I have a concern regarding adding too large quantity of ammonia solution for the formation of Hydroxy-apatite. Basically I used calcium nitrate tetra-hydrate and di-ammonium hydrogen phosphate as my initial precursor, where both of them are at 0.5M and made in 100 ml solution. To maintain Ca/P ratio as 1.67, I added 60 ml of di-ammonium hydrogen phosphate to calcium nitrate tetrahdydrate. Now apatite are formed generally for pH>9.5. So what I noticed is that, I used about 400ml of ammonia solution to make pH of 10 and extra 140ml to make it pH of 10.8 or close to 11. My concern is the beaker was smelled full of ammonia solution. Will this large amount of ammonia added will affect the formation of Hydroxy-apatite or not as the pH of ammonium hydroxide measured was 11.4 and of pure ammonia was of 11.75. Also does it matter if we add pure ammonia or ammonium hydroxide, as pH of ammonia is more than ammonium hydroxide?
First of all, the concentration of phosphate source should be 0.3 M instead of 0.5 M, to maintain the ratio of Ca/P = 1.67. After that it is better to mix the precursors solutions including the dilute solution of the base drop by drop to get the desired size and morphology of the apatite at the required pH. For detail information please refer these articles.Article Synthesis and Characterization of Bismuth-Doped Hydroxyapati...
10.1088/2053-1591/acca65Article Facile synthesis of bismuth and iron co-doped hydroxyapatite...
@Dagne. Thank you for your reply. I think you misread it. I made both 0.5 molar but added them in such a way that it will give me 5:3 ratio, if you can resee my question. Also if you understand my logic, pH of ammonia is itself 11.6 and if we keep on adding dropwise, i guess it will take a whole day but still pH will be no more closer to 11. If possible, you can reanswer and help me with my concerns other which are mentioned. Thank you
Hello Anshul, the higher pH during the HAP formation may not affect the Ca/P ratio if you can minimize the effect of CaCO3 formation. If you exposed your solution to the air during the synthesis, that will introduce a considerable amount of CO2 sorption from air by alkaline solution, leading to form CaCO3 in the HAP formation process and a higher Ca/P ratio. You may refer to my published paper: HAP Synthesis and appraisal of a hydroxyapatite/pectin hybrid material for zinc removal from water
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