Preparation And Properties Of Nanomaterial Antifouling Composite Films

Most membrane materials are restricted by their relatively high inherent hydrophobicity which is very prone to membrane pollution during operation,and severely limits the membrane's development and application.Moreover,how to balance the permeability and selectivity of the membrane is also a very important research aspect.In order to overcome the above limitations,it is required to improve the membrane's performance,increasing its permeability and selectivity while improving its antifouling performance.With the development of nanomaterials,researchers have gradually focused on combining nanomaterials with polymer membranes to prepare nano-composite membranes with excellent antifouling performance and comprehensive performance.The main contents of this paper are as follows:(1)The polydopamine-functionalized carboxyl multi-walled carbon nanotubes(OMWCNTs-PDA)as nanofillers were introduced into polyethersulfone(PES)mixed matrix obtained OMWCNTs-PDA/PES blended membrane.The resulted show that the separation performance of the blended membrane reached the optimal when the addition amount of OMWCNTs-PDA was 0.75 wt.%.Compared with the pristine PES membrane(90°),its water contact angle(WCA)was reduced to be 56.8°,and the hydrophilicity was greatly improved;the permeation flux of pure water was increased to 1.75 times with high BSA rejection rate(above 99%);the mechanical properties were also improved 2 times as much;retention rates for MB and CR were kept above 97%and 98%,respectively;and had good retention stability in long-term dye separation testing.The antifouling performance of CR and NOM pollutants(BSA,SA and HA)had been enhanced:For CR solution,compared with M0,the FRR of M2 increased by18.45%and R_t decreased by 6.43%;for BSA,HA and SA solution,the FRR of M2increased by 30.01%,29.41%and 19.49%,and the R_t value of M2 decreased by 31.48%,14.97%and 25.01%,respectively.(2)The PES ultrafiltration membrane was selected as the support layer to provide a sizeable active filtration area with using trimesoyl chloride(TMC)as the oil phase,piperazine(PIP)and tannic acid(TA)reduction functionalized graphene oxide(TA-rGO)mixed solution as the water phase,thus,a series of TFC/TA-rGO/PES polyamide(PA)nanofiltration(NF)composite membrane with high permeability and selectivity was obtained.When the addition amount of TA-rGO was 0.02 wt.%,the overall performance of TFC-M2 showed the best:compared with TFC-M0,the hydrophilicity of TFC-M2 had been significantly improved,and the WCA had been reduced from 28.5°(TFC-M0)to 11.8°(TFC-M2);the water flux had been greatly improved,reaching17.6 L·m^-2·h^-1·bar^-1,which was about 2.6 times that of TFC-M0(6.9 L·m^-2·h^-1·bar^-1)with excellent mechanical properties and thermal stability.For four kinds of salts(Na₂SO₄,MgSO₄,MgCl₂ and NaCl)and six different dyes(MB,CR,AR 27,RB,SY and MLB),TFC-M2 showed excellent retention and pure water permeability.Morever,TFC-M0 and TFC-M2 were selected for the chlorine resistance test,and the results showe that TFC-M2 had better chlorine resistance than TFC-M0.The rejection rate of NaSO₄ was much higher than that of TFC-M0 within 54 h of chlorination.Besides,select pristine PES membrane,TFC-M0 and TFC-M2 filtered BSA,HA and SA solutions to evaluate the antifouling properties.The results showed that compared with pure PES membrane and TFC-M0,TFC-M2's antifouling properties is further improved,the FRR of TFC-M2 for BSA,HA and SA pollution increased by 39.11%and 0.98%;35.53%and 3.78%;32.46%and 4.36%,respectively;R_t decreased by 23.85%and 9.66%;54.80%and 4.01%;51.94%and 4.93%respectively.In addition,in order to study the antifouling mechanism,using the extended Derjaguin-Landau-Verwey-Overbeek(XDLVO)theory to study the interface interaction energy between NOM pollutants and membrane during membrane fouling.It was further confirmed that the antifouling performance of the TFC/TA-rGO/PES PANF composite membrane had been improved.(3)Polyaniline(PANI)nanofibers were used as additives to prepare PANI/polysulfone(PSF)blended membranes.The effects of different amounts of PANI on the properties of the membranes were investigated.The results showed that when the content of PANI was 2 wt.%(M2),the performance of the PANI/PSF blended membrane was the best.The fouling behavior between the membrane and NOM pollutants was further analyzed by XDLVO theory.The results show that compared with pristine PSF membrane(M0),M2 has higher porosity,pore size,mechanical strength and thermal stability;the hydrophilicity is significantly improved,and WCA is reduced from 92.1°(M0)to 74.6°(M2);the M2 water permeability increased to 2.3times that of pristine PSF,reaching up to 169 L·m^-2·h^-1·bar^-1.;and it maintains an excellent BSA rejection rate(above 92%).In particular,M0 and M2 were selected for antifouling testing.The results showed that with the addition of PANI,the anti-fouling performance of the M2 was enhanced.Compared with M0,the FRR of M2 for BSA,HA and SA pollution increased by 22.16%,14.98%and 15.66%,respectively;R_tdecreased by 24.80%,19.19%and 12.11%,respectively.Regular interaction between the NOM pollutants molecules and membranes confirmed that there are reduced attractive interaction energies between the M2 and NOM pollutants molecules in comparison to the interaction between the M0 and NOM pollutants molecules.(4)Using oxidized multiwalled carbon nanotube(OMWCNT)as nanofillers and graphene oxide(GO)solution as a membrane-forming coagulation bath,functionalized carbon nanomaterials/PVDF(GO-PVDF/OMWCNTs)hybrids membranes were prepared by a combination of mixed matrix and solution coagulation bath.The results showed that compared with pristine PVDF membrane,GO-PVDF/OMWCNTs hybrid membrane has the best comprehensive performance,which achieved higher porosity,pore size and mechanical strength;the hydrophilicity is significantly improved,and WCA is reduced from 80.0°(pristine PVDF)to 61.3°The water flux is greatly improved,reaching 126.6 L·m^-2·h^-1·bar^-1,which is about 1.7 times that of pristine PVDF with high pollutant rejection rate and better antifouling property.The synergistic effect of OMWCNTs and GO enabled GO-PVDF/OMWCNTs had excellent conductivity,which can be used in membrane fouling sensor and the fouling degree of membrane can be analyzed by establishing the relationship between electrical parameters and the thickness of fouling layer so as to achieve the purpose of real-time monitoring and then provide a new idea for membrane fouling monitoring.