Optimized CO₂ photoreduction using cuprous oxide (Cu₂O) nanoparticles synthesized using Psidium guajava extract

This work aims to propose earth-abundant materials for CO₂ photoreduction to generate renewable solar fuels to provide practical solutions to global warming. The selected material in this case is cuprous oxide (Cu₂O), one of the most promising photocatalysts for CO₂ photoreduction due to its high affinity to solar radiation and electronic properties. Cu₂O nanoparticles (NPs) were synthesized using Psidium guajava residue for the photocatalytic CO₂ reduction. The aqueous residue of the Psidium guajava fruit proved to be suitable for stabilizing and acting as a reducing agent for the synthesis of Cu₂O NPs. The XRD analysis confirmed the formation of the cubic structure of Cu₂O. The nanoparticles absorb light from 430 nm with a direct bandgap value of around 1.8 eV. Cu₂O NPs exhibited activity for CO₂ photoreduction, whose efficiency was optimized by an orthogonal Taguchi L₉ design. The factors studied were catalyst loading, air flow, and temperature. During the use of Cu₂O NPs in the CO₂ photoreduction HCOOH was identified as the main product, with an optimized production of 103.4 µmol h^− 1 under visible light. Also, it was demonstrated the photocatalytic activity of the Cu₂O NPs for H₂ evolution by water splitting.