Abstract

Amine functionalized layered double hydroxide (LDHs) adsorbents prepared using three different routes: co-precipitation, sono-chemical and ultrasonic-assisted high pressure hydrothermal. The prepared adsorbent samples were characterized using X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning electron microscope-Energy dispersive X-ray spectroscopy (SEM-EDX), Temperature Programmed Desorption (TPD), Brunauer-Emmett-Teller (BET), and Thermogravimetric analysis (TGA), respectively. The performance of the prepared adsorbents was tested in a controlled thermal-swing adsorption process to measure its adsorption capacity, regeneration and cyclic efficiencies subsequently. The characterisation results were compared with those obtained using the conventional preparation routes but taking into account of the impact of sonochemical and hydrothermal pre-treatment on textural properties, adsorption capacity, regeneration and cyclic efficiencies. Textural results depicts a surge in surface area of the adsorbent synthesised by hydrothermal route (311m2/g) from 25 to 171m2/g for conventional and ultrasonic routes respectively. Additionally, it has been revealed from the present study that adsorbents prepared using ultrasonic-assisted hydrothermal route exhibit a better CO2 uptake capacity than that prepared using sonochemical and conventional routes. Thus, the ultrasonic-assisted hydrothermal treatment can effectively promote the adsorption capacity of the adsorbent. This is probably due to the decrease of moderate (M-O) and weak (OH− groups) basic sites with subsequent surge in the number of strong basic sites (O2−) resulting from the hydrothermal process. Moreover, the cyclic adsorption efficiency of the ultrasonic mediated process was found to be 76% compared with 60% for conventional and 53% for hydrothermal routes, respectively. According to the kinetic model analysis, adsorption mechanism is mostly dominated by physisorption before amine modification and by chemisorption after the modification process.

Highlights

  • Adsorption of carbon dioxide is perceived as the most suitable method for Carbon Capture and Storage (CCS) technology [1, 2]

  • The total pore volume showed a tremendous increase indicating that the sonication and hydrothermal preparation methods enhances the porosity of the sample as well as the surface area when compared to other studies

  • The results obtained using the kinetic models clearly indicate that prior to amine extraction, the adsorption of Mg-Al Layered double Hydroxides (LDHs) adsorbent is mostly facilitated by physisorption while adsorption is mainly promoted by chemisorption after amine extraction

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Summary

Introduction

Adsorption of carbon dioxide is perceived as the most suitable method for Carbon Capture and Storage (CCS) technology [1, 2]. LDHs are anionic clay minerals known as mixed-metal layered hydroxides or hydrotalcites-like compounds They possess two dimensional structure of layers shaped by trivalent and divalent cations parted by water and anions molecules (see Figure 1) with a general formula: where M2+ and M3+ are divalent and trivalent cations respectively, Am- is a compensating anionic charge, x is the partial substitution of M2+ and M3+, usually within a M2+/M3+ ratio of 2 and 5 [46]. They possess two dimensional structure of layers shaped by trivalent and divalent cations parted by water and anions molecules (see Figure 1Figure 1) with a general formula: Formatted: Font: Not Bold where M2+ and M3+ are divalent and trivalent cations respectively, Am- is a compensating anionic charge, x is the partial substitution of M2+ and M3+, usually within a M2+/M3+ ratio of 2 and 5 [46]

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