In vain
Definition 1 of 2
Pro Tip 1/3Context Matters
The phrase often implies effort was put forth despite the lack of results, not just the absence of outcome. 
She studied all night in vain, as the exam questions were on different topics.
Pro Tip 2/3Emotional Weight
'In vain' can express a sense of disappointment or frustration over futile efforts. 
After hours of negotiations, the delegates realized their work was in vain.
Pro Tip 3/3Not For Casual Use
This phrase is more formal and can sound dramatic; use it in serious or formal contexts. 
The rescue team's efforts to save the hikers were in vain.