Foreign institutional investors (FIIs) were net buyers of Rs 459 crore on September 15, Friday according to data released by Sebi today.While FIIs made gross purchases of Rs 1597.30 crore, gross sales totalled Rs 1138.30 crore.Mutual funds (MFs) were net sellers of Rs 98.84 crore on Friday. MFs made purchases of Rs 264.62 crore and sales of Rs 363.46 crore.