Tetracycline removal with activated carbons produced by hydrothermal carbonisation of Agave americana fibres and mimosa tannin

Two series of carbons were prepared from Agave americana fibres (A) mixed with mimosa Tannin (T) at different T to A weight ratios W = 0/4; 1/3; 2/2; 3/1 and 4/0. The first series, CTAW, was produced by direct pyrolysis of the precursors (T, A, or blends) and the second one, CHTAW, was produced in two steps, hydrothermal carbonisation (HTC) and then pyrolysis. Materials from the CHTAW series presented higher surface areas, H/C atomic ratios and carbon yields than those of the CTAW series. CHTA2/2 was next activated with CO2 during 1, 2 or 3 h. The appropriate selection of the synthesis conditions allowed obtaining high-surface area activated carbons (ACs) with similar carbon yields and average pore diameters as non-activated, low-surface area, carbon materials. CHTA2/2 activated for 2 h was tested for tetracycline (TC) adsorption, and the equilibrium was reached much faster than for a reference commercial AC due to the presence of macropores and mesopores provided by carbonised A. TC adsorption was spontaneous, and adsorption kinetics was adequately fitted by a pseudo-second-order model. TC adsorption essentially depends on surface area, and the results reported herein are in the range of those reported in the open literature.