Can I run conduit containing 120V wires inside larger conduit for 240V wires?
I assume you are in the USA for this answer.
120 volt circuits are not considered “low voltage”. Low voltage means 60 volts (I believe) or lower. 120 volts and 240 volts are the same voltage class and it is perfectly fine to run both of them in the same conduit.
Besides, in the USA, 240 volt circuits are simply two legs of 120 volts in opposite phase. While you have 240 hot-to-hot, it’s still 120 volts hot-to-ground, just like a 120 circuit.
Edit: typo