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

Abstract

A sea urchin-shaped, single-layer, and hollow NiO–NiS photocatalyst with a large surface area was designed for carbon dioxide (CO2) 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, CO2 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 m2 g−1) catalyst. The CO2 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 CO2 and H2O, the adsorption of water molecules on the Ni–S surface and that of CO2 gas on the Ni–O surface during CO2 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 CO2 photoreduction performance under sunlight.