# 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  
Volatile organic compounds (VOCs) are one of air pollutants mainly produced by fossil fuel combustion [81; 82], painting [83], refining [84], building [85], and other industries [86; 87]. In recent decades, rapid development of industry has led to a dramatic increase in anthropogenic VOCs. There are more than 300 chemical structures of VOCs, which can be classified as alkanes, aromatics, esters, and aldehydes, among others [88; 89]. Many VOCs are harmful to humans in even small amounts, such as benzenes and formaldehyde, which are suspected carcinogens [90]. Xylene and aliphatic hydrocarbons are mainly produced by the paint industry and are harmful to the environment and humans [91; 92]. In sunlight, photochemical reactions of VOCs and NOx will generate ozone, peroxide, nitro-aldehydes, and other photochemical smog compounds that cause secondary pollution and affect people's eyes and respiratory systems, endangering human health [93; 94; 95; 96]. Table 4 shows some VOCs harmful to human health [97]. Thus, the reduction and control of VOCs from air are important research topics for air purification. [PERSON] et al. [98] evaluated adsorption capacity of seven building materials (activated carbon, gypsum board mixed with a given quantity of activated carbon, board made out of activated carbon, humidity-controlling porous ceramic material, humidity-controlling silicate calcium, ceramic tile and ordinary gypsum board) for adsorption of four kinds of VOCs in a small test chamber. They showed that activated carbon has the highest VOCs adsorption capacity compared with other building materials. [PERSON] et al. [99] studied the reduction of VOCs from coal combustion using electron beam treatment and found that the concentration of polycyclic aromatic hydrocarbons (VOCs) was greatly reduced from 40% to 98%. Other researchers have also found that other materials effectively reduce VOCs, including cashew nut shell liquid [100; 101], sol-gel [102], CuO-CeO\({}_{2}\) mixed oxides [103], Mn-Cu mixed oxide [104], manganese oxides [105], and other metal oxide catalysts and  
\begin{table}
\begin{tabular}{|c|c|c|c|c|} \hline
**Volatile Organic** & \begin{tabular}{c} **Dangerous** \\ **Concentration** \\ \end{tabular}  & **Unit** & **Sources** & **Health Effects** \\ \hline Benzene & 500 & ppm & Petroleum products; Incomplete combustion of liquid fuels; Adhesives; & Carcinogen; Damage the ozone layer; Produce photochemical \\ \hline Toluene & 500 & ppm & Lacquers & smog \& pose mutagenic hazards \\ \hline Ethylene & 800 & ppm & & hazards \\ \hline Carbon tetrachloride & 200 & ppm & & \\ Chlorobenzene & 1000 & ppm & Chemical extractions; & Strong bioaccumulation \\ \hline
1,1,2-Tichloroethane & 100 & ppm & Paints; Adhesives; & potential; Acute toxicity; \\
1,1,2-Zetrachlorethane & 100 & ppm & Polymer synthesis; & Destruction of the ozone; \\ \hline Trichoethylene & 1000 & ppm & Water purification systems & Cause greenhouse gas effects \\ \hline Tetrachloroethylene & 150 & ppm & & \\ \hline Acetone & 2500 & ppm & \begin{tabular}{c} Varnishes; Window deamers; \\ Pantin thiners; Adhesives \\ \end{tabular}  & \ \begin{tabular}{c} Irritation of eyes, nose, \& \\ throat; Central nervous system \\ depression; \\ Headache and nausea \\ \end{tabular}  \\ \hline Ethyl butyl ketone & 1000 & ppm & & \\ \hline Formaldehyde & 20 & ppm &
\begin{tabular}{c} Decorative \& \\ Materials; Cosmetics \& \
oble metals [106; 107]. Among them, activated carbon is one of the most common adsorbents because of its low-cost, high availability, excellent specific surface area, pore size, porosity, chemical functional group, and other properties [108; 109; 110]. Nevertheless, activated carbon adsorption of macromolecules and hydrophilic VOCs is not good because it has a multi-microporous structure and is a nonpolar adsorbent [97].