Amoxicillin separation from pharmaceutical solution by pH sensitive nanofiltration membranes

•pH sensitive polyacrylic acid layer was deposited on polysulfone membrane by photopolymerization.•The deposited polyacrylic acid improved amoxicillin separation of nanofiltration membranes.•Surface charge is more effective than membranes pore size in amoxicillin separation efficiency.•The pH sensitivity of membranes makes charge repulsion as dominant separation mechanism.•Effect of pH on separation membrane efficiency was assessed by FTIR spectra.

In this study, pH-sensitive polysulfone (PSf)/polyacrylic acid (PAA) nanofiltration membranes were synthesized for separation of amoxicillin from pharmaceutical wastewater. Moreover, amoxicillin separation was enhanced by pH of filtration environment. In order to do so, a flat sheet ultrafiltration (UF) membrane with different pore sizes was prepared by the phase inversion process. A further layer of polyacrylic acid which is sensitive to filtration media pH was grafted onto this fabricated PSf UF membrane surface by UV-initiated graft. Efficiency of amoxicillin separation improved as a result of pH-sensitive nature of amoxicillin as well as surface activity and pH-sensitivity of developed nanofiltration membranes. The results confirmed that increase in molecular weight of polyethylene glycol (PEG) as the pore forming agent in the phase inversion stage, increased the pore size, the amount of acrylic acid deposition on the membrane walls and pH-sensitivity. Also, an increase in grafting intensity decreased the pore sizes and increased their surface charges as well as amoxicillin separation. AFM analysis showed that surface roughness decreases which reflect the reduction in deposition of acrylic acid onto membrane surface valleys. Since the membrane pores are electrically charged, which was confirmed by zeta potential measurement, when the pH of solution increases, the amoxicillin separation by these pH-sensitive membranes increases. Finally, the amoxicillin separation of synthesized nanofiltration membranes at pH = 10 successfully reached relatively high amount of 91%, while acceptable flux of 108.3 l h−1 m2 was maintained. The SEM images also confirmed increase in membrane pore sizes due to increase of PEG molecular weight. The FTIR analysis revealed that the amount of amoxicillin fouled on the membrane surface declined at higher pH due to high repulsion of amoxicillin by membrane.

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