# Application of Nanofluids in CO\({}_{2}\) Absorption: A Review
## 3 Effective Factors in the CO\({}_{2}\) Absorption by Nanofluid
### Effect of Nanoparticle Concentration  
In one investigation, an isothermal quasi-static high pressure stirred reactor was utilized to study the effect of temperature and concentration of ZnO and SiO\({}_{2}\) nanoparticles in water-based nanofluid on CO\({}_{2}\) absorption. Results indicated temperature enhancement slightly reduces the CO\({}_{2}\) absorption, whereas the addition of 0.1 wt.% ZnO and SiO\({}_{2}\) increases the CO\({}_{2}\) absorption by 14% and 7%, respectively [88]. The influence of MWCNTs addition to the CO\({}_{2}\) absorbent fluid was investigated by [PERSON] et al., and the outcomes indicated that 0.02 wt.% concentration of MWCNTs with carboxyl functional groups in Sulfinol-M absorber results in a 23.2% enhancement in CO\({}_{2}\) equilibrium solubility compared to the base fluid [89]. CO\({}_{2}\) absorption in a bubble absorber system was studied by [PERSON] et al., to evaluate the performance of a nanofluid containing SiO\({}_{2}\) nanoparticles on CO\({}_{2}\) absorption. The 0.21 wt.% nanofluid showed a 24% enhancement in CO\({}_{2}\) absorption performance compared to pure water as its base fluid [90]. [PERSON] et al., investigated the  
Figure 4: The main parameters of nanoparticles in CO\({}_{2}\) absorption.  
effect of Ag nanoparticle addition into water/NH\({}_{3}\) mixture on the mass transfer performance of an absorption column, they found that the rate of CO\({}_{2}\) absorption was increased by 55% when 0.02 wt.% Ag nanoparticles were added to the solution [91]. [PERSON] and [PERSON] used a bubble column system to investigate the influence of Al\({}_{2}\)O\({}_{3}\) nanoparticles addition to a NaCl solution on the CO\({}_{2}\) absorption performance of the system and observed that only 0.01 vol% of Al\({}_{2}\)O\({}_{3}\) nanoparticles can improve the CO\({}_{2}\) solubility. All these investigations indicate that the addition of small amounts of nanoparticles to an absorption fluid can enhance its absorption capacity [92]. The CO\({}_{2}\) absorption capacity of a nanofluid containing Fe\({}_{2}\)O\({}_{3}\) nanoparticles was recently investigated by [PERSON] et al. [93] and it was shown that the maximum mean CO\({}_{2}\) flux of \(2.8\times 10^{-5}\) mol/(m\({}^{2}\).s) was achieved at a Fe\({}_{2}\)O\({}_{3}\) concentration of 1 wt.%, which decreased after a while. The effect of HKUST-1 with polyethyleneimine functional groups was studied on the CO\({}_{2}\) absorption capacity of an aqueous solution of 40 wt.%. This study which was carried out by [PERSON] et al., showed a 16% enhancement in CO\({}_{2}\) absorption capacity when only 0.2 wt.% nanoparticles were used [94]. [PERSON] et al., studied the influence of Al\({}_{2}\)O\({}_{3}\) nanoparticles on mass transfer of a water-based nanofluid and reported the maximum CO\({}_{2}\) absorption enhancement at 0.6 vol% concentration of Al\({}_{2}\)O\({}_{3}\) nanoparticle [95]. [PERSON] et al. [96] and [PERSON] et al. [97; 98] added SiO\({}_{2}\) nanoparticles to a solution mixture of MEA, DEA, and Disopropanolamine to evaluate its performance in CO\({}_{2}\) absorption in a stirred cell. They witnessed a reduction in the CO\({}_{2}\) absorption rate by increasing the nanoparticle concentration, which is believed to be related to the elasticity of the solution [99]. According to these investigations, the addition of small amounts of nanoparticles to a fluid significantly enhances the CO\({}_{2}\) absorption of the nanofluid.