The search for new antimicrobial substances has increased in recent years. Antimicrobial nanostructures are one of the most promising alternatives. In this work, titanium dioxide nanotubes were obtained by an atomic layer deposition (ALD) process over electrospun polyvinyl alcohol nanofibers (PVN) at different temperatures with the purpose of obtaining antimicrobial nanostructures with a high specific area. Electrospinning and ALD parameters were studied in order to obtain PVN with smallest diameter and highest deposition rate, respectively. Chamber temperature was a key factor during ALD process and an appropriate titanium dioxide deposition performance was achieved at 200 °C. Subsequently, thermal and morphological analysis by SEM and TEM microscopies revealed hollow nanotubes were obtained after calcination process at 600 °C. This temperature allowed complete polymer removal and influenced the resulting anatase crystallographic structure of titanium dioxide that positively affected their antimicrobial activities. X-ray analysis confirmed the change of titanium dioxide crystallographic structure from amorphous phase of deposited PVN to anatase crystalline structure of nanotubes. These new nanostructures with very large surface areas resulted in interesting antimicrobial properties against Gram-positive and Gram-negative bacteria. Titanium dioxide nanotubes presented the highest activity against Escherichia coli with 5 log cycles reduction at 200 μg/mL concentration.

The search for and synthesis of new antimicrobial nanostructures is important to reduce microbial incidence that induces infectious diseases and to aid in the antibiotic resistance crisis, which are two of the most pressing issues in global public health. In this work, novel, hollow, calcined titanium dioxide nanospheres (CSTiO2) were successfully synthesized for the first time through the combination of electrospinning and atomic layer deposition techniques. Poly(vinylpyrrolidone) (PVP) electrosprayed spherical particles were double-coated with alumina and titanium dioxide, and after a calcination process, hollow nanospheres were obtained with a radius of approximately 345 nm and shell thickness of 17 nm. The structural characterization was performed using electron microscopy, and X-ray diffraction and small-angle X-ray diffraction evidenced an anatase titanium dioxide crystalline structure. Thermogravimetric analysis and Fourier-transform infrared spectroscopy studies demonstrated the absence of polymer residue after the calcination process. The antimicrobial properties of the developed CSTiO2 hollow nanospheres were evaluated against different bacteria, including resistant E. coli and S. aureus strains, and when compared to commercial TiO2 nanoparticles, CSTiO2 nanospheres exhibited superior performance. In addition, the positive effect of UV irradiation on the antimicrobial activity was demonstrated.

High-aspect ratio Al2O3/Ni/Al2O3 core–shell hollow nanotubes were prepared by combining electrospinning, atomic layer deposition, and a subsequent chemical reduction process. Electrospun poly(vinyl alcohol) (PVOH) nanofibers were obtained by electrospinning. Then, these fibers were coated with atomic layer deposition to obtain PVOH/Al2O3/NiO/Al2O3 core–shell nanowires. Since the NiO must be deposited at 200 °C, the PVOH nanofibers must first be coated with Al2O3 at 80 °C, which act as a protective layer of the fibers so that they can withstand higher temperatures. Once PVOH/Al2O3/NiO/Al2O3 core–shell nanowires are obtained, they are subjected to a chemical reduction process that generates Al2O3/Ni/Al2O3 core–shell hollow nanotubes. Their morphologies were studied by scanning and transmission electron microscopies, the thickness was determined by ellipsometry, and all magnetic measurements were performed in an alternating-gradient force magnetometer. Finally, assuming that the nanostructures exhibit a curling reversal process, the authors have analytically calculated the coercivity of the nanotubes.