What is/are the best air purifiers for removing cigarette smoke in Singapore?

I doubt you'll get one that will have much effect on cigarette smoke in Singapore - they're just not powerful enough.

The one comes with Negative Ions generator and pick the powerful one, Honeywell brand, or running many such devices at the same time.

Install many powerful suction fans to suck out the harmful cigarette smoke is the best way.

Telling him to smoke outside and let him watching the lung cancer image and video can be found from youtube, that smoking causes painful lung cancer, no only happen to him but to all the family member whom live in the same house !!

BEST WAY, MOVE AWAY FROM THIS HOME !

The very best device is a Smokeeter / Austin Air Cleaner,

but even that won't remove it all.

You really need to get away from the source ---

or the source needs to get away from you.