I think the answer is yes but there are a lot of reasons. Assuming identical morphological properties (primary and secundary particle size, shape and porosity) anatase materials typically showed higher activity than rutile/brookite. Of course such comparison is somewhat ideal and not easy to carry out with real samples. The reasons for high activity are unclear but nice works mentioned a series of issues: very small QSE (bohr radii is very low leading to negligible band gap effects for samples above 4 nm), highly active surfaces (001) for specific shapes, less dense paking and higher charge mobility and possibly, larger control of defects (lower recombination rates). There is also discussions about the effects of polydispersity in photocatalytic activity as a induced effect of defect distribution.

Dear Sridhar

Anatase phase forms at relatively low temperature up to ~450C, but Rutile usually forms at ~750C. So Anatase phase is more hydophilic in nature than Rutile. so greater percentage of Anatase phase is i think more favorable for photocatalysis.

Yes, anatase should be more active. If I remember well it's because the bandgap of anatase is a little bit smaller so a larger part of the solar spectrum could be captured.

I think the answer is yes but there are a lot of reasons. Assuming identical morphological properties (primary and secundary particle size, shape and porosity) anatase materials typically showed higher activity than rutile/brookite. Of course such comparison is somewhat ideal and not easy to carry out with real samples. The reasons for high activity are unclear but nice works mentioned a series of issues: very small QSE (bohr radii is very low leading to negligible band gap effects for samples above 4 nm), highly active surfaces (001) for specific shapes, less dense paking and higher charge mobility and possibly, larger control of defects (lower recombination rates). There is also discussions about the effects of polydispersity in photocatalytic activity as a induced effect of defect distribution.

The rutil bandgap smaller (3 eV) than for anatase (3.2 eV), but maybe the recombination of electron-hole pairs is slower in anatase maybe the above mentioned resons. That si why is it better in photocatalysis.

Dear Dr.Marcos Fernández-García,

Thank you very much for your valuable answer regarding anatase phase.Most of the papers reported that anatase phase is more active than other phases. But some paper reported that the appropriate ratio of anatase and rutile enhances the photocatalytic efficiency than the anatase phase alone. can you help me out my doubt?

To Mr. Sampath

I think you are right. The activity of a highly active phase (like anatase) can be further improved while in contact with another with adequate band properties. The latter is a function of a lot of physical variables and, of course, additional variables of the composite materials (like the surface composition) need to be considered for high activity. I send you the link for a review which may help to interpret the general situation:

https://www.researchgate.net/publication/51820731_Advanced_nanoarchitectures_for_solar_photocatalytic_applications?ev=prf_pub

Article Advanced Nanoarchitectures for Solar Photocatalytic Applications

Dear Mr Sampath,

There is evidence that a mixture of rutile and anatse gives the best results. from our work this appears to be due to the formation of junctions between the different crystallites causing separation of charges and probably reducing recombination. Check out the attached papers.

Dear Mr. Sampath,

I have attached another paper which might interest you.

Dear David Cameron,

Thank you very much for sending me the paper....The combination of anatase and rutile phases of TiO2 suppresses the recombination rate due to the different electronic structure( I mean synergistic effect). If that is the reason , then, why is 50% anatase and 50% rutile phase combination not showing higher photocatalytic activitiy? .Whatever may be the particle shape , size, volume and defect level......~70:30 ratio only shows the enhancement.

Good question! I don't have the answer to that.

Interesting remarks. In this paper they argue rutile acts as a small(er) band gap antenna, while anatase is more active so it is beneficial to have more anatase.

Dr. Fernández-García lists some very important points which could explain why 'anatase is more active'. In addition, the most active material is determined by your light source: if solar energy capture is the ultimate goal, the wide anatase band gap can be a major drawback.

Article Explaining the Enhanced Photocatalytic Activity of Degussa P...

To Mr. Sampath,

thank you for your nice email. The review tries to summarize the current knowledge in TiO2 (and other systems) but of course this is a big and yet open field which will see a lot of new contributions which will clarify our understanding of the photocatalysis field.

as far as I know you can get enhanced photocatalytic properties using different ratios of anatase-rutile, not just 70-30. as some people already mentioned above you may improve charge separation when you have a mixture of the two and EPR studies (to me that the most reasonable and scientific explanation provided in literature on this matter) indeed confirm electrons can move from one phase to the other one, leaving the hole behind (hence you get separation and better photoactivity). good luck with your experiments!

Dear Dr.Domenico Regonini,

Thank you very much for your useful information.

Hello Mr Sampath,

I hope this article might help you:

http://www.nature.com/nmat/journal/v12/n9/full/nmat3697.html

Regards