Photocatalytic reduction of CO2 over Ti3+ self-doped TiO2-based nanomaterials

Abstract

In this study, we explored the photocatalytic efficacy of Ti3+-doped TiO2-based photocatalysts for CO2 reduction. The Ti3+ self-doped photocatalysts were synthesized using a straightforward chemical reduction with sodium borohydride (NaBH4). Our investigation aimed to elucidate the intricate interplay between the synthesis process and the quantity of NaBH4 reductant on the physical-chemical and photocatalytic attributes of the defective TiO2-based photocatalysts. We explored three different commercially available TiO2 materials labeled P25, (S) TiO2, and KRONOClean7050, which were reduced (2 g of TiO2) with 0.75 and 1.5 g of NaBH4. The reduction with 0.75 g of NaBH4 led to a significant decrease of photocatalytic activity in all three cases. It was caused by clogging of the photocatalysts surface by sodium ions which resulted in the surface recombination of charge carriers. Oppositely, the reduction with 1.5 g of NaBH4, led to an increase of the photocatalytic activity with superior performance of KRONOClean7050. The comprehensive characterization of all the samples explained this superior performance of KC7050_RED_1.5 sample. Importantly, it did not contain any amorphous phase and the crystal size was two times higher compared to other 2 samples reduced by 1.5 g of NaBH4. In the addition to higher crystallinity, the formation of a disordered TiO2_x layer, enriched with Ti3+ defects and oxygen vacancies, was confirmed. These structural features enhance the light absorption and mitigate undesired recombination of photogenerated charge carriers. These results would trigger farther investigation of defect engineering towards enhancement of the efficiency of metal oxide photocatalysts.