO nano-particles,and the content of SiO2 in SiO2-GO nanohybrid particles were less than SiO2 nano-particles when they were with equal mass,which resulted in the decrease of the antifouling property of composite membrane modified by SiO2-GO nanohybrid particles. |
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