2. Experimental

technology on a large scale capture operation which could produce a series of bad effects such as toxicity, degradability, high regeneration energy requirements and corrosivity [2]. Hence, developing efficient and environmental friendly CO2 adsorbents will be crucial to CO2 capture. Layered double hydroxides (LDHs) are considered as good candidates for CO2 adsorption because of their fast sorption/ desorption kinetics and simple regenerability [3, 4]. LDHs are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. The typical structure of LDHs consists of positively charged brucite-like layers, containing anions and water molecules in the interlayer spaces. Metal cations occupy the centre of octahedral structures and hydroxides occupy the vertices. The general formula of LDHs can be expressed as [M2+1xm3+x(OH)2][An]x/n zH2O, where M2+are divalent cations, such as Mg2+, Zn2+, Ni2+, etc., and M3+ are trivalent cations, such as Al3+, Ga3+, Fe3+, Mn3+, etc. An is a non-framework charge com-

<sup>2</sup>, Cl, SO4

found that similar CO2 capture capacities (0.41–0.46 mmol g<sup>1</sup>

The performance of LDHs and derived CO2 adsorbents have been investigated for several years, and most of the studies are focused on the effects of divalent cations [6, 7], trivalent cations [8], charge compensating anions [9, 10], Mg-Al ratio

, Cs+

[17], the presence of SO2 and H2O [18, 19], particle size [3, 20] and calcination temperature or adsorption temperature [21, 22]. Yong and Rodrigues compared several commercial hydrotalcite-like compounds that can have the average CO2

when using Mg3Al1, Mg3Ga1 and Mg3Fe1 at different calcination temperatures [8]. Except for changing the composition of LDHs, controlling its particle size is also believed to be an effective way for improvement of the CO2 capture capacity. Significant amount of efforts have been made on developing new methods to control its particle size. Hanif et al. investigated the effect of synthetic routes (co-precipitation, ultrasonication and microwave irradiation) on improving the CO2 adsorption capacity of hydrotalcite-based sorbents in the temperature range 300–400°C [17]. They have reported that the CO2 adsorption capacity of LDHs prepared by ultrasound-assisted route and microwaving are better than that of

Adoption of confined impinging T-jet mixer (CITJ) is a simple component that

hydrotalcites. Ultrasonication and microwave irradiation of the synthesis gel during hydrotalcite precipitation leads to disruption in the layer stacking which in turn increases surface area [17]. To the best of our knowledge, the effect of the synthesis for the preparation of LDHs by applying jointly co-precipitation and ultrasonication in a T-jet mixer on the CO2 absorption capacity of LDHs has not yet been reported

In the present study, we will present a hybrid two-step method approach for preparation of MgAl layered double hydroxide (MgAl LDHs). The novel two-step preparation route utilising the MgAl LDHs synthesized from confined impinging T-jet mixer (CITJ) as seeds for future preparation. The synthesized samples were

contains two inlet tubes and let two streams flow out from the tube. The local micromixing effect could be intensified during the CITJ reactor, which is beneficial for a fast homogenization of reactors. The mass transfer rate and chemical reaction rate can also be enhanced during the preparation process. This has been confirmed by the studies on the preparation of FePO4 nanoprecursor particles of LiFePO4 cathode material where the high specific areas can be obtained [23, 24]. Coprecipitation method is the conventional procedure used for synthesis of

, Na+

<sup>2</sup>, etc., and the value of x is between 0.10

) at 300°C and 1 bar of CO2 [6]. Wang et al.

, etc.) [13–16], synthetic method

) can be obtained

pensating anion, such as CO3

co-precipitation method.

in the literature.

124

[6, 11, 12], alkaline metal cations (e.g. K<sup>+</sup>

adsorption capacity (0.2–0.5 mmol g<sup>1</sup>

and 0.33 [5].

Sorption in 2020s
