The whole concept of charitable hospitals, hospices and nursing homes that have Catholic roots is huge. Somebody like Danny Thomas that organized St Jude and all the good it has done over the years. All the shelters and care facilities.
The whole concept of charity is Christian origin, care for the old, hungry and sick and widowed and orphans was one of the first things the organized church did, setting up deacons to care for these pitiful people, to show them the love of God. St Stephen was a deacon who waited on tables (See Acts 6-8 or so)
If you want to engage your friend in useful dialogue say the one of the forum members has a question:Ask your atheist friend a question for me? Why do charitable works at all if there is no judgement / afterlife? Why not just spend it on himself? What is the point to help the sick, underpriviledged, handicapped and weak? They are just in the way? I think he might be an agnostic looking for answers, not an atheist. Be sure to thank him for asking questions, and always give answers in love.
Bless your efforts with love and success