This study investigates the use of black brookite, a form of titanium dioxide (TiO₂) with a high concentration of lattice defects, as a photocatalyst for CO₂ conversion. The black brookite was produced using high-pressure torsion (HPT) to introduce defects such as oxygen vacancies, dislocations, and grain boundaries. These defects enhance light absorbance, narrow the optical bandgap, and reduce the recombination rate of electrons and holes, leading to improved photocatalytic activity. The black brookite demonstrated significantly higher CO₂ conversion efficiency compared to commercial brookite and benchmark P25 catalyst powders. First-principles calculations confirmed that the presence of oxygen vacancies not only reduces the optical bandgap but also provides active sites for CO₂ adsorption on the TiO₂ surface. The study highlights the potential of black brookite as an effective photocatalyst for CO₂ conversion and suggests that similar strategies can be applied to other defective black catalysts.This study investigates the use of black brookite, a form of titanium dioxide (TiO₂) with a high concentration of lattice defects, as a photocatalyst for CO₂ conversion. The black brookite was produced using high-pressure torsion (HPT) to introduce defects such as oxygen vacancies, dislocations, and grain boundaries. These defects enhance light absorbance, narrow the optical bandgap, and reduce the recombination rate of electrons and holes, leading to improved photocatalytic activity. The black brookite demonstrated significantly higher CO₂ conversion efficiency compared to commercial brookite and benchmark P25 catalyst powders. First-principles calculations confirmed that the presence of oxygen vacancies not only reduces the optical bandgap but also provides active sites for CO₂ adsorption on the TiO₂ surface. The study highlights the potential of black brookite as an effective photocatalyst for CO₂ conversion and suggests that similar strategies can be applied to other defective black catalysts.