Selective solvent resistant polyimide composite membranes with efficient separation performance in antibiotics

• The composite membrane exhibited high rejections for TC and CIP, but low rejection to NaCl. • The S NaCl/TC and S NaCl/CIP separation factors are calculated to be 29 and 27, respectively. • 3.The composite membrane maintains stable flux after immersed in different solvents for 18 days. As the pharmaceutical industry has evolved, the efficient separation of antibiotics has become a key technical challenge. This study presents a solvent-resistant polyamide/polyimide (PI) composite nanofiltration membrane that overcomes the stability and selectivity issues associated with traditional membrane materials in organic solvents. A high-performance polyamide functional layer was fabricated via interfacial polymerization using a PI ultrafiltration membrane as the substrate. The aqueous monomers were 2,4,6-triaminopyrimidine (TAPI) and m-phenylenediamine (MPD), while the oil-phase monomer was trimesoyl chloride (TMC) dissolved in cyclohexane. Tuning the concentration ratio of the aqueous monomers TAPI and MPD optimized the membrane's structure and properties. Separation performance tests were conducted using salt solutions, such as NaCl, Na₂SO₄ and MgCl₂, as well as antibiotics, such as tetracycline hydrochloride (TC), ciprofloxacin (CIP) and chloramphenicol (CAP). The results showed that when TAPI was used as the monomer in aqueous solution, the polyamide layer formed on the composite membrane exhibited a high permeation flux (above 10.8 L‧m –2 ‧h –1 ) and rejections of 96.7 % and 96.5 % for TC and CIP, respectively, but a low rejection to NaCl (4.2 %). The S NaCl/TC and S NaCl/CIP separation factors were calculated to be 29 and 27, respectively, and the permeation flux was high. The composite membrane maintained stable flux when immersed in 50 wt. % N,N -dimethylacetamide (DMAc) solution, acetone and methanol for 18 days. This study provides a theoretical basis for the antibiotic desalination with organic solvent nanofiltration membranes.