Generally metal oxide nanoparticles like ZnO, TiO2, SiO2 etc. have surface hydroxyl groups. what could be the reason and is it possible for them to participate in hydrogen bondings?
Dear Vijaykumar,
There are quite a few reasons for that...sure there are more but I will show some of them:
-Acydity conditions introduce -OH surface groups in oxide surfaces. It is usual in TiO2, SiO2, etc.
-Capping agents in the nanoparticles synthesis (capping agent=protecting layer of molecules that stabilize the nanoparticles in solution). If you have used for the synthesis this capping agents, they are absorbed in the nanoparticles surface. In case they are oriented in a perpendicular conformation in the surface and they have OH groups, these OH groups could be exposed outwards in the solid/liquid interface. In this case, you will have to exchange this molecules by others not exposing OH groups to the external surface of the nanoparticles.
-Of course, the could participate in hydrogen bonding, which may be the cause to agglomarate the nanoparticles in solution (instable dispersion of particles) going to the bottom of the flask. Depend on your interest this may be a drawback of not.
I hope this comment can help you. Good luck.
Cheers
Hi
Yes, its possible to have hydrogen bonding between surface hydroxyl groups :) but these hydoxyl groups can be removed by heating the oxides at higher temperature , where dehydroxylatio of -OH group may occur.
These are mainly formed due to coordination unsaturation of metal during the synthesis :)
regards
vijay
have a look at
http://dx.doi.org/10.1021/jp0349740
http://dx.doi.org/10.1002/chem.200400351
Dear Vijaykumar,
There are quite a few reasons for that...sure there are more but I will show some of them:
-Acydity conditions introduce -OH surface groups in oxide surfaces. It is usual in TiO2, SiO2, etc.
-Capping agents in the nanoparticles synthesis (capping agent=protecting layer of molecules that stabilize the nanoparticles in solution). If you have used for the synthesis this capping agents, they are absorbed in the nanoparticles surface. In case they are oriented in a perpendicular conformation in the surface and they have OH groups, these OH groups could be exposed outwards in the solid/liquid interface. In this case, you will have to exchange this molecules by others not exposing OH groups to the external surface of the nanoparticles.
-Of course, the could participate in hydrogen bonding, which may be the cause to agglomarate the nanoparticles in solution (instable dispersion of particles) going to the bottom of the flask. Depend on your interest this may be a drawback of not.
I hope this comment can help you. Good luck.
Cheers
It is of no surprise that the surface of metal oxides (MeO) "is covered" by surface
Me-OH groups. These groups are frequently use to modify the properties of the nanoparticles made of Metal Oxides. For Example - the concentration of SiOH groups on the surface of silice is about 4-groups per 100 square Angstroms of surface and could be sligtly increased by treatment of SiO2 by saturated water vapor in autoclave.
The same is true for TiO2 and ZnO nanoparticles. All the above information is well described in the literature and is knonw for more than 30 years. See for example the early works of J.L. Koenig and H. Ishida od CWRU.
Regards, Leonid
Dear Dr. Marakatti
Thanks for your favorable reply to that question. Please, I want to know the temperature that can cause dehydroxylation of -OH group.
Regards,
on a slightly relevant issue. My material is In2O3. I would like to generate dense -OH group on the surface of the oxide. I saw people use Oxygen plasma or Pirahan etch or a mixture of very aggressive oxidizing agents. I cant put my samples through those processes as I also have SU8 (a photo resist layer-polymer). Could you please point me to some liturature or give me some advise as to how a could achieve a layer of -OH group on the surface of the oxide in a non-destructive way to my sample ( I was thinking of just soaking in some water, buffer or very mild acid solution). Thank you very much in advance.
Kind regards
Thuy
i saw a paper said that -OH of TiO2 can be removed at temperature above 773K.
On the similar note, How can I generate the -OH group on the surface of boron oxide nanoparticles so that I can design the new surface engineering of the nano particles?
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