# A Brief Review of Formaldehyde Removal through Activated Carbon Adsorption
## 6 Summary  
Formaldehyde removal is important to maintain clean air in indoor environments. Among the formaldehyde removal options, activated carbon adsorption is attractive because of its economic application. Lately, diverse origins of activated carbon materials have been explored to evaluate whether a customized activated carbon performs efficiently in the removal of emerging contaminants. Activated carbon has been examined in various applications, such as wastewater treatment and gas-phase adsorption. The present paper briefly reviewed the thermodynamics and kinetics for the adsorption of formaldehyde on AC, as well as the current progress in surface modification of AC by animation. The major factors affecting the adsorptive removal of formaldehyde over AC are presented and discussed in terms of humidity and temperature. The adsorption capabilities of formaldehyde seem complicated in the presence of moisture. The competition between water adsorption and formaldehyde adsorption on the surface of activated carbons seems to be a complicating factor. The chemical modification of the AC surface, especially through introducing amine functional groups onto the surface, to improve the adsorption capacity is reviewed and highlighted. The surface modification of AC by animation is an important strategy to increase the adsorption capacity for removing formaldehyde. In addition, the physical fabrication and safe handling options for animation in AC applications were proposed and discussed. Better performance can be achieved from well-designed activated carbons that have high surface area, well-distributed micropores, and mechanical hardness. The  
Figure 5: Conceptual diagram of recycling process for customized bead-type AC with 0.5 mm diameter, on average.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Chemicals**} & **Toxic/Non-Toxic** & **Ref.** \\ \hline Polyethylenemime & Toxic & [31] \\ Discyandiamide & Toxic & [42] \\ Thiourea & Toxic & [42] \\ Penicillin G & Toxic & [42] \\ Nitric Acid/Sulfuric Acid & Toxic & [50] \\ Hexamethylene Diamine & Toxic & [57] \\ Urea & Non-toxic & [60] \\ Melamine & Non-toxic & [62] \\ Diethylene triamine & Toxic & [64] \\ P-aminobenzzoic acid & Toxic & [65] \\ Eilenodiamina & Toxic & [66] \\ Hexamethylenetetramine & Toxic & [67] \\
3-aminopropyltriethoxysilane & Toxic & [68] \\ Diallyamine & Toxic & [69] \\ Piperazine & Non-toxic & [70] \\ \hline \hline \end{tabular}
\end{table}
Table 5: Amine sources based on toxic/non-toxic chemicals.  
authors are preparing and evaluating customized polymer-based activated carbons with previously fabricated morphologies combined with surface modification options. The performance results will be presented in future studies. The surface-modified bead-type AC by amination is highly promising for practical application in removing formaldehyde from indoor air. A suggested activated carbon called the bead-type activated carbon, which is not a granular activated carbon, could be part of a convenient recycling process, because it conveys used and recycled activated carbons in a flow-loop system. However, it should be verified whether commercialization is viable.  
Conceptualization, methodology and writing (original draft, review and editing): K.O. and J.-I.P.; supervision and funding acquisition: J.-I.P.; experiment performance, data processing, software and formal analysis: Y.-J.K., H.-K.J., M.-H.J., X.M. and Y.J. All authors have read and agreed to the published version of the manuscript.  
This work was supported by Korea Environment Industry & Technology Institute (KEITI) through the Prospective Green Technology Innovation Project, funded by Korea Ministry of Environment (MOE) (2020003160004).  
The authors declare no conflict of interest.