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

Convert K 2 CO 3 in filtrate in KOH by adding Ca(OH) 2 to simultaneously obtain CaCO 3 . • Superior cracking efficiency of KOH promotes the formation of micropores. • CaO as hard template facilitates generation of meso - and macropores, • Adding Ca(OH) 2 retains hollow honeycomblike structure in activated carbon (AC). • High mesoporosity and graphitic structure in AC determines tetracycline adsorption. Activation with K 2 C 2 O 4 generates K 2 CO 3 that could be recycled for second-round activation. However, activation with either K 2 C 2 O 4 or K 2 CO 3 produces activated carbon (AC) with mainly micropores. Herein, recycled K 2 CO 3 reacted with Ca(OH) 2 to generate KOH, CaO and CO 2 for activation of poplar, cellulose and lignin. The results indicated that K 2 CO 3  + Ca(OH) 2 showed superior cracking capability, generating AC from poplar with higher S BET (1822.1 versus 1179.4 m 2 /g with K 2 CO 3 or 1255.6 m 2 /g with K 2 C 2 O 4 ) and higher meso -porosity (43.3 % versus 10.0 % with recycled K 2 CO 3 and 3.1 % with K 2 C 2 O 4 ). This was due to strengthened activity for cracking with KOH and CaO, CO 2 for gasification, and CaO as a hard template. The in-situ DRIFTS characterization showed that K 2 CO 3  + Ca(OH) 2 interrupted dehydration of –OH, dehydrogenation of −C–H and even aromatization via cracking. The AC activated with Ca(OH) 2 /K 2 CO 3 showed the highest capability for tetracycline adsorption via monolayer mode, and membrane diffusion was the key rate-determining step. Download: Download high-res image (232KB) Download: Download full-size image