Study On Anti-biological Fouling Ability Of Nanofiltration Membrane Enhanced By Molybdenum Disulfide-copper Combined Modification

Nanofiltration has attracted much attention in drinking water treatment due to its unique advantages such as greenness,environmental protection,high efficiency,and low energy consumption;however,membrane pollution has severely restricted its promotion and application.Membrane biofouling is an important part of membrane fouling,in which microorganisms accumulate and multiply on the surface of membrane,thus reducing water yield and deteriorating water quality.Due to historical reasons,the existing commercially available nanofiltration membranes mainly focus on the design of salt rejection rate and organic pollution resistance,but lack the consideration of the ability to resist biological pollution.Aiming at the problem of membrane biofouling,this topic uses a new hydrophilic two-dimensional nanomaterial molybdenum disulfide（MoS₂）and antibacterial material copper ion(Cu²⁺)to modify the conventional polyamide（PA）nanofiltration membrane.A nanofiltration membrane with strong anti-biological fouling ability was prepared by interfacial polymerization.The main research conclusions are as follows:（1）Based on the pure water flux and salt rejection rate of the membrane,it is determined that the performance of the PA membrane is the best when the concentrations of m-phenylenediamine（MPD）and trimesoyl chloride（TMC）are 0.375wt%and 0.01875wt%,respectively,Use this as a reference film.Taking the membrane’s antibacterial ability,pure water flux and salt interception rate as the main evaluation indicators,it was determined that the effect of the modified membrane was the best when the molar concentration ratio of MoS₂and Cu²⁺was 1:0.3.Compared with the original membrane,the inactivation rate of the modified membrane to Bacillus subtilis reached 96.7%;the inactivation rate to Escherichia coli reached 99.1%;and the pure water flux of the modified membrane increased by 44%;the salt rejection rate（calculated as NaCl）is slightly lower than that of the original membrane by1.91%,about 65.12%.（2）The characterization of MoS₂ before and after exfoliation by transmission electron microscopy,atomic force microscopy,X-ray diffraction and Zeta potential shows that bulk MoS₂ has been successfully exfoliated into MoS₂ nanosheets.The modified film was characterized by scanning electron microscope atomic force microscope,water contact angle tester and inductively coupled plasma spectrometer.It can be seen that MoS₂ and Cu have been successfully loaded on the original film.Due to the high antibacterial ability of metal Cu²⁺,the modified membrane has excellent anti-biological fouling ability;due to the high hydrophilicity of MoS₂ nanosheets,the pure water flux of the modified membrane is larger than that of the original membrane.At the same time,the modified agent can be uniformly dispersed on the membrane surface;because the outer layer of the exfoliated MoS₂ nanosheets contains abundant S atomic contact sites,and the S ion is a soft Lewis base,which has a strong attraction to the heavy metal ion Cu²⁺.Therefore,MoS₂ and Cu²⁺combine to form a stable compound,which makes the modified film have better stability.When the modified membrane was immersed in water for 5 consecutive days,the drop rates of Cu²⁺and Mo²⁺on the membrane were both below 7%.（3）Using simulated water（containing humic acid,bovine serum albumin,Escherichia coli and Bacillus subtilis）as raw water,the effects of water chemical conditions（pH,ionic strength,calcium ion）on the flux and antibacterial properties of the modified membrane were explored.The results showed that with the decrease of pH（8.5→4.7）,the membrane flux showed a downward trend,this is because the lower the pH value,the lower the membrane surface charge,and the weaker the electrostatic repulsion effect,which would aggravate the membrane surface fouling;With the increase of NaCl concentration（0.1M→1M）,the electric double layer on the membrane surface is compressed,resulting in more serious membrane fouling;besides,with the increase of calcium ion concentration（0M→1m M）,the charge shielding effect is enhanced,thus Reduce the electrostatic repulsion of pollutants and membrane surface,aggravate membrane fouling.Under different hydrochemical conditions,the modified membranes have good antibacterial effect,and the antibacterial rate is above 92%.（4）The antibacterial effect and filtration performance of the modified membrane in the actual water body were evaluated by taking the actual water body of different water sources as the NF influent water.The results show that the sterilization rate of the modified membrane to the actual water body has reached 100%;the water flux of the modified membrane is still1.5～2.0 times that of the original membrane after filtration for 120 minutes;At the same time,the modified membrane shows better pollutant retention effect,with a rejection rate of more than 99%for turbidity,more than 93%for UV₂₅₄,and more than 94%for TOC.（5）Compared with the existing modification schemes from the perspective of technology and economy,it can be seen that the modification method of this subject is simple to operate,the cost of consumables is low and easy to obtain,and has obvious economic advantages;In addition,the modification method of this subject not only makes the membrane have excellent antibacterial ability,but also can greatly improve the water flux of the membrane,which has obvious technical advantages.