Hi all, I've read hundreds of articles on the use of TiO2 as a photocatalyst to degrade Methylene Blue from water. I have also conducted my own work on this particularly via the sol-gel route as well as nano powder slurries and nano powder immobilised in PVA crosslinked with PEG. I've replicated 10 or so methods from various papers, often with completely different results than they had. Actually with failures. The one thing I did not replicate, is when they specify they used a UVC (254nm) light, I did not. I always used an 11W UVA (385nm) light (replacing the bulb often for certainty. In trying to find what my error was, I switched to a UVC light and got the same results as the authors. I then removed the catalyst and also still got the same results, with a UVC light only. Indicating Methylene Blue was being degraded via Photolysis. My results always checked on a Thermo Helios Spectrophotometer with an absorbance peak of 664. My question is, are these research articles, none of whom described running a control without the catalyst, actually achieving photocatalysis in their lab reactors? Or are they being led to believe they've succeeded due to Photolysis? Why is no-one talking about removal of Methylene Blue via 254nm UVC light? My reactor is Quartz glass with the UVC light sitting externally and the reaction occurring under stirring. I have replicated it 8 times with the same results. When I switch to 385nm only, I get no removal of MB. When I install a TiO2 catalyst, I also get no changes. Clearly my catalysts are flawed but I've asked that in another question with no real answers so far.
Troy Warry
You are right and wrong in your research and questions. The decomposition of methylene blue can occur without a catalytic agent. All catalysts reduce the activation energy of a reaction and therefore speed up the reaction. Reviewers of some paid journals may pass up an article with no experience, that is, without a catalyst for their profit. I wrote about such citations in my post.
https://www.researchgate.net/post/Increasing_the_citation_rate_of_articles
Titanium dioxide has a number of allotropic forms: anatase, rutile, mixtures of them and various catalysts. It is necessary to check their structure and particle size. The smaller the nanoparticle size, the better the catalyst.
Thankyou @Yuri Mirgorod, i understand your point. I am specifically referring to catalysts of predominantly Anatase phase TiO2 and the activation of these catalysts with UVC light. I see results comparing wt/vol ratios of TiO2 catalyst to contaminated solutions. Great. But I do feel the data should be shown for the UVC light without the catalyst first and this should form the baseline to determinethe effectiveness of the catalyst in improving the reaction. Thabkyou for sending your post also.
Dear Troy,
although this type of chemistry is not my primary field of experience, I was frequently asked to review papers on photodegradation of MB (and other organics). What I found was that, in most cases, experimental design and experimental setup were described insufficiently (which is very important in photochemistry). Another flaw was the lack of reference experiments (photolysis in absence of a catalyst) in these papers. My personal conclusion is, the results in many published studies are not of great value. I remember that in only one of the manuscript there was a reference to a previous study where such a "blank" experiment was mentioned, and indeed, MB degradation was also observed under irradiation in absence of any titania or other photoactive substances.
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