Coffee is a diuretic. It does help in weight loss but considering only coffee will not help.
The following factors are very important.
1. a balanced diet
3. adequate sleep
4. adequate amounts of water
5. having small meals every 3 hourly
Additionally, carry home food, one fruit and few dry fruits.
If home food is not an option, order for whole wheat bread sandwich with a simple stuffing without dressing. Sleep well after getting home. Indulge one hour of your day in some physical activity.
I hope practicing above mentioned activities will help you reach your target soon.