Space and special characters problems on post

I got a problem with blank space and special characters during a POST action using this AJAX function:

function comments(id,postId,user_id) {
        var user_comments = encodeURIComponent($("#commentsId_"+id).val());
        if(user_comments!=''){
            var img = $("#img_"+id).val();
            var username = "<?php echo $this->session->userdata('username'); ?>"
            $.ajax({
                    type: "POST",
                    url: "<?php echo base_url() ?>social/userscomment/" +user_id+"/"+postId+"/"+user_comments,
                    data:{ user_comments : user_comments},
                    success: function(data) { 
                        $("#commentsId_"+id).val('');
                        var $sparkLines = $('.comments_body_'+id);
                        $("#comments_add_"+id).append('<div id="id' + ($sparkLines.length + 1) + '" class="comments_body_"'+id+'><div class="feed-element comments_body_"'+id+'><a class="pull-left"><strong>'+username+' <i class="fa fa-comment-o"></i></strong></a><div class="media-body">'+user_comments+'<br></div><div class="col-lg-12"><a id="span_'+postId+'" onclick="callajaxcommcool('+postId+')" class="btn btn-xs btn-white"><i class="fa fa-star"></i><span id="span1_'+postId+'" style="display:none;">1</span> Cool </a></div></div></div></div>');
                    }
            });
        }
    }

The PHP controller:

public function userscomment($comment_id,$post_id,$user_comments){

    $this->load->model('comments');

    $user_comments = utf8_decode(trim(mysql_real_escape_string($user_comments)));

    if(!empty($user_comments)){

        $data = array("user_id"         => $this->session->userdata('user_id'),
                      "comment_user_id" => $comment_id,
                      "comments"        => $user_comments,
                      "post_id"         => $post_id,
                      "username"        => $this->session->userdata('username')
                );
        $this->comments->insertComments($data);

        //logged user
       $userRow = $this->register->get_login($this->session->userdata('user_id'));
       redirect('social/userprofile/'.$userRow[0]['username']);
    }
}    

When an user post a comment like: "a b c d" the results showed in the view is: a%20b%20c%20d, if an user try to wrote a special characters like € i got this results %E2%82%AC

How can i prevent this problem?