| Thin-film composite（TFC）polyamide（PA）nanofiltration（NF）membranes is considered as promising technologies for the removal of organic pollutants and inorganic salts during advanced water treatment.Although some improvements in the performance of the NF were achieved,a further application in the pilot and even larger-scale research was hindered,considering the trade-off between water permeability and salt selectivity,insufficient material preparation,and imperfect related mechanism theory.Based on the nanomaterials can effectively improve the performance of NF membranes by introducing into the substrates and the polyamide layer,we fabricated a new high-performance thin film nanocomposite（TFC）polyamide NF membrane by modified with different molybdenum disulfide（Mo S2）nanomaterials introducing methods.In addition,the influence of Mo S2 on the micro-structure and properties of NF membranes was explored.We revealed the underlying membrane modification mechanisms and its interception mechanism for different target pollutants.The membrane fabricated conditions were optimized basdd on the performance feedbacks,which help to enhance the permeability and selectivity synergistically.This research has some implications for the development of a new generation of water treatment membrane theory and method with targeted pollutant removal function.Firstly,based on the one-step hydrothermal method,polyvinyl pyrrolidone（PVP）-modified hydrophilic hierarchical flower-like structured molybdenum disulfide nanosheets（HF-Mo S2）was successfully prepared.Then,we fabricated a thin-film composite membranes with a nanocomposite substrate（TFCn）nanofiltration membranes（NFMs）by interfacial polymerization on polyvinylidene fluoride（PVDF）substrates modified with HF-Mo S2.The physical and chemical properties of the control membrane and the modified nanofiltration membrane were characterized by morphological characterization means and spectral chemical analysis methods.The TFCn membranes exhibited a water flux up to 21.5 LMH/bar and rejection rates of 98.6%for Na2SO4.Steric hindrance and Donnan exclusion together contributed to high salt rejection rates,as evidenced by a less polyamide layer thickness such as 56 nm and a high surface negative charge at p H 3-10.Note that the nanocomposite substrate became more porous,more hydrophilic,and rougher than the non-nanocomposite one,due to an increase in the fraction of macroporous on the surface,which was known to affect the performance of the polyamide layer.The high content of HF-Mo S2 incorporated in PVDF substrate led to enhanced hydrophilicity and,consequently,a cross-linking degree of defect-free polyamide,resulting in declines in thickness and increases in water permeability and salt rejection.Furthermore,TFCn NFMs exhibited an excellent organic solvent resistance and long-term stability,indicating that HF-Mo S2incorporation had no adverse effect but even improved their structural stability.Compared to NFMs without Mo S2 modification,NFMs with Mo S2 modification showed a better performance for desalination of mixed salt solution and excellent anti-biofouling properties for lysozyme and bovine serum albumin.Taking together,the TFN NFMs provide high permeability and rejection rate without a decline in structural stability.Therefore,TFCn NFMs were promising candidates for practical water desalination treatment.Then,we introduced the nanomaterials during the interfacial polymerization reaction to achieve polyamide matrix modification.First,we prepared the HF-Mo S2dispersion solution with long-term stability for nine months by combining probe-ultrasonic and high-speed centrifugation.And then,the thin-film nanocomposite（TFN）membranes with crumpled nanochannels were fabricated by vacuum filtration assisted co-deposition of the HF-Mo S2/piperazine（PIP）aqueous monomers.The PIP monomer solution stored in the space between nanosheets enabled HF-Mo S2 to participate in the interfacial polymerization reaction,which will enhance the adhesion of the nanomaterial and polyamide cortex.And the prepared TFN membranes can maintain structural stability during the membrane filtration process.TFN has a rougher surface than the smooth surface of the control membrane,possibly because of the appeared tent structure centered on the nanomaterial or a striped crumpled structure morphology after150-200 nm HF-Mo S2 deposited on PES substrate membrane surface.The features of the crumpled morphology of slender front and thick strips on the back prove that inwardly concave nano-water channels are formed around the nanoparticles in the polyamide layer.This structure significantly increaseed the surface roughness and the effective membrane surface area and provide additional water transport channels,which is conducive to improving the permeability of the NFMs.The M3 