Effect of basicity on amination of activated carbon pellets modified for CO2 adsorption

Abstract

Acid pre-oxidation was used on activated carbon (AC) pellets to increase the amount of oxygen complexes that could serve as sites for creating surface nitrogen functionalities (SNFs) during amination. Four acids with different basicity (HNO3, H2SO4, H3PO4) and H2O2 were used as pre-oxidants. The study of pHpzc showed that H2SO4 and H3PO4 induced highest acidity on AC whilst non-acidic H2O2 had the least effect. Results of textural examination indicated that H2SO4 brought about highest depreciation to the sample’s textural properties whilst H2O2 somehow improved them. Upon amination, both the structural and basic properties were improved. Based on the amount of SNFs created, the efficiency of the oxidants follows this trend HNO3 > H3PO4 > H2SO4 > H2O2. Pure CO2 adsorption test revealed that adsorption capacity of the modified adsorbents depend largely on the available surface area and micropore proportion, while 10% CO2 adsorption rely both on the proportion of micropores (Vmicro/VT) and the nature and amount of SNFs. Consequently, pre-washing with either H2O2 or H2SO4 is most efficient for pure CO2 adsorption at ambient condition while H2SO4 or H3PO4 pre-washing seems more efficacious for selective CO2 capture.