How to store binary data (in the form of 0s and 1s) as a set of 8 0s and 1s as 1 byte each into a file

I have a string of 0s and 1s. I want to take groups of 8 of these digits and assume them as a single byte and write it into a file to save as much space as possible. How should I encode this so that each group of binary string takes exactly 1 byte

I have tried using utf-8 and utf-16 ASCII but I am not able to successfully convert string to encoded characters