PDO statement’s execute() method not working as expected

Doing some DB work with PHP’s PDO. The code is very simple. Just trying to create a table in the database with prepared statement. But code is not working.

    $dsn = "mysql:host=$hostname;port=$port;dbname=$database;charset=UTF8";
    $pdo = new PDO($dsn, $username, $password);
    $dn  = 'pns';
    $query_string    = 'CREATE DATABASE IF NOT EXISTS :db';
    $query_statement = $pdo->prepare($query_string);
        
    if ($query_statement !== FALSE)
    {
        print 'Hi'; **// Code reaches here**
        $statement_execute = $query_statement->execute([
            ':db' => $dn
        ]);
    }

I am getting the below error instead…

Exception : SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''pns'' at line 1

Please help.

Thanks.