Black: Q-e4
White: K-e1, P-e2, R-a1

Now castling goes through the Q's attack on b1. I know this is a legal move to make. What I'm not certain of is whether the Q can then move to b1 and take the rook similar to en passent

No. Taking a pawn en passant (French for "in passing") applies only to pawns, and is a historical adjustment to allowing pawns to move 2 squares on their first move.

Suppose a black pawn is on d4. If White moves a pawn from c2 to c4, on the immediately following half move, Black may capture the pawn on c4 en passant by moving the black pawn from d4 to c3, capturing exactly as if the white pawn had advanced only one square. If Black does not do this on the very next half move, the opportunity is lost. Only pawns can be captured en passant, only pawns on the fifth rank can make en passant captures, and en passant captures can only take place immediately after the pawn to be captured has advanced 2 squares.

Patzer