Non-organic solvent prepared nanofiltration composite membrane from natural product tannic acid (TA) and cyclohexane-1,4-diamine (CHD)

Conventional nanofiltration membrane fabrication generally includes the usage of toxic organic solvent that poses threats to the environment and public health. Herein, we explored preparing nanofiltration membrane through a non-organic solvent method utilizing the highly reactive natural product, tannic acid (TA), along with cyclohexane-1,4-diamine (CHD). Fabrication process was carried out through sequential immersion of a polyethersulfone (PES) support in two aqueous monomer phases. The absence of a solvent interface facilitated the diffusion and mixing of the two monomers, and the highly reactive quinone derivative of TA enabled the rapid film formation via Michael addition and Schiff base formation. Membrane performance was optimized through investigation of fabrication parameters. The TA-CHD membrane exhibited a negatively charged surface, with a molecular weight cut-off (MWCO) of 600 Da. The membrane prepared at optimal conditions showed approximate 97% and 50.7% rejections towards Na2SO4 and NaCl, with a water flux at approximate 35 L m(-2) h(-1) (10 bar). Fouling behaviour of the TA-CHD membrane was studied and a chemical cleaning test under two extreme pH was performed to demonstrate the chemical stability. The proposed non-organic solvent method here provides an eco-friendly way to utilize the potential of polyphenol natural products in water purification membrane preparation.