5204 J. Phys. Chem. B, Vol. 108, No. 17, 2004
Song et al.
Cu(DEHP)2/n-heptane solution was the van der Waals inter-
action forces between n-heptane solvent molecules and the alkyl
group chains. However, in Cu(DEHP)2/chloroform solutions,
there were not only the van der Waals interaction forces between
the alkyl group chains and the chloroform molecules, but also
the slightly weak hydrogen-bonding interaction between H-CCl3
and the polar groups (P-O).40 Obviously, this additional
hydrogen bonding might weaken the coupling interaction
between the Cu center and coordination O atoms, resulting in
the release rate of Cu2+ ions faster. In this case, the nucleation
rate of Cu(OH)2 at the interface between the polar solvent/
aqueous phase was relatively faster in comparison to those
between the nonpolar solvent/aqueous. We assumed that it was
helpful for the formation of Cu(OH)2 nanowires when the rate
of connection of copper ions and OH- matched the rate at which
DEHP- was lost. When the loss of DEHP- was faster, it was
not favorable for the formation of Cu(OH)2 nanowires; only
short Cu(OH)2 wiskers were obtained. From the above analysis,
it can be known that solvent polarity may affect the coordination
strength of DEHP- to Cu2+, which can further affect the
morphology of the products.44 Therefore, the choice of solvent
played a key role in synthesizing of Cu(OH)2 nanowires.
Conclusion
In summary, we have successfully synthesized Cu(OH)2
nanowires at the liquid-liquid interface by taking a metallo-
organic precursor in the organic layer and the appropriate
alkaline concentrations in the aqueous layer. These nanowires
are several nanometers in width, and up to 4 µm in length. From
the above study, it can be known that the novel structure of the
Cu(DEHP)2 and its orderly arrangement at the interface played
a significant role in the formation of Cu(OH)2 nanowires.
Furthermore, we have also demonstrated that wirelike and
wiskerlike CuO products can conveniently be obtained by
dehydration of Cu(OH)2 under ambient condition. It is well
known that HDEHP as an extractant can interact with
many metal ions of the aqueous phase to form complexes
(M(DEHP)2). We hope this method can extend to fabricate
similar inorganic materials.
Figure 9. TEM images of the Cu(OH)2 obtained at the static interface
between (a) Cu(DEHP)2 ) 0.05 M in n-hexene and NaOH ) 0.05 M
and (b) Cu(DEHP)2 ) 0.05 M in CHCl3 and NaOH ) 0.05 M.
>OH to OH-. These formed H2O molecules more easily depart
away because the coupling interaction between the formed H2O
and the remainder bridging >O centers is weak. Obviously, the
more basic the medium, the greater the free OH- concentration,
the more the possibility of OH- to capture the H+ linked to the
bridging >O centers per unit time. Therefore, with an increase
of the NaOH concentration, the transformation rate of the Cu-
(OH)2 products to monoclinic CuO becomes faster. In this
experiment, under the condition of the relatively low concentra-
tion of NaOH ) 0.1 M, Cu(OH)2 products could spontaneously
turn to CuO at ambient temperature. This phenomenon might
be related to the small sizes of Cu(OH)2 formed at the static
interface. On the other hand, by using the organic phase as a
buffer to separate Cu2+ and OH-, the explosive reaction can
be made less vigorous, which can facilitate to form Cu(OH)2
having a flexible and loose structure. The Cu(OH)2 products
with loose structure might transform more easily into CuO in
comparison with those large bulk products.
For comparison, we selected other organic solvents in which
to dissolve Cu(DEHP)2. By replacing n-heptane with n-hextane,
n-hexene, and n-octane at the same experiment condition,
respectively, long Cu(OH)2 nanowires were also obtained (See
Figure 9a). However, in chloroform solvent, only short Cu(OH)2
wiskers with length of ca. 200-300 nm were observed (see
Figure 9b). These differences indicated that the organic solvent
properties also affected the sizes and morphology of Cu(OH)2.
For this experimental phenomenon, it might be explained as
follows. There were different solute-solvent interactions in both
cases. As is known, those nonpolar solvents such as n-heptane
did not possess any active functional groups, the interaction in
Acknowledgment. This work was supported by the National
Science Foundation of China (NSFC 20171029).
References and Notes
(1) Hu, J. T.; Odom, T. W.; Lieber, C. M. Acc. Chem. Res. 1999, 32, 435.
(2) Ozin, G. A. AdV. Mater. 1992, 4, 612.
(3) Wu, Y. Y.; Yang, P. D. Chem. Mater. 2000, 12, 605.
(4) Liang, C. H.; Meng, G. W.; Lei, Y.; Phillipp, F.; Zhang, L. D.
AdV. Mater. 2001, 13, 1330.
(5) Morales, A. M.; Lieber, C. M. Science 1998, 279, 208.
(6) Zhang, Y. F.; Tang, Y. H.; Wang, N.; Yu, D. P.; Lee, C. S.; Bello;
Lee, S. T. Appl. Phys. Lett. 1998, 72, 1835.
(7) Yazawa, M.; Koguchi, M.; Muto, A.; Hiruma, K. Appl. Phys. Lett.
1992, 61, 2051.
(8) Choi, Y. C.; Kim, W. S.; Park, Y. S.; Lee, S. M.; Bae, D. J.; Lee,
Y. H.; Park, G. S.; Choi, W. B.; Lee, N. S.; Kim, J. M. AdV. Mater. 2000,
12, 746.
(9) Huang, M. H.; Choudrey, A.; Yang, P. Chem. Commun. 2000, 12,
1063.
(10) Zhang, J. H.; Yang, X. G.; Wang, D. W.; Li, S. D.; Xie, Y.; Xia,
Y. N.; Qian, Y. T. AdV. Mater. 2000, 12, 1348.
(11) Qi. L. M.; Ma, J. M.; Cheng, H. M.; Zhao, Z. G. J. Phys. Chem.
B 1997, 101, 3460.
(12) Murphy, C. J.; Jana, N. R. AdV. Mater. 2002, 14, 80.
(13) Rees, G. D.; Gowing, R. E.; Hammond, S. J.; Robinson, B. H.
Langmuir 1999, 15, 1993.
(14) Li, Y. D.; Liao, H. W.; Ding, Y.; Qian, Y. T.; Li, Y.; Zhou, G. E.
Chem. Mater. 1998, 10, 2301.
(15) Wang, W. Z.; Geng, Y.; Yan, P.; Liu, F. Y.; Xie, Y.; Qian, Y. T.
Inorg. Chem. Commun. 1999, 2, 83.