# Application of Nanofluids in CO\({}_{2}\) Absorption: A Review
## 4 Classification of Nanofluids Based on Base Liquid
### Water-Based Nanofluid
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Researchers**} & \multirow{2}{*}{**Base Fluid**} & \multirow{2}{*}{**Nanoparticle**} & \multicolumn{2}{c}{**Size of**} & \multirow{2}{*}{**Contactor Type**} & \multirow{2}{*}{**Enhancement \%**} & **Absorbent** \\  & & & & & & & \\ \hline [PERSON] et al. [116] & MDEA & nMWCNT & 11.6 & Stirred reactor & 141.6 & 0.05 wt.\% \\  & MEA & & 11.6 & & & 20.79 & 0.1 wt.\% \\ [PERSON] et al. [42] & MEA & TiO\({}_{2}\) & 20 & Bubbling reactor & 9 & 0.6 kg/m\({}^{3}\) \\  & MDEA & TiO\({}_{2}\) & 20 & & & 30 & 0.4 kg/m\({}^{3}\) \\  & MEA & Al\({}_{2}\)O\({}_{3}\) & 20 & & 4 & 0.6 kg/m\({}^{3}\) \\  & MDEA & Al\({}_{2}\)O\({}_{3}\) & 20 & & 15 & 0.8 kg/m\({}^{3}\) \\ [PERSON] et al. [114] & MDEA & GO & 29.3-35.16 & Stirred cell reactor & 10.4 & 0.2 wt.\% \\ [PERSON] et al. [117] & DEA & Al\({}_{2}\)O\({}_{3}\) & 10-20 & WWC & 33 & 0.05 wt.\% \\  & & SiO\({}_{2}\) & 10–15 & & 40 & 0.05 wt.\% \\ [PERSON] et al. [94] & MDEA & PEI-HKUST-1 & - & PSE & 16 & 0.2 wt.\% \\ [PERSON] et al. [72] & MDEA & GO & - & Stirred cell reactor & 10.4 & 0.2 wt.\% \\  & PEI-CO & - & & 15 & 0.1 wt.\% \\ [PERSON] et al. [84] & MDEA & CNT & \(\star\) & Batch vessel & 23 & 0.02 wt.\% \\ [PERSON] et al. [118] & PZ & TiO\({}_{2}\) & 20 & Stirrer Bubble column & 14.7 & 0.05 wt.\% \\  & ZnO & 10-30 & & 16.6 & 0.1 wt.\% \\  & & ZrO\({}_{2}\) & 20 & & 3.7 & 0.05 wt.\% \\ [PERSON] et al. [119] & MDEA & TiO\({}_{2}\) & 15 & Stirred cell reactor & 11.54 & 0.8 wt.\% \\ [PERSON] et al. [99] & MDEA & Fe\({}_{3}\)O\({}_{4}\) & 15 & WWC & 90 & 0.39 vol\% \\ [PERSON] et al. [112] & MEA & Al\({}_{2}\)O\({}_{3}\) & 15 & Bubble Column & 10 & 0.06 wt.\% \\  & & SiO\({}_{2}\) & 15 & & 10 & 0.06 wt.\% \\ [PERSON] et al. [113] & MEA & Al\({}_{2}\)O\({}_{3}\) & 20 & WWC & 7 & 0.02 wt.\% \\  & SiO\({}_{2}\) & 15 & & 10 & 0.06 wt.\% \\ [PERSON] et al. [120] & MDEA & Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)-NH\({}_{2}\) & 31–39 & Stirred cell reactor & 16.36 & 0.1 wt.\% \\  & & Fe\({}_{3}\)O\({}_{4}\)-proline & 10–16 & & 6.78 & 0.02 wt.\% \\  & & Fe\({}_{3}\)O\({}_{4}\)-lysine & 13–18 & & 12.13 & 0.1 wt.\% \\ [PERSON] et al. [121] & TETA & SiO\({}_{2}\) & 45 & Bubble reaction system & 29 & 0.10 wt.\% \\ \hline \hline \end{tabular}  
*: Outside diameter = 8 nm, Inside diameter = 2.5 nm and Length= 10 \(\upmu\)m.  
\end{table} 
Table 2: Summary of various types of amine-based nanofluids. of the nanofluid after the addition of magnetic nanoparticles in the CO\({}_{2}\) capture process [34]. [PERSON] et al., could achieve 22.35% and 59% enhancement in CO\({}_{2}\) mass flux and mass transfer coefficient just by using a wetted wall column for CO\({}_{2}\) absorption, which was equipped with an external magnetic field. The nanofluid that was used in their experiments was Fe\({}_{3}\)O\({}_{4}\)/water [127]. The Fe\({}_{3}\)O\({}_{4}\) nanofluid was also examined by [PERSON] et al., for the CO\({}_{2}\) absorption in constant and alternating magnetic fields. The results indicated that high strength magnetic fields increase both mass transfer rate and solubility of CO\({}_{2}\). The results showed a maximum value of CO\({}_{2}\) solubility and the average molar flux of absorption into the nanofluid when an AC field was applied. They indicated that as the strength of the magnetic field increases, the renewal surface factor and CO\({}_{2}\) mass diffusivity in the nanofluid increase as well, while the thickness of the diffusion layer decreases [93]. [PERSON] et al., utilized a batch stirred vessel to study CO\({}_{2}\) solubility in SiO\({}_{2}\)/water and ZnO/water nanofluids. The ZnO/water nanofluid showed better CO\({}_{2}\) absorption than the SiO\({}_{2}\)/water nanofluid in their experiments. Furthermore, CO\({}_{2}\) absorption was examined by some researchers in membrane Contactors with water as the absorption media. They found that the addition of some materials as promoters to deionized water can enhance the absorption rate and capacity of CO\({}_{2}\)[88].