My function returns same data without do the jobs

Question

I have made function like below to remove html tags and special characters from the string.

function input_filter_data($data) {
        $data= trim($data);
        $data= stripslashes($data);
        $data= htmlspecialchars($data);
        $data= strip_tags($data);
        return $data;
}

and I am trying to use it like below

$affiliate_id =input_filter_data("Hello <b><i>world!</i></b>","<i>");

echo $affiliate_id;

But its giving me same result like

Hello <b><i>world!</i></b>","<i>

But if I use simple like

echo strip_tags("Hello <b><i>world!</i></b>","<i>");

then its removing all html tags from string.

I am not getting idea why its happening like this, let me know if anyone here can help me for solve the puzzle.

Thanks!