The global shortage of fresh water and increasing water pollution – especially from dye wastewater – pose major challenges for the environment [1]. In China alone there are around 160 million m3 Every year, 100,000 tons of dye wastewater are discharged into bodies of water [2]. Due to its low cost, high efficiency and lack of secondary pollution, membrane separation technology has gained great attention in wastewater treatment [3,4].
The performance of composite membranes depends on the material of the interface [5]. While inorganic porous materials such as aluminum oxide [6]mesoporous silica [7]Activated carbon [8] and zeolite [9] Although widely used, weak interfacial adhesion with support layers often leads to delamination, limiting compatibility with polymer matrices. [[10], [11], [12]]. Therefore, compatibility with polymer matrices remains an ongoing challenge [8,13,14]. Covalent organic frameworks (COFs) [15,16]which emerge as versatile organic porous nanomaterials, offer ordered pore structures (0.5–4.7 nm), tunable surface chemistry, and exceptional stability [15,17,18]. Their pore sizes correspond to those of dye molecules (0.5–3.5 nm). [[18], [19], [20], [21], [22], [23]]and hydrated salt ions (0.6–1 nm) [6,24]which enables selective separation. For example the COF-LZU1 membranes (1.8 nm pores) [24] reject most dye molecules [25] while H is allowed2O molecules (0.28 nm) [26] and ions pass through [25]. Compared to graphene, MOF or metal oxide based membranes [[27], [28], [29]], which rely primarily on interlayer distance for molecular separation, COF-based membranes offer superior rejection and permeability via their single-layer ordered nanoscale pore structure [24,30]. Rational design of COF pore size is therefore crucial for optimizing dye wastewater treatment.
Most COFs are synthesized using toxic solvents (e.g. mesitylene and 1,4-dioxane). [[31], [32], [33]], which pose a threat to environmental sustainability and human health. Furthermore, traditional COF synthesis methods (such as the solvothermal method and microwave heating approaches) often yield insoluble microcrystalline powders [34,35]which tend to agglomerate in solution and cause voids in thin film nanocomposite membranes (TFN). [36]. To address these challenges, Xu et al. [37] developed an environmentally friendly COF synthesis method. By stirring organic monomers in water and acetic acid at room temperature, highly crystalline and porous COFs were prepared within a very short reaction time (up to 1 minute). This provides a route for the green synthesis of various COFs. Banerjee et al. [38] initially produced continuous and defect-free COF membranes by interfacial polymerization (IP), thereby laying the foundation for the production of various COF membranes. In the in-situ IP process, two highly reactive monomers dissolve in immiscible water-organic liquid phases, resulting in high-quality COF thin membranes through interfacial polymerization [39,40]. For example, Hao et al. [40] fabricated a self-contained two-dimensional (2D) COF membrane using the IP method. However, free-standing COF membranes generally have low flexibility and low impact resistance. To overcome this limitation, COF composite membranes were fabricated directly on porous polymer substrates using the IP process [19,[41], [42], [43], [44]]. This approach offers several advantages, including mild reaction conditions, ease of operation, and easy scalability [22]. Wang et al. took advantage of this strategy. [19] fabricated a COF composite membrane on a polysulfone (PSf) substrate and achieved 50 L m−2 H−1 Bear−1 Permeability and 99.5% Congo Red rejection.
However, traditional in situ interfacial polymerization often uses toxic organic solvents such as dichloromethane (DCM), chloroform, mesitylene, and 1,4-dioxane [15,[45], [46], [47]]. She et al. [45] I used a 3:7 v/v N-Hexane/DCM mixture with tris(4-aminophenyl)amine (TAPA) monomers as organic phase to prepare TAPA-GA (SDS) TFC SCOF membranes, while Fan et al. [24] Dioxane was used to dissolve it P-Phenylenediamine (PDA) and benzene-1,3,5-tricarboxaldehyde (TFB) for COF-LZU1 membrane synthesis on alumina tubes. These organic solvents are toxic and harmful. In addition, their use can lead to corrosion of equipment, resulting in increased manufacturing costs. Ong et al. [48] reported an environmentally friendly approach using decanoic acid as a solvent for trimethyl chloride, which reached about 52 L m−2 H−1 Bear−1 Water permeability. Therefore, the development of non-toxic solvents for the production of COF membranes is crucial to overcome sustainability and cost challenges.
In this work, COF/HPAN membranes were prepared by in situ interfacial polymerization at room temperature using monomer in metaposition M-Phenylenediamine (MPD) and TFB. Ethyl acetate (EA) was chosen as an environmentally friendly alternative to DCM for the organic phase, enabling sustainable synthesis of COF membranes. Permeability tests, dye repellency and antifouling properties were then evaluated to evaluate the performance of the membranes and its relationship to their structural properties.