There's no need for us to explain here why you would want to separate them, but if you ended up here first then take a look at our article;
What Is? 2.4Ghz and 5Ghz WiFi
There are too many Routers out there to explain every one so we thought the simplest way would to be links to articles for as many as we can.
If your router isn't listed then drop us an email and we will get it added;