How can we relate the increase in the size of the precipitate of semiconductor catalyst (TiO2)after photocatalytic degradation with photocatalysis?
I found a few papers that reported that there is no increase in the size of the catalyst after photocatlytic degradation, another article reported a decrease in the size of the catalyst after photocatalytic degradation while I came across only one article that reported an increase in size of ZnO after photocatalytic degradtion but did not give any reason for the increase in the size.
In my present study, the powder of TiO2 that precipitates after photocatalytic degradation has bigger sizes than its size before the catalytic experiment. I have repeated this several times, and the result remains the same. Is there any better and detailed explanation for this?
Your observation regarding the increase in the size of TiO₂ particles after photocatalysis is quite interesting. It occurs to me that a possible explanation for this phenomenon could be the adsorption of molecules onto the surface of the catalyst.
During photocatalysis, organic pollutants do not always degrade completely into CO₂ and H₂O. In many cases, some intermediate products or by-products of the reaction may remain adsorbed on the TiO₂ surface, potentially leading to an apparent increase in particle size. This occurs due to the formation of a surface layer of adhered molecules which, although not altering the core of the catalyst, can make the particles appear larger.
Additionally, the presence of ions or organic residues could promote the formation of bridges between nearby particles, encouraging aggregation. This effect is more pronounced in certain reaction media, especially if there are changes in pH or in the surface charge of the material.
To confirm whether adsorption is the cause of the size increase, you could perform analyses such as FTIR or XPS to detect changes in the surface composition of TiO₂ after photocatalysis. A TGA (thermogravimetric analysis) could also help determine if there is residual organic material adsorbed, or you could try washing the TiO₂ powder with ethanol or ultrapure water and measuring its size again.
Have you noticed any change in the color of the material or its behavior in suspension after the reaction? That could provide further clues as to whether adsorption is playing a role in this phenomenon.
Francisco Javier Cano Thank you very much for your response. After subjecting the solution containing the dye substrate and Titania to UVc lamp irradiation, we obtained a clear solution. Therefore, the precipitate of the catalyst does not show any change in colour. The changes that we noted were in the FTIR and XPS. There were appearance of C=O and C-H bands that were not present in the spectrum of the titania before degradation.
Thank you once again.
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