Accelerating Charge Separation and CO₂ Photoreduction in Aqueous Phase under Visible Light with Ru Nanoparticles Loaded on Ga-Doped NiTiO₃ in a Batch Photoreactor

Abstract

Titanate perovskite (ATiO 3 ) semiconductors show prospects of being active photocatalysts in the conversion of CO 2 to chemical fuels such as methanol (CH 3 OH) in the aqueous phase. Some of the challenges in using ATiO 3 are limited lightharvesting capability, rapid bulk charge recombination, and the low density of catalytic sites participating in CO 2 reduction. To address these challenges, Ga-doped NiTiO 3 (GNTO) photocatalysts in which Ga ions substitute for Ti ions in the crystal lattice to form electron trap states and oxygen vacancies have been synthesized in this work. The synthesized GNTO was then loaded with Ru nanoparticles to accelerate charge separation and enable excellent CO 2 photoreduction activity under visible light. CO 2 photoreduction was conducted in a batch photoreactor charged with a 0.1 M NaHCO 3 aqueous solution at room temperature and a 3.5 bar pressure using a 1.0 wt % Ru-GNTO photocatalyst to yield methanol at a rate of 84.45 μmol g −1 h −1 . A small amount of methane was produced as a side product at 21.35 μmol g −1 h −1 , which is also a fuel molecule. We attribute this high catalytic activity toward CO 2 photoreduction to a synergistic combination of our novel heterostructured 1.0 wt % Ru-GNTO photocatalyst and the implementation of a pressurized photoreactor. This work demonstrates an effective strategy for metal doping with active nanospecies functionality to improve the performance of ATiO 3 photocatalysts in valorizing CO 2 to solar fuels.