[RawSQL] Cannot bind string has `/` character to find in DB

I have table urlTable contain url like this:

id    url
1     abc.com/zyx.html
2     abc.com/xyz123.html

To find one of them, i use the RawSQL:

$url = 'abc.com/zyx.html';
$sql    = "SELECT id FROM urlTable WHERE url = ':url'";
$result = \Phalcon\DI::getDefault()->getDb()->fetchAll($sql, \Phalcon\Db::FETCH_ASSOC, ['url' => $url]);

But result is empty. SQL log is:

SELECT id FROM urlTable WHERE url = ':url' [{"url":"abc.com\/zyx.html"}]

So, phalcon has escaped the / character to \/.

I have what I need when I use:

$url = 'abc.com/zyx.html';
$sql    = "SELECT id FROM urlTable WHERE url = '$url'";
$result = \Phalcon\DI::getDefault()->getDb()->fetchAll($sql, \Phalcon\Db::FETCH_ASSOC);

SQL log is:

SELECT id FROM urlTable WHERE url = 'abc.com\/zyx.html'

What is wrong when I use the first way to avoid SQL injection?