The filter-based air purifier filters the particulate matter and pollutants to clean the room air physically. On the other hand, air sterilizer does not have filters. The air sterilizer generates active oxygen or ionic substances with high-voltage discharge, UV, and plasma to reduce the airborne bacteria or odor-causing substances chemically. 

The biggest difference between the air purifier and air sterilizer is the filter. The air sterilizer does not guarantee removal of particulate matters.