Not really, you can’t just do random chem lab experiments in the middle of the airport and have no one question you. It’s a lengthy process and it involves freezing. You’d also have to be there before the flight you wanted was scheduled. Which would involve trying to use a boarding pass suspiciously early. That being said, yes, it’s absolutely possible to construct something dangerous in the post-screening area. That’s why it’s called security theater.
Realistically, we’re simply fortunate that terrorists haven’t figured out that bombing security screening logjams would actually be much more effective. We’re so focused on airplanes as a security risk that we fail to take into consideration how easy it is to buy a gun and go hog-wild in any populated space. That’s why the most recent attacks have all been recruiting center shootings.