Why do you want to use the ICL7667? While it is probably great when it is the right part for a particular job, in my opinion, it is NOT the right part for a 0-24V buck converter.
Your prof is correct in saying that you can use it if you put he mosfet in the ground leg, but that will add unnecessary complexity to the rest of the design. Starting with the fact that the output voltage will not be at the same ground potential as the input. And, while that may not be important in some applications, it will make the voltage feedback loop more complicated.