Characteristics of zinc oxide/activated carbon composites and their degradation of carbon dioxide in the gas phase

Zinc oxide (ZnO) was coated on activated carbon (AC) with a large surface area to enhance the photocatalytic degradation of gas-phase CO₂. Both ZnO and ZnO/AC composites were prepared by hydrothermal synthesis. The optimal composite ratio of ZnO to AC was obtained through characterization and photocatalystic testing. The specific surface area and pore volume of ZnO/AC composites are 100 times larger than those of ZnO powder, and coating ZnO on AC can increase the active sites and improve the degradation performance of gas-phase CO₂. The results showed that the composite AZ-30-za (i.e., 30 wt.% ZnO) had great potential for converting CO₂ into methane (CH₄) in a 12-h photocatalytic test, with a total of 8.341 μmol CH₄ produced. When sample AZ-30-za was used as the photocatalyst, the highest CH₄ production rate was 0.579 µmol/g-cat·h. After 24 h, the CH₄ production rate was still 0.385 µmol/g-cat·h. Furthermore, cyclic photocatalytic tests were performed using the same photocatalyst for a total of three cycles, each lasting 12 h. The photocatalytic performance of the ZnO/AC composites remained almost unchanged during long-term tests.