2.2.2 XRD

The structure of the prepared samples were analysed by XRD through conducting in a Bruke-AXS D8 advance powder diffractometer using Cu-Ka radiation (λ = 1.5418 Å) and a power of 40 kv\*20 Ma, where the diffraction patterns were recorded in the range 2θ = 5–80° with a step size of 0.01°.

## 2.2.3 SEM and EDXS

The morphologies of synthesized LDHs were observed using SEM produced from ZEISS ZIGMA 174C CZ. The element analysis was conducted by use of an Oxford Instrument INCAx-act PentaFET® Precision EDXs.

## 2.2.4 TEM

High-resolution TEM images were obtained using JEM-2100 electron microscope operating at 200 kV, whereby a drop of solution was placed onto a Cu grid and dried in infrared lamp for several minutes.

Hybrid Two-step Preparation of Nanosized MgAl Layered Double Hydroxides for CO2 Adsorption DOI: http://dx.doi.org/10.5772/intechopen.86608

## 2.3 Carbon dioxide adsorption measurements

The CO2 adsorption test and regenerability of the synthesized adsorbents were measured by Netzsch TG 209 F1 thermogravimetric analyser (TGA) at atmosphere pressure under dry conditions. Pure CO2 gas was used to carry out the whole adsorption/desorption measurement. Before adsorption test, all the samples were calcined at 500°C for 5 h in an Ar atmosphere. About 10 mg of sample loaded into an alumina crucible was heated from 25 to 105°C at 10°C min�<sup>1</sup> under N2 atmosphere for 60 min and then switched to desired temperature (80, 150 and 200°C) at the rate of 10°C min�<sup>1</sup> . During the isothermal stage, the gas input changed from N2 to CO2 and held for 90 min. The CO2 adsorption capacity of the sample-qt (mmol g�<sup>1</sup> ) was calculated according to the weight gain of the sample and expressed as the mole of CO2 absorbed per gram of adsorbent:

$$q\_t = \frac{m\_t - m\_o}{m \times M} \times 1000\tag{1}$$

where mO and mt (mg) are the initial mass of adsorbent for CO2 adsorption and mass of adsorbent for CO2 adsorption at time t, respectively. m is the total mass of sorbent (mg) and M is molar mass of CO2 (44 mol g�<sup>1</sup> ).

In the absorption/desorption cycle, about 10 mg of the above calcined samples was heated from 25 to 105°C at 10°C min�<sup>1</sup> under N2 atmosphere (40 mL min�<sup>1</sup> ) for 60 min and then switched to 80°C at a cooling rate of 10°C min�<sup>1</sup> . After adsorption, the desorption process was carried out as the gas input was switched from CO2 to N2 at 105°C. The adsorption/desorption process was repeated in six cycles.

#### 2.4 Error analysis

2.2 Materials characterization

2.2.1 BET

Figure 1.

Sorption in 2020s

2.2.2 XRD

2.2.4 TEM

126

2.2.3 SEM and EDXS

and transmission electron microscope (TEM).

The structures of MgAl LDHs were characterized using a combination of methods including BET-specific surface areas, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) analysis

Schematic illustrating the preparation process of MgAl LDHs by hybrid two steps.

Nitrogen adsorption/desorption isotherms were carried out on a Micromeritics ASAP2020 surface area and pore size analyser at 77 K. Before conducting each measurement, the prepared LDHs were first degassed at 110°C overnight.

The structure of the prepared samples were analysed by XRD through conducting in a Bruke-AXS D8 advance powder diffractometer using Cu-Ka radiation (λ = 1.5418 Å) and a power of 40 kv\*20 Ma, where the diffraction patterns were

The morphologies of synthesized LDHs were observed using SEM produced from ZEISS ZIGMA 174C CZ. The element analysis was conducted by use of an

High-resolution TEM images were obtained using JEM-2100 electron microscope operating at 200 kV, whereby a drop of solution was placed onto a Cu grid

recorded in the range 2θ = 5–80° with a step size of 0.01°.

Oxford Instrument INCAx-act PentaFET® Precision EDXs.

and dried in infrared lamp for several minutes.

To determine the validity of isotherm and kinetics models, two different error functions, i.e. chi-square (X<sup>2</sup> ) and normalized standard deviation Δqð Þ % , and correlation coefficient equation R2 were evaluated between experimental and calculated data, which are given by

$$\text{Chi} - \text{square} : X^2 = \sum\_{i=1}^{n} \frac{\left(q\_i - q\_\epsilon\right)^2}{q\_\epsilon} \tag{2}$$

$$\text{Normalized standard deviation} : \Delta q(\%) = \sqrt{\frac{\sum\_{i=1}^{n} \left[ (q\_t - q\_\epsilon) / q\_\epsilon \right]^2}{n - 1}} \times 100 \tag{3}$$

$$\text{Correlation coefficient equation}: R^2 = \mathbf{1} - \left(\frac{\sum\_{j=1}^{\mathbf{N}} (q\_t - q\_\epsilon)^2}{\sum\_{j=1}^{\mathbf{N}} (q\_t - \overline{q\_\epsilon})^2}\right) \times \left(\frac{\mathbf{N} - \mathbf{1}}{\mathbf{N} - \mathbf{p}}\right) \tag{4}$$

where qt and qe are CO2 uptake determined by experiment and computed by model, respectively. qe is the mean experimental data, p is the number of model parameters and N is total number of experimental points. The most suitable model to describe the CO2 adsorption process is the one with highest R2 value.
