Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Experime ntal Design on Nano Calcite Production
Murat Molva 1 and Ekrem Özdemir 1 *
1 -Izmir, Turkey
Abstract- Based on the carbonation route, nano calcite crystals were produced by Ca(OH) 2 – CO 2 - H 2 O system in the presence of different
organic solvents (methanol, ethanol, hexane, toluene and benzene). A three factor – two level (2 3 ) full factorial methodology was studied to
understand the combined and interaction effects of Ca(OH) 2 amount, organic solvent / water ratio, and the stirring rate on the precipitation
time. Regression model equations were derived as functions of the main three factors to predict the reaction times for the intermediate, lower
or upper values of the factor levels. Effects of these factors on shape were also determined by X-ray diffraction and scanning electron
microscopy.
At room temperature, some organic solvents, such as
hexane, toluene and benzene can not exhibit amphiphilic
property since they are not miscible in water. However, these
organic solvents can exhibit amphiphilic property to some
extent under vigorous stirring. Thus, generally, molecular
structural framework and solvating degree of additive may
affect the initial formation of crystallization by blocking of
growth site and confining the reaction solutions with
organized media and can lead to high localized accumulation
of ionic charge with high spatial density, thereby determining
the size, shape, and organization of the crystal forms.
Therefore, it can be speculated that the amphiphilic property
of organic solvent plays an important role in determining
both polymorph and morphology of CaCO 3 [1,2]. Various
unusual crystal morphologies, such as dendrite-shaped,
flower-like, wheatgrass-like, needle-like, whiskers, doubletaper-like,
cubical, spherical etc. can be obtained depending
on the experimental conditions [1,3].
pH and conductivity curves were obtained by CO2 injection
in the presence of various organic additives (methanol,
ethanol, hexane, toluene and benzene) / water mixtures and
Ca(OH) 2 . Methanol and ethanol were miscible in water. On
the other hand, hexane, toluene and benzene were immiscible
in water but they were used above their solubility limits.
Therefore, mixtures of water and solvents were formed in
order to obtain attraction with the Ca(OH) 2 powders.
Ca(OH) 2 in mixtures was both below the solubility limit (20
mM ) and above the solubility limit (40 mM). The main
intention of the usage of those additives was to modify the
precipitate morphologies and create a database for the
precipitation time with different additives.
The experimental design and optimization study reports the
effects of Ca(OH) 2 amount in slurry, additives (methanol,
ethanol, hexane, toluene, benzene) and stirring rate on
precipitation time. A 2 3 full factorial methodology with three
factors involving two levels of each variable (40 runs with 1
replicates, totally 40 experiments) were carried out to
determine the significant parameters and the interaction
effects. Factors and their levels for screening design of
experiments are given in Table 1.
Tables 2 give the contributions for the effects of three main
factors and their interaction effects. Sign (+) refers to positive
effects of factors on the response (precipitation time), and
sign (-) represents the negative effects of factors on the
precipitation time. If a factor represented by a (+) sign, this
factor increase the precipitation time, if it is represented by a
(-) sign, it decreases the precipitation time. For examp le,
hexane and toluene increase the precipitation time
individually. Factor C (stirring rate) has negative effects on
precipitation time for all sets. A striking example can be
given to understand the interaction effect: when the methanol
and benzene concentrations were increased, the precipitation
time decreased, however, when Ca(OH) 2 amount was
increased together with methanol and hexane, the
precipitation time was seen to decrease. Further details will
be discussed during the presentation.
Table 1. Factors and their levels for screening design of
experiments
Low High Response
Factors
A - Ca(OH) 2 20 mM 40 mM
B - Additives
Ethanol
Methanol
Hexane
Toluene
Benzene
5 % 20 %
C- Stirring 400 rpm 800 rpm
Precipitation
time
(minutes)
Table 2. Sign of standardized effects of the main factors and their
interactions. (A: Ca(OH)2 B: Additive C: Stirring Rate)
0T*Corresponding Author: ekremozdemir@iyte.edu.tr
Main
Interactions
SET Additive A B C AB AC BC ABC
1 Methanol + + - - - + -
2 Ethanol + + - + + - -
3 Hexane - - - + - + -
4 Toluene + - - + - - +
5 Benzene + + - - - - -
[1] Lei, M., Li, P. G., Sun, Z. B. and Tang, W. H. (2006) Effects of
organic additives on the morphology of calcium carbonate particles
in the presence of CTAB. Materials Letters 60, 1261-1264
[2] Dickinson, S. R. and McGrath, K. M. (2004) Aqueous
precipitation of calcium carbonate modified by hydroxyl-containing
compounds. Crystal Growth & Design 4, 1411-1418
[3] Carmona, J. G., Morales, J. G., and Clemente, R. R. (2003).
"Rhombohedral-scalenohedral calcite transition produced by
adjusting the solution electrical conductivity in the system
Ca(OH) 2 -CO 2 -H 2 O." Journal of Colloid and Interface Science,
261(2), 434-44
6th Nanoscience and Nanotechnology Conference, zmir, 2010 300