HYBRID NANOCOMPOSITES PREPARED BY REDUCTION
OF INCORPORATED COPPER AND NICKEL IONS TO MICROCRYSTALLINE
CELLULOSE
Mikhailidi A. M. (St. Petersburg State University of Industrial Technologies and
Design, St. Petersburg, [email protected]),
Kotelnikova N. E. (Institute of Macromolecular Compounds, Russian Academy of
Sciences, St. Petersburg, [email protected])
Synthetic procedures have been successfully developed to incorporate copper and nickel
nanoparticles of different size and shape into the microcrystalline cellulose (MCC) template.
As a result, MCC  nanoparticle hybrid nanocomposites have been prepared. The content of
copper and nickel in the nanocomposites strongly depended on the experimental procedure,
particularly on the reaction medium and the reducer type. The techniques WAXS, ASAXS,
XANES, XPS, SEM and TEM were applied to illustrate specific features of the metal
nanoparticle incorporation into the cellulose support and to study the structure of the
cellulose-metal nanocomposites.
Polymer nanocomposites which consist of metal nanophase dispersed throughout a
polymer scaffold are one of the major application areas for nanoscale technology which has
been studied in the last decades. This is due to their novel functional material properties,
which differ from both the isolated atoms and the bulk phase.
A large number of physical and chemical methods for the preparation of nanomaterials
has been developed. In this study microcrystalline cellulose (MCC) was used as a porous
template for copper and nickel particles. The properties of MCC have been described
elsewhere [1]. The DPv of MCC was 170. The pore volume, the pore radius and the specific
area were 2.16 cm3/g, 20 µm, and 230 m2/g, respectively.
The synthesis procedure included diffusion of Cu2+ and Ni2+ ions from solutions of their
salts CuSO4 or Cu(CH3COO)2 and NiSO4∙7H2O or Ni(NO3)2∙6H2O into the cellulose matrix
and their reduction with reducers sodium boron hydride NaBH4, hydrazine sulfate
N2H4∙H2SO4 or hydrazine dihydrochloride N2H4∙2HCl and potassium hypophosphite
KH2PO2∙H2O in various media. The media included H2O or ammonium hydrate NH3∙H2O;
sometimes glycerol was added [1, 2]. As a result MCC-Cu and MCC-Ni composites with
various metal contents were prepared.
Experimental conditions, namely the type and the concentration of reducer, the reaction
medium as well as the temperature of ions diffusion into the matrix and that of their reduction
strongly affect the metal content in the bulk MCC-metal composites. The maximum Cu
content in the bulk MCC-Cu samples was 13.0 w. % (NH3·H2O medium, reducer cellulose
itself) and the maximum Ni content in the bulk MCC-Ni samples was 12.8 w. % (NH3·H2O
medium, reducer KH2PO2·H2O) (Tab. 1).
The results obtained with WAXS indicated that the crystalline arrangement of the MCC
template did not change during the formation of nanoparticles, i.e. the nanoparticles were
anchored on the surface or in the amorphous parts of the microfibrils. The oxidation state of
metals was determined from XANES results. Crystalline CuO, Cu2O and Cu0 nanoparticles
were prepared with reducers cellulose itself, NaBH4 and N2H4∙H2SO4, correspondingly.
Crystalline Ni0 and NiO nanoparticles were synthesized with N2H4∙2HCl and NaBH4, whereas
Ni0 nanoparticles in amorphous form were prepared with KH2PO2∙H2O.
1
Table 1. Metal content in the bulk of MCC-metal nanocomposites (elemental analysis)
and on the surface (XPS), and crystallite sizes of metal nanoparticles
XPS results showed that the metal content on the fibre surface in the MCC-metal
samples was much higher than that in the bulk (Tab. 1). The only exception was MCC-Ni
samples prepared with KH2PO2∙H2O. In the XPS spectra of MCC-Cu and MCC-Ni samples
prepared with NaBH4, Cu1+ (in Cu2O) and Ni2+ (in NiO) predominate, respectively. In the
samples prepared with N2H4·H2SO4 Cu0 and Ni0 are mainly distributed on the surface. A good
correlation of these results with the determination of the crystalline phase of metals made with
WAXS and XANES can be seen from the data listed in Tab. 1. These data also show that
metals on the surface are only slightly subjected to further oxidation. Thus, the MCC matrix
protected metal nanoparticles from oxidation not only in the bulk but also on the fibre surface.
SEM micrographs of MCC-Cu and MCC-Ni samples show their µm-scale structure.
The globular spheres mainly aggregated into larger agglomerates on the fibre surface of the
samples. TEM micrographs visualized the particle shape and size distribution in the bulk. The
size of nanoparticles in the bulk was much smaller than that on the surface. Thus, the average
size of Cu0 particles on the surface was 500-600 nm; Ni0 particles ranged 120-380 nm.
However, the average size of copper nanoparticles in the bulk was only 5-25 nm and nickel
nanoparticles was only 5-40 nm [3]. In the bulk and on the surface smaller particles clustered
together to form larger aggregates of particles. The pores in the fibrous cellulose assisted
separate growth of particles inside the fibres so that the particles were not as aggregated as on
the surface of the fibres as seen by SEM.
References
[1] Kotelnikova, N. E., Paakkari, T., Serimaa, R., Wegener, G., Windeisen, E.,
Kotelnikov V.P., Demidov, V.N., Schukarev, A.V. // Macromol. Symp., 138: 175 (1999).
[2] Kotelnikova, N. E., Wegener, G., Paakkari, T., Serimaa, R., Windeisen, E.,
Knoezinger, H., Scheithaet, M., Demidov, V.N., Schukarev, A.V., Gribanov, A.V. // Cellul.
Chem. Technol. 36(5-6): 445 (2002).
[3] Pirkkalainen, K., Vainio, U., Kisko, K., Elbra, T., Kohout, T., Kotelnikova, N.,
Serimaa, R., J. // Appl. Cryst. 40: 489 (2007).