I prepared nonmetal doped tio2 without adjusting PH and the band gap energy of tio2 is also reduced.
The first step of sol-gel synthesis is always the hydrolysis of a metal-organic compound (usuaaly M(OR)n type), and the hydrolysis rate obviosuly depends on the pH. The hydroxide precipitate may dissolve in very acidic or in very basic environment. The condensation of the precipitate to metal-oxide may also depend on the pH, concentration, temperature etc. The nature of the R group in M(OR)n is also an important factor influencing the hydrolysis rate.
The first step of sol-gel synthesis is always the hydrolysis of a metal-organic compound (usuaaly M(OR)n type), and the hydrolysis rate obviosuly depends on the pH. The hydroxide precipitate may dissolve in very acidic or in very basic environment. The condensation of the precipitate to metal-oxide may also depend on the pH, concentration, temperature etc. The nature of the R group in M(OR)n is also an important factor influencing the hydrolysis rate.
Moreover, hydroxide forms from the organic precoursors and it is quite obvious that formation of the R(OH)n type compounds strongly depends on the pH of solution.
Have a look on this handbook:
http://books.google.pl/books/about/Sol_Gel_Science.html?id=V2vRvsTaCwMC&redir_esc=y
http://books.google.pl/books?id=V2vRvsTaCwMC&printsec=frontcover&hl=pl&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
"Sol-gel Science" by Brinker.
Depends on your precursor. Guessing that its Ti alkoxide, at lower pH values of 2-4 you will get predominantly anatase, and at higher pH it will be brookite.
Dear Dr. Wojciech Stępniowski,
Thank you very much for your valuable suggestions on pH
Dear Dr. Sridhar Vadahanambi,
whether pH affects the band gap energy of TiO2?
In addition to all of the above mentioned comments to which I perfectly agree, you should also be aware that the pH will seriously influence the doping of your material, aka the chemistry of the dopant.
What kind of elements/materials do you consider as dopants for the TiO2? Fe-oxides? Zr-Oxides?
And what is the major purpose of the doping - the size stabilization, or the influence on the electronic structure?
Enjoy your week-end, best regards, Dirk
Dear Dr.Dirk Luetzenkirchen-Hecht ,
my main aim is to prepare visible light active TiO2 photocatalyst. i just taken TiCl4 as TiO2 precursor and aqueous Na2CO3 as C dopant. so i need to create interband state between VB and CB of TiO2 Which leads to absorb visible light...yeah i mean my major purpose of the doping is to modify the electronic structure of TiO2. but i got reduced band gap energy for c-tio2 (pH is not adjusted and measured) ...I am waiting for your suggestions
@sampath...
Band gap of TiO2 is dependent on its crystallinity., which is dependent on the pH in sol-gel synthesis... so, pH will definitely affect band gap...
Since your aim is photocatalyst, you must aim for anatase-TiO2.. so lower pH will be better.
I agree in principle with Sridhar, but nevertheless, the chemistry of the dopant (here carbon) should be taken into consideration - I have to say that I do not know how sodium carbonate behaves at low pH, and how eventually it may also be affected by the chloride from the precursor. My personal feeling is that it might be a complex interplay between all the present anions and cations that decisively drives the reaction towards the endproducts and their physico - chemical - structural properties...
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