Characterization and adsorption properties of polymer-based microporous carbons with different surface chemistry

Polymers are promising activated carbon precursors due to their high percentage of carbon and also due to their abundance in a relatively pure state from waste recovery. Microporous activated carbons were prepared from poly(ethyleneterephthalate) (APETW, APETOX) and polyacrylonitrile (APAN). Their surface behaviour was characterized under dry and wet conditions by X-ray photoelectron spectroscopy (XPS), pH, pH_PZC and Boehm titration. The oxygen content of the nitrogen-free APETW and APETOX (S_BET = 1440 and 1509 m²/g) is 4.3 and 10.0 at.%, respectively. APAN (356 m²/g) contains 5.4 at.% oxygen and 5.3 at.% nitrogen. The ratios of the surface density of the titrated groups are approximately 20:28:65 in APETW, APETOX and APAN, respectively. The last has the most basic character. The larger oxygen content of APETOX yields greater affinity towards water, as does the presence of nitrogen functionalities in APAN. The higher the concentration of the functional groups, the higher is the water uptake at low relative humidity.

The greatest formaldehyde uptake per unit surface area was found in APAN, which is decorated with both nitrogen and oxygen functional surface groups. Due to the competitive adsorption of formaldehyde and water, increasing oxygen concentration in the APETW sample changed the kinetics of sorption but did not affect the formaldehyde uptake at saturation.