We are not sure whether our photocatalyst is a perfectly soluble complex or an aggregation of very small nanoparticles, or even something in between like a cluster.
There is neither visible particle suspension no perceivable Tyndall effect. DLS tells us that for sure we don't have nanoparticles bigger than 10 nm.
I've read some papers reporting a control experiment consisting in measuring the rate of the reaction in the presence of mercury in solution. If no inhibition is observed, the absence of nanoparticles can be deduced. Honestly, I don't know how the principle of this control experiment should work.
The ultimate options would be to hope to see something from TEM or to try to get single crystals by evaporation to obtain the crystallogrphic structure. Do you have any other idea?
Andrea Rogolino
You did not write the most important thing whether the supposed suspension is photocatalysis or not. To prove heterogeneity
1. Separate by long standing
2. Separate by centrifugation
3.Add an immiscible solvent and see the distribution of substances in each of them
4. Add larger nanoparticles and view by DLS.
5. Add coagulant chloride or aluminum sulfate and check if there is precipitation
6. Change the pH and see the change in precipitation
You must know the possible nanoparticles of the photocatalyst then you can discuss the problem more specifically.
Everything Yuri Mirgorod makes sense and may work under the right circumstances. But if you have information about an effective catalyst inhibitor maybe you should also try that route, although it may mean quite a bit of work.
I'm not sure how mercury is supposed to work in your case. However, let's suppose (a) you know how much (photo)catalyst you have in your solution, (b) you know a good inhibitor, mercurial or otherwise, and (c) you can make an educated guess about the stoichiometric ratio of the inhibiting reaction (in which the inhibitor reacts - quantitatively, hopefully - with the catalyst and prevents it from acting as a catalyst).
Now you need to test the kinetics of the reaction with increasing amounts of inhibitor and measure the excess reaction rate over the uncatalyzed reaction. If the catalysis is homogeneous - i.e., it's in true dissolved state - there will be a continuous decrease in the excess reaction rate up to the point where the stoichiometric ratio is reached. However, if most of the active sites are on particle surfaces and if the particles are not "too small" (so most catalyst molecules are not at the surface), the amount of inhibitor needed for full inhibition of the catalyst will be much less than predicted by the stoichiometric ratio. As a result, the curve of excess reaction rate vs. inhibitor will show a sharp break. This test may give you useful information even if some of the catalyst is in true dissolved form and the (substantial) rest is in particle form.
This is the really hard question to give any general answer. You need to use several approaches. e.g. as described in our paper. Article Differentiating Homogeneous and Heterogeneous Water Oxidatio...
First, I would advice you to look at the dependence of UV-vis spectrum on the catalyst concentration.
The "Hg" test was developed to check whether Pt-metal is present in solution. Pt-metal is soluble in liquid mercury.
Thank you for the valuable discussion.
Hi Andrea Rogolino
You may run an FTIR analysis of the filtered solution after the photocatalytic test and compare it with the synthesized material. This process may be the simple method to detect this problem as I think from my side.
Regards
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