The friction between some nanomaterials and teflon magnetic stirring rods has recently been found responsible for dye degradation by magnetic stirring in dark. In this work, a study is conducted on the reduction of CO₂ by TiO₂ nanoparticles under magnetic stirring in water. In a 100-mL reactor filled with 50-mL water, 1.00-g TiO₂ nanoparticles and 1-atm CO₂, 50-h magnetic stirring results in the formation of 6.65 × 10^–6 (volume fraction) CO, 2.39 × 10^–6 CH₄ and 0.69 × 10^–6 H₂; while in a reactor without TiO₂ nanoparticles, the same magnetic stirring leads only 2.22 × 10^–6 CO and 0.98 × 10^–6 CH₄ to form. Four magnetic stirring rods are used simultaneously to further enhance the stirring, and 50-h magnetic stirring can form 19.94 × 10^–6 CO, 2.33 × 10^–6 CH₄, and 2.06 × 10^–6 H₂. A mechanism for the catalytic role of TiO₂ nanoparticles in the reduction of CO₂ and H₂O is established, which is based on the excitation of electron-hole pairs in TiO₂ by mechanical energy absorbed through friction. This finding clearly demonstrates that nanostructured semiconductors are able to utilize mechanical energy obtained through friction to reduce CO₂, thus providing a new direction for developing and utilizing the mechanical energy harvested from ambient environment.