dir() would be for your csv's rather than your data.frames... so it would be better to call it list_of_csvs or change to ls funtion and filter the result based on the class containing data.frame.
I note that the syntax for the for loop isnt right, as its missing round brackets like
for (i in list_of_dfs){
but I would also recommend purrr functions over for loops, something to think about
further note, all the functions such as dir() or ls() whether they are listing files on your drive, or frames in your r environment only list the names of the objects (as character vectors), so if you want to treat them as symbols , or get() the contents you would need an extra step