# Application of Nanofluids in CO\({}_{2}\) Absorption: A Review
## 6 Conclusions  
In this study, we have investigated hybrid systems, unique properties of nanomaterials, and their wide application in CO\({}_{2}\) absorption. In the last few decades, the properties of nanoparticles on a small scale with different structures have been significantly efficient in the energy field. Accordingly, we believe that such technology provides one of the effective \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Researchers**} & \multirow{2}{*}{**Base Fluid**} & \multirow{2}{*}{**Nanoparticle**} & **Size of** & \multirow{2}{*}{**Contactor Type**} & \multirow{2}{*}{**Enhancement \%**} & **Absorbent** \\  & & & & & & **Loading** \\ \hline [PERSON] et al. [24] & Salt solutions & Al\({}_{2}\)O\({}_{3}\) & \(<\)40 & Stirred cell reactor & \(-\)5.68  & 1 to 3.1 wt.\% \\ [PERSON] et al. [92] & NaCl solution & Al\({}_{2}\)O\({}_{3}\) & 40–50 & Bubble column & 12.5 & 0.01 vol\% \\ [PERSON] et al. [89] & Sulfinol-M & Fe\({}_{3}\)O\({}_{4}\) & ** ** & Quasi-static high & 14.7 & 0.02 wt.\% \\  & & MWCNT & 20–30 & & 23.2 & 0.02 wt.\% \\ [PERSON] et al. [83] & Ammonia solutions & Fe\({}_{3}\)O\({}_{4}\) & 20 & Bubbling reactor & 14.5 & 0.3 g/L \\ \hline \hline \end{tabular}  
* \({}^{1}\): decreases the absorption **: Inside diameter: 5–10 nm, outside diameter: 20–30 nm and length: 10–30 \(\mu\)m.  
\end{table} 
Table 5: Different based nanofluids for the improvement of CO\({}_{2}\) absorption. solutions for CO\({}_{2}\) absorption. In this review study, in addition to the nanofluid explanation, its application, and properties using the nanofluid preparation, we have tried to address the reasons behind the base liquid selection, stability, mass transfer enhancement mechanisms in the nanofluids (shuttle effect, Bubble Breakup effect, and micro convection), and the CO\({}_{2}\) absorption increasing factors following the nanofluids. One of the most important points of the hybrid systems is the role of the base solvent, in which by properly selecting the nanoparticles-base solvent pair, the mass transfer rate and mechanism for CO\({}_{2}\) absorption have been substantially increased, accelerating the CO\({}_{2}\) reaction kinetics. On the contrary, lower energy consumption is required for solvent regeneration in the desorption process by decreasing the heat transfer in such systems. For this reason, in this study, the effect of 3 types of base liquid, e.g., water, amine and methanol, with different nanoparticles have been evaluated on the CO\({}_{2}\) absorption level. In the following, we will briefly explain the main results of this short review. 1. CO\({}_{2}\) absorption using nanofluids depends on several factors, i.e., particle size, nanoparticle type, temperature, and base liquid. 2. The nanoparticles preparation method and their stability are some of the important properties of nanofluids that should be taken into consideration. This is because the hybrid systems create sediments and settle over time. Accordingly, in order to control this issue, we can reform the nanoparticles' surface or the low-cost dispersions so that the stability of the nanofluids is increased. 3. The suspension preparation process is of paramount importance in terms of the type and the extent of solid particles since the nanoparticles' cost as an additive solid material to the base solvent is one of the important economic issues. Similarly, in hybrid systems, the nanoparticles synthesis is usually done using the 2-step method that is cost-effective. 4. The main mechanisms for the CO\({}_{2}\) absorption, the shuttle effect, bubble breakup, and the Brownian motion leading to the nanoparticles' micro convection have been thoroughly explained. It is expected that other mechanisms will be explained in this field in the future. 5. The CO\({}_{2}\) absorption in the nanofluid depends on the different surfaces of the nanoparticles; as a nanoparticle has a larger surface, it is dispersed better in the base liquid, increasing the absorption level. 6.