Nope. That would require completely sealing both sides from each other, and having two sets of filters, heaters and everything else on each side. Youd spend so much money on that, it isnt even worth it.
If you want both, just get another 30 gallon. Thatd still be cheaper than spending all that money to divide a tank.
Saltwater tanks are so much different than freshwater. Water quality has to be perfect. If you are just starting a saltwater, I would recommend at least a 20 gallon tank, but the 30 gallon would be even better. Larger volumes of water take longer to make a change, so youd have more time to fix it before it became lethal.