I encountered this really awesome project by Boyan Slat, an undergraduate at the Delft University of Technology. Using a platform with floating booms, he manages to collect plastic from oceans and reuse them. Known as “The Ocean Cleanup”, here are some useful links:
Watch this youtube video to understand more about the project as well as how he deals with criticisms leveled at him.
Read his LinkedIn page to know more about the feasibility studies he has done in collaboration with plenty of people worldwide.
Read this report to understand some in-depth criticisms directed at The Ocean Cleanup.