One-step solution combustion synthesis of micro-nano-scale porous Cu/CeO2 with enhanced photocatalytic properties*

The Cu/CeO2 nanoporous composite material was prepared via a one-step and energy-saving method of solution combustion synthesis (SCS). The phase composition, surface morphology and optical characteristics of Cu/CeO2 were studied. The results show that the SCS products are composed of cubic fluorite CeO2 and Cu. Due to the generation and escape of gas during the synthetic reaction, the SCS CeO2 shows porous structure, in which the mesopores (diameter 10-17 nm) nest in the wall of large pores (diameter 80-300 nm). X-ray photoelectron spectroscopy (XPS) outcomes indicate that the oxygen vacancy concentration of CeO2 increases (18.97%-30.93%) with the increase of Cu concentration. The decoration of Cu greatly enhances the catalytic activity of CeO2 nanomaterials. 30 wt% Cu/CeO2 composite material shows the best photocatalytic activities for the degradation of methyl orange (MO) (95.99%), which is about 4.3 times that of CeO2 at the same time (120 min). UV-vis diffuse reflectance spectroscopy (DRS) results show that the semiconductor band gap is reduced with the addition of metallic Cu, which leads to the enhancement of photocatalytic activity. The free radical trapping experiments demonstrate that $O-2- and h(+) are the main active species in the photocatalytic degradation of MO. Based on the above results, a hypothesized mechanism for enhanced photocatalysis of Cu/CeO2 nanomaterials was proposed: the porous structure provides more reactive sites and channels for mass transfer, and the presence of metallic Cu improves the oxygen vacancy concentration of CeO2 and then promotes charge-carrier separation, which helps enhance the photocatalytic performance of Cu/CeO2. (c) 2022 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.

Automated summary

The Cu/CeO2 nanoporous composite material was prepared using a one-step and energy-saving method known as solution combustion synthesis (SCS). The phase composition, surface morphology, and optical characteristics of Cu/CeO2 were investigated. The study found that the SCS products consisted of cubic fluorite CeO2 and Cu. The CeO2 synthesized via SCS exhibited a porous structure due to the generation and escape of gas during the reaction, with mesopores nested in the walls of large pores. XPS analysis revealed an increase in oxygen vacancy concentration in CeO2 with increasing Cu concentration. The presence of Cu greatly enhanced the catalytic activity of CeO2, and the 30 wt% Cu/CeO2 composite material exhibited the highest photocatalytic activity for the degradation of methyl orange (MO), approximately 4.3 times that of pure CeO2. UV-vis diffuse reflectance spectroscopy showed a reduction in the semiconductor band gap with the addition of metallic Cu, leading to enhanced photocatalytic activity. Free radical trapping experiments identified $O-2- and h(+) as the main active species in the photocatalytic degradation of MO. Based on the results, a proposed mechanism for the enhanced photocatalysis of Cu/CeO2 nanomaterials was suggested, involving the porous structure providing more reactive sites and channels for mass transfer, and the presence of metallic Cu improving oxygen vacancy concentration in CeO2 and promoting charge-carrier separation, thereby enhancing the photocatalytic performance of Cu/CeO2.