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. 2022 Dec 24;24(1):305.
doi: 10.3390/ijms24010305.

PEO Coatings Modified with Halloysite Nanotubes: Composition, Properties, and Release Performance

Igor Imshinetskiy  1 , Victoria Kashepa  1 , Konstantine Nadaraia  1 , Dmitry Mashtalyar  1 , Sergey Suchkov  1 , Pavel Zadorozhny  1 , Aleksander Ustinov  1 , Sergey Sinebryukhov  1 , Sergey Gnedenkov  1
Affiliations

PEO Coatings Modified with Halloysite Nanotubes: Composition, Properties, and Release Performance

Igor Imshinetskiy et al. Int J Mol Sci. .

Abstract

In this work, the properties of the coatings formed on the Mg-Mn-Ce alloy by plasma electrolytic oxidation (PEO) in electrolytes containing halloysite nanotubes (HNTs) were investigated. The incorporation of halloysite nanotubes into the PEO coatings improved their mechanical characteristics, increased thickness, and corrosion resistance. The studied layers reduced corrosion current density by more than two times in comparison with the base PEO layer without HNTs (from 1.1 × 10-7 A/cm2 to 4.9 × 10-8 A/cm2). The presence of halloysite nanotubes and products of their dihydroxylation that were formed under the PEO conditions had a positive impact on the microhardness of the obtained layers (this parameter increased from 4.5 ± 0.4 GPa to 7.3 ± 0.5 GPa). In comparison with the base PEO layer, coatings containing halloysite nanotubes exhibited sustained release and higher adsorption capacity regarding caffeine.

Keywords: caffeine release; halloysite nanotubes; multifunctional coatings; plasma electrolytic oxidation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM images of the coatings surfaces: H0 (a), H10 (b), H20 (c), H30 (d), H40 (e).
Figure 2
Figure 2
SEM images of coatings cross sections: H0 (a), H10 (b), H20 (c), H30 (d), H40 (e).
Figure 3
Figure 3
High-magnification SEM images of coatings surface: H0 (a), H10 (b), H20 (c), H30 (d), H40 (e).
Figure 4
Figure 4
High-magnification SEM images of H40 sample (a) with details of the nanoparticles agglomerates (b) and HNTs themselves (c).
Figure 5
Figure 5
High-magnification SEM images of the H10 sample pore.
Figure 6
Figure 6
Surface topography of the H0 (a), H10 (b), H20 (c), H30 (d), H40 (e) samples.
Figure 7
Figure 7
SEM image and EDS maps of elements distribution for the H40 sample: Mg, Si, Al, O, Na.
Figure 8
Figure 8
SEM image and EDS maps of elements distribution for the cross section of H40 sample: Mg, Si, Al, O.
Figure 9
Figure 9
XPS survey spectra of the surface of the H40 coating: spectrum for raw HNTs powder (1), as-prepared H40 sample (2) and for the sample after 5 min Ar+ etching (3) (a); high-resolution XPS spectra of O 1s (b), Si 2p (c), Al 2p (d) for the raw HNTs and O1s (e), Si 2p (f), Al 2p (g) for the H40 sample.
Figure 10
Figure 10
Polarization curves for the studied samples.
Figure 11
Figure 11
Bode plots (dependences of impedance modulus |Z| and phase angle θ on frequency for the obtained samples. Spectra were acquired after exposure to the corrosive medium for 2 h (a,b) and 24 h (c,d). Impedance spectra presented by experimental data (scatter plot) and fitting curves (solid lines).
Figure 12
Figure 12
Equivalent electrical circuits used for fitting the impedance spectra.
Figure 13
Figure 13
The appearance of H0, H10, H20, H30, H40 samples after 28 days of exposure to 3.5 wt.% NaCl solution.
Figure 14
Figure 14
Images of scratch failures of the H0 (a), H10 (b), H20 (c), H30 (d), H40 (e) samples.
Figure 15
Figure 15
Concentration of caffeine in the release medium for the H20-P, H20-E, and H0-C samples. Data are represented as means ± SD (n = 3).
Figure 16
Figure 16
Caffeine release curves for the H20-C and H0-C samples (solid lines are for perception simplifying only).
Figure 17
Figure 17
Interaction mechanism between HNTs lumen surface and caffeine.
See this image and copyright information in PMC

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