I've been wondering how to properly convert Latin words into names to signify the importance of certain concepts to a person, and met conflicting information online. My default assumption would be to replace the -as ending with -us for a male name, but am unsure if that applies to surnames or already Latin-based nouns.
Voluntas comes from the verb volo. Roman verb-derived names are fairly common. For instance, from valeo we have Valens and Valentinus; from vinco we have Victor and Victorius.
From volo I would derive Volens, Volentinus, or Voluntarius. Of those three, only Voluntarius really seems to derive immediately from the noun form.