In this work, we have investigated the capability of CO2 capture by single-walled, carbon-deficient silicon carbide nanotubes (Si12C12-X; X = 1; 2). All calculations of the properties of the investigated systems were performed using density functional theory with plane wave basis sets and pseudopotentials. Electronic interactions were determined using the generalized gradient approximation method in terms of the Perdew-Burke-and Ernzerhof exchange–correlation functional. The analysis of the photoabsorption properties of the investigated systems was based on structural, electronic and optical properties. Analysis of the structural properties revealed that as number of C vacancy increases, bond length decreases, which agrees well with previous literature. Regarding the CO2 overpotential value, both Si12C11:Vc1 and Si12C10:Vc2 showed band edges of -1.5 eV and -1.45 eV, respectively, which are more negative than the standard overpotential value (-1.4 eV) for CO2 reduction. Analysis of the optical absorption spectra revealed good photon absorption by Si12C11:Vc1 (4.16% defect) and Si12C10:Vc2 (8.33% defect) in the visible region accompanied by negligible electron–hole recombination, while pristine SWSiCNT showed absorption in the UV region accompanied by strong electron–hole recombination. This study found that Si12C11:Vc1 and Si12C10:Vc2 are well-suited for CO2 capture and storage, while underlining the CO2 capture capability of pristine SWSiCNT.