# Application of Fly Ash as an Adsorbent for Removal of Air and Water Pollutants
## 5 Conclusions  
Fly ash (FA) can be used as the base material of some adsorbents to treat air and water pollution due to its high porosity, high surface area, appropriate pore size, CaO percentage and surface functional groups. It can be fabricated into a variety of composite materials including zeolites and fiber membranes. They have excellent adsorption capacity in controlling air and water pollutants, such as VOCs, NOx, heavy metals and toxic organic dyes. In this paper, the mechanism of FA for adsorption of air pollutants and water pollutants has been studied, in addition to a comparison of FA production of different countries, as well as the physical and chemical properties of FA. Detailed results are as follows:  
1. Fly ash can be used in building materials, building works, roads construction, agriculture, and other fields.
2. To improve the adsorption capacity and efficiency of fly ash on environmental pollutants and make full use of fly ash, new technologies for the efficient utilization of fly ash should be developed, such as nanofiber technology.
3. Fly ash can be converted to inexpensive and high performance adsorbents by simple modifications due to its unique porous properties. For example, is can be made into various kinds of zeolites.
4. Modified fly ash can adsorb VOCs, NOx and SO2 emissions in the air and can also remove some heavy metals and other organic/inorganic pollutants (e.g., phosphorous, fluoride, boron, phenolic compounds, pesticides and dyes) from wastewater, due to its high porosity, high surface area, appropriate pore size, high porosity, alkalinity, negative charge, unburned carbon remaining in the fly ash particles and other unique characteristics.
5. In addition, the adsorption effect is not only related to the physicochemical properties of the adsorbent itself but also to the physicochemical properties of the adsorbate, e.g., polar/non-polar, and functional groups.
6. Pristine fly ash is a powder, which limits its scope of use. Using nanotechnology, it can be synthesized into low-cost, multi-functional and multi-purpose porous hybrid composites for adsorption of air pollutants and water pollutants. Fly ash porous hybrid composites as an emerging material, which has great potential in the future.  
[PERSON] made suggestions, analyzed the physicochemical properties of fly ash, summarized the adsorption mechanism of the fly ash composite materials for treatment of environmental pollutants, and drafted this manuscript. [PERSON] summarized and analyzed the production and consumption of fly ash from several representative countries, summarized the synthetic methods of the fly ash composite materials and analyzed their development trend in the future. [PERSON] guided the idea of this manuscript, analyzed the application of the fly ash composite materials in the control of environmental pollutants, and supervised the work and the manuscript. All authors participated in the evaluation of the data, and reading and approving the final manuscript.  
This research was funded by [the Ministry of Education] grant number [2016R1D1A1B03931616].  
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Project No. 2016R1D1A1B03931616).  
The authors declare no conflict of interest.