I have crystalline TiO2 colloids in PH 7. When I added 0.1 M HCL little by little, the colloid became unstable. I know the isoelectric point of Tio2 is about PH 4 to 5.5 but I need TiO2 aqueous solution in PH3!
I hope you are able to reach near the isoelectric point by drop wise addition of HCl( say at pH appxo. 4.5. Now start adding a buffer solution obtained by mixing equal volumes of 0.1 M H3PO4 and 0.1MH2PO4.Go on adding dropwise this buffer solution till the pH reaches appxo.3 [ As the 1st pKa of H3PO4=2.2,so the pH of this buffer solution will in the range of 2.2-2.5. The mixing of two solutions ; one of TiO2 at its isoelectric point with pH=4.5(Say) and the other of the buffer solution with pH=2.5( Say) will make pH around 3 at some concentration of of the mixture of TiO2 and buffer].
The presence H3P4 hardly affects Titanium because Corrosion rate of 0.006 75 inches per year has been recorded by immersion test of titanium plate in very high concentration( 85% ) of H3PO4 at 19−26 C.
Dear Maryam,
I would suspect that reversing the pH to 3 should restore the stability, at least after redispersion. You might think on changing your strategy from drop-wise to 1 aliquot during intense mixing.
Mdm. Maryam Anjidani
For a moment-
Did you try the QUANTITATIVE addition of the buffer ON or BEFORE the isoelectric point ?
Dear Manohar Sehgal, thank you very much for your comments. I am worry about using buffer solution for reaching pH 3 because additional ions may affect on LBL procedure. Beside, I will try the method that you suggested.
About your question, I used HCl for changing of pH. I did not try the quantitative addition of the buffer.
Dear Titus Sobisch
Thank you for your answer. I tried 1 aliquot during intens stirring. The solution remained stable for few hours and then it became gel!
Also,in another attempt, I prepared aqueous solution with pH 3 with deionized water and 0.001 M HCl and then tio2 colloid solution added to that. Again, the TiO2 became gel! and we have unstable solution.
Did not went through in detail but this paper may provide a starting point, it is about preparation of titania at different pH including pH3.
http://www.fis.cinvestav.mx/~smcsyv/supyvac/18_1/SV1814605.pdf
Physical properties of TiO2 prepared by sol-gel under different pH conditions for
photocatalysis
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