Under the isothermal and isobaric conditions the surface specific Gibbs free energy plays the dominant role on the reactivity of solid surfaces, and this might be anisotropic in general. Surface Gibbs free energy involves capillary term (Gama Area), which is in deformed solids replaced by  the double inner product of  the surface strain and stress tensors . It turns out that the  sign of the surface stress whether it is compressive or biaxial tension makes difference.

Dear Dr. Tarik Ömer Oğurtani,

Thanks for your answer. In other words, the reactivity as higher as less stable the surface is. Defectivity and surface free energy define surface reactivity. Actually, we talk different languages, but would you be so kind to answer the following question, as a theoretician?

If a face of a crystal has the highest free energy, does it mean that it a priori would have the highest reactivity as well?

Dear Mikhail, you are perfectly right in your comments. the highest free energy faces would be the most reactive since the global free energy, which includes not only the bulk but also surface contribution is always tried to be minimized. and the high surface free energy surfaces and edges and corners would be the first as candidates in the agenda. 

Thanks, Dr. Tarik Ömer Oğurtani

Dear Mikhail,

                                         dealing with the " reactivity "    of a crystal face, it is worth remembering that this term means " the  aptitude  for interacting with a surrounding phase". In other words, for a given crystal, every  hkl  form  shows  its own reactivity, with respect to another h'h'l' form,  because every form shows its own surface profiles .

There is one method (the best one)   to find the most stable surface profiles of a given crystal face. This is the Hartman-Perdok method, published 50 years ago. The faces of a crystal can be classified according to their character:  Flat  (F), Stepped  (S) and Kinked  (K) faces. Their growth mechanism  (reactivity) depends on their character : F faces grow by spiral growth or 2D nucleation (slow growth rate) , while S and K faces grow by diffuse growth (rapid growth rate), being less stable than the F ones.  

Here you will find a paper of mine, in which a deep analysis has been carried out to find the growth behaviour of the different faces of Gypsum.  The same analysis can be performed on anatase (which should be easier), if you will be interested in.

All the best

Dino            

Dear Prof. Dino Aquilano,

Thank you very much for your answer and the paper.

However, I meant fundamental properties of the surfaces like the defectivity and surface free energy. I do believe that the growth mechanisms depend mostly on the parameters of the processes.

Dear Mikhail ıf you are interested in the non equilibrium thermodynamics of surfaces and interfaces, and their morphological evolution kinetics with and without growth under the elastostatic and  electrostatic(electromigration) driving force fields I would recommend  for you two papers cited in   above. These theories were tested by computer simulations by applying variety of problems, which have technological merits. Above our five key papers related to this topic have  been  also selected to appear in The Virtual Journal of Nano Science and Technology published by AIP. Theory for the anisotropic surfaces is treated in following paper. If you don't like to deal with mathematics you might fine them boring somewhat!

Dear Prof. Dino Aquilano,

Thank you very much for the papers and so detailed answer.

I will certainly keep this thread in mind in case I will need so thorough Information about the topic. However, currently, I need just general knowledge about it.

Best regards,

Mikhail

Dear All

Please, Can the incomplete binding between P25 (TiO2) and graphene oxide decrease the photocatalytic activity?

I prepared P25/GO using colloidal blending method and tried GO from different companies and prepared it by myself, but it still P25 has a higher activity than P25/GO.

I used this method of preparation P25/GO 1%:

an aqueous dispersion of graphene oxide (0.01) was dissolved in 30 mL of deionized water.0.99 g TiO2 powder (P25, Degussa) was dispersed in 50 ml deionized water and subsequently added to the graphene oxide solution. The mixture was sonicated for 1.5 h and further stirred for 12 h at room temperature to obtain a homogeneous solution. The product was filtered and

dried in a vacuum at 50 ◦C for 4 h.

I do not know what is the problem. Does P25 not have enough hydroxyl groups or what?

Dear All

Please, Can the incomplete binding between P25 (TiO2) and graphene oxide decrease the photocatalytic activity?

I prepared P25/GO using colloidal blending method and tried GO from different companies and prepared it by myself, but it still P25 has a higher activity than P25/GO.

I used this method of preparation P25/GO 1%:

an aqueous dispersion of graphene oxide (0.01) was dissolved in 30 mL of deionized water.0.99 g TiO2 powder (P25, Degussa) was dispersed in 50 ml deionized water and subsequently added to the graphene oxide solution. The mixture was sonicated for 1.5 h and further stirred for 12 h at room temperature to obtain a homogeneous solution. The product was filtered and

dried in a vacuum at 50 ◦C for 4 h.

I do not know what is the problem. Does P25 not have enough hydroxyl groups or what?

Dear All

Please, Can the incomplete binding between P25 (TiO2) and graphene oxide decrease the photocatalytic activity?

I prepared P25/GO using colloidal blending method and tried GO from different companies and prepared it by myself, but it still P25 has a higher activity than P25/GO.

I used this method of preparation P25/GO 1%:

an aqueous dispersion of graphene oxide (0.01) was dissolved in 30 mL of deionized water.0.99 g TiO2 powder (P25, Degussa) was dispersed in 50 ml deionized water and subsequently added to the graphene oxide solution. The mixture was sonicated for 1.5 h and further stirred for 12 h at room temperature to obtain a homogeneous solution. The product was filtered and

dried in a vacuum at 50 ◦C for 4 h.

I do not know what is the problem. Does P25 not have enough hydroxyl groups or what?

Dear All

Please, Can the incomplete binding between P25 (TiO2) and graphene oxide decrease the photocatalytic activity?

I prepared P25/GO using colloidal blending method and tried GO from different companies and prepared it by myself, but it still P25 has a higher activity than P25/GO.

I used this method of preparation P25/GO 1%:

an aqueous dispersion of graphene oxide (0.01) was dissolved in 30 mL of deionized water.0.99 g TiO2 powder (P25, Degussa) was dispersed in 50 ml deionized water and subsequently added to the graphene oxide solution. The mixture was sonicated for 1.5 h and further stirred for 12 h at room temperature to obtain a homogeneous solution. The product was filtered and

dried in a vacuum at 50 ◦C for 4 h.

I do not know what is the problem. Does P25 not have enough hydroxyl groups or what?

Dear All

Please, Can the incomplete binding between P25 (TiO2) and graphene oxide decrease the photocatalytic activity?

I prepared P25/GO using colloidal blending method and tried GO from different companies and prepared it by myself, but it still P25 has a higher activity than P25/GO.

I used this method of preparation P25/GO 1%:

an aqueous dispersion of graphene oxide (0.01) was dissolved in 30 mL of deionized water.0.99 g TiO2 powder (P25, Degussa) was dispersed in 50 ml deionized water and subsequently added to the graphene oxide solution. The mixture was sonicated for 1.5 h and further stirred for 12 h at room temperature to obtain a homogeneous solution. The product was filtered and

dried in a vacuum at 50 ◦C for 4 h.

I do not know what is the problem. Does P25 not have enough hydroxyl groups or what?