Unless your website is password protected, it is publicly accessible, meaning anyone, not just your students, may access it. As a result, you are therefore communicating materials to an unlimited audience, which would greatly impede the fairness of your dealing and may circumvent licenses, permissions, or other Terms of Use when posting copyright protected works. 

Posting copyright protected works to a personal (open) website is acceptable when you have explicit permission from the copyright owner to do so or your use clearly falls within a user right, such as fair dealing or an educational user right.