If there is a gap between the end of the synthesis and the exit of the product from the reactor, until the powder is washed and dried, what change in the morphology of the powder occurs?
Dear Zahra Rajabimashhadi thank you for asking this very interesting technical question. Quite often it is crucial in hydrothermal syntheses e.g. of MOFs to cool the reactor to room temperature in a carefully controlled manner (e.g. 10 °C per hour). The cooling rate can greatly influence the morphology and crystallinity of the product. After the reaction mixture has reached room temperature, I assume that there will be no major further changes.
For some important information about the influence of reaction conditions in hydrothermal reactions please have a look at the following relevant article:
Research on the effects of hydrothermal synthesis conditions on the crystal habit of MIL-121
Article Research on the effects of hydrothermal synthesis conditions...
This paper has been posted as public full text on RG and can be freely downloaded as pdf file.
Also please go thopugh this interesting paper:
Temperature and reaction time effects on the structural properties of titanium dioxide nanopowders obtained via the hydrothermal method
https://www.scielo.br/j/bjce/a/nPGYBM4WMhLD4j7mtT8hpdL/?lang=en
(see attached pdf file)
Good luck with your research! 👍
Washing is for extracting the remained precursors or reaction's by-products and etc. Drying is for deleting the adsorbed H2O on the surface of the nanomaterials and I don't think that drying would change material morphologies but if you dry your nanomaterial in high temperatures then calcination may occurs that will change the morphology because of deleting the structural H2O or OH.
Dear Zahra Rajabimashhadi "how can I control the cooling rate?" This just depends on the equipment you have available. If you do the hydrothermal reaction in an oven, chances are that the oven has an outside temperature control. There are also programmed temperature controls, but I don't have any experience with them. In general, when you try a new reaction, no one knows in advance if and how the cooling rate influences your product. In general we can say that slow cooling increases the probability of obtaining a nicely crystalline product. As so often in the chemistry of MOFs, it's a matter of trial and error.
Dear Zahra Rajabimashhadi washing is the process of removing the by-product, surfactant (if added) so that desired synthesized could be found in pure form. Drying time should be ~6-10 hr with high temperature(~300 C depend upon your material)
Dear Zahra I think gap between cool down and washing , only makes particles aglomeration. I don't think so it has effect on morphology.
Because morphology is under effect of surfactants, hydrothermal reaction time and temperuture and things like this, that exist in hydrothermal process.
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