I got good results over smooth surfaces for photocatalytic reduction of CO2. What is the general perception about such reactions on different surfaces i.e. smooth and/or rough?
Normally, a rough surface will be more photocatalytically acitve compared to smooth surfaces. A rough surface will display a higher surface area, leading to more photocatalytic sites, thus leading to a higher activity.
Actually, in my case, the smooth surface showed better activity. I had other evidences for the smooth surface to have better activity. I just wanted to know if there are some cases already reported somewhere if smooth surface showed better activity. Well.. thank you for such informative answers/suggestions!!
We work with TiO2 films by simple sedimentation method, rough surfaces shown best activity but smooth surface shown best adherence and stability in long operation times. In sputtering films (not published yet), best activity was for smooth surfaces, I think all depends on the scale of the catalyst form type.
Rough surface is better and you can try "thermal choc" technique to make the surface become more "rough"
Best regards
The photocatalyst efficiency depends heavily on the crystal structure of your catalyst. Technically speaking, if both are constituted by the same crystal phases, rough surfaces are expected to perform better, as mentioned by the others, due to (i) higher specific surface area, and (ii) higher porosity. These properties, however, can have a negative effect to the overall efficiency if we consider the possibility of trapping reaction by-products and, thence, blocking the catalytic sites for further reactions and leading to a quicker deactivation. This could be one explanation for your observed results.
Another parameter that cannot be neglected when drawing this comparison is the thickness of the catalytic layer (for immobilised catalysts), or the diameter of the particles (for slurry systems). Were they comparable in your case?
Best regards!
I believe rough surface creates more BET surface so as to improve PCO performance. The only problem I found is that uniform coating is more difficult for rough surface in comparison with smooth surface.
The atomic level structure will also have a large effect as it is widely believed that reactions occur on step edges and defects. Recent work on anatase TiO2 (Setvin et al, Angewandte Chemie Int Ed DOI 10.1002/anie.201309796) seems to show charge becomes trapped at step edges and would therefore be available to drive photo-catalysed reactions. What may look like a smooth surface may in fact have many terraces on it. That said I would agree that in general that rough surfaces would be expected to exhibit the higher activity as the roughness would suggest more defects and step edges AND a larger surface area.
Rough surfaces should present better photocatalytic activity over given the higher surface area and more reaction sites.
The photocatalytic activity of a photocatalyst depends on several factors. So Just smoothness or roughness of the surface is not a comprehensive criterion for judgment about photocatalytic performance.
Is your photocatalyst is an intrinsic semiconductor or a doped semiconductor? How much is the available surface for exposure of UV/Vis. light? What about the sensitizers of your designed photocatalyst?
Although, it is obvious the the surface area of a rough surface is more than the smooth one, but in the case of photocatalysts, the effective surface (i.e. surface could absorbed the light) is more important regarding to your purpose.
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