When a first name (given name) is used with a van surname, the van is not capitalized.  When a surname is used alone, without a first name, in a sentence, the Van is capitaliized.  A.J.F. van Laer, the great historian and translator, had it consistently correct in his published writings.  Whenever he referred to someone  in a sentence without using the first name, Van Laer always capitalized the Van.  But when he referred to someone including the first name or initials, A.J.F. van Laer used a small v in van.