I am synthesizing ZnO nanostructures via co-precipitation technique using ZnCl2. Please explain me the possible effects of drop wise addition of NaOH solution into ZnCl2 solution on morphology, particle size etc of obtained sample? What will be the effects if NaOH solution is added directly (not drop wise) ?
The drop-wise addition is always the best way of mixing the two reactants. Direct mixing in one portion may cause dramatic change in a short period of time, leading to insufficient conversion of ZnCl2. Drop-wise mixing produces a homogeneous reaction environment and on the other hand if one add directly the NaOH solution to the ZnCl2 solution, it creates different reaction rate at different part of the mixture. So, direct mixing may affect the growth of the particles also.
The drop-wise addition is always the best way of mixing the two reactants. Direct mixing in one portion may cause dramatic change in a short period of time, leading to insufficient conversion of ZnCl2. Drop-wise mixing produces a homogeneous reaction environment and on the other hand if one add directly the NaOH solution to the ZnCl2 solution, it creates different reaction rate at different part of the mixture. So, direct mixing may affect the growth of the particles also.
Direct addition may lead to a very high nucleation rate on the initial stage and because a large amount of Zn species are consumed in the nucleation stage, further crystal growth is suppressed. I think maybe your nanoparticles will not have a uniform shape and size. By increasing the time of reaction in hydrothermal condition, you can have a better product.
this article may be helpful:
http://link.springer.com/article/10.1007%2Fs13738-012-0095-2
Performing injection method is very effective method to produce very small well dispersed and crystalline ZnO nanopartcles at room temperature. Compare to the explaining contribution.
Article Synthesis and testing of ZnO nanoparticles for photo-initiat...
Direct addition (at higher temperatures) may result in ZnO nanorod clusters.. and if you use a flat and active substrate like graphene or GO.. you may get ZnO nano flowers.
A huge number of publications can be found concering structures mentioned by Sridhar Vadahanambi. An introduction in such structures may be found in the work of Aleksandra B. Djurisic.
http://onlinelibrary.wiley.com/doi/10.1002/smll.200600134/abstract
A huge number of publications can be found concering structures mentioned by Sridhar Vadahanambi. An introduction in such structures may be found in the work of Aleksandra B. Djurisic.
http://onlinelibrary.wiley.com/doi/10.1002/smll.200600134/abstract
You can prepare Zinc oxide by adding directly of NaOH solution into ZnCl2 solution for synthesizing ZnO nanostructures, but not in excess.. Zn2+ is known to form hexa-aqua ions at high water concentrations and tetra-aqua ions at low concentrations of water. If excess sodium hydroxide is added, the precipitate of zinc hydroxide will dissolve, forming a colorless solution of zinc hydroxide complex, Zn(OH)42−.
You can prepare Zinc oxide by adding directly of NaOH solution into ZnCl2 solution for synthesizing ZnO nanostructures, but not in excess.. Zn2+ is known to form hexa-aqua ions at high water concentrations and tetra-aqua ions at low concentrations of water. If excess sodium hydroxide is added, the precipitate of zinc hydroxide will dissolve, forming a colorless solution of zinc hydroxide complex, Zn(OH)42−.
As mentioned within the publication, see above, for nanoparticle preparation MeOH or EtOH is the solvent of choice leading to phase-pure ZnO nanoparticles which can be modified or grown after the separation. If using ZnCl2 in water simonkolleite will be formed and the particels may be large. But everything is dependent from the application which is desired (e.g. for large concentration the acid basic properties of ZnO influence the dispersion/solvent (viscosity etc.))
As mentioned within the publication, see above, for nanoparticle preparation MeOH or EtOH is the solvent of choice leading to phase-pure ZnO nanoparticles which can be modified or grown after the separation. If using ZnCl2 in water simonkolleite will be formed and the particels may be large. But everything is dependent from the application which is desired (e.g. for large concentration the acid basic properties of ZnO influence the dispersion/solvent (viscosity etc.))
@Sir Michael Schmitt ... Thank you so much for detailed guidance.
In addition , You must be more precise about reaction time as it also affects the growth and morphology of the particles. if your reaction time would extend to < 40 mins, then you can get 3Dimensional nano structures...
By performing the reaction without water restriction of the size is given by the non-solubility of the products. No Oswald ripening "only" aggregation. (For ZnO)
By performing the reaction without water restriction of the size is given by the non-solubility of the products. No Oswald ripening "only" aggregation. (For ZnO)
Direct addition leads to nonuniform and larger particle size while dropwise addition leads to uniform particles and of smaller size.
Attached you may find an example of uniform particles synthesised by injection method (not dropwise, reaction time 12 h (or more precisely less than 1 min plus 12 h stirring) and modification with levulinic acid).
As a matter of fact if you add NaOH directly the nanoparticles of ZnO formed would have large size because rapid precipitation takes place in a small volume portion of the reacting mixture converting all Zn+2 to Zn(OH)2. If you add NaOH dropwise it will form small nanoparticles as a small portion of Zn+2 ions will be available for conversion. Thus small particles are formed.
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