Study On The Water Treatment Performance Of Functionalized Silver Phosphate Photocatalyst And Its PVDF Composite Membrane

The rapid development of industry has led to a series of environmental problems.Various kinds of water pollution are threatening the living environment of mankind.With the vigorous development of textile,printing and dyeing industry,amounts of dye wastewater is discharged,affecting the available water resource.As a new green method,photocatalytic technology is widely used in organic degradation.But at the same time,the photocatalyst also has some disadvantages,such as poor photodegradation performance and difficult to recover.The practical development of photocatalytic technology is restricted.In addition,poly（vinylidene fluoride）（PVDF）,owing to its excellent performance,is widely used as membrane material.However,the hydrophobicity of PVDF material makes it difficult to be wetted by water for the membrane surface,and pollutants are adsorbed on the membrane surface,resulting in the membrane fouling,which limits the application of PVDF membrane.Therefore,if the membrane technology is combined with photocatalytic technology can be achieved synergistic effect.It not only exerts the separation function of membrane,but also utilizes the degradation performance of photocatalyst.At the same time,the recovery problem of catalyst and the improvement of membrane fouling are both solved.In this paper,two kinds of Ag₃PO₄ composites were prepared by the modification of silver phosphate（Ag₃PO₄）,and the photocatalytic properties of the composite catalysts were analyzed.Then two kinds of photocatalytic membranes were prepared by blending and coating methods.And the degradation and rejection properties of photocatalytic membranes were discussed.Firstly,the silver phosphate（Ag₃PO₄）nanoparticles and graphene oxide（GO）were uniformly dispersed in ethanol and water,then Ag₃PO₄/GO/APTES composite was synthesized by the modification of 3-aminopropyltriethoxysilane（APTES）.At the same time,the mixture of Ag₃PO₄ and GO was modified by dopamine（DA）to prepare Ag₃PO₄/RGO/PDA composite.The structure and optical properties of two composites were characterized by XRD,FTIR,TEM,TGA,DRS and photoluminescence.Both composites showed better visible light responsiveness and photocatalytic activity.In the experiment of dye degradation,comparing with pure Ag₃PO₄ catalyst,the two materials has excellent degradation efficiencies on methylene blue（MB）and Rhodamine B（RhB）under visible light condition,especially the degradation efficiency of Ag₃PO₄/RGO/PDA was over 96%.In addition,the degradation efficiency of Ag₃PO₄/RGO/PDA was higher than 90%after 4 cycles.Secondly,the Ag₃PO₄/GO/APTES/PVDF composite photocatalytic membranes were prepared with phase inversion method by blending Ag₃PO₄/GO/APTES composite into PVDF casting solution.Due to the existence of hydrophilic groups on the surface of GO and ATPES,the hydrophilicity and water flux of membranes were increased.Using BSA solution as the pollution model,the anti-fouling ability of composite membrane in multi-period cycles was investigated and the anti-fouling ability was improved.Moreover,the rejection efficiency of composite membrane for dye molecules was also discussed.The results showed that with the increase of Ag₃PO₄/GO/APTES content,the rejection rate of dyes increased significantly.In addition,the composite membrane showed good antibacterial properties.Lastly,Ag₃PO₄/RGO/PDA/PVDF photocatalytic membranes were prepared by coating Ag₃PO₄/RGO/PDA on the basis of PVDF membrane.SEM and AFM were used to chatacterize the composite membrane.The hydrophilicity of coating membrane was strengthened and the contact angle was reduced to 52.3°.Correspondingly,the permeation flux of the membrane decreased with the increase of Ag₃PO₄/RGO/PDA content.Moreover,the efficiency of degradation and rejections under visible light was investigated.The results showed that the dye rejection rate of the composite membrane under visible light reached 97.5%.At the same time,the Ag₃PO₄/RGO/PDA/PVDF photocatalytic membrane maintained a high rejection rate after 5 cycles.