{about a 0-2V input, 0-24V output amplifier]
Probably, that's because your op amp has poor pull-down drive. You can put a (for instance) two-transistor current mirror to draw
1 mA down, which will probably linearize the output down to about 0.3V or lessWarning: bad ASCII art follows
(+24V) | R1 |\ | | \ | | >--+------ output +---+ | / | | / |/ / +--|-------------------| \ \ V V (GND)-+-------------------+
(obviously, R1 is 24k ohms, and preferably a dual NPN transistor)