Ternary TiO2-SiO2-Ag nanocomposites with enhanced visible-light photocatalytic activity have been synthesized through a facile biomimetic approach by utilizing lysozyme as both inducing agent of TiO2 and reducing agent of Ag(+). TiO2 nanoparticles (∼280 nm) are at first fabricated by the inducing of lysozyme. Afterward, SiO2 layers are formed as "pancakes" stuck out of TiO2 nanoparticles through a sol-gel process. Finally, Ag nanocrystals (∼24.5 nm) are deposited onto the surface of TiO2-SiO2 composites via the reduction of lysozyme, forming TiO2-SiO2-Ag nanocomposites. The resultant nanocomposites display a high photocatalytic activity for the degradation of Rhodamine B under the visible-light irradiation, which can be attributed to the synergistic effect of enhanced photon absorption from the surface plasma resonance of Ag nanocrystals and the elevated adsorption capacity for Rhodamine B from the high specific surface area of SiO2. This study may provide some inspiration for the rational design and the facile synthesis of composite catalysts with a high and tunable catalytic property through a green, efficient pathway.
A very low dosage
of graphene oxide (GO) can enhance the mechanical
durability of cement composites, but the reinforcing enhancement is
highly dependent on the uniform dispersion of graphene in the matrix.
Carboxylic groups at GO nanosheets have a decisive effect on GO aggregation
in an alkaline cement solution because they have a strong complexation
ability with aqueous Ca2+ released by cement hydration
and subsequently crosslinks the adjacent graphene sheets, causing
the immediate coagulation of GO. The available methods of homogeneously
dispersing GO in a cement slurry cannot completely eliminate this
carboxylic-crosslinking-induced GO coagulation. In this study, many
hydroxyl groups were introduced onto the edge and planar nanosheets
to prepare water-soluble hydroxylated graphene (HO-G) by facile ball
milling. The structure of HO-G was thoroughly characterized in detail,
and its dispersion behavior in pure water and Ca(OH)2 was
extensively investigated. These results showed that the prepared HO-G
exhibited good hydrophilicity and excellent colloidal dispersion ability
against high pH and Ca2+ ions compared to GO. The effect
of HO-G on the workability, mechanical strength, and chloride penetrability
of a cement mortar was further studied. At a content of 0.03% by cement
mass, HO-G provided 28.62 and 21.19% enhancements of compressive strength
and 3.85 and 7.89% enhancements of flexural strength at 3 and 28 days,
respectively, while the non-steady-state migration coefficient decreased
by 31.51% compared to the reference mortar. Compared to GO, a lower
dosage of HO-G exhibited a similar reinforcing effect to cement composites
with little adverse impact on the fluidity of the fresh cement slurry.
Moreover, the addition of HO-G could refine the pore structure, accelerate
the hydration process of cement to some degree, and generate more
hydration products so that the structure of the cement mortar was
densified. Considering its environmentally friendly preparation, HO-G,
as a promising reinforcing nanofiller, could provide a new solution
to develop nanoengineered cement composites.
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