7 Hour Layover in Beijing Capital airport

We will be arriving on a domestic flight at Terminal 1 at 14:35 and out internaitonal flight out of China is at 22:00 from Terminal 3 so we have a total of 7 hours between flights. We will have already seen the major sights of BJ. Can you recommend something to do in this time? I thought of going into the city for some shopping, what would be the best way to do this and where would be the best place to shopping this time for clothes etc?