Civil Engineering Reference
In-Depth Information
Figure 2.22
Typical a) TEM images of Au@SiO
2
NPs; and b) SEM image of BC/Au@SiO
2
NPs.
Reproduced with permission from [235].
of the size of the Au@SiO
2
NPs [235], which therefore can be tuned to obtain materials
with dif erent optical properties, to be used for example in security papers.
With a dif erent objective BC nanocomposites with Au NPs (~ 9 nm) without any
coating were prepared to be used as templates for the deposition of heme proteins (oxid-
azes) for the amperometric detection of hydrogen peroxide used on the quantii cation
of glucose [223, 224]. h e application of this biosensor was successfully demonstrated
in the determination of glucose in human blood samples with lower detection limit
when compared with other reported immobilization systems [223, 224]. h e prepara-
tion of BC nanocomposites with nickel (BC/Ni NPs) has also been studied by
in situ
reduction of Ni
2+
aqueous solutions, obtaining Ni NPs of size ranging from 10 to 60
nm [236], or 3.2 nm to 140 nm [237], inside the BC membrane, along with Ni(OH)
2
which was proposed to be formed by water reduction to gaseous hydrogen [236]. h e
resulting materials have shown to be ferromagnetic, with a saturation magnetization
of 2.81 emu.g
-1
at room temperature [236, 237]. Finally, Sun
et al.
[238] described the
preparation of BC hybrids with Pd/Cu nanoparticles by
in situ
reduction of Pd
2+
and
Cu
2+
which showed to have high catalytic activity for water denitrii cation. Yang
et al.
[210] reported the
in situ
deposition of 3-4 nm Pt spherical nanoparticles on BC. It was
demonstrated that BC/Pt NPs have high electrocatalytic activity in the hydrogen oxida-
tion reaction, with potential application as membranes in fuel cells.
2.4.3 Bacterial Cellulose Hybrids with Silica Nanoparticles (BC/SiO
2
NPs)
BC/SiO
2
NPs can be prepared by addition to BC culture media of SiO
2
NPs prepared
ex situ
[241]; however, most BC/SiO
2
hybrids are prepared by
in situ
polycondensation
of a silica precursor (tetraethoxysilane (TEOS)) from aqueous solutions [239-241, 244,
246], leading to partially transparent and homogeneous materials with sphere like silica
NPs with average diameters of 10-30 nm [240, 246], in variable weight percentages,
embedded between the nano and micro i brils of the BC matrix [239, 240, 244, 246].
Furthermore, SiO
2
NPs can be isolated upon thermal degradation of the organic phase
[240] (Figure 2.23).
h e BC/SiO
2
NPs hybrids have shown to be robust and l exible materials with con-
siderable increments in mechanical properties [239, 244]; for example, the tensile
strength and Young's modulus showed 35 and 18-fold increases, respectively, with 7%
TEOS, which is due to the excellent interaction between SiO
2
NPs and BC hydroxyl
groups [244]. However, it was demonstrated that these mechanical properties can be
substantially af ected by the pressing/drying process [244].
