Synthesis, characterization, and photocatalytic properties of Au nanoparticle-anchored TiO2 and CaCO3 core–shell composite particles

• Hybrid core–shell photocatalysts of titanium TiO 2 and CaCO 3 were synthesised • TiO 2 and CaCO 3 core–shell photocatalysts with surface-anchored Au nanoparticles • The CaCO 3 layer of Au-anchored CaCO 3 coated TiO 2 exhibited smaller crystallite size • Au-anchored core–shell particles of CaCO 3 on TiO 2 exhibited superior CH 4 production TiO 2 -based photocatalysts have garnered considerable attention, yet a deeper understanding of their photoreduction mechanism is essential for improved material design and application. In this study, core–shell composites were synthesised by coating CaCO 3 , with TiO 2 via a sol-gel method using titanium tetraisopropoxide. Gold nanoparticles (AuNPs) were subsequently anchored onto the composite surface. The CaCO 3 @TiO 2 composite was prepared by precipitating CaCO 3 on TiO 2 using a carbonation method in which CO 2 was passed through a saturated aqueous solution of Ca(OH) 2 containing TiO 2 . The AuNPs were anchored to the surfaces of the core–shell particles via precipitation using HAuCl 4 · 4H 2 O as the precursor. Various physicochemical characterizations were performed on the synthesised photocatalysts. The photocatalytically produced amounts of CH 4 and CO were evaluated. As compared to AuNP/TiO 2 @CaCO 3 , AuNP/CaCO 3 @TiO 2 produced 17 times more CH 4 and 1.4 times more CO via CO 2 reduction. The obtained results suggest that multi-electron reduction in AuNP/CaCO 3 @TiO 2 to produce CH 4 occurs near CaCO 3 , which is an insulator with CO 2 adsorption ability. Furthermore, the amount of CH 4 produced using AuNP/CaCO 3 @TiO 2 was 1.1 times higher than that produced by a reported catalyst, which was prepared by physically mixing TiO 2 and CaCO 3 in the same ratio as that in AuNP/CaCO 3 @TiO 2 ; the dissimilarity in the chemical structures of the physically mixed and precipitated photocatalysts was held responsible for the observed differences in their photocatalytic efficiencies. This study advances the existing knowledge about the mechanism of photocatalytic reduction reactions using TiO 2 -based materials.