Abstract
The aim of this work was to investigate the effect of free oxygen radicals and free electrons in a Ca12Al14O33 (C12A7) cement structure on the optical, electronic and antibacterial activity of this material. Ca12Al14O33 was successfully fabricated via rapid heating to high temperatures by high frequency electromagnetic induction. Ca12Al14O33 cement samples were characterized using XRD and UV-Vis-DRS spectroscopy. The morphology and chemical composition of the samples were also investigated using SEM and EDS techniques. The presence of free oxygen radicals (O2−ions) in the insulating structure of Ca12Al14O33 was confirmed using Raman spectroscopy showing a spectrum peak at 1067 cm−1. The excitation of free electrons in the Ca12Al14O33 cement was indicated by UV-Vis absorption spectra at 2.8 eV and an optical energy gap of 3.5 eV, which is consistent with the first-principles calculations for the band energy level. The effects of free oxygen radicals and free electrons in the Ca12Al14O33 structure as antibacterial agents against Escherichia Coli (E. coli) and Staphylococcus Aureus (S. aureus) were investigated using an agar disk-diffusion method. The presence of O2− anions as a reactive oxygen species (ROS) at the surface of Ca12Al14O33 caused inhibition of E. coli and S. aureus cells. The free electrons in the conducting C12A7 reacted with O2 gas to produce ROS, specifically super oxides (O2−), superoxide radicals (O2•-), hydroxyl radicals (OH•) and hydrogen peroxide (H2O2), which exhibited antibacterial properties. Both mechanisms were active against bacteria without effects from nano-particle sized materials and photocatalytic activity. The experimental results showed that the production of ROS from free electrons was greater than that of the free O2− anions in the structure of Ca12Al14O33. The antibacterial actions for insulating and conducting Ca12Al14O33 were different for E. coli and S. aureus. Thus, Ca12Al14O33 cement has antibacterial properties that do not require the presence of nano-particle sizes materials or photocatalysis.
Highlights
The use of antimicrobials to promote public health is a research topic with much attention [1, 2, 3, 4]
These X-ray diffractometer (XRD) results show a pattern corresponding to the JCPDS#09–0413 file
The results showed that the CAO@1200C, CAO@1350C, and CAO@1450C energy gap values were close to 4.0 eV, indicating the insulating nature of this Ca12Al14O33 cement
Summary
The use of antimicrobials to promote public health is a research topic with much attention [1, 2, 3, 4]. ROS are comprised of hydroxyl radicals (OH), hydrogen peroxide (H2O2) and superoxide ions (O2- ) [4, 8] These materials cause death by contacting bacterial membranes and directly damaging their surfaces [4,7]. ROS species can be generated from the reaction of free particles (free electrons and holes) in the course of photocatalytic activities [9, 10, 11]. TiO2 and ZnO used phonon energy at 3.1 eV [13] and 3.2 eV [7], respectively, to photocatalytically produce ROS They are produced from O2 and H2O adsorption promoting a reaction of free electrons and holes at the surfaces of materials to produce OHÀ, H2O2 and O2-. TiO2 and ZnO act through photocatalysis and nanoparticle effects to produced antibacterial activity
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