Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Precipitation and characterizat ion of nano-zinc oxi de and laye red zinc hydroxyc hloride from aqueous
zinc chloride solutions
Seyed Behnam Ghaffari *, Javad Moghaddam
1 Faculty of Materials Engineering, Sahand University of Technology, Sahand New Town, Tabriz, Iran
1
2
Abstract-Various shapes of wurtzite-type ZnO nanoparticles were selectively produced in a simple aqueous system prepared by mixing ZnCl 2
and MgO and Ca(OH) 2 as neutralizing agents at 95 °C for one hour. Layered zinc hydroxychloride (ZHC) synthesized when magnesium oxide
was used and the elipsoidal particles of zinc oxide were obtained after calcination of the ZHC at 520 °C for 4 hours while nanorods were grown
by destabilization ZHC with NaOH. Nanorods directly were obtained by neutralization with Ca(OH) 2 (lime) when the pH static neutralizing
approach was selected while elipsoidal nano particles were prepared when aqueous zinc chloride solution was dropped into lime solution. The
techniques of XRD, TGA–DTA, FT-IR, BET and FESEM were applied for the characterization of the produced materials.
Zinc oxide is a wide bandgap semiconductor material with
many promising properties for blue/UV optoelectronics,
transparent electronics, spintronic devices and sensor
applications [1]. Depending on the adopted synthesis method,
zinc oxide nanocrystals would show various morphologies
under different formation mechanisms [2]. The size and
morphology are important parameters to determine the
physical and physicochemical properties of ZnO crystals [3].
Layered zinc hydroxychloride (Zn 5 (OH) 8 Cl 2 -H 2 O:ZHC),
which is one of the basic zinc salts has received attention in
applications such as catalyst and adsorbent. [4]
In this paper, we selectively produced nanoparticles and
nanorods of ZnO and layered zinc hydroxychloride crystals by
homogeneous precipitation method using a simple mixing
technique of Zncl2 and MgO or Ca(OH) 2 as neutralizing
agents. This work also would provide fundamental
information for shape control of nanoparticles prepared
through the crystal growth in aqueous solutions. Final
products characterized by means of powder X-ray diffraction
(XRD) and field-emission scanning electron microscope
(FESEM), The Brunauer-Emmett-Teller (BET) and fourier
transform infrared spectra (FTIR).
We first studied the condition of precipitation of zinc oxide
and ZHC from aqueous zinc chloride solutions. Neutralization
was carried out by slowly adding a certain amount of
magnesium oxide till the mole ratio of Zn/Mg=3.0 was
reached. The addition of MgO must be substoichiometric to
obtaine zinc oxide with high quality [5]. Zinc oxide is stable
in the pH range of 8-11. Neutralization with MgO can reach a
maximum pH of 8, which decrease as temperature increases to
an extent that only pH 6 can be reached at 85°C and zinc
hydroxychloride is stable under this situation [5]. Zinc
hydroxychlorides are destabilized through the action of dilute
chloride solution at high pH and temperature to convert the
zinc hydroxychlorides to zinc oxide. The pH was adjusted
using NaOH and lime. After fixing the pH of 11, solid
remained in contact with the solution for one hour, to obtain
zinc oxide (route 1). We found that the ZHC also can be
converted to zinc oxide by calcination. The ZHC was calsined
in air at 520 °C for four hours, based on it
' s decomposition
temperature obtained from TGA-DTA analysis. By using
Ca(OH) 2 as neutralizing agent, a direct neutralization was
performed [5]. The addition of lime was stoichiometric to the
concentration of zinc present in the aqueous zinc chloride
solution. In route 2 , the pH static neutralizing approach (with
lime) was selected and in route 3, aqueous zinc chloride
solution was dropped into lime solution.
Figure 1. FESEM images of (a) ZHC (b) zinc oxide prepared through
route 1 (c) route 2 and (d) route 3.
The crystalline ZnO and ZHC materials produced were
analyzed and characterized with a variety of techniques. The
XRD patterns, were verified the formation of wurtzite-type
ZnO. The FESEM images show that ZnO nanorods with a low
aspect ratio can obtain with destabilization the ZHC (route 1).
ZnO nanorods with a high aspect ratio were obtained at pH 11
through neutralization with lime (route 2) while ellipsoidal
nanoparticles obtained in route 3. The morphology of ZnO
particles would be governed by the balance of the nucleation
and crystal growth determined by the reaction route. The
FESEM images of ZnO obtained after calcinations shows
spherical particles. The nanostructured character of the
produced zinc oxide and ZHC was verified by employing the
Williamson-Hall method in XRD patterns, FESEM
examination and BET measurements.
In summary, nanosized ZnO powders were successfully
obtained by neutralization of aqueous ZnCl 2 solutions with
Ca(OH) 2 .ZnO also is formed on destabilization and
calcination of the ZHC after neutralization with MgO. Various
shapes of wurtzite-type ZnO crystals including nanomeric
ellipsoidals, nanorods were prepared. The morphology of ZnO
particles would be governed by the balance of the nucleation
and crystal growth determined by the reaction route.
*Correspondign author: behnamghaffari@yahoo.com
[1] Chennupati. Jagadish, Stephen. Pearton. 2006.
[2] Yang Liu, Jian-er Zhoua, Andre Larbot, Michel Persin., Journal
of Materials Processing Technology, 189, 379–383, 2007.
[3] Tetsuo Kawano, Hiroaki Imai, Colloids and Surfaces A,
Physicochem. Eng, Aspects 319, 130–135, 2008.
[4] Hidekazu Tanaka, Akiko Fujiok, , M aterials Research Bulletin 45,
46–51, 2010.
[5] Allen, US Patent 6,395,242. 2002.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 322