Preparation And Performance Study Of High-performance Nanofiltration Membrane Based On Interface Temperature Regulatio

Due to the advantages featuring satisfactory effluent quality,no phase change in the separation process and simple process operation,nanofiltration（NF）membrane separation technology has attracted much attention in membrane water treatment.However,the high operating cost of NF membrane modules limits its further promotion and application.Under the premise of not increasing the operating pressure and maintaining the quality of the produced water,increasing the flux of the NF membrane can greatly reduce the operating energy consumption.Although the thin-film composite（TFC）NF membrane prepared by the interfacial polymerization（IP）method has been commercialized,there are still existing issues such as low flux,unsatisfactory selective separation and inferior anti-fouling properties in the field of drinking water treatment.To address these issues,a new temperature-assisted strategy was proposed in this work to prepare high-performance NF membranes for drinking water treatment.The effects of interfacial temperature regulation on the morphological characteristics,structural composition and separation properties of NF membranes were systematically evaluated.In addition,the application potential was also assessed for the treatment of typical heavy metals and natural surface water.The effect of interfacial reaction temperature on the performance of NF membranes was investigated by adjusting the oil phase temperatures（-15,5,20,35 and 50℃）.It was found that the lower interfacial temperature facilitated the formation of ultrathin and smooth polyamide（PA）membranes,and the modified NF membranes exhibited high permeability,superior rejection and excellent antifouling properties.In contrast,NF membranes prepared at high interfacial temperatures exhibited rough,dense and thick PA membranes with moderate permeability,excellent desalination and high heavy metal removal efficiency.Impressively,the high interfacial temperature-assisted NF membranes exhibited uniform coffee-ring-like surface morphologies,which may be attributed to the temperature-induced interfacial instability.In addition,the NF membranes prepared at low temperature exhibited superior anti-fouling performance and better operational stability in a three-cycle fouling tests.Considering the excellent separation efficiencies and operational feasibility,the temperature-assisted interfacial polymerization（TAIP）strategy has great promise in regulating the performance of the TFC membranes for practical environmental applications.Based on the TAIP strategy,low-pressure NF membranes featuring smooth surfaces were prepared by adjusting the piperazine（PIP）dosing amount（0.2,0.4,0.6,0.8 and 1.0 wt%）at an interface temperature of-15°C.The potential of low-pressure NF membranes for resource reuse was investigated in depth using natural water.Experimental results show that low-temperature-assisted interfacial polymerization（LTIP）can effectively reduce the PIP diffusion and IP reaction rate to form ultra-thin and smooth PA films.The optimized NF membrane（NFM-0.2）showed ultrahigh water permeance and high rejection of Na₂SO₄.During the filtration of natural surface water,NFM-0.2 presented 75.5%higher removals of DOC,UV₂₅₄,and bisphenol A.Furthermore,after the treatment of groundwater,the organic matter and total hardness were significantly reduced,and the quality of drinking water is significantly improved.Combined with the feasibility and practicability of the LTIP method,the facile strategy provides a simple method for tailoring low-pressure NF membranes.Based on the LTIP strategy,the support membrane,aqueous phase and oil phase were subjected to low-temperature treatment to deeply investigate the effects of different cryogenic processing on the performance of PA NF membranes.The results showed that different low-temperature treatments methods have a significant influence on the surface morphology and filtration performance of NF membranes.Among them,the permeability of TFC-aqueous phase membrane was improved by 67.2%compared to TFC-ambient temperature membrane,while maintaining a high retention rate of 97.5%for Na₂SO₄.In addition,low-temperature induction promoted the generation of less defective and more negatively charged PA layers in TFC-oil phase membrane,which significantly improved the separation performance of NF membranes and demonstrated higher rejection capacity for natural organic matter in groundwater filtration experiments.The results demonstrate that low-temperature treatment of the aqueous and oil phases can lead to a guided design of high-performance NF membranes,which is expected to extend the potential for applications in drinking water treatment.In this work,high permeability and high selectivity NF membranes were prepared around the interfacial temperature regulation strategy,which solved the problem of low operating efficiency of NF membranes in the drinking water treatment process.Different types of NF membranes were characterized in detail in terms of surface morphology,chemical structure and membrane performance evaluation,while the mechanism of membrane performance enhancement and the application potential in the drinking water treatment process was thoroughly analyzed and discussed.Thus,this study provides a cost-effective method for the preparation of high-performance NF membranes.