If certain mass of gas is made to undergo separately adiabatic and Isothermal expansion to same pressure. Starting from the same initial conditions of temperature and pressure then as compared to that of Isothermal expansion in adiabatic expansion the final

In isothermal expansion, there is no change in the internal energy of the system.

W = - Q

This implies, work is done at the cost of heat supplied and not from the internal energy of the system.

In adiabatic expansion, there is no supply of heat to the system. 

$W=\Delta E$

This implies, work is done at the cost of the internal energy of the system. Therefore, in such a case the final temperature of such a system decreases. Moreover, since work is done at the cost of the internal energy of the system, it is obvious to have a less amount of work. This can be well understood when one try to compare the area under curve for adiabatic and isothermal processes. So it will not be able to expand more.