In the face of increasing global carbon dioxide emissions and the urgent need to mitigate climate change, the development of efficient and sustainable strategies for CO₂ conversion has gained significant attention. One of the methods of eliminating the harmful effects of CO₂ is its photoreduction. In this paper, ZnO was used as an effective photocatalyst for the photoreduction of CO₂ in a gas-phase system. The influence of particle size on the process efficiency was investigated. The ZnO materials applied in the studies were characterized using XRD, SEM, and low-temperature nitrogen adsorption (BET) methods. The pore volume distribution was calculated based on the DFT method. The investigation confirmed that it had a significant impact on the formation of the product of photocatalysis carbon dioxide. The main identified product was carbon monoxide. Hydrogen and methane were detected as well. Based on the results, it was found that the process efficiency was enhanced with decreasing ZnO particle size, and the most effective catalyst for the photoreduction of CO₂ was the ZnO sample with the smallest particle size (18 nm).

A new photocatalyst for CO₂ reduction has been presented. The photocatalyst was prepared from a combination of a commercial P25 with a mesopore structure and carbon spheres with a microporous structure with high CO₂ adsorption capacity. Then, the obtained hybrid TiO₂-carbon sphere photocatalysts were deposited on a glass fiber fabric. The combined TiO₂-carbon spheres/silica cloth photocatalysts showed higher efficiency in the two-electron CO₂ reduction towards CO than in the eight-electron reaction to methane. The 0.5 g graphitic carbon spheres combined with 1 g of TiO₂ P25 resulted in almost 100% selectivity to CO. From a practical point of view, this is promising as it economically eliminates the need to separate CO from the gas mixture after the reaction, which also contains CH₄ and H₂.

This paper presents new photocatalysts obtained by treating carbon spheres (CS) and TiO₂ in a microwave reactor at a pressure of 20 atm and a temperature of up to 300 °C for 15 min and then depositing TiO₂/CS composites on glass fibre cloths. Such highly CO₂-adsorbing photocatalysts showed photoactivity in the simultaneous water-splitting process, generating H₂, reducing CO₂ to CO and CH₄, and reducing N₂ to NH₃. In addition, calculations of the hydrogen balance involved in all reactions were performed. Adding 1 g of carbon spheres per 1 g of TiO₂ maintained the high selectivity of nitrogen fixation at 95.87–99.5%, which was continuously removed from the gas phase into the water as NH₄⁺ ions.