Clean XSS PHP function

<?php
 define('DB_SERVER', 'localhost');  
 define('DB_USERNAME', 'root');
 define('DB_PASSWORD', '');
 define('DB_DATABASE', 'student_db');
 
 
 
 define('PROJECT_NAME','Student Tutorial');
 define('SERVER_NAME','localhost');


class DB_Class
{
    function __construct()
    {
        $connection = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD,DB_DATABASE) or die('Oops connection error -> ' . mysqli_connect_error());
    }
}
$connection = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD,DB_DATABASE) or die('Oops connection error -> ' . mysqli_connect_error());

/**********************General WebSite Settings************************************/
date_default_timezone_set("UTC");
?>

<?php
public $dbcon;
class Dbfunctions{
    
    public function __construct(){      
        $this->dbcon = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD,DB_DATABASE) or die('Oops connection error -> ' . mysqli_connect_error());                                
    }
    /* Clean xss */
    function xss_clean($data){
        
        $data = str_replace(array('&','<','>'), array('&amp;','&lt;','&gt;'), $data);
        $data = preg_replace('/(&#*\w+)[\x00-\x20]+;/u', '$1;', $data);
        $data = preg_replace('/(&#x*[0-9A-F]+);*/iu', '$1;', $data);
        $data = html_entity_decode($data, ENT_COMPAT, 'UTF-8');
        
        $data = preg_replace('#(<[^>]+?[\x00-\x20"\'])(?:on|xmlns)[^>]*+>#iu', '$1>', $data);
        
        $data = preg_replace('#([a-z]*)[\x00-\x20]*=[\x00-\x20]*([`\'"]*)[\x00-\x20]*j[\x00-\x20]*a[\x00-\x20]*v[\x00-\x20]*a[\x00-\x20]*s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:#iu', '$1=$2nojavascript...', $data);
        $data = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*v[\x00-\x20]*b[\x00-\x20]*s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:#iu', '$1=$2novbscript...', $data);
        $data = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*-moz-binding[\x00-\x20]*:#u', '$1=$2nomozbinding...', $data);
        
        $data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?expression[\x00-\x20]*\([^>]*+>#i', '$1>', $data);
        $data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?behaviour[\x00-\x20]*\([^>]*+>#i', '$1>', $data);
        $data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:*[^>]*+>#iu', '$1>', $data);
        
        $data = preg_replace('#</*\w+:\w[^>]*+>#i', '', $data);
        do{
        
        $old_data = $data;
        $data = preg_replace('#</*(?:applet|b(?:ase|gsound|link)|embed|frame(?:set)?|i(?:frame|layer)|l(?:ayer|ink)|meta|object|s(?:cript|tyle)|title|xml)[^>]*+>#i', '', $data);
        }while ($old_data !== $data);
        
        return $data;
    }
}
?>