Toughened chitosan-based composite membranes with antibiofouling and antibacterial properties via incorporation of benzalkonium chloride

Abstract

Biofouling due to biofilm formation is a major problem in ultrafiltration membrane applications. In this work, a potential approach to solve this issue has been developed by functionalization of chitosan-based membranes with benzalkonium chloride (BKC). The chitosan composite membranes consisting of poly(ethylene glycol) (PEG), multiwalled carbon nanotubes (MWCNT), and BKC were synthesized by mixing the membrane precursors and the antibacterial solution, and casting via an inversed phase technique. The effects of the BKC content on the morphology and performance of the membranes are investigated by varying the BKC feed compositions. The composite membranes demonstrate better antibacterial efficacy against Staphylococcus aureus than Escherichia coli. The permeability and selectivity performances of the composites as filter membranes are examined by employing a dead-end filtration system. Interestingly, enhanced toughness of the membranes is observed as a function of the BKC content. Mechanisms of the structural formation are investigated. The results from SEM, XRD, and FTIR spectroscopy revealed that MWCNT/BKC are located as nanoclusters with π-π stacking interactions, and are covered by PEG chains. The shape of the dispersed domains is spherical at low BKC contents, but becomes elongated at high BKC contents. These act as soft domains with an anisotropic shape with toughening of the brittle chitosan matrix, leading to enhanced durability of the membranes, especially in ultrafiltration applications. The composite membranes also demonstrate improved rejection in dead-end ultrafiltration systems due to high porosity, high hydrophilicity, and the positive charges of the membrane surface.

Fig. 1. (a) ZOI, (b) total plate count, and (c) bacteria-killing ratio of composite membranes, at different BKC contents against E. coli and S. aureus.

Fig. 2. SEM and AFM surface images of composite membranes containing different BKC contents: (a) and (b) M-0, (c) and (d) MB-60, (e) and (f) MB-80, and (g) and (h) MB-100.

Fig. 3. SEM images of composite membranes after 1 year of storage and being incubated under sonication for 3 h: (a) M-0, (b) MB-60, (c) MB-100, (d) MB-120, and (e) proposed structures of the composite membranes.

Fig. 4. Water contact angle of the composite membranes.

Fig. 5. Tensile stress–strain plots of composite membranes containing different BKC contents: (a) M-0, (b) MB-60, (c) MB-80, (d) MB-100, and (e) MB-120.

Fig. 6. XRD traces: (a) neat chitosan, and composite membranes with different BKC contents: (b) M-0, (c) MB-60, (d) MB-80, (e) MB-100, (f) MB-120, and (g) MB-400.

Fig. 7. FTIR spectra of freshly prepared composite membranes with various BKC contents: (a) neat chitosan, (b) M-0, (c) MB-60, (d) MB-80, (e) MB-120, (f) BKC, and (g) PEG.

Fig. 8. FTIR spectra of composite membranes with various BKC contents after 1 year of storage: (a) M-0, (b) MB-60, (c) MB-80, (d) MB-120, (e) BKC, and (f) PEG.

Fig. 9. FTIR spectra of composite membranes with various BKC contents, which were stored for 1 year, after being sonicated in water for 3 h: (a) M-0, (b) MB-60, (c) MB-120, (d) PEG, and (e) BKC.

Fig. 10. The results on (a) average water flux during a 10 min filtration process, and (b) rejection % of the composite membranes using a dead-end filtration system toward dye and BSA.