Preparation And Performance Study Of Anti-biofouling Reverse Osmosis Composite Membrane

As a high-efficiency and low-energy desalination technology,reverse osmosis(RO)membrane separation technology has been widely used in various water treatment fields such as seawater desalination,brackish water desalination and wastewater treatment.However,in the actual application of reverse osmosis membranes,there is still a serious problem of membrane biological fouling.Biological fouling of reverse osmosis membranes will not only cause irreversible decline in composite membranes performance,but also increase the cost of reverse osmosis engineering operation and the difficulty to use in the process of cleaning and flux recovery after biologically contaminated membranes,which have severely affected and restricted the further development and application of reverse osmosis membrane technology.Tannic acid(TA),also known as gallic acid,has good oxidation resistance,high hydrophilicity,metal ions chelating ability and is used as a reducing agent and stabilizer to prepare precious metal nanoparticles.In this paper,a green surface in-situ reduction method is used to introduce silver nanoparticles into the composite membrane transition layer with the help of the reducibility of tannic acid,so as to effectively improve the anti-biological pollution performance of the membrane without sacrificing the membrane's selective permeability.Firstly,TA and Fe Cl₃ are deposited on the surface of the commercial polysulfone ultrafiltration membrane,and the two compounds are cross-linked to form an ultra-thin TA-Fe intermediate layer.Then,the phenolic hydroxyl group in tannic acid is used to directly reduce the Ag⁺in the Ag NO₃ solution to in-situ load the silver nanoparticles in the middle layer.Whereafter,the polyamide selective layer is prepared by the traditional interfacial polymerization(IP)method on the surface of the polysulfone membrane that contains the middle layer,and finally the TA-Fe-Ag polyamide composite reverse osmosis membrane is prepared.The results show that when 0.8 g/L tannic acid solution soaks for 2 min,0.2 g/L Fe Cl₃ solution soaks for 30 s,1.0 g/L Ag NO₃ solution soaks for 3 min,the aqueous phase monomer m-phenylenediamine(MPD)concentration is 0.4%(w/v),and the immersion time is 2 min,the organic phase monomer trimesic acid chloride(TMC)concentration is 0.02%(w/v),and the reaction time is 1 min,the composite reverse osmosis membrane performance is the best.Compared with unmodified membranes,the permeation flux of TA-Fe⁺-Ag NPs modified membrane is improved under the premise of keeping the rejection rate unchanged.The anti-biological pollution experiment shows that after the TA-Fe-Ag NPs modified membrane is contacted with E.coli and S.aureus for a certain period of time,the killing rate of the membrane to bacteria is 100%.At the same time,laser confocal microscope(CLSM)is used to observe the surface of the membrane after contacting with the bacterial solution.It is found that the number of bacteria attached to the membrane surface is far less than that of the unmodified membrane,indicating that the modified membrane has excellent bactericidal and anti-adhesion properties.