Graphene Oxide (GO) Membrane Structure Regulation, Stability Research And Its Application

Through pressure-assisted method,a series of membranes were fabricated by filtering graphene oxide?GO?or its derivatives?modified by different molecular weightofpoly?ethyleneimine??PEI?,poly?iminocarbonimidoyliminocarbonimidoylimino-1,6-hexanediyl?hydrochloride?PHMB?or 1,3-diaminoguanidine monohydrochloride,and tetrabutyl titanate?on nylon microfiltration membranes with a pore size of 0.22?m.The improved performances of modified membranes were investigated.Moreover,the layered structure and electric charge effect of resultant membranes were also studied.Firstly,GO was prepared by graphite powder and then modified by different molecular weight of PEI(MW=600 g·mo L^-1,1800 g·mo L^-1,10000 g·mo L^-1,and70000 g·moL^-1,respectively).The products,which were named on the basis of the molecular weight of the grafted PEI?PGO-600,PGO-1800,PGO-10000,and PGO-70000?,were filtered to be modified membranes?PGOM-600,PGOM-1800,PGOM-10000,and PGOM-70000?.The results show that the layered structure of GOM,PGOM-600,and PGOM-1800 were obvious and when dry,PGOM-10000 and PGOM-70000 cracked up.It inferred that with the increase molecules weight of PEI,steric exclusion played an important role in destroying the hydrogen bonding and?-?interactions of GO molecules.However,the permeating flux of PGOMs did not increase linearly.The pure water flux?PWF?of GOM was 27 L·m^-2·h^-1·bar^-1.And the PWF of PGOM-600,PGOM-1800,PGOM-10000,and PGOM-70000 is 208L·m^-2·h^-1·bar^-1,60 L·m^-2·h^-1·bar^-1,450 L·m^-2·h^-1·bar^-1 and 420 L·m^-2·h^-1·bar^-1,respectively.Attributed by its low molecule weight and small steric effect,the PEI-600 was small enough to install itself in GO sheets.It meant the mostly amines from PEI-600 probably reacted with GO and the interlamellar space of PGOM-600was enlarged at utmost.The interlamellar space of PGOM-1800 was second,which was concluded from XRD.Oppositely,PEI-10000 and PEI-70000 destroyed the hydrogen bond and?-?interactions of GO molecules and the PWF of them increased dramatically.The dye penetrating flux of PGOMs is affected by dye charge and the separation of dyes and salts is well.The dye rejection was almost 100%,and the salt rejection was less than 20%.Secondly,at the base of the previous study,the effects of derivatives?polymer and monomer?and the thickness of membrane were further explored.The PHMB was as the graft polymer,while 1,3-diaminoguanidine monohydrochloride was as the graft monomer.Correspondingly,the membranes were recorded as DGOM and SGOM.The PWF of DGOM was 887 L·m^-2·h^-1·bar^-1,and that of SGOM was 265L·m^-2·h^-1·bar^-1.Due to destroying the hydrogen bonding and?-?interactions of GO molecules by the large molecules weight of PHMB,the thickness of DGOM was increased to make up the rejection rate of membrane.The dye penetrating flux of DGOMs and SGOMs is affected by dye charge and the separation of dyes and salts is well.The dye rejection was almost 100%,and the salt rejection was less than 20%.It is suitable for desalination of dyes.Finally,by sol-gel method,the derivatives?Ti-GO?was prepared by functionalizing GO with titanium dioxide?TiO₂?.Through pressure-assisted method,the Ti-GO was filtered to be membranes?Ti-GOM?.The Ti-GOM was used to investigate the conditions for photocatalytic degradation of dye absorbed on membrane surface.The conditions were mainly discussed from illumination medium?air,treatment solution,and deionized water?and illumination time?1h and 2h?.Because the photoelectron?e^-?from TiO₂ can be easily captured by oxidizing substances?e.g.dissolved oxygen?and the electron hole?h⁺?can oxidize the organics which was absorbed on the surface of TiO₂ or oxidize OH^-and H₂O to be·OH free radical.The·OH free radical was the strongest oxidant in water and it can oxidize most of organic and inorganic pollutants to be inorganic molecules,CO₂ and H₂O and other harmless substances.And the experimental results show the same conclusion and deionized water as illumination medium is the most suitable.The illumination time is the most suitable for 1 hour because the long illumination time brought higher temperature and the structure of Ti-GOM would be destroyed,although the long illumination time promoted the photocatalytic degradation completely.