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Article Cite This: ACS Omega 2019, 4, 5382−5391
http://pubs.acs.org/journal/acsodf
Adsorption and Oxidative Desorption of Acetaldehyde over Mesoporous FexOyHz/Al2O3
Jae Hwan Jeong,† Soong Yeon Kim,† Jeonghun Kim,‡ Byeong Jun Cha,† Sang Wook Han,† Chan Heum Park,† Tae Gyun Woo,† Chul Sung Kim,*,‡ and Young Dok Kim*,† †
Department of Chemistry, Sungkyunkwan University, Suwon 16419, Republic of Korea Department of Physics, Kookmin University, Seoul 02707, Republic of Korea
‡
ACS Omega 2019.4:5382-5391. Downloaded from pubs.acs.org by 5.62.154.110 on 03/19/19. For personal use only.
S Supporting Information *
ABSTRACT: FexOyHz nanostructures were incorporated into commercially available and highly porous alumina using the temperature-regulated chemical vapor deposition method with ferrocene as an Fe precursor and subsequent annealing. All processes were conducted under ambient pressure conditions without using any high-vacuum equipment. The entire internal micro- and mesopores of the Al2O3 substrate with a bead diameter of ∼2 mm were evenly decorated with FexOyHz nanoparticles. The FexOyHz/Al2O3 structures showed substantially high activity for acetaldehyde oxidation. Most importantly, FexOyHz/ Al2O3 with a high surface area (∼200 m2/g) and abundant mesopores was found to uptake a large amount of acetaldehyde at room temperature, and subsequent thermal regeneration of FexOyHz/Al2O3 in air resulted in the emission of CO2 with only a negligibly small amount of acetaldehyde because FexOyHz nanoparticles can catalyze total oxidation of adsorbed acetaldehyde during the thermal treatment. Increase in the humidity of the atmosphere decreased the amount of acetaldehyde adsorbed on the surface due to the competitive adsorption of acetaldehyde and water molecules, although the adsorptive removal of acetaldehyde and total oxidative regeneration were verified under a broad range of humidity conditions (0−70%). Combinatory use of room-temperature adsorption and catalytic oxidation of adsorbed volatile organic compounds using FexOyHz/Al2O3 can be of potential application in indoor and outdoor pollution treatments.
1. INTRODUCTION Volatile organic compounds exist in indoor and outdoor environments. Indoor atmospheres contain materials used for interior construction such as paints and adhesives that consist of organic solvents, which are volatile and known to cause “sick-building syndrome”.1−5 In the outdoor atmosphere, volatile organic compounds are emitted from vehicles, power plants, and anything using fossil fuels. In these cases, incomplete combustion of fuel and subsequent emission of volatile organic compounds are unavoidable.1,2,6−9 Volatile organic compounds in outdoor environments are recently of more concern because these molecules act as seeds for secondary organic aerogels under atmospheric conditions by interacting with light and nitrogen-containing compounds.10,11 Toxicity of the volatile organic compounds themselves and that of the secondary organic aerogels induced by volatile organic compounds have been widely reported in the literature.1−5,10,11 Therefore, removal of volatile organic compounds has become more and more important in environmental science and engineering. Adsorbents with very high surface area materials are one of the most widely used methods for removing volatile organic compounds. Activated carbon is the most widely used adsorbent for pollutants in air, and more recently, novel materials with high surface areas and porosities such as metal− organic frameworks have shown potential for applications as adsorbents.12−16 Adsorbents are one of the most efficient ways © 2019 American Chemical Society
for removing volatile organic compounds, and they also have the advantage that the energy consumption for operation of an adsorbent-based filtering system seems to be quite low. However, once all the surface adsorption sites are occupied by molecules, the adsorbent should be replaced by a new one, and the used adsorbents should be regenerated (e.g., by thermal treatment). During the thermal regeneration process, adsorbed species can be re-emitted into the air, causing a secondary pollution problem.12,17 An alternative way of removing volatile organic compounds is heterogeneous catalysis. Here, volatile organic compounds consisting of C, H, and O and oxygen gas (or water vapor) can adsorb on the surface of catalysts and react to form CO2 and H2O. Ideally, heterogeneous catalysts can be permanently used because the reaction products (CO2 and H2O) desorb from the surface of the catalyst, thus always providing free adsorption sites to the next volatile organic compound.17 Generally, nanoparticles of Pt-group metals supported by mesoporous alumina or silica are widely used for the catalytic oxidation of volatile organic compounds.2,18,19 Catalytic converters are widely used for exhaust gas treatments in vehicles. In this case, emitted gas is at a relatively high temperature (
