**5. Concluding remarks**

The present chapter has covered the topic of metal oxide nanoparticles (MO-NP) and nanocomposites (MO-NCP) and their application for carbon capture utilization and storage (CCUS). It was shown that MO-NP (or MO-NCP) can be synthesized using physical, chemical, and biological methods. Each approach is tuned to give a MO-NP (or MO-NCP) with specific features. Regardless the production route, it was highlighted the stability of the nanofluid was the main challenge.

In respect of CCUS application, the most prominent results were obtained from silica (SiO2) and alumina (Al2O3) oxides. SiO2-NP could alter the wettability in a manner to increase the production of heavy oil. Dispersed into polymeric base fluid, it was shown SiO2-NP could yield a gel-structure, which can plug the large voids of formation, leading to either an increment of oil production or prevent the leakage of sequestered gases. On the other, Al2O3-NP and its silicate composite could delay the deposition in heavy materials during the oil production using carbon dioxide (CO2) injection. On the other hand, it was shown that ferrous and ferric nanofluids could improve the heat transfer of the fluid, making them good candidate for solar thermal energy.
