Photocatalytic activities and chemically-bonded mechanism of SiO2@ TiO2 nanocomposites coated cement-based materials

Highlights: • Two samples have different deposited density of TiO₂ nanoparticles on each SiO₂ nanosphere, which depend on the difference of the water dosage. • When the curing time is 28 days, water adsorption rates of mortar-2 at 270 min have decreased by 17.8%, which may be attributed to pozzolanic reactivity of SiO₂ on cement-based materials. • The formation of C-S-H gels via pozzolanic reaction of SiO₂ on cement-based materials has been demonstrated by XPS and NMR spectra. • Cem-1 and cem-2 show excellent photocatalytic property. - Abstract: Photocatalytic technology has been studied in building materials, especially for the surface. However, the drawback of surface-treatment application is weak adhesion between coatings and the substrates resulting poor durability in outdoor environments. In the study, two SiO₂@TiO₂ core-shell nanocomposites were synthetized and coated cement-based materials, and the photocatalytic activity (rhodamine B removal efficiency) and surface modification/densification performances of coated cement-based materials were studied. The two samples have different deposited densities of TiO₂ nanoparticles on each SiO₂ nanosphere. Water adsorption rates of coated mortar measured at 270 min decreased by 17.8% when curing time was 28 days. Reaction experiments of SiO₂@TiO₂ nanocomposites and Ca(OH)₂ with different dosages were carried out to investigate the reaction mechanism. The formation of C-S-H gel was confirmed due to the pozzolanic reaction of samples and Ca(OH)₂. The coated cement pastes show excellent photocatalytic activity for rhodamine B removal.