XPS, structural and antimicrobial studies of novel functionalized halloysite nanotubes

Abstract

A novel robust preparation method based on thermal salt decomposition has been elaborated for synthesis of halloysite nanotubes (HNTs) impregnated with silver and iron oxide nanoparticles. The developed method is simple, time-effective, and can be employed for large scale material fabrication. Different characterization techniques, including X-ray diffraction (XRD), scanning and transmission electron spectroscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS) have been used to characterize the functionalized HNTs composite materials. Surface elemental and chemical state analysis was conducted using X-ray photoelectron spectrometer (XPS). The functionalized HNTs exhibit enhanced total surface area (by 17.5%) and pore volume (by 11%) compare to the raw HNTs calculated by using the Brunauer-Emmett-Teller (BET) method. It was shown that functionalized HNTs possess high antimicrobial properties towards both gram- positive and gram-negative bacteria species. The enhanced surface area and bactericidal properties of functionalized HNTs could be beneficial for employing of the prepared material as low cost filtration media for water treatment applications. Molecular dynamics (FPMD) were performed to obtain insights about possible physiochemical mechanisms for chemical adsorption and on the HNT thermal stability.

Figure 1

In (a), the optimized spiral HNT structure. In (b), a zoom on the structure showing the coordination of Al with 4 hydroxyl group and two –O–Si-. In (c) and (d), the structure at 300 and 800 K, respectively, after ~ 10 ps molecular dynamics. Atom color code Al (cyan), Si (yellow), O (red), and H (white). The blue arrow highlights the unfolding of the HNT spiral, the red ones the break of the HNT sheets.

Figure 2

XRD spectra of raw HNTs (a), HNTs + Fe₂O₃ + Ag (b), Fe₂O₃ (c) and Fe₂O₃ + Ag nanocomposites (d).

Figure 3

TEM images of raw HNTs before functionalization.

Figure 4

HR-TEM images of HNTs functionalized by iron oxide and silver nanoparticles.

Figure 5

EDS mapping and EDS spectrum of HNTs before functionalization.

Figure 6

EDS mapping and EDS spectrum of HNTs functionalized by iron oxide and silver nanoparticles.

Figure 7

HRTEM images (a and c) and their corresponding FFT (b and d) of Fe₂O₃ and Ag nanoparticles, respectively. The corresponding d-spacing of Ag and Fe₂O₃ nanocrystals are shown.

Figure 8

HNT XPS spectra including data fitting for (a) Survey, (b) Al 2p, (c) Si 2p, (d) C 1 s, (e) O 1 s. Surface treated HNT spectra including data fitting for (f) Survey, (g) Al 2p, (h) Si 2p, (i) C 1 s, (j) O 1 s, (k) Ag 3d, (l) Fe 2p.

Figure 9

In (a) the root mean square displacement (RMSD) respect the starting structure, as a function of time for all the atom in the system and (b) for the Si and Al atoms only.

Figure 10

Bactericidal properties of (a) raw HNTs and (b) HNTs functionalized by iron oxide and silver nanoparticles towards the gram-negative E.coli bacteria.

Figure 11

Bactericidal properties of (a) raw HNTs and (b) HNTs functionalized by iron oxide and silver nanoparticles towards the gram-positive B. subtilis bacteria.