(258j) Semiconducting Perovskite Oxides (ABO3: A = La; B = Cr, Mn, Fe) for Photocatalytic Reduction of CO2

Photocatalysis is one of the most researched protocols for harvesting solar energy. There have been several efforts towards solar photocatalytic water and CO₂ splitting. Though, titanium dioxide (TiO₂) has been one of the most popular photocatalysts, it has always suffered from the intrinsic inability to utilize a major range of solar spectrum due its large band gap, and hence, mostly suited for harvesting UV light. Thus, there is a significant interest in creating efficient photocatalysts that can capture the visible light.

Perovskite oxides of the form (ABO₃) is a unique material having a broad range of band gaps. They are mostly prevalent in cubic forms and suited for a vast range of applications from photocatalysis, electrocatalysis, photovoltaics, sensors etc. They are stable in varied conditions and exhibit high oxygen mobility. Usually they have a Group II element like calcium, strontium, barium or lanthanides as the â??Aâ? site component while they have transition elements as the â??Bâ? site component. These materials can accommodate different elements in their â??Aâ? and â??Bâ? sites and can form mixed metal oxide phases like A1_(1-x)A2_xBO₃, AB1_(1-y)B2_yO₃ and A1_(1â??x)A2_xB1_(1â??y)B2_yO₃. Thus, it presents a huge opportunity to control the material properties by simply compositional tuning.

We hereby, investigated the effect of varying the â??Bâ? site elements on the band gap and band edge positions. The different â??B1â? and â??B2â? elements in AB1_(1-y)B2_yO₃ were chromium, manganese and iron in different compositions while the â??Aâ? site had been fixed for lanthanum. We synthesized the materials via Pechini process and characterized through x-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS). These materials were henceforth, tested for photocatalytic CO₂ conversion using our lab-built reactor set-up. LEDs of different wavelengths were used to test the photo-reduction effect under visible and UV light. For better understanding of the reaction mechanism, we performed Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS) experiments of CO₂ photo-reduction under different light sources. Theoretical calculations based on density functional theory (DFT) have been performed as well to probe the band-structure of these perovskite oxides. Results have been compared for various functionals like LDA, PBE-GGA, B3LYP, HSE06. The effect of composition on band gap tuning of LaB1_(1â??y)B2_yO₃ perovskite oxides and its implications towards photocatalytic reduction of CO₂ are thus being explored.