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    Mechanical, dielectric, thermal and antibacterial properties of reduced graphene oxide (rGO)-nanosized C3AH6 cement nanocomposites for smart cement-based materials
    This work aimed to fabricate nanocomposites of reduced graphene oxide (rGO)-nanosized C3AH6 cement via a rapid cement hydration for enhancing its micro-hardness, dielectric constant, thermal conductivity, electrochemical and antibacterial properties.rGO-nanosized C3AH6 nanocomposites (∼10–20 nm in diameter) with 1, 2, 3, and 4% weight of rGO, were successfully synthesized from a Ca12Al14O33 and rGO colloid that was rapidly heated with water to a temperature of 100 °C. Nanocomposites of x%rGO-C3AH6 (x = 1, 2, 3, and 4) were characterized using XRD, UV–vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and TGA techniques. The chemical composition was confirmed using SEM and EDX characterization. The results revealed a nanocomposited rGO-C3AH6 material with nanosheet and nanoflaked rGO, as well as nanosized C3AH6 particles. The results presented rGO-C3AH6 with high performance multifunctional properties that included enhanced mechanical, dielectric, and thermal properties. The vickers micro-hardness and dielectric constant were enhanced by the effect of rGO-C3AH6 nanocomposites. The thermal conductivity of rGO-C3AH6 was higher than that of C3AH6. The electrical conductivity and electrochemical properties were effectively increased with greater levels of rGO in the material. Its antibacterial activity was confirmed by the formation of clearing zones on a Petri plate seeded with Escherichia coli (E. coli). The diameter of these zones increased with the rGO content. These results confirmed that nanocomposited rGO-C3AH6 was effective in enhancing mechanical, dielectric and thermal properties while serving as a high performance multifunctional cement-based material.
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    Optical and dielectric properties of nano-sized tricalcium aluminate hexahydrate (C3AH6) cement
    (2018-08-10) ; ;
    Maensiri, Santi
    ;
    Chindaprasirt, Prinya
    ;
    The present study investigates the optical and dielectric properties of nano-sized C3AH6 cement hydrates. A cement product was fabricated via a simple hydration process using a derivative of a C12A7 cement precursor reacting with de-ionized water while raising the reaction temperature to 100 °C. A crystalline phase of the C3AH6 cement product was characterized and confirmed using an XRD technique. Its morphology was also evaluated using TEM and SEM techniques. It was found that nano-sized C3AH6 (in size 10–50 nm) was successfully derived via this process. This cement product was thermodynamically stable over the range of room temperature to 300 °C. The optical direct gap was 4.1 eV and the indirect energy gap was 2.45 eV. Over the range of 20 Hz to 2 MHz, the observed capacitance was 10<sup>−10</sup> F–10<sup>−11</sup> F and the dielectric constant varied from 20 to 150. The dielectric properties were enhanced over those of general cement compounds. This effect was due to its complex structure in which –O–H bonding appeared in the structure and the formation of nano-sized structures from this process. These results suggested that the nano-C3AH6 hydrated particles were transparent to visible light and exhibited a high frequency electrical response. This implies an important role for these cement-based materials as potential candidates having optical and dielectric properties appropriate for applications such as smart building materials in the form of transparent electrode windows, smart wall capacitors, triboelectric devices and supercapacitors.
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    Effect of free oxygen radical anions and free electrons in a Ca12Al14O33 cement structure on its optical, electronic and antibacterial properties
    (2019-05-01) ; ;
    Srepusharawoot, Pornjuk
    ;
    Maensiri, Santi
    ;
    Chindaprasirt, Prinya
    The aim of this work was to investigate the effect of free oxygen radicals and free electrons in a Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> (C12A7) cement structure on the optical, electronic and antibacterial activity of this material. Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> was successfully fabricated via rapid heating to high temperatures by high frequency electromagnetic induction. Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> 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<inf>2</inf> <sup>−</sup>ions) in the insulating structure of Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> was confirmed using Raman spectroscopy showing a spectrum peak at 1067 cm<sup>−1</sup>. The excitation of free electrons in the Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> 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<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> 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<inf>2</inf> <sup>−</sup> anions as a reactive oxygen species (ROS) at the surface of Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> caused inhibition of E. coli and S. aureus cells. The free electrons in the conducting C12A7 reacted with O<inf>2</inf> gas to produce ROS, specifically super oxides (O<inf>2</inf> <sup>−</sup>), superoxide radicals (O<inf>2</inf> <sup>•-</sup>), hydroxyl radicals (OH<sup>•</sup>) and hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>), 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<inf>2</inf> <sup>−</sup> anions in the structure of Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf>. The antibacterial actions for insulating and conducting Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> were different for E. coli and S. aureus. Thus, Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> cement has antibacterial properties that do not require the presence of nano-particle sizes materials or photocatalysis.