Here’s an alternative method for adapting monochrome images in Photoshop with adjustment layers
If the Black & White adjustment layer isn’t a part of your inventory, another good method for removing colour is using the Channel Mixer adjustment (Layer>New Adjustment Layer>Channel Mixer).
Tick the Monochrome box in the adjustment’s menu to remove all colour and, like with the Black & White adjustment, you have control over RGB channels.
Or try out the various black and white presets that are found inside the adjustment. When creating your own effect, make sure the Total value comes to 100%, although this isn’t a hard-and-fast rule (as seen in the above example).