Ferric/Aluminium Ions Or Polyaluminum Chloride Crosslinked Graphene Oxide Membrane For Natural Organic Matter Removal In Drinking Water Treatment

Graphene oxide（GO）is a kind of novel carbon nanomaterial.GO has been widely used in various fields because of its unique physical and chemical properties.The single atom layer structure and hydrophilic properties of GO nanosheets enable it to be stacked layer by layer into hydrophilic thin membrane with nano-scaled channels,which can be applied in the field of water purification.In this paper,a kind of new stable GO membrane has been prepared by a simple method,and the efficiency and mechanisms of removing natural organic matter（NOM）in raw drinking water was studied.In this work,two trivalent cations(Al³⁺and Fe³⁺)and polyaluminum chloride（PAC）were employed as crosslinking agents to stack GO nanosheets layer by layer on a PVDF membrane support to fabricate a suitable GO membrane.The microstructure,physicochemical properties and organic matter rejection of the GO membranes were characterized.The trivalent cations greatly improved the bonding strength between the GO nanosheets through electrostatic forces and coordination bonds,and thus enhanced the stability of the GO membrane to make it stable in solutions.The initial interlayer spacing of GO nanosheets（0.80 nm）could be increased up to 0.86～0.95 nm by changing the ion concentration of Al³⁺or Fe³⁺.It was found that the GO membrane flux ranged between 79and 902 LMH/MPa when treating three representative NOM solutions and real surface water.Increasing the cation concentration reduced the interlayer spacing of GO membrane and resulted in a decline in flux.The flux of the Fe³⁺cross-linked GO membrane was approximately 1.1～2.3 times of that of the Al³⁺cross-linked GO membrane,while both cation-modified GO membranes achieved a similar separation efficiency of the organic contaminants.The cation-modified GO membranes had great treatment performance in terms of TOC removal of 90～95%for the three model NOM solutions,and 60～70%for the surface water.GO membranes with controllable interlayer spacing and strong stability in solution were prepared through the electrostatic force by using PAC with different B value(Molar ratio of OH^-to Al³⁺)as GO crosslinker and interlayer spacing modifier.The lamellar structure of the GO membranes was obvious and the GO membranes were tightly bound to the substrate.Besides,PAC could be used to flexibly adjust the interlamellar spacing of the membranes between 0.80-1.09 nm by changing the concentration and B value of PAC.When the concentration of PAC was between 0.1 m M-10 m M,PAC-GO membranes showed outstanding stability in DI water,Na Cl solution or organic solution even after two weeks.Even after long periods of ultrasonic vibration,the amount of shedding GO remained less than 0.1%.Moreover,the PAC-GO membranes showed excellent resistance to the substitution of monovalent ion（Na⁺）.The interlayer spacing of PAC-GO membranes increased with increasing of B value of PAC,and the flux of the membranes could reach as high as 1300 LMH/MPa.The removal efficiency of PAC-GO membrane of organic matters in NOM solutions could reach about 95%,while that of PAC-GO membrane of organic matters in surface water could reach about 50%.