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 CO ₂by TiO ₂nanoparticles under magnetic stirring in water. In a 100-mL reactor filled with 50-mL water, 1.00-g TiO ₂nanoparticles and 1-atm CO ₂, 50-h magnetic stirring results in the formation of 6.65 × 10 ^–6(volume fraction) CO, 2.39 × 10 ^–6CH ₄and 0.69 × 10 ^–6H ₂; while in a reactor without TiO ₂nanoparticles, the same magnetic stirring leads only 2.22 × 10 ^–6CO and 0.98 × 10 ^–6CH ₄to form. Four magnetic stirring rods are used simultaneously to further enhance the stirring, and 50-h magnetic stirring can form 19.94 × 10 ^–6CO, 2.33 × 10 ^–6CH ₄, and 2.06 × 10 ^–6H ₂. A mechanism for the catalytic role of TiO ₂nanoparticles in the reduction of CO ₂and H ₂O is established, which is based on the excitation of electron-hole pairs in TiO ₂by mechanical energy absorbed through friction. This finding clearly demonstrates that nanostructured semiconductors are able to utilize mechanical energy obtained through friction to reduce CO ₂, thus providing a new direction for developing and utilizing the mechanical energy harvested from ambient environment.