**1. Introduction**

Pollution treating technologies have been studied and applied for a long time. Up to now, they still attract a lot of attention from scientists to aim for a new material, technology with high efficiency, thorough and convenient processing. In particular, the appearance of nanomaterials has a positive impact on almost every aspect of engineering, technology and life. Environmental treatment technology is no exception to that influence. Nanotechnology involves the fabrication of nanoscale materials, along with the means and techniques to control them, in order to utilize the superior properties of this material. Nanotechnology was discovered in the late 1960s and has been

applied in many different fields from science, engineering, technology, medicine, bringing great efficiency [1]. In the field of environmental remediation, nanotechnology also promises to bring new advances. With nanomaterials having the advantage of large specific surface area, chemical activity of the surface of the material as well as the ability to transform and functionalize the surface, it opens countless research directions to bring a high performance on pollutant treatment and increase the ability to handle some stubborn pollutants. There have been many studies on this research direction, different water pollution treatment technologies have been used. In the past, the removal of pollutants often relied on adsorption technology. Accordingly, nanomaterials with adsorption affinity for pollutants are fabricated, they adsorb pollutants on the surface to help clean water flow. Of course, their limitation is that usually all materials have a certain adsorption capacity. Post-treatment material collection and an additional step of handling this material is required. A recent new direction uses materials with photocatalytic activity to combine the adsorption and treatment of organic pollutants right on the surface of the material. This type of material is usually semiconducting metal oxides, which have a wide band gap suitable for excitations by sunlight. However, nanomaterials also have disadvantages in the treatment of pollutants, especially in aqueous solution. It is because they are nanosized that recovery will be very difficult, which easily leads to secondary contamination. To overcome this situation, scientists have thought of magnetic nanomaterials. Thanks to its magnetism, this material is easily recovered after processing.
