Effect of UV-C on pre-oxidation prior amination for preparation of a selective CO2 adsorbent

In order to enhance the selectivity of activated carbon (AC) toward CO2, surface modification was carried out in a two-step approach viz. pre-oxidation and amination. First, the most suitable oxidation was determined by using O3 and H2O2 with or without UV-C (λ ≈ 253.7 nm), to impregnate surface oxygen functionalities (SOFs) on the AC surface, followed by optimization of the most efficient technique. Chemical characterization showed that pre-oxidation increased the total amount of SOFs tethered on the AC surface. However, it was reduced when the oxidation was carried out under the influence of UV-C. Upon amination, less thermally refractory SOFs such as ether, carbonyl and carboxylic groups, tend to favor the formation of surface nitrogen functionalities such as pyridine and pyrrole-N types, which showed comparatively higher affinity toward CO2. Pre-oxidation and amination parameters of AC treatment with O3 in the presence of UV-C (ROUV), which exhibited most favorable condition for CO2 low-level selectivity, were optimized. The intrinsic capture affinity of AC for low and high levels CO2 was ultimately enhanced from 0.016 and 0.46 to 0.36 and 0.9 mmol/g respectively. Conclusively, UV-C inhibits the formation of recalcitrant SOFs during oxidation, thereby reducing steric hindrance and promoting amination and eventual CO2 adsorption.