Setting database collation

How can I se my collation to utf8mb4_general_ci? I am getting this error:

Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8mb4_general_ci,COERCIBLE)

If add this to database connection, I no loger get error, but trying to save emojis to database will save only ??????

  "options" => array(

I am not quite sure where the problem is.

edited Mar '16

Just some thoughts:

1) You should set your charset when connecting to your db. With phalcon like so:

    // Database connection     
    $di['db'] = new \Phalcon\Db\Adapter\Pdo\Mysql(array(
        'host' => $config->database->host,
        'username' => $config->database->username,
        'password' => $config->database->password,
        'dbname' => $config->database->name,
        'charset' => 'utf8',

2) Check if your database has the same collation, perhaps you changed it in your code but forgot the db? Or this specific column has wrong collation by mistake?

3) Check if you have models metadata cache running and you forgot to clear it after changing database?