Efficient Antibacterial Membrane based on Two-Dimensional Ti3C2Tx (MXene) Nanosheets

Abstract

Advanced membranes that enable ultrafast water flux while demonstrating anti-biofouling characteristics can facilitate sustainable water/wastewater treatment processes. MXenes, two-dimensional (2D) metal carbides and nitrides, have attracted attention for applications in water/wastewater treatment. In this work, we reported the antibacterial properties of micrometer-thick titanium carbide (Ti₃C₂T_x) MXene membranes prepared by filtration on a polyvinylidene fluoride (PVDF) support. The bactericidal properties of Ti₃C₂T_x modified membranes were tested against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) by bacterial growth on the membrane surface and its exposure to bacterial suspensions. The antibacterial rate of fresh Ti₃C₂T_x MXene membranes reaches more than 73% against B. subtilis and 67% against E. coli as compared with that of control PVDF, while aged Ti₃C₂T_x membrane showed over 99% growth inhibition of both bacteria under same conditions. Flow cytometry showed about 70% population of dead and compromised cells after 24 h of exposure of both bacterial strains. The damage of the cell surfaces was also revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis, respectively. The demonstrated antibacterial activity of MXene coated membranes against common waterborne bacteria, promotes their potential application as anti-biofouling membrane in water and wastewater treatment processes.

Figure 1

(A) Schematic of the Ti₃C₂T_x membrane fabrication on a PVDF support; (B) Cross-sectional SEM image of a Ti₃C₂T_x film; (C) TEM image of a pristine Ti₃C₂T_x flake; (D and E) 3D AFM images of a PVDF membrane and a Ti₃C₂T_x/PVDF film, respectively; (F) EDX spectrum of Ti₃C₂T_x/PVDF; (G) XRD patterns of Ti₃C₂T_x and a Ti₃C₂T_x/PVDF membrane.

Figure 2

Antibacterial activity of Ti₃C₂T_x MXene. (A) Photographs of E. coli and B. subtilis growth on unmodified PVDF (control), and fresh and aged Ti₃C₂T_x MXene coated PVDF membranes incubated at 35 °C for 24 h. (B) Cell viability measurements of E. coli and B. subtilis grown on fresh and aged Ti₃C₂T_x MXene coated PVDF membranes for 24 h. Survival rates were obtained by the colony forming count method. Error bars represent the standard deviation of triplicate experiments.

Figure 3

SEM images of the E. coli (top panels) and B. subtilis (bottom panels) colonies grown on (A) PVDF and (B) Ti₃C₂T_x modified membranes, at low and high magnifications. Control bacterial cells were viable with no observed membrane damage or cell death, and the higher magnification images show that the bacteria were protected by intact cytoplasmic membrane.

Figure 4

AFM images of E. coli and B. subtilis colonies grown on PVDF and Ti₃C₂T_x modified PVDF membranes. The black square areas indicate where a 0.5 × 0.5 μm zoom scan has been performed (right hand of each panel); showing fine detail of the bacterial capsule surfaces.

Figure 5

Cell viability measurements of (A) E. coli and (B) B. subtilis exposed to MXene membranes at different time intervals during 24 h of contact time. Survival rates were obtained by the colony forming count method as compared to that of control PVDF membrane. Error bars represent the standard deviation. First order rate plot for the inactivation of (C) E. coli and (D) B. subtilis.

Figure 6

Cell viability measurement of E. coli and B. subtilis exposed to PVDF and Ti₃C₂T_x. Flow cytometry dot plots of E. coli (A,C) and B. subtilis (B,D) bacterial cells exposed to control PVDF (A and B) and MXene films (C,D) for 24 h.