在非对象上调用成员函数format（）

In codeigniter, I have written the following line of code under my methods in the controller:

            $dt = new DateTime();

In my views page, I've created an h1 tag and placed the following in it:

<h1><?php $dt->format('M, d Y'); ?></h1>

But I get the following error:

I would appreciate if anyone can explain this to me in detail.