| Low-pressure membrane filtration technology has the advantages of low operating pressure(1-2 bar),low energy consumption,stable operation and simple operation,and is widely used in field of advanced wastewater treatment.Nevetheless,the pore size of low-pressure membrane is relatively large,and cannot effectively intercept low molecular weight organic pollutants.Carbon nanorube(CNT),due to its large specific surface area,excellent electrical,mechanical and thermal and adsorption properties,can be used as adsorbent material to remove low molecular weight organic pollutants.The disadvantage of poor dispersion and easy agglomeration of CNT still limits its adsorption efficiency for the low molecular weight organic pollutants.In addition,the ecotoxicity of CNT may harm the aquatic organisms in water environment and further endanger human health.The non-covalent functionalization of CNT can effectively improve the dispersibility of CNT in aqueous solution without destroying the structure of CNT.In this study,biological macromolecular humic acid(HA)and sodium alginate(SA),common surfactants sodium dodecyl sulfate(SDS)and polymer molecule polyethylene glycol(PEG)were selected to non-covalent functionalize CNT.And the HA/SDS/SA non-covalent functionalized CNT low-pressure membrane was prepared by vacuum filtration.In addition,three CNT with different surface properities(MWCNT,MWCNT-COOH and SWCNT)were selected to prepare low-pressure membrane.The removal capacity and mechanism of two organic dyes(cationic dye MB and anionic dye RB19)and four PPCPs(Bisphenol A,Sulfamethazine,Metronidazole and Ibuprofen)by CNT low-pressure membranes during dynamic filtration were investigated.The impact of CNT type,HA/SDS/SA concentration,PEG’s molecular weight and solution environmental conditions(p H value and ionic strength)on the removal of organic dyes and PPCPs by CNT membranes and noncovalent functionalized CNT membranes were systematically analyzed.The results of IR and XPS showed that HA/SDS/SA/PEG had been successfully introduced into the surface of CNT.Zeta potential results showed that the electronegativity of HA/SDS/SA non-covalent functionalized CNT was enhanced,while the electronegativity of PEG non-covalent functionalized MWCNT was almost unchanged.Nitrogen adsorption and desorption results showed that the specific surface area of SWCNT and HA/SDS/SA non-covalent functionalized SWCNT was much larger than that of MWCNT,MWCNT-COOH and HA/SDS/SA/PEG non-covalent functionalized MWCNT,and HA/SDS/SA/PEG non-covalent functionalization did not increase the specific surface area of CNT.The pure water flux results showed that all the CNT membranes and HA/SDS/SA/PEG non-covalent functionalized CNT membranes prepared in the experiment belonged to the category of low-pressure membrane.The results of dynamic filtration by CNT low-pressure membrane showed that due to the negative charge on the surface of MWCNT/MWCNT-COOH membrane,the electrostatic attraction between MWCNT/MWCNT-COOH membrane and cationic dye MB promoted the adsorption,and the electrostatic repulsion between MWCNT/MWCNT-COOH membrane and anionic dye RB19 inhibited the adsorption.In this dynamic filtration process,π-π interaction also impacted the removal of RB19 by CNT membrane.Compared with MWCNT membrane,HA-MWCNT membrane promoted the removal of MB and inhibited the removal of RB19,as HA-MWCNT membrane had stronger electronegativity than MWCNT membrane,and had stronger electrostatic interaction than MWCNT membrane.Similarly,SDS-MWCNT membrane,SA-MWCNT membrane and PEG-MWCNT membrane verified the electrostatic interaction mechanism.And MWCNT/MWCNT-COOH membrane had the best removal of Bisphenol A,followed by Sulfamethazine and Ibuprofen,and Metronidazole was the worst,the π-π interaction was the dominant role,hydrogen bond interaction and electrostatic interaction also impacted the removal of PPCPs by CNT membrane.Compared with the MWCNT membrane,HA-MWCNT membrane inhibited the removal of PPCPs due to the competitive adsorption between HA and PPCPs.Similarly,SDS-MWCNT membrane,SA-MWCNT membrane and PEGMWCNT membrane verified the competitive adsorption mechanism.During the filtration process,SSA was the main factor to impact the removal of low molecular weight organic pollutants by CNT membrane,SWCNT membrane showed the highest the removal of organic dyes and PPCPs due to the large specific surface area of SWCNT.After the HA/SDS/SA non-covalent functionalized SWCNT,HA/SDS/SA-SWCNT membrane could promote the removal of MB and almost not inhibit the removal of RB19.The removal of PPCPs by HA/SDS/SA-SWCNT membrane had no obvious inhibition.In the dynamic filtration process,SA-SWCNT membrane showed higher removal efficiencies than that of SWCNT membrane due to its porous structure.In addition,the presence of ions in solution had little impact on the removal of organic dye/PPCPs by CNT membrane and HA non-covalent functionalized CNT(HA-CNT)membrane.The p H value strongly impacted the removal of organic dyes and PPCPs by CNT membrane and HA-CNT membrane.The removal of MB was favorable under alkaline condition,and the removal of RB19 was favorable under acidic condition.For PPCPs,the removal rate was highest under neutral condition.The study results showed that the combination of CNT and low-pressure membrane filtration technology improved the dynamic filtration removal of low molecular weight organic pollutants by low-pressure membrane and reduced the ecological risk of CNT released into the environment.And non-covalent functionalization could change the surface properties of CNT,which would impact the removal capacity and mechanism of carbon nanomaterial low-pressure membrane for low molecular weight organic pollutants. |
