Civil Engineering Reference
In-Depth Information
particular, inexpensive, disposable, and environmentally friendly cellulose-based sen-
sors made of bacterial cellulose and gold nanoparticles nanocomposites have been real-
ized, exhibiting good sensitivity, low detection limit and fast response toward hydrogen
peroxide and making these materials suitable matrices for enzyme immobilization [91,
92]. Conductive or semi-conductive nanocomposites containing gold nanoparticles are
also very attractive for electronic applications: electrical conductive cellulose i lms have
been prepared by self-assembly showing electrically conducting above a gold loading
of 20 wt% [93].
h e preparation of thermally stable proton-conducting membranes has been also
reported, obtained by the
in-situ
deposition of Pt nanoparticles on bacterial cellulose
membranes, via liquid phase chemical deoxidization method in the presence of the
reducing agent [94]. h e introduction of cobalt nanoparticles in cellulose matrices has
been a topic of interest due to the potential application as magnetic nanocomposites.
h e properties of magnetic Co particles are determined in large extent by size distribu-
tion and particles, that af ect the response of the material when submitted to a magnetic
i eld: specii cally, the structure and morphology of Co nanoparticles synthesized in cel-
lulose matrix and resulting magnetic properties have been analysed and reported [95].
Lightweight porous magnetic aerogels made of nanoi brils of bacterial cellulose have
been compressed into a stif magnetic nanopaper [58]. h e thick cellulose i brils act as
templates for the growth of discrete ferromagnetic cobalt ferrite nanoparticles forming
a dry, lightweight, porous and l exible magnetic aerogel with potential application in
microl uidics devices and as electronic actuators. In the case of cellulose nanocrystals,
due to their unique and well-dei ned physical-chemical properties, cellulose nanocrys-
tals (CNC) have become one of the most promising renewable nanomaterials. Natural
biopolymers in the form of cellulose nanocrystals are shown to have the required char-
acteristics to serve as chemically reactive biotemplates for metallic and semiconductor
nanomaterial synthesis. Silver, gold, copper and platinum, cadmium suli de (CdS), zinc
suli de (ZnS) and lead suli de (PbS) nanoparticles, nanoparticle chains and nanowires
may be synthesized on CNC by exposing metallic precursor salts to a cationic surfac-
tant, cetyltrimethylammonium bromide (CTAB), and a reducing agent (Figure 6.2A ).
h e nanoparticle density and particle size may be controlled by varying the concentra-
tion of CTAB, pH of the salt solution, as well as the reduction time or reaction time
between the reducing agent and the metal precursor. h e results shed light on methods
to stabilize metal nanoparticles, control their nucleation, and highlight the potential
of CNC in metal nanoparticle synthesis [96]. In the case of nano- or microi brillated
cellulose, examples are reported in which hydrogels, aerogels and i lms of nanoi bril-
lated cellulose (NFC) functionalized with metal nanoparticles using silver were pro-
duced, due to the negatively charged surface carboxylate groups on NFC that provide
high binding capability to transition metal species [97]. In another study, native cel-
lulose nanoi bers were functionalized using luminescent metal nanoclusters to form
a novel type of functional nanocellulose/nanocluster composite with l uorescence and
antibacterial activity [63, 87]. Many examples are also available in which the cellulosic
materials are considered as a substrate for ferromagnetic nanoparticles synthesis. In
Li
et al.
[98] , nanocellulose i bers (NCFs) aerogels were prepared from polar alkaline
peroxide mechanical pulp (APMP) using physical ultrasonication method and the pre-
pared NCF network aerogels acted as matrix, preventing the growth and aggregation of
attaching ferromagnetic CoFe
2
O
4
nanoparticles.
