Single layered hollow NiO-NiS catalyst with large specific surface area and highly efficient visible-light-driven carbon dioxide conversion.

A sea urchin-shaped, single-layer, and hollow NiO-NiS photocatalyst with a large surface area was designed for carbon dioxide (CO ₂ ) conversion in this study. A d-glucose polymeric hollow frame was fabricated using a d-glucose monomer, and NiO particles were stably grown on it using the hydrothermal method to form a hollow NiO surface. The d-glucose frame was removed by heat treatment to create hollowed NiO; hollowed NiO-NiS (h-NiO-NiS) was subsequently obtained through ion exchange between the O ions in NiO and S ions in the sulfur powder. Additionally, we attempted to determine the correlation among the surface area of the h-NiO-NiS catalyst, CO ₂ gas adsorption capacity, and catalyst performance. The surface area of the h-NiO-NiS catalyst was ten times larger than that of the nanometer-sized NiO-NiS (n-NiO-NiS, 21.2 m ²  g ^-1 ) catalyst. The CO ₂ photocatalytic conversion performance of the hollowed catalyst was approximately seven times larger than that of the nanosized catalyst. As the amount of ion-exchanged S increased, methane selectivity increased, and optimal methane production was obtained when the weight ratio of NiO and sulfur powder was 1 : 4. Using temperature-programmed desorption (TPD) analyses of CO ₂ and H ₂ O, the adsorption of water molecules on the Ni-S surface and that of CO ₂ gas on the Ni-O surface during CO ₂ conversion reaction were confirmed. The h-NiO-NiS catalyst facilitated an effective charge separation through a well-developed interfacial transition between the linked NiS and NiO, and resulted in increased CO ₂ photoreduction performance under sunlight.
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