3.5 CO2 adsorption/desorption cycling test

For practical applications, the stability of adsorbents during the adsorptiondesorption process should be considered. Hence, it is badly needed to test its cycle operation. Figure 9 shows six successive runs of adsorption-desorption isotherms of LDHs at 80°C. TUC-LDHs shows an initial cyclic adsorption capacity (0.33 mmol g<sup>1</sup> ). However, it decreased to CO2 adsorption capacity of 0.21 mmol g<sup>1</sup> at second cycle, which is 67% of the original capacity. At six cycles of absorption, the adsorption capacity is still 0.2 mmol g<sup>1</sup> with 60.6% of the original capacity although CO2 adsorption is fluctuated during the middle process. The decrease of adsorption capacity over several cycles has also been reported by several research groups. The main reason for the decrease of CO2 adsorption is possible that some chemical sorption sites are blocked during the subsequent adsorption/ desorption cycles. TU-LDHs and CC-LDHs show an initial CO2 adsorption capacity of 0.30 and 0.24 mmol g<sup>1</sup> , in which the retentions could achieve as high as 69.8 and 54.7%, respectively. These results indicate that the TU process played a role not only in increasing CO2 sorption capacity, but also in improving the cyclic performance. The experimental results show that stability of hydrotalcites synthesized by both TUC and TU method are higher than the conventional prepared LDHs, which seems promising adsorbents for CO2 adsorption.

## 4. Conclusions

The present studies have demonstrated that the MgAl LDHs as a CO2 adsorbent can be synthesized successfully through an ultrasonic assisted 'T-mixer' (TU-LDHs), hybrid two-step preparation method (TUC-LDHs) and conventional copreparation (CC-LDHs) method. The conclusions reached as the results of the current study are as follows:


### Acknowledgements

This work was financially supported by National Natural Science Foundation of China (NSFC) (Grant No. 21576141) and Zhejiang Provincial Natural Science Foundation (Grant No. LY15B060001). This work was carried out at the International Doctoral Innovation Centre (IDIC). Xiani Huang would also like to

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

acknowledge the support through the Ph.D. scholarship of the International Doctoral Innovation Centre (IDIC) of University of Nottingham Ningbo China.
