Civil Engineering Reference
In-Depth Information
and l exibility of the pristine material was maintained while ei cient barrier properties
against water vapor were obtained (two orders of magnitude lower than those of BC),
opening opportunities of using these materials in transparent light emitting diode dis-
plays (OLED) [243].
2.4.4 Bacterial Cellulose Hybrids with Titanium Oxide Nanoparticles
(BC/TiO
2
NPs)
BC/TiO
2
NPs hybrid target mainly the preparation of materials that take advantage of
the well-known TiO
2
photocatalytict properties. One of the i rst studies on the prepara-
tion of BC/TiO
2
NPs hybrids was reported by Sun
et al.
[248], by an
in situ
approach
at er exchanging water inside the BC membrane by ethanol followed by soaking with
an ethanolic solution of Ti(OBu)
4
and by autoclave thermal treatment, resulting in the
formation of uniform arrays of spherical TiO
2
nanoparticles with 4.3-8.5 nm on the
surface of BC nanoi bers. Similar approaches have been used in several other stud-
ies dealing with the preparation and evaluation of new properties of BC/TiO
2
NPs
nanocomposite materials [249, 250, 252, 254, 255]. BC/TiO
2
NPs hybrids can also
be prepared
in situ
, during BC biosynthesis, provided adequate aqueous soluble TiO
2
precursors, such as titanium (IV) bis-(ammonium lactate) dihydroxide (Ti-BALDH)
[242]; or by addition of
ex situ
prepared TiO
2
NPs to the culture media. It was shown
that their presence does not af ect the activity of the bacteria [253] and an uniform
distribution of NPs in the BC matrix was described [249, 250, 252-255]. As mentioned
above, the BC/TiO
2
NPs key application studied is in photocatalysis, and their poten-
tial, for example, in the successful UV degradation of methyl orange [248], stearic acid,
crystal violet and methylene blue [255], or by the so-called methanol conversion test
[253] where the presence of photo-generated OH radicals is measured. h is last study
demonstrated that the amount of generated radicals increases with the increasing con-
tent of TiO
2
NPs [253]. h e potential photocatalytic applications of BC/TiO
2
comprise
for example the application in i ltering media for water and air purii cation [253] and
coating of photo active surfaces [255]. In addition, the photocatalytic activity of BC/
TiO
2
NPs hybrid materials is considerably improved by doping the TiO
2
structure with
rare earth ions as La
3+
and particularly with Ce
4+
, with which a quantitative degradation
of the model compound was reported [249, 250]. A distinct application searched for
BC/TiO
2
NPs deals with their conductive properties, which has been accessed based on
the distinct response of TiO
2
in the nanocomposite compared to the pure one towards
Electrostatic Force Microscopy (EFM), which was assumed as a result of the electro-
static interactions with BC [252].
h e production of photochromic nanopapers with titanium oxide, as well as vana-
dium oxide NPs or mixtures of both, has also been investigated for application in sen-
sors and other optical devices [254]. Semitransparent materials, with the typical white
and green colors of the used NPs, and which retained the l exibility of the starting BC
membranes were obtained (Figure 2.25). h ese BC/TiO
2
NPs containing nanopapers
showed substantially increased tensile modulus (up to 6 GPa) and reduced elongation
at break (down to 0.83%) than those produced from pure BC. Interestingly, titanium
oxide produces more pronounced ef ects than the vanadium counterpart, but when
