CO₂ Sorbents Based on Spherical Carbon and Photoactive Metal Oxides: Insight into Adsorption Capacity, Selectivity...

This work aimed to obtain hybrid composites based on photoactive metal oxide and carbon having adsorption properties. The materials, composed of titanium dioxide or zinc oxide and spherical carbon, were obtained from resorcinol-formaldehyde resin, treated in a solvothermal reactor heated with microwaves and then subjected to carbonization, were received. The functional groups of pure carbon spheres (unsaturated stretching C=C, stretching C-OH and C-H bending vibrations), CS/ZnO and CS/TiO₂ samples were determined by FT-IR analysis. The characteristic bands for ZnO and TiO₂ were observed below 1000 cm^-1. The thermal oxidative properties are similar for TiO₂- and ZnO-modified carbon spheres. We have observed that the increased carbon sphere content in nanocomposites results in starting the decomposition process at a lower temperature, therefore, nanocomposites have a broader combustion temperature range. The effect of the oxides' addition to carbon spheres on their adsorption properties was evaluated in detail by examining CO₂ adsorption from the gas phase. The selectivity of CO₂ over N₂ at a temperature of 25 °C and pressure of 1 bar (a novelty in testing CS-based sorbents) calculated for 3.00 CS/TiO₂ and 4.00 CS/ZnO was 15.09 and 16.95, respectively. These nanocomposites exhibit excellent cyclic stability checked over 10 consecutive adsorption-desorption cycles.