Preparation Of Thin-film Nanocomposite Membrane And Its Research On Deodorization Efficacy And Mechanism

Thin-film composite membrane（TFC）has been widely used in the field of membrane water treatment technology,and is now used for seawater desalination,water purification,and sewage reuse.However,in the application process,TFC membranes still have certain limitations.How to control membrane pollution and balance its permeability and selectivity is an important research direction and hotspot of membrane modification technology at this stage.Based on this,this project make use of the acid which generated in the interface polymerization process of MPD and TMC to catalyze the hydrolysis of silane coupling agent 3-aminopropyltriethoxysilane（APTES）to prepare the thin-film polyamide nanocomposite（TFN）containing silica（SiO₂）nanoparticles.Scanning electron microscopy（SEM）and X-ray photoelectron spectroscopy（XPS）initially confirmed that the leaf structure on the thin layer of polyamide（PA）and the surface of the film did contain SiO₂ nanoparticles,and the agglomeration between the polyamide main body and the nanoparticles Phase separation is the key to TFN film formation.However,as the amount of APTES added increased,the nanoparticles agglomerated and the leaf-like structure appeared to stick.At the same time,compared with TFC,the cross-linking degree of TFN film is lower,and the proportion of C—O/Si—O is significantly increased.Atomic force microscope（AFM）,membrane flow potential analyzer,contact angle analyzer（CA）,and Fourier infrared spectroscopy（ATR-FTIR）were used to characterize the surface properties of the membrane.SiO₂ nanoparticles can be bonded to the polyamide matrix via covalent bonds and hydrogen bonds.As the APTES concentration increases,the overall negative charge of the membrane surface decreases first and then increases.When C_APTES=0.01%（w/v）,the negative charge of the membrane weakens the most and is closer to neutral.The roughness tends to increase first and then decrease.The higher APTES concentration causes more SiO₂ nanoparticles to be incorporated into the polyamide layer,increasing the roughness,but too high concentration of APTES will cause the leaf-like structure to stick and reduce the roughness slightly.It is precisely because of the formation of SiO₂ nanoparticles on the surface of the film,which is more conducive to the wetting of the film,thereby forming a more hydrophilic and permeable polyamide film,the contact angle of the TFN film is reduced instead.The dissolution-diffusion model and XDLVO theory were used to fully analyze the selective permeability and anti-pollution performance of TFC membrane and TFN membrane.Compared with the original TFC membrane,the pure water transmission coefficient of the TFN membrane with an APTES addition of 0.01% is 12.2LMH/MPa,which is significantly higher than the TFC membrane’s 7.9 LMH/MPa,which fundamentally explains the large flux of TFN membrane pure water.In terms of salt interception rate,although the TFN membrane is slightly lower than the original TFC film,it is basically above 90%,which satisfies the application.According to the extended XDLVO theory calculation,the adhesion free energy of TFC film is less than 0,while the TFN film is greater than 0,and the additive amount is 0.01%,the adhesion free energy is 66.26 m J/m².At the same time,the △G of the free energy of the TFN film and the surface of the pollutants is also the largest,so its anti-pollution performance is the strongest.In addition,the adhesion free energy between the TFN membrane and the BSA has always dominated the filtration pollution process,and the free energy of the cohesion between the BSA molecules contributed less,which also explains the enhanced anti-pollution performance of TFN.In particular,the target pollution of this subject selected the smelling substances in drinking water-geosmin（GSM）and 2-methylisotitol（2-MIB）.It is determined that the TFN film has a better removal effect on the above two odor substances,especially the removal rate of GSM,which is basically guaranteed to be above 97%.The p H and ionic strength of the solution have a certain effect on the removal effect.With the increase of p H,the charge repulsion disappears,only the combined effect of size repulsion and adsorption.In addition,p H will also interfere with the formation of hydrogen bonds between the membrane and the surface of the odorant,which affects the adsorption of the odorant on the surface of the membrane,and ultimately in appearance It shows that the removal rate of olfactory substances decreases.The effect of NaCl on the chemical potential of water will change the degree of swelling and relaxation of the polymer,thereby changing the thickness of the film.Therefore,as the concentration of NaCl in the solution increases,the removal rate increases steadily.The TFN membrane and TFC membrane with 0.01% APTES added were calculated by the dissolution-diffusion model.The parameters DK?δ used to characterize the membrane permeability to 2-MIB were 0.5785 and 0.6632,respectively.Contrary to salt permeability,TFN membranes have lower 2-MIB permeability,mainly due to differences in materials,not differences in membrane thickness.