Unable to set client connection character set: utf8mb4

I am creating a web app with ios developer, ios developer send text message with emoji and i store it on server db.
The emoji is not storing in table column someone told me change the column collation to utf8mb4_unicode_ci from utf8_unicode_ci and also change the application/config/database.php char_set to utf8mb4 and dbcollat to utf8mb4_unicode_ci but it gives me error on server on localhost it is working.

Please help thanks.