membrane prepared with a load of 10μg/cm2 has the best performance with the water flux of 18.4 LMH/bar,which is nearly 2 times higher than that of control membrane（M0,9.1 LMH/bar）.At the same time,the retention rates of Na Cl,Ca Cl2,Mg Cl2,Mg SO4 and Na2SO4 were30.85%,39.6%,45.6%,98.2%and 99.1%,respectively.Compared with the control membrane,the mixed salt solution permeability of M3 membrane is increased by nearly3 times,while maintaining the desalination effect on the mixed salt solution.The enhanced permeability and separation properties,and long-term operational stability of the TFN membrane make it have certain application prospects,especially in the field of drinking water treatment.To further decreace adverse effect on the integrity of the polyamide layer due to the heterostructural incompatibility of inorganic molybdenum disulfide nanoparticles and organic polyamide matrices,we successfully grafted the carboxyl functional group on the surface of HF-Mo S2 based on the carboxyl functional mechanism for chemically conjugated of Mo S2 nanosheets with thioglycolic acid.And then prepared a covalent modified TFN NFMs by vacuum filtration assisted co-deposition of the carboxyl@Mo S2/PIP aqueous monomers.Comparative analysis of the load contents of HF-Mo S2 direct modified nanofiltration membrane and carboxyl@Mo S2 covalent modified nanofiltration membrane,it was calculated that about 10.13 carboxyl functional groups are successfully grafted on the surface of per Mo S2 molecule,which effectively increases the hydrophilicity of the material.Benefiting from the better compatibility between carboxyl@Mo S2 and polyamide matrix,the carboxyl@Mo S2TFN membrane exhibites a better integrity and has a higher membrane surface hydrophilicity and water filtration area.The M4 membrane prepared with a load of 49.7μg/cm2 had the best performance,with a water flux of 25.8 LMH/bar,which was 2.7times higher than that of the control film M0（9.6 LMH/bar）.The rejection of M4 for Mg SO4 and Na2SO4 were 97.8%and 98.5%,respectively.Under the condition of maintaining a high retention of organic pollutants,the retention rate of calcium and magnesium ions by TFN membrane is significantly reduced,so that it can effectively remove harmful organic pollutants in practical applications and retain calcium and magnesium ions beneficial to the human body.The modified carboxyl@Mo S2 modified nanofiltration membrane shows better nanofiltration membrane performance than direct aqueous phase doping modification,indicating that the surface modification of nanomaterials can also effectively enhance the characteristics of the material itself,and the grafted organic functional group can further increase the compatibility with the organic polyamide matrix,alleviate the membrane defect problem caused by heterogeneous structure,and provide certain theoretical support for the grafting modification of nanomaterials.Compared with aqueous phase modification,the organic phase modification method could make the nanomaterials distributed on the surface of the polyamide layer instead being covered.This structure enabled the nanomaterials contacted with water molecules or target pollutants directly during filtration process,which is more conducive to the advantages of the nanomaterials themselves.By grafting the acyl chloride group in the Mo S2 material,we constructed a two-dimensional nanosheet nanoflower with rich acyl chloride functional group on the outside（acyl chloride@Mo S2）.Though no obvious change in morphology of acyl chloride@Mo S2,the vacuum XPS characterization proved the success of acyl chloride.And it was introduced into the PA layer of TFN by covalent doped organic phase.The zeta potential and hydrophilicity of TFN membrane surface were enhanced.The basic separation performance of the control membrane and the TFN membrane was analyzed,and the results showed that the introduction of the acyl chloride@Mo S2 material could significantly improve the pure water flux,up to 34.2 LMH/bar,and the rejection of the inorganic salt solution was also improved.Under the rentention rates close to the control membrane,the mixed salt solution permeation flux of the modified film can reach 15.6LMH/bar,which is 3.5 times higher than that of the control membrane（M0,4.4LMH/bar）,which can significantly reduce the energy consumption and have a better application potential for water treatment.This paper constructed and analyzed the performance of modified nanofiltration membranes prepared by four different HF-Mo S2 modification methods,and the results show all modification membrane could effectively improve the filtration performance,which to provide scientific reference and technical support for improving the performance of the polyamide nanofiltration membrane. |
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