Modeling and simulations of the removal of formaldehyde using silver nano-particles attached to granular activated carbon

다국어 초록 (Multilingual Abstract)

<P><B>Highlights</B></P><P>► Silver nano-particles were attached onto the surface of GAC for the simultaneous catalytic oxidation and adsorption reactions of formaldehyde. ► By the silver nano-particles, formaldehyde oxidation to carbon dioxide as expressed as pseudo-first-order. ► The nano-particle deposits reduced the available surface area of the GAC and blocked the openings of the micro-pores. ► The modified numerical model yielded an accurate prediction of the performance of the Ag-GAC. ► Depending on the surface coverage ratio, the factions of catalytic oxidation and the formaldehyde mass removed were proportionally changed.</P> <P><B>Abstract</B></P><P>A combined reaction, consisting of granular activated carbon (GAC) adsorption and catalytic oxidation, has been proposed to improve the removal efficiencies of formaldehyde, one of the major indoor air pollutants. In this study, silver nano-particles attached onto the surface of GAC (Ag-GAC) using the sputtering method were evaluated for the simultaneous catalytic oxidation and adsorption of formaldehyde. The evolution of CO<SUB>2</SUB> from the silver nano-particles indicated that formaldehyde was catalytically oxidized to its final product, with the oxidation kinetics expressed as pseudo-first order. In addition, a packed column test showed that the mass of formaldehyde removed by the Ag-GAC was 2.4 times higher than that by the virgin GAC at a gas retention time of 0.5s. However, a BET analysis showed that the available surface area and micro-pore volume of the Ag-GAC were substantially decreased due to the deposition of the silver nano-particles. To simulate the performance of the Ag-GAC, the homogeneous surface diffusion model (HSDM), developed for the prediction of the GAC column adsorption, was modified to incorporate the catalytic oxidation taking place on the Ag-GAC surface. The modified HSDM demonstrated that numerical simulations were consistent with the experimental data collected from the Ag-GAC column tests. The model predictions implied that the silver nano-particles deposited on the GAC reduced the adsorptive capacity due to decreasing the available surface for the diffusion of formaldehyde into the GAC, but the overall mass of formaldehyde removed by the Ag-GAC was increased due to catalytic oxidation as a function of the ratio of the surface coverage by the nano-particles.</P>