Coupling recycled K2CO3 from first-round activation with Ca(OH)2 for facilitating development of mesopores for enhancing tetracycline adsorption.

Activation with K2C2O4 generates K2CO3 that could be recycled for second-round activation. However, activation with either K2C2O4 or K2CO3 produces activated carbon (AC) with mainly micropores. Herein, recycled K2CO3 reacted with Ca(OH)2 to generate KOH, CaO and CO2 for activation of poplar, cellulose and lignin. The results indicated that K2CO3 + Ca(OH)2 showed superior cracking capability, generating AC from poplar with higher SBET (1822.1 versus 1179.4 m2/g with K2CO3 or 1255.6 m2/g with K2C2O4) and higher meso-porosity (43.3 % versus 10.0 % with recycled K2CO3 and 3.1 % with K2C2O4). This was due to strengthened activity for cracking with KOH and CaO, CO2 for gasification, and CaO as a hard template. The in-situ DRIFTS characterization showed that K2CO3 + Ca(OH)2 interrupted dehydration of -OH, dehydrogenation of -C-H and even aromatization via cracking. The AC activated with Ca(OH)2/K2CO3 showed the highest capability for tetracycline adsorption via monolayer mode, and membrane diffusion was the key rate-determining step.