Collocations for concentrate - verb

hard, intensely (esp. AmE), intently (esp. BrE)
She was sitting at her desk concentrating hard.

fully, properly
I was tired and couldn't concentrate properly.

mainly, mostly, predominantly, primarily
particularly
entirely, exclusively, purely, solely

be unable to, cannot
I tried to work but I found I couldn't concentrate.

be difficult to, be hard to, be impossible to
tend to
Banks tend to concentrate on short-term lending.

try to

on
He concentrated mainly on the flying and spoke very little.

Concentrate is used with these nouns as the object:
attention, effort, energy, mind, wealth