There is a possibility to come to Mainz from Frankfurt International airport (FRA) via train.
The regional train S8 leaves two times per hour, usually at :29 and :59 from FRA "Regionalbahnhof" (regional train station), platform "Regio 3".
You can also use the more expensive travel via ICE.
Exit in any case at "Mainz Hauptbahnhof" (Mainz main station).
Tickets have to be bought either on the ticketvending machine located at the platform or at the ticket desk of Deutsche Bahn.
You might also take a look at the website of FRA.
At Mainz Hauptbahnhof, there are several possibilities to come to the University via bus.
If there are any further questions, please do not hesitate to ask.