According to your knowledge, could you please suggest a liquid-phase chemical treatment to be carried out on pure TiO2 nanopowders, whose purpose is favoring their aggregation through the setup of chemical bonds between nanoparticle surfaces (possibly, avoid having at process end "complex chemicals" among nanoparticles). Thank you.
Actually TiO2 nanoparticles tend to aggregate without any help. The surface of TiO2 is plenty with hydroxyl groups that form stable hydrogen bonds in aqueous solution. The result is the formation of agglomerated nanoparticles with sizes of hundreds of nm.
In the other hand, if you prefer a more controlled agglomeration you have rather to control the solution pH or use a mixture of solvents. Usually the isoelectric point of TiO2 lies around pH 5 (in fact depends on the surface characteristics of the TiO2 and, indirectly, on the synthesis process), so at that value the particles quickly aggregate. At higher pH values, say pH 7-8, the aggregation will be slower and maybe you can control the final size of TiO2. Anyhow, this process will be difficult to control.
It seems better to otherwise use a mixture of aqueous solvents to control the precipitation of TiO2. Mixing H2O and EtOH would help to prevent agglomeration to some extent. Other combinations may include isopropanol or related primary alcohols.
Hello Prof. Barborini. I think firstly you may need to check if the "nanopowders" are actually TiO2 spherulites. Sometimes TiO2 will grow into spheres,specifically at low supersaturations. The nanoparticles in one spherulites actually develop from one core. The morphology sometimes looks like flower. If there are spherulites, then separating them will not be so easy, because all the nanoparticles in one spherulite are tightly bonded together. If the nanopowders just simply aggregate, then maybe you can try Chondroitin Sulfate (ChS). This organics could strongly bind to positive ions, and eliminate the aggregation. You could try to add the TiO2 in 0.5g/l ChS solution and sonificate. Hope it helps...
Thank you Yifei for comment. However I do not want eliminate the aggregation between nanoparticles, instead I would like to promote it.
Sorry for my mistake...Because usually people would like to prevent the aggregation. May I know why do you need the TiO2 nanoparticles in aggregation? If you just need to have a bulk TiO2 structure composed by nano building-blocks, may be you could consider to grow some TiO2 spherulites. The growth of TiO2 spherulites on substrate will lead to TiO2 nanoarrays, which are widely reported in recent years. The nanoarray could be quite dense and thick, like a bulk material. However, the TiO2 spherulites are usually rutile. If you need only anatase, maybe the best way is to make them smaller. Actually anatase with size of about 3 nm has been reported, and these particles will certainly be easier to aggregate~~~~
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