Macro..Compare 2 columns and return unmatched results

Sub test()
Dim a, e
With Sheets("Sheet1")
     a = .Range("a1",.Range("a" & Rows.Count).End(xlUp)).Value
End With
With CreateObject("Scripting.Dictionary")
     .CompareMode = vbTextCompare
     For Each e In a, i As Long, y
          If Not IsEmpty(e) And Not .exists(e) Then .add, e, Array(e,1)
     Next
     With Sheets("Sheet2")
          a = .Range("c1",.Range("c" & Rows.Count).End(xlUp)).Value
     End With
     For Each e In a
          If Not IsEmpty(e) Then
               If Not .exists(e) Then
                    .add e, Array(e,2)
               Else
                    If .item(e)(1) = 1 Then .item(e) = Empty
               End If
          End If
     Next
     y = .items
End With
With Sheets("sheet3").Range("a1")
     .Resize(,2) = [{"Item","Sheet"}]
     With .Offset(1)
          For i = 0 To UBound(y)
               If Not IsEmpty(y(i)) Then
                    .Offset(n).Resize(,2).Value = y(i)
                    n = n + 1
               End If
          Next
     End With
End With
End Sub