Synthesis, characterization, and selective CO2 capture performance of a new type of activated carbon-geopolymer composite adsorbent

Abstract

Surface modification of activated carbon is an effective strategy to enhance its adsorption performance. However, most studies have focused on the use of chemical modifiers, and the products are usually in a powder form. Herein, we report the effective surface modification of activated carbon through geopolymer chemistry via simultaneous alkali-activated functionalization and polycondensation, thus yielding a monolithic adsorbent. The CO2 adsorption capacity of the optimized adsorbent was 2.25 times higher than that of the average of the constituents. Moreover, geopolymers can also function as efficient binders to supply a sufficient compressive strength of 22.3 MPa for the resultant adsorbent. Under different conditions, significant surface texture reconstruction of activated carbon was observed and confirmed via systematic XRD, FESEM, BET, XPS, and Raman spectrum characterisations combined with density functional theory (DFT) calculations. The effective surface modification was associated with the high alkaline environment during the geopolymerization reaction, which intercalates –CO, -OK, and -COOK functional groups on the activated carbon surface. These groups exhibited stronger CO2 affinity than that of pure activated carbon and thus endowed the high-strength adsorbent with enhanced CO2 adsorption capacity.