I wouldn’t look for anything that absorbs… I’m not even sure what kind of chemicals you are storing in the garage. Two sheets of drywall, drywall tape, compound, 4 - 2x4 studs, some fiberglass insulation (with paper vapor barrier which should be facing garage side drywall sheet), screws, primer and paint… probably under $100 for all that material. If you can do that kind of a job by yourself you can probably have it finished in less than a day worth of work.
If you’d like to keep the door operational; install adjustable threshold so it will close and seal the gap and apply new weather stripping around the door jamb.
If your door opens into the house / its surface is flush with the living space wall surface, to minimize the cost; you could just remove the door frame trim from the garage’s side (if there’s any), secure one 2x4 in the middle of the door frame, apply fiberglass insulation in both cavities created by the 2x4, pre-cut and secure with screws single sheet of drywall (garage side only / at least 1/2 “ thick / drive screws into the 2x4 and to the door frame), tape and seal the seams using compound, you can also reapply removed trim if possible, prime and paint.