Reduction of CO<sub>2</sub> by TiO<sub>2</sub> nanoparticles through friction in water

Abstract

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