Effect of free oxygen radical anions and free electrons in a Ca12Al14O33 cement structure on its optical, electronic and antibacterial properties

The aim of this work was to investigate the effect of free oxygen radicals and free electrons in a Ca 12 Al 14 O 33 (C12A7) cement structure on the optical, electronic and antibacterial activity of this material. Ca 12 Al 14 O 33 was successfully fabricated via rapid heating to high temperatures by high frequency electromagnetic induction. Ca 12 Al 14 O 33 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 (O 2 − ions) in the insulating structure of Ca 12 Al 14 O 33 was confirmed using Raman spectroscopy showing a spectrum peak at 1067 cm −1 . The excitation of free electrons in the Ca 12 Al 14 O 33 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 Ca 12 Al 14 O 33 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 O 2 − anions as a reactive oxygen species (ROS) at the surface of Ca 12 Al 14 O 33 caused inhibition of E . coli and S . aureus cells. The free electrons in the conducting C12A7 reacted with O 2 gas to produce ROS, specifically super oxides (O 2 − ), superoxide radicals (O 2 •- ), hydroxyl radicals (OH • ) and hydrogen peroxide (H 2 O 2 ), 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 O 2 − anions in the structure of Ca 12 Al 14 O 33 . The antibacterial actions for insulating and conducting Ca 12 Al 14 O 33 were different for E . coli and S . aureus . Thus, Ca 12 Al 14 O 33 cement has antibacterial properties that do not require the presence of nano-particle sizes materials or photocatalysis.