just follow the steps:
$ hdiutil convert -format UDRW -o destination_file.img source_file.iso
$ diskutil list
$ diskutil partitionDisk /dev/disk2 1 "Free Space" "unused" "100%"
$ dd if=destination_file.img.dmg of=/dev/disk2 bs=1m
note: ‘disk2’ is your USB, you may need to use ‘sudo dd’
see more: bootable usb