# A Brief Review of Formaldehyde Removal through Activated Carbon Adsorption
## 1 Introduction
The boiling point of formaldehyde is \(-19.5\)\({}^{\circ}\)C. To improve the adsorption efficiency, AC surface modification is often employed. Surface modification allows the physical and chemical characteristics of the AC surface to enable effective adsorption of formaldehyde. The adsorption capabilities of formaldehyde appear complicated in the presence of moisture. The adsorption competition between water and formaldehyde on the surface of activated carbons seems indispensable. The chemical \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Methods** & **Technology** & **Concentration** & **Operating Temp.** & **Operating Cost** \\ \hline Recovery & Adsorption & Low, High & Ambient & Acceptable \\  & Membrane & High & Ambient & High cost of material \\  & Condensation & High & Ambient and cryogenic & High cost of energy \\ \hline Destruction & Thermal Oxidation & High & \(-815\)\({}^{\circ}\)C & High cost of Energy \\  & Catalysis & Low, High & Ambient, \(200\)\({}^{\circ}\)C & Acceptable \\  & Photo catalysis & Low, High & Ambient & Costly dopants required \\  & Non-thermal plasma w/wo catalyst & Low & Ambient & High cost of system assembly \\  & Biological/Botanical filtration & Low & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of formaldehyde removal options. modification of the AC surface, especially through introducing amine functional groups onto the surface, is reviewed and highlighted. In addition, the physical fabrication option followed by the safe handling of amination options for AC applications are proposed and discussed in Section 5. We hypothesize that a better performance can be achieved through well-designed activated carbons, such as high surface area, well-distributed micropores, and mechanical hardness. In the near future, the authors are expecting to evaluate our customized polymer-based activated carbons with previously fabricated morphologies combined with surface modification options. In brief, the surface-modified bead-type AC by amination is highly promising for practical application in removing formaldehyde from indoor air. The suggested activated carbon is not a granular activated carbon but a bead-type activated carbon, which would be applicable to a convenient recycle process operated in a flow-loop system. However, the viability of commercialization should be verified. This paper briefly reviews thermodynamics and kinetics for adsorption of formaldehyde on AC and the current progress in surface modification of AC by amination for adsorptive removal of formaldehyde from an indoor atmosphere. Various physical (operational) and chemical factors that may affect the effective adsorption of formaldehyde are presented and discussed. In Sections 3 and 4, the effect of amination of the AC surface is highlighted, and the adsorption mechanism of formaldehyde on AC and modified AC is discussed. In addition, strategies for the practical application of AC are proposed by sharing our recent work. In the Section 5, as mentioned above, two aspects of AC modification are suggested in terms of the usage of less toxic amines as well as physical modification options for favorable fluidization in the regenerability of spent adsorbent.