Benzene/toluene/water vapor adsorption and selectivity of novel C-PDA adsorbents with high uptakes of benzene and toluene

A series of novel porous carbon-based material C-PDA (Carbonized Polydopamine Adsorbent) was prepared using one-step synthesis method for VOCs adsorption, and then characterized. The BET surface area and pore volume of C-PDAs can reach as high as 3291 m2/g and 1.78 cm3/g, respectively. FTIR spectra suggested the presence of N/O functionalities on the surfaces of C-PDAs, and its contents decreased with the increasing KOH/C ratio at which the samples were prepared. Adsorption capacity of C-PDAs for VOCs at low pressure increased with the surface N and O contents of C-PDAs. And the adsorption capacity under a high relative pressure depends on the pore volume of the materials. Adsorption capacities of C-PDA for C6H6 and C7H8 reached as high as 19.1 and 15.8 mmol/g (1491.9 and 1455.8 mg/g) at P/P0 of 0.6, much higher than many other adsorbents. Isotherms of C-PDAs for water vapor exhibited S-shaped type of isotherms, indicative of weak adsorption of water vapor on the sample surfaces at low relative humidity. TPD experiments revealed adsorption mechanism of VOCs on C-PDAs. The isosteric heats of benzene and toluene adsorption on C-PDA-4 were significantly higher than that of water vapor, which made C-PDA-4 possess a characteristic of favorable adsorption of benzene or toluene over water vapor. The adsorption selectivities of the C-PDA-4 for C6H6/H2O(g) and C7H8/H2O(g) were estimated by means of DIH (Difference of Isosteric Heats) equation, which reached as high as 99 and 13.6, respectively, much higher than those of MIL-101(Cr). The resultant C-PDA-4 is a promising adsorbent for adsorption of VOCs.