Activated charcoal is a good detoxifying agent thus it is a good teeth whitener too. It changes the pH of the mouth, eliminates bad bacteria, prevents cavities and deodorizes the mouth. It also eliminates stains. While you cannot expect the same results as a professional whitening gel, it does a decent job of adding the sparkle to your set of pearly whites.
Just mix activated charcoal with coconut oil to make a thick paste and apply it on your teeth. Rub the paste on all exposed surfaces of your teeth. Leave it on for 2-3 minutes at least and the split it. Then again brush your teeth using your regular toothpaste. Activated charcoal absorbs tannins and maintains the pH level of your mouth.