In the sem analysis of CaCO3 nanaoparticles, the morphology images showed spherical shaped particles but the proposed morphology for these type of nanoparticles is trigonal. I prepared the samples using sonication for 3-4 hours for uniform dispersion. What can justify my results
Dear Atia Sandhu , SEM images shows just the morphology of your samples, so that your CaCO3 nanoparticles appear as spherical particles don´t tell you anything about the crystalline structure of such nanoparticles. To assess the crystalline structure of your NP´s you should use other techniques such as electron diffraction on a TEM. High resolution TEM could provide also information of plane distances and angles from the unit cell. X-ray diffraction would retrieve also information about the crystalline structure of your NP´s.
May be your CaCO3 synthesis yields nanoparticles which show a particular crystal habit, say for instance trigonal prisms, it could happen that their edges and corners get rounded due to sonication, but they would conserve their internal crystalline structure.
Also remember that a crystal habit could or not match with the internal crystalline structure:
https://en.wikipedia.org/wiki/Crystal_habit
Hope it helps.
Dear Atia Sandhu , SEM images shows just the morphology of your samples, so that your CaCO3 nanoparticles appear as spherical particles don´t tell you anything about the crystalline structure of such nanoparticles. To assess the crystalline structure of your NP´s you should use other techniques such as electron diffraction on a TEM. High resolution TEM could provide also information of plane distances and angles from the unit cell. X-ray diffraction would retrieve also information about the crystalline structure of your NP´s.
May be your CaCO3 synthesis yields nanoparticles which show a particular crystal habit, say for instance trigonal prisms, it could happen that their edges and corners get rounded due to sonication, but they would conserve their internal crystalline structure.
Also remember that a crystal habit could or not match with the internal crystalline structure:
https://en.wikipedia.org/wiki/Crystal_habit
Hope it helps.
Dear Atia Sandhu , Manuel Gómez has given a perfect answer.
It is not a surprise that CaCO3 is resulting in spherical morphology. Please see the following paper for an instance.
Article Effects of EDTA and boric acid on the morphology of CaCO3 particles
I think sonication is only one factor which can effect the morphology. The chemicals(agents) used during the sample preparation will also have a significant impact on the morphology.
Additionally, it is also possible that during the sonication the nanoparticles of CaCO3 agglomerate over each other expressing a spherical morphology. It is important to ensure that you are capable of dispersing the nanoparticles properly from each other.
Generally speaking, the shape of NPs after their fabrication properties should respond to a couple of thermodynamic requirements:
1. minimal bulk energy
2. minimal surface energy.
Both of them "must" be satisfied in a way or another.
The first requirement relates to the lattice energy of the specific material considered as an "infinite" bulk material, that is a given crystal structure arises minimising the enegy of each unit cell in the net as that cell were infinitely serrounded by other similar ones.
The second requirement is naturally related to the symmetry breaking of any crystalline material at its surface, which shows up as a reconstruction at the surface which distorts to minimise the surface energy contribution to the total energy. In a process environment where a continuous isotropic and homogeneous source of atpomic/molecular components is provided for the nanoparticle growth, the end shape will naturally tend to a sphere or something similar, while keeping the bulk crystal structure metched to the bulk expected one again for minimising the total energy.
This is the reason why not only your CaCO3 NPs but a plethora of different material nanoparticles (each of them with its own bulk lattice structure, forms spherical nanoparticles when the process environment and parameters assure an isotropic and homogeneous interaction of the growing NP with the incoming atoms or molecules of the same species.
Therefore, a way to preserve a bulk-like shape is to minimise the surface energy of the growing particle without allowing the same surface to reconstruct that much, for example by using capping agents of proper molecular type/weight, or by designing non-linear or highly non-linear fabrication processes where the particle growth is "switched off" suddenly, as is the case of proper laser ablation processes (either in gas or in liquid environment)
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