The Composites of PCL and Tetranuclear Titanium(IV)-oxo Complexes as Materials Exhibiting the Photocatalytic and the Antimicrobial Activity

Abstract

Excessive misuse of antibiotics and antimicrobials has led to a spread of microorganisms resistant to most currently used agents. The resulting global threats has driven the search for new materials with optimal antimicrobial activity and their application in various areas of our lives. In our research, we focused on the formation of composite materials produced by the dispersion of titanium(IV)-oxo complexes (TOCs) in poly(ε-caprolactone) (PCL) matrix, which exhibit optimal antimicrobial activity. TOCs, of the general formula [Ti₄O₂(OⁱBu)₁₀(O₂CR')₂] (R' = PhNH₂ (1), C₁₃H₉ (2)) were synthesized as a result of the direct reaction of titanium(IV) isobutoxide and 4-aminobenzoic acid or 9-fluorenecarboxylic acid. The microcrystalline powders of (1) and (2), whose structures were confirmed by infrared (IR) and Raman spectroscopy, were dispersed in PCL matrixes. In this way, the composites PCL + nTOCs (n = 5 and 20 wt.%) were produced. The structure and physicochemical properties were determined on the basis of Raman microscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), electron paramagnetic resonance spectroscopy (EPR), and UV-Vis diffuse reflectance spectroscopy (DRS). The degree of TOCs distribution in the polymer matrix was monitored by scanning electron microscopy (SEM). The addition of TOCs micro grains into the PCL matrix only slightly changed the thermal and mechanical properties of the composite compared to the pure PCL. Among the investigated PCL + TOCs systems, promising antibacterial properties were confirmed for samples of PCL + n(2) (n = 5, 20 wt.%) composites, which simultaneously revealed the best photocatalytic activity in the visible range.

Keywords: PCL; antimicrobial activity; composite; photocatalytic activity; physicochemical properties; reactive oxygen species; titanium(IV)-oxo complex.

Figure 1

SEM images of isolated micro-powders of oxo-complexes (1) and (2) and cross sections of the produced PCL + nTOCs (TOCs = (1) and (2)) composite fittings.

Figure 2

Raman microscopy maps and spectra of PCL + 5(1), PCL + 20(1), and PMMA + 20(1) composites.

Figure 3

Raman microscopy maps and spectra of PCL + 5(2), PCL + 20(2), and PMMA + 20(2) composites.

Figure 4

SEM images and EDX patterns of (PCL + 20(1)) and (PCL + 20(2)) composites, the pure PCL spectra are given for comparison.

Figure 5

Thermogravimetric curves (TGA) (a,c) and the differential scanning calorimetry curves of (DSC) (b,d) of the produced composite materials.

Figure 6

UV–Vis–DRS spectra of PCL and studied PCL + nTOCs composites.

Figure 7

Changes in the concentrations of the methylene blue (MB) solution as a function of time for the respective composite materials irradiated with VIS radiation ((a) PCl + n(1), (b) PCL + n(2) (n = 5, 20 wt.%), (c) PMMA + 20(1), (d) PMMA + 20(2) (n = 20 wt.%).

Figure 8

EPR spectra of PCL + 20(1) (a) and PCL + 20(2) (b).

Figure 9

Fittings produced by injection molding method, samples after breaking on a testing machine: (a) PCL, (b) PCL + 20(1), and (c) PCL + 20(2).