Activated carbon is actually oxidized charcoal. In addition to not being as pure or oxidized as activated carbon, charcoal briquettes generally have other chemicals added to them to bind and make them combust better- e.g. borax, lime, nitrate, etc.
First the charcoal isn't oxidized to have the pores and binding sites for use in aquaria, and second is all the other "stuff"
The pores give activated carbon a massive surface area that allows it to adsorb organic chemicals and some other stuff. Charcoal will also adsorb organics, but it has way less surface area to do so. Don't bother with charcoal, it's totally worthless for our purposes.
I would also recommend you stick with aquarium specific activated carbon. But if you wanted to do some kind of experiment with normal charcoal, at least buy chunk charcoal, not briquettes. But it wouldn't be a very productive experiment. Charcoal is better for searing tuna steaks.
Bulk activated carbon can be found a variety of places online... it is used in drinking water filters a lot.... coal based acid washed is what is typically boxed as "activated carbon" for aquariums... there are a few other varieties, but I haven't used them.
Mostly I don't use the activated carbon in my filter so it doesn't matter to me, but I did use quite a bit once to build a stink-stack for my septic system... i.e. septic tank vent was stinky, so built a vent stack from PVC pipe, screen mesh, and activated carbon... no more stink....
46 gallon bowfront, Dalmatian Mollies, Swordtails, Otos
75 gallon Lake Malawi African Cichlids
3 gallon nano desktop with Betta at the office
Ok, so I make loaded carcoal. I take organic charcoal add worm tea and blood meal and so many other wonderful items one doesn't want splashing in their mouth. It soaks it up making a time release plant food. I was wondering why I couldn't use it in my tanks. It's pure and has nothing added, just good clean charcoal that pulls nutrients out of liquids at a fraction of the price as what's sold at the lfs. So from what I have gathered, it's not that it wouldn't work. It's just that it wouldn't work as well. Right? Oh, give you spent activated charcoal to your plants, they will love you for it.
Activated carbon does not remove most plant fertilizers from the aquarium.
It has some affinity for chelated minerals, so it can remove some chelated iron.
Activated carbon hangs onto most of the things that it adsorbs so well that there is no way in a home setting to get it to give up what it has taken in. It is not a good vehicle to carry fertilizers into the tank.