This material has more potential as a spacecraft structural component. Weight is the #1 concern for anything going to space.
As far as collecting space junk - I have yet to see a proposal that addresses the real enormity of space. Imagine building a net or block (made of anything) on the surface of the earth. You want to use this net to clean up random trash people dropped. How much progress would you make over, say, Ohio. Or how about the USA. Maybe you just focus on North America. How big does your net need to be to make a dent?
Now factor in that space is a 3D volume. Even the cubic volume between LEO and geosynchronous is mind boggling.
Say LEO is 160 kilometers up, geosynchronous is 35,786 kilometers up. Area of 2nd sphere less 1st sphere is: 192044931750177-17164190 =
192,044,914,585,987 cubic kilometers.
Tell me again how big your net is? And how are you going to move around something that large?
After all that, you've neglected the space junk above geosynchronous.