Synthesis of Polyethersulfone Nano-composite Membrane with Controlled Silver Ions release and Enhanced Antibacterial properties

Abstract

In the present research work polymer nano-composite membrane with prolong silver release causing long-lasting disinfection effects have been extensively studied. New, facile and novel composite materials have been reported, three different materials are reported in this work. (i) APES-AgNPs, (ii) Silica-AgNPs@(crust and core) and (iii) Gr-AgNPs. The first study (Chapter 2) reports the antibacterial disinfection properties of a series of AgNPs(AgNPs) immobilized membranes. Initially, polyethersulfone (PES) was functionalized through the introduction of amino groups to form aminated polyethersulfone (NH2-PES, APES). AgNPs were then coordinately immobilized on the surface of the APES composite membrane to form AgNPs-APES. The properties of the obtained membrane were examined by FT-IR, XPS, XRD, TGA, ICP-OES and SEM-EDAX analyses. These structural characterizations revealed that AgNPs ranging from 5-40 nm were immobilized on the surface of the polymer membrane. Antibacterial tests of the samples showed that the AgNPs-APES exhibited higher activity than the AgNPs-PES un-functionalized membrane. Generally, the AgNPs-APES 1 cm × 3 cm strip revealed a four times longer life than the un-functionalized AgNPs polymer membranes. The evaluation of the Ag+ leaching properties of the obtained samples indicated that approximately 30% of the AgNPs could be retained, even after 12 days of operation. Further analysis indicated that silver ion release can be sustained for approximately 25 days. The present study provides a systematic and novel approach to synthesize water treatment membranes with controlled and improved silver (Ag+) release to enhance the lifetime of the membranes. Secondly, a novel, facile and one-pot approach to develop silica nanoparticle with silver at its core and crust. A modified stöbers method was used to make silica-AgNPs@ (Core&Crust). A significant reduction in the size of silica nanoparticle was seen, clearly 2-5 nm AgNPs was uniformly distributed on the surface while10-20 nm AgNPs were seen in the center. A typical mesoporous silica from stöbers method was transformed to nanoporous silica by this modified stöbers method. Nanoporous silica was advantageous for slow and consistent silver release which was confirmed by Ag+ ion release test. Antibacterial activities of the samples were carried out to investigate the disinfection performance of the samples on the Gram negative bacteria (Escherichia coli) using disk diffusion and LB-agar method. Silica-AgNPs@ (Core&Crust) showed prolonged silver release for more than 20 days and improved antibacterial properties even after 5 days of incubation. The final study demonstrates a novel, systematic and application route synthesis approach to develop size-property relationship and control the growth of AgNPs(AgNPs) embedded on reduced graphene oxide (rGO). A sequential repetitive chemical reduction technique to observe the growth of AgNPs(AgNPs) attached to rGO, was performed on a single solution of graphene oxide (GO) and silver nitrate solution (7 runs, R1-R7) in order to manipulate the growth and size of the AgNPs. The physical-chemical properties of the samples were examined by RAMAN, XPS, XRD, SEM-EDAX, and HRTEM analyses. It was confirmed that AgNPs with diameter varying from 4nm in first run (R1) to 50nm in seventh run (R7) can be obtained using this technique. A major correlation between particle size and activities was also observed. Antibacterial activities of the samples were carried out to investigate the disinfection performance of the samples on the Gram negative bacteria (Escherichia coli). It was suggested that the sample obtained in the third run (R3) exhibited the highest antibacterial activity as compared to other samples, toward disinfection of bacteria due to its superior properties. This study provides a unique and novel application route to synthesize and control size of AgNPs embedded on graphene for various application.