Wettability control of defective TiO 2 with alkyl acid for highly efficient photocatalytic ammonia synthesis

Ammonia is an important chemical raw material and non-carbon-based fuel. Photocatalytic ammonia production technology as a mild alternative to the traditional Harbor–Bosch route is carried out at the air, liquid, and solid three-phase interface. Promoting the activation of N 2 , depressing hydrogen evolution reaction (HER), and increasing the local N 2 concentration around the catalyst surface are critical factors in achieving high conversion efficiency. In this paper, we proposed that defective TiO 2 is surface-modified by alkyl acids with different carbon chain lengths (C 2 , C 5 , C 8 , C 11 , and C 14 ) to tune the catalyst surface properties. The defect sites greatly promote N 2 adsorption and activation. The wettability of the catalyst can be regulated from hydrophilic to hydrophobic by the length of the alkyl chain. The hydrophobic surface enhances the N 2 adsorption and increases the local N 2 concentration due to its aerophile. Meanwhile, it depresses the proton adsorption and HER. Overall, the nitrogen reduction reaction (NRR) is greatly promoted. Among the series of samples, they present a systematic change and have a maximal NRR performance for n-octanoic acid-defective TiO 2 (C 8 -Vo-TiO 2 ; Vo = oxygen vacancy). The rate of ammonia production can be as high as 392 µmol·g −1 h −1 . This work provides a new strategy for efficient ammonia synthesis at the three-phase interface using photocatalyst technology.