My version, converst first letter of the first word in the string to uppercase

public function mb_ucfirst($str) {
        $aParts = explode(" ",$str);
        $firstWord = mb_convert_case($aParts[0],MB_CASE_TITLE,"UTF-8");
        unset($aParts[0]);

        return $firstWord." ".implode(" ",$aParts);
    }