I was trying to prepare a carbonate intercalated LDH by hydrothermal method. I followed the standard procedure, with M2+ and M3+ with Na2CO3 in required amount stirring at 60 0C with slow addition of NaOH untill pH was above 10. Then hydrothermal treatment at 120 0C for 12 h. However, the XRD result showed no peak untill around 300, suggesting formation of hydroxide not layered double hydroxide. I think LDH showed characteristic 003 and 006 plane around 11 and 230 2 theta. I am a bit confused where i am doing something wrong. Can anyone suggest any specific reason. I have even repeated the process two time.
The removal of the peak should not come from your instrument, it could be preferred orientation, but this should affect all of your peaks. try measuring in a transmission geometry and see if you get the same result or even better if you have a Gandolfi camera (this completely removes any preferred orientation)
other the that it could be destructive interference from the intercalation, but carbonate and hydroxide should not be able to do that on their own.
hope it helps. it is a diffractogram and not a diffraction spectrum.
Best Regards
Which M2+/M3+ metals are you using exactly for your LDH synthesis? Because 'a single standard procedure’ for the synthesis all carbonate exchanged LDHs does not exist, as a successful LDH synthesis by coprecipitation requires both the M2+ and M3+ cation to precipitate within defined limits. The latter obviously depends on the precipitation chemistry of the specific cations you use. You could check the elemental composition of your material, and perhaps also an XRD characterization of the precipitate you obtain right before the hydrothermal treatment can provide some more insight on how to optimize your synthesis.
Maarten Everaert Thank you for your response. I used Zn2+ and Fe3+ in 3:1 ratio (1.5: 0.75 mM) with 10 times the Na2CO3 (22.5 mM) concentration. Would analysis of precipitate before hydrothermal treatment give any important information? From literature it seems like the main role of hydrothermal teatment is to increase crystalline nature of the material. I have also seen report where, LDH was formed without hydrothermal treatment.
Osama Rahil Shaltami Thank you for your response. We don't have XRD in our institute and send the sample outside for analysis. Therefore i don't have any practical knowledge of handling XRD instrument. Can you guide me towards some paper or book where i can get more information regarding "measurement in transmission geometry" or "Gandolfi camera" etc? Thank you again
Gautam Kumar Sarma What I mean is that it could be helpful to first focus on the material you obtain right after coprecipiation (and before hydrothermal treatment): this material should be a phase pure LDH, of which you can increase its crystallinity later on with a hydrothermal treatment. If it is not a phase pure LDH, the hydrothermal treatment will probably ripen phase impurities (e.g. iron oxyhydroxides) at the expense of a minor LDH phase.
My best guess to improve your setup would be to more accurately control your synthesis pH. Generally, synthesis methods with a constant pH during precipitation give purer LDH phases compared to methods with precipitation over a pH range (e.g. your method, urea method), as shown by Pushparaj et al. in ‘How the Method of Synthesis Governs the Local and Global Structure of Zinc Aluminum Layered Double Hydroxides’. For Zn/Fe precipitation for example, increasing the pH decreases the solubility of Fe, while the solubility of Zn only increases to a certain value and then decreases again due the amphoteric character of Zn. Therefore you could end up with a precipitate with a too low Zn/Fe ratio, and thus, a precipitate with major phase impurities (which will be further ripened during hydrothermal treatment). A pH stat system would be preferred to control the synthesis pH. Alternatively you could play around with other synthesis parameters, such as the volume of your synthesis mixture, to minimize pH fluctuation.
And indeed, as Luofu Min mentioned, it would definitely be useful to identify the phases you obtained using your XRD pattern.
Maarten Everaert i think that ur explanation is very helpfull , but my question about the value of pH , increasing the pH value from??? to??
Maarten Everaert , pls explain "For Zn/Fe precipitation for example, increasing the pH decreases the solubility of Fe " your explanation based on which theory???
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