Not any kind of chemist, but I'm seeing molybdenum disulfide plus (metal) coated on alumina support used as a catalyst, as well as magnetic Al/Fe composite nanoparticles used for same. Usually the metal is something more punk rock, like platinum, cobalt, or ruthenium, but copper is an obvious choice on the poisonous/cheap axis

And this can be tested. Do a huge number of cycles of water treatment. Maybe 1000 or something.

Measure the amount of aluminum in the powder before and after. And/or measure the amount of aluminum added to the water too.

You're going to have to do some testing similar to this anyway since you need to know how long the stuff stays effective. At some point it could wear out and lose its germ-killing powers. Or maybe it doesn't, but you need to know that.