Boosting solar-driven N2 to NH3 conversion using defect-engineered TiO2/CuO heterojunction photocatalyst

Ammonia (NH3) is one of the important energy sources for sustainable chemical products and carbon-free energy carriers. Artificial N-2 photofixation is one of the promising approaches for the clean production of NH3 using photocatalysts in N-2-dissolved water as a hydrogen source. We prepared defect-engineered TiO2/CuO hetero-junction photocatalysts by the simple evaporation-induced self-assembly (EISA) method followed by post-thermal annealing under inert gas flow. The formation of a type-II using TiO2 and CuO facilitated light ab-sorption in near IR to UV light and the separation of photoexcited electron-hole pairs. In addition, the further post-thermal annealing under N-2 gas flow resulted not only in an increase in crystallinity for the photoactive Anatase TiO2 and Tenorite CuO in the bulk but also in the in-situ formation of Ti3+ defect sites on the TiO2 surface. The increased crystallinity enhanced the photoexcited charge transport, while the defect sites improved N-2 adsorption and activation, promoting the photocatalytic conversion of N-2 to NH3. The defect-engineered TiO2/CuO photocatalysts exhibited a high NH3 production rate (1.575 (mu) mol g(-1)h(-1)) under visible light irra-diation (lambda >= 420 nm) without any sacrificial agent, this value is 9.4 times and 2.5 times higher than those ob-tained with pristine TiO2 and TiO2/CuO photocatalysts, respectively. This work clearly demonstrates the synergistic effect of heterojunction and defect-engineering and provides insights into how each strategy can affect solar-driven NH3 production.

Automated summary

This study presents the preparation of defect-engineered TiO2/CuO hetero-junction photocatalysts for visible light-driven NH3 production through N-2 photofixation. The introduction of a type-II hetero-junction between TiO2 and CuO enhances light absorption and electron-hole separation. Moreover, the post-thermal annealing under N-2 gas flow increases the crystallinity and induces the formation of Ti3+ defect sites on the TiO2 surface. The defect-engineered TiO2/CuO photocatalysts show significantly improved NH3 production rate compared to pristine TiO2 and TiO2/CuO photocatalysts.