Which synthesis route did you use?

How do you do the test? Which conditions? Wavelength?

Do you know the particle size and the SSA?

I did some experiments with anatase nanoparticles and the MB amount it has to be really small.

I'm not an expertise but I could observe MB degradation and maybe is just a problem preparing the test (I had many problems until I found the best conditions).

You can send me a private message if you want and we talk about it.

Regards.

It is not common that colour! How you did the synthesis?

Check out this article:

http://www.sciencedirect.com/science/article/pii/S0009261406012425

where they concluded:

"The results indicate that there are two significant problems in the photocatalytic activity test. One is the inadequacy of MB as a probe molecule for semiconductor photocatalysis, since the photoinduced reaction by MB photoabsorption may mislead into believing that a given semiconductor material has visible-light photocatalytic activity."

M. Borlaf: I used precipitation of titanyl sulfate by addition of ammonium hydroxide and EDTA as purification agents since Iron (III) will co-precipitate with TiO2 during the process.

Particle size

Carlos Enrique Daza: I know the colour is really weird. But I have checked purity of my TiO2 through ICP which shows 96% is TiO2 by weight.

Dear Mr. Borhan,

That is a very interesting result you observed! At what temperature did you carry the oxidation of the TiO2? I think the yellow colour is common, at least by comparing the samples we use here in our lab, but after baking the yellow colour is faded. Maybe you have some remaining organics surrounding the TiO2 particles and blocking their active faces.

If you did not use thermal treatment, you could try baking some of your sample at 500 ~ 600 degC (below the crystal phase conversion temperature) for 3 to 5 hours in order to ensure the removal of any possibly organics remaining on the catalyst.

Best of luck! 

XRD pattern show that your anatase is not crystallized enough. Maximum intensity is 150 and it is very low. You should calcined it at 500 C degree. As I thinking, there are some impurity ( organic molecules) on your anatase.

You have 96 % of TiO2 and 4% of impurities mainly Fe (I think so !!!), the impurities are greater in my concept .

Thank you for the details.

I'm going to answer what I think and what I had:

My anatase nanoparticles have a yellow color too, but not too strong... is really weak. The crystal size is around 6-7 nm and present photocatalytic activity, I think this is not the problem. And also I did my tests with the presence of some organics (acetates and isopropanol).

But I know thanks to some coleagues that Fe impurities can inhibit the photocatalytic activity. Do you have UV-VIS spectrum? Maybe you can see the BG and to conclude if you are using the correct irradiation wavelength and if you have Fe or not in your particles.

Regards,

Mario

Bruno Ramos: TQ for participating in this discussion and really appreciate your responses. I calcined at 400-500 C. I am different from your case where after calcinantion process my TiO2 become yellow. Organic traces? can you give an example of it and how to remove it. My process only involve Titanyl sulfate, Ammonium hydroxide, EDTA and distilled water. Sulfate ions have been removed (confirmed by BaCl2 test). Iron (III) oxide was prevented to precipitate by EDTA. Maybe organic traces comes from EDTA. But I have done oxidation at 600 C. I think it sufficient to remove EDTA.

Mr. Borhan,

If you did calcinate at 600 C, there should be no organics left indeed. Did you develop the method yourself or are you following a paper/patent? I would suggest you to review carefully the steps of the synthesis versus a well-establish method and compare with yours, that can be helpful.

This paper (http://link.springer.com/article/10.1163/156856707779238702) provides an interesting discussion of TiO2 synthesis from TiOSO4, identifying some of the effects of the preparation methodology on the photocatalytic activity of the prepared material. Maybe it can provide you some insights on your own methodology.

Best of luck! 

Mr. Bruno: I carefully follow patents and papers. I don't know what are the factors. Can you email the paper because the link is broken. Here my email [email protected]

TQ

Maybe sulfur was doped in TiO2. You can use visible light or use DRS test.

Sulfur change the color of TiO2 to yellow.

Have you measured the BET surface area of your anatase? May be it is low.

May be you are right, but methylene blue is too weak in photocatalytic degradation.

I agree with Mr Borlaf :Do you have UV-VIS spectrum?  

If you have thorough UV-VIS spectrum of  methylene blue (300-800nm) before and after your runs for both (P25 and your Tio2) , we can talk better.

From your pattern of P25 from XRD can you confirm the phases? again is your P25 active and do you have the same phase from your synthesis samples and the P25, have you checked the effect of calcination temperature and time? I suggest you look at this two. Also what is your precursor?

P25 has SSA of about 50 m2/g. Your sample probably much lower. Therefore low activity.

You`d better try photocacalytic activity with  other dye.for example Acid red 5

As per your XRD data, it is clear that your TiO2 is not completely anatase, you need to increase the calcination temperature, you need to have sharp peak corresponds to anatase. Another thing i would like to know that  what is your irradiation source and what is your concentration of dye and how much catalyst you are using for the reaction? check the photocatalytic activity with P-25 under same condition also.

I had faced the yellow TiO2 too, but that sample represented neither photocatalytic activity nor XRD peaks, I found my problem, that was hydrothermal leakage and was obviated after repeating the synthesis procedure carefully ...

As i know the normal color of TiO2 is white ...