| GAO Wan,QIAN Meng,FENG Yan-yan,LI Yan-jie.Adsorption of CO2 on Porous MgAl Hydroxides Prepared by Alkaline Etching of KOH Solution[J],52(11):386-393 |
| Adsorption of CO2 on Porous MgAl Hydroxides Prepared by Alkaline Etching of KOH Solution |
| Received:September 16, 2022 Revised:July 15, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.11.033 |
| KeyWord:MgAl hydroxides CO2 adsorption alkaline etching specific surface area active sites adsorption kinetic models |
| Author | Institution |
| GAO Wan |
Department of Chemistry and Bioengineering, Guilin University of Technology, Guangxi Guilin , China |
| QIAN Meng |
Department of Chemistry and Bioengineering, Guilin University of Technology, Guangxi Guilin , China |
| FENG Yan-yan |
Department of Chemistry and Bioengineering, Guilin University of Technology, Guangxi Guilin , China |
| LI Yan-jie |
Department of Chemistry and Bioengineering, Guilin University of Technology, Guangxi Guilin , China |
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| Abstract: |
| A large amount of CO2 has caused adverse effects on people's life, and it is imperative to reduce the concentration of CO2 in the atmosphere. As an effective way to capture CO2, hydrotalcite-like compounds have problems of poor dispersion and low effective specific surface area for use in CO2 adsorption. To address these problems, MgAl layered double hydroxides (LDHs) were firstly prepared via one-pot hydrothermal method with Mg(NO3)2∙6H2O and Al(NO3)3∙9H2O as precursors and urea as precipitator. Then, taking advantage of the amphoteric nature of Al species, MgAl hydroxides were treated by alkaline etching of KOH solution to remove Al species to obtain porous MgAl hydroxides with high CO2 adsorption capacity. The morphologies and structures of porous MgAl hydroxides with various alkaline etching times were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption/desorption and Fourier transform infrared spectroscopy (FT-IR), respectively. The characterization results showed that with alkaline etching, the characteristic peaks at 2θ of 23.6°, 39.7° and 47.1° changed from narrow and sharp single peaks to double peaks. The removal of Al species led to the destruction of the characteristic peaks of MgAl hydroxides, along with the appearance of characteristic peaks of Mg(OH)2 and Al(OH)3. With the alkaline etching time increased, more Al species were removed, and the characteristic peaks of Al(OH)3 became weaker, while the characteristic peaks of Mg(OH)2 became stronger. Compared with the sample LDH-0 without alkaline etching, with the alkaline etching time of 12 h, the specific surface area and pore volume of the sample LDH-12 increased, and the specific surface area of LDH-12 changed from 8.8 m2/g to 16.6 m2/g, which was conducive to the exposure of adsorption active sites. In addition, after the alkaline etching treatment, the modified samples still maintained the regular hexagonal morphology, but the layer structure of the samples became thinner with the rougher surface, indicating that the alkaline etching could remove some Al species from the sample. With the prolongation of the alkaline etching time, the sample LDH-24 presented a regular hexagonal ring, and part of the structure began to be destroyed. CO2 adsorption performances of the samples were conducted by a thermogravimetric analyzer, and the adsorption data were fitted by the first-order and pseudo-second-order models. Obviously, the adsorption of the alkaline-etched adsorbents was significantly improved, and the sample LDH-12 possessed the superior CO2 adsorption capacity of 19.6 mg/g. As the alkaline etching time further increased, the CO2 adsorption capacity of LDH-18 declined. Additionally, the fitting coefficient of the pseudo-second-order model was higher than that of the first-order model, which suggested the existence of chemical adsorption. These above results show that the alkaline etching treatment had an obvious effect on the morphology and structure of the samples, and the adsorption performance of the alkaline-etched samples are greatly improved. Moreover, an appropriate alkaline etching time could advance the development of pore structure of the adsorbent and facilitate the contact between CO2 molecules and the active sites over the adsorbent, thus promoting CO2 capture to a large extent. Consequently, this work will be beneficial to solve the problems in traditional hydrotalcite-like compounds for CO2 adsorption and have great potential and important academic significance for fabricating high-efficient CO2 adsorbent materials. |
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