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Emergence of dark ZnO nanorods by hydrogen plasma treatment
Remeš, Zdeněk ; Buryi, Maksym ; Sharma, Dhananjay K. ; Artemenko, Anna ; Mičová, J. ; Rezek, B. ; Poruba, A. ; Hsu, H.S. ; Potocký, Štěpán ; Babin, Vladimir
We employed a custom-built inductively coupled plasma (ICP) 13.56 MHz reactor with up to 300 W RF discharge power. Hydrothermally grown ZnO nanorods were exposed to the ICP plasma with a mixture of hydrogen and argon for up to 30 min, followed in-situ by plasma oxidation. Plasma properties were monitored by optical emission spectroscopy (OES) and by measuring the self-bias potential of the stainless steel sample holder separated from the ground by a blocking capacitor. The exciton-related UV photoluminescence of ZnO nanorods and optical absorption increases significantly after the plasma treatment. We attribute it to the complex changes of ZnO surface electronic states that also give rise to its black color visually.
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Plasma-synthesised zinc oxide nanoparticle behavior in liquids
Rutherford, D. ; Jíra, J. ; Kolářová, Kateřina ; Matolínová, I. ; Remeš, Zdeněk ; Kuliček, J. ; Padmanaban, D. ; Maguire, P. ; Mariotti, D. ; Rezek, B.
ZnO nanoparticles have been synthesized using non-thermal atmospheric pressure plasma (ZnO-NTP). We investigated the behavior of these ligand-free as a colloid suspension using different solvents, from deionized water to physiological saline and microbial culture broth. We found that the zeta potential of ZnONTP became more negative after exposure to microbial culture broth relative to water, which suggests increased colloid stability. Photoluminescence spectra of ZnO-NTP were similar regardless of liquid type, yet optical and fluorescent images of samples showed different agglomeration behaviour depending on liquid type. Scanning electron microscopy images revealed large agglomerates of ZnO-NTP interacting with the surface of bacteria cells, ranging in size from 200 nm up to 2 µm. We also studied effect of sub-lethal concentrations of ZnO-NTP on bacteria under illumination. There was no significant difference in viable bacteria concentration after 24h exposure to 10 µg/mL ZnO-NTP.
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Plasma hydrogenation of hydrothermally grown ZnO micropods
Remeš, Zdeněk ; Aubrechtová Dragounová, Kateřina ; Mičová, J.
The hydrothermally grown ZnO micropods have been placed on grounded stainless-steel holder and exposed to an inductively coupled plasma (ICP) monitored in-situ by optical emission spectroscopy (OES). OES shows the immediate release of oxygen during Ar ion bombardment. The prolonged exposure to hydrogen plasma leads to deterioration of the optical properties as well. The exposure, rf power and hydrogen pressure have been optimized to enhance UV-photoluminescence peak at the wavelength 384 nm related to surface bounded excitons and reduce the defect-related photoluminescence in red spectral range. The strong UV photoluminescence appears just after 1 minute of plasma hydrogenation in a radio frequency plasma discharge with power density 40 W/dm3 and hydrogen pressure 17 Pa.
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Mass production of hydrogenated ZnO nanorods
Chang, Yu-Ying ; Remeš, Zdeněk ; Míčová, J.
We have developed an inexpensive and efficient technology of hydrothermal growth of ZnO nanorods from zinc nitrate hexahydrate (Zn(NO3)2·6H2O), as a precursor and hexamethylenetetramine (HMTA) (C6H12N4), as a surfactant followed by plasma hydrogenation in a novel inductively coupled plasma (ICP) quartz reactor and equipped with the rotary sample holder to stir powder during plasma treatment. We have optimized the photoluminescence spectroscopy for measuring optical scattering samples with the high sensitivity, precise sample positioning and very low influence of the scattered excitation light. Here we present the latest results on the enhancement of the UV photoluminescence of the ZnO nanorods after plasma hydrogenation. The exciton-related photoluminescence has been significantly enhanced whereas the deep defect related yellow photoluminescence has been significantly decreased.\n
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Comparison of microbial interactions of zinc oxide nanomaterials in various size and shape
Rutherford, D. ; Jíra, J. ; Mičová, J. ; Remeš, Zdeněk ; Hsu, H.S. ; Rezek, B.
Zinc oxide nanoparticles (ZnO NP) have shown great potential as a novel antibacterial material at a time when resistance towards conventional antibiotics is becoming more prevalent. We report bacteria inactivation by ZnO NP with novel hedgehog-like morphology using model gram-negative (E. coli) and gram-positive (S. aureus) bacteria. E. coli exposed to the novel ZnO hedgehog NP during growth resulted in 4 orders of magnitude reduction in viable cell concentration after 24 h, which is more than 2 orders higher reduction compared to commercially available ZnO NPs with nominal sizes from 50 nm to 20 um. There was a positive correlation between hedgehog NP concentration and bacteria cell concentration reduction within the range tested 0.1 – 1.0 mg/mL. S. aureus was less sensitive to ZnO NP exposure and inactivation effect of various ZnO NP, was comparable. The effect can be thus attributed to direct mechanical damage of the bacterial mebrane that is the most effective for the novel hedgehog ZnO NP. This conclusion was corroborated also by disk diffusion assays.\n
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