3 research outputs found

    Microstructure Evolution Mechanism of Quaternary Phase Paste Containing Metakaolin and Silica Fume

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    To promote the sustainable development of high-performance calcium aluminate cement (CAC)-based material and the efficient utilization of supplementary cementitious materials (SCMs) in CAC, the evolution mechanism of the microstructure of quaternary phase (Q phase, Ca20Al26Mg3Si3O68) paste containing metakaolin (MK) and silica fume (SF) was investigated. The strength of SF-blended paste decreases with time when cured at 40 °C, while that of MK-blended paste shows sustained strength gain. The microstructure of outer products (OPs) for SF-blended paste suffers from significant damage when the age increases from 3 to 28 d, whereas that for MK-blended paste exhibits no significant difference, showing a dense morphology. The microstructure evolution of OP is mainly controlled by the reactions between SCMs (i.e., MK and SF) and early metastable hydrates (i.e., CAH10 and C2AH8). The dissolved silica from SF reacts with CAH10 to form C2ASH8 but cannot completely hinder its conversion to C3AH6, while the preferentially dissolved alumina from MK can stabilize CAH10 due to the common-ion effect. As the rate of conversion of C2AH8 to C3AH6 is much faster than that of CAH10, the rapid conversion of C2AH8 cannot be effectively suppressed by MK or SF

    Density Functional Simulation of Adsorption Behavior within the Dicalcium Silicate-Accelerated Carbonation System

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    In this study, the adsorption behavior of various molecules, including H2O, CO2, and H2CO3, on the C2S surface in the carbonation system was systematically compared to elucidate the microscopic mechanism in early accelerated carbonation using density functional theory and ab initio molecular dynamics. The electronic structures on β-C2S and γ-C2S surfaces differ, in that the valence band maximum is contributed by the O p orbital and Ca s orbital, respectively. This difference results in different proton–surface interactions. The protons hydroxylated the [SiO4]4– tetrahedra on the β-C2S surface. On the γ-C2S surface, the protons enter the interior surface to form a three-coordination configuration with Ca atoms in addition to bonding with the [SiO4]4– tetrahedra. The adsorption energy for the dissociative adsorption of H2CO3 on both β-C2S and γ-C2S surfaces is significantly higher than that of H2O, and the dissociative adsorption configurations are also more stable. CO2 only has a strong adsorption tendency on the γ-C2S surface, where it acquires electrons from the surface Ca atoms to become activated. In the molecular adsorption phase, γ-C2S interacts more strongly with CO2, H2CO3, and its dissociation products

    Phenylamine-Functionalized rGO/TiO<sub>2</sub> Photocatalysts: Spatially Separated Adsorption Sites and Tunable Photocatalytic Selectivity

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    The preferential adsorption of targeted contaminants on a photocatalyst surface is highly required to realize its photocatalytic selective decomposition in a complex system. To realize the tunable preferential adsorption, altering the surface charge or polarity property of photocatalysts has widely been reported. However, it is quite difficult for a modified photocatalyst to realize the simultaneously preferential adsorption for both cationic and anionic dyes. In this study, to realize the selective adsorption for both cationic and anionic dyes on a photocatalyst surface, the negative reduced graphene oxide (rGO) nanosheets and positive phenylamine (PhNH<sub>2</sub>) molecules are successfully loaded on the TiO<sub>2</sub> surface (PhNH<sub>2</sub>/rGO-TiO<sub>2</sub>) with spatially separated adsorption sites, where the negative rGO and positive PhNH<sub>2</sub> molecules work as the preferential adsorption sites for cationic and anionic dyes, respectively. It was interesting to find that although all the TiO<sub>2</sub> samples (including the naked TiO<sub>2</sub>, PhNH<sub>2</sub>/TiO<sub>2</sub>, rGO-TiO<sub>2</sub>, and PhNH<sub>2</sub>/rGO-TiO<sub>2</sub>) clearly showed a better adsorption performance for cationic dyes than anionic dyes, only the PhNH<sub>2</sub>/rGO-TiO<sub>2</sub> with spatially separated adsorption-active sites exhibited an opposite photocatalytic selectivity, namely, the naked TiO<sub>2</sub>, PhNH<sub>2</sub>/TiO<sub>2</sub>, and rGO-TiO<sub>2</sub> showed a preferential decomposition for cationic dyes, while the resultant PhNH<sub>2</sub>/rGO-TiO<sub>2</sub> exhibited an excellently selective decomposition for anionic dyes. In addition, the resultant PhNH<sub>2</sub>/rGO-TiO<sub>2</sub> photocatalyst not only realizes the tunable photocatalytic selectivity but also can completely and sequentially decompose the opposite cationic and anionic dyes