# Application of Fly Ash as an Adsorbent for Removal of Air and Water Pollutants
## 4 Application of Fly Ash for Treatment of Pollutants
### Removing Air Pollutants
#### 4.1.1 Removal of Volatile Organic Compounds
On the other hand, activated carbon fibers adsorb VOCs better than activated carbon because of their short and straight thin-fiber shaped micropores that increase intraparticle adsorption kinetics compared to activated carbon [111; 112]. In addition, activated carbon fibers also play an important role during adsorption or desorption, have large adsorption capacity and have high mass transfer rates [113; 114]. Similar to adsorption on activated carbon fibers, FA can be used to fabricate a functional adsorption fibrous membrane through simple electrospinningning [32]. Electrospinning is an efficient method for fabricating fibers from nanometer to micrometer, with advantages of high efficiency, low cost, and easy operation [115]. Figure 10 shows a schematic of an electrospun fibrous membrane and a VOCs adsorption experiment. The spinnable functional material (e.g., fly ash) and polymer (e.g., polyacrylonitrile (PAN), polyurethane (PU), and Polylactic acid (PLA)) are mixed with the chemical solvent (e.g., N,N dimethylformamide (DMF) and methyl ethyl ketone (MEK)) at a certain ratio, then as-prepared spinning solution is further processed using magnetic stirring and ultrasonication to obtain a homogenous spinning solution, and finally the composite membrane is collected on the roller under the action of the electrostatic field. The size and arrangement of electrospun fibers are affected by viscosity, conductivity and feed rate of spinning solution, distance between nozzle and collector, supply voltage, etc. [88; 116]. [PERSON] et al. [33] successfully synthesized polyurethane fibers containing different amounts of FA and analyzed their adsorption of chloroform, benzene, toluene, xylene, and styrene (Figure 11). They found that polyurethane fibers containing 30 wt % FA had the smallest fiber diameter and the maximum specific surface area, it results in the highest VOCs adsorption capacity compared to other fibrous membranes. Furthermore, the adsorption of VOCs by fibrous membranes was in the following order: styrene > xylene > toluene > benzene > chloroform. This is because adsorption of VOCs not only depends on the surface area and fiber diameter, but also on other characteristics, including molecular polarity, molecular structure, molecular weight, pore size, porosity, chemical functional groups electronic and steric effects, \(\pi\)-complexes, adsorption kinetics, ionization potential, dipole moment, boiling point, temperature and humidity [97; 117; 118]. In general, lower ionization potential aromatic compounds are easier to be absorbed by FA fibrous membranes due to their instability [32]. The adsorbent with high C/O ratio has the high adsorption capacity for adsorption of nonpolar VOCs [119]. Use of FA fibrous membrane to adsorb VOCs from air is an innovative research, which provides a new idea for using FA fibrous membrane to filter air pollutants. As an emerging material, FA fibrous membrane can be modified into a variety of air filters with great development potential in the field of environmental pollution management [32; 33].