Ni(OH)2 and Co(OH)2 modified g-C3N4 for photocatalytic CO2 reduction

Abstract

This study presents the synthesis and characterization of composite photocatalysts based on g-C₃N₄ modified with Ni(OH)₂ and Co(OH)₂ for CO₂ reduction under visible light (λ = 410 nm). XRD, UV-Vis spectroscopy, and high-resolution TEM analyses revealed that the deposition of hydroxides did not disrupt the g-C₃N₄ structure but caused a slight increase in the interlayer spacing and band gap; Ni(OH)₂ formed nanoparticles of ~7 nm, whereas Co(OH)₂ crystallized as larger particles of ~24 nm. TEM showed that after the photocatalytic CO₂ reduction, partial agglomeration of Ni(OH)₂/NiO occurs. The catalyst containing 0.1 wt.% Ni(OH)₂ exhibited the highest activity – 7.04 μmol·g^-1·h^-1, achieving a CO₂ reduction rate 1.9 times higher than that of pristine g-C₃N₄. The 0.5 wt.% Co(OH)₂/g-C₃N₄ photocatalyst was achieved a 1.3-fold increase in activity compared to pristine g-C₃N₄. This enhancement is attributed to the formation of a II type heterojunction between g-C₃N₄ and Ni(OH)₂, which facilitates charge transfer and suppresses recombination.