Effective Cd²⁺ removal from water using novel micro-mesoporous activated carbons obtained from tobacco: CCD approach,...

This research aimed to develop activated carbons from tobacco by double (thermal-physical) and triple activations (thermal-chemical-physical) for high-efficiency removal of Cd²⁺.

The adsorbents were characterized by their chemical composition, point of zero charge (pH_PZC), SEM, FT-IR, BET, and BJH. The subsequent adsorption studies were conducted: optimal conditions (CCD on adsorbent dose versus pH of Cd²⁺ solution), kinetics, equilibrium, thermodynamics, and desorption studies.

The activated carbons have irregular and heterogeneous morphology, surface functional groups COO-, C-O, C-O-C, C=O and O-H, pH_PZC of 11.11 and 10.86, and enhanced SSA (especially for CT NaOH + CO₂ = 103.40 g m^-2). The optimal conditions for Cd²⁺ adsorption occur using 4.0 g L^-1, pH from 3.0 to 7.0, with most of the Cd²⁺ adsorbed in the first 10-20 min. The goodness of the fit found for pseudo-first order, pseudo-second order, intraparticle diffusion, Langmuir, Freundlich, Dubinin-Radushkevich, Sips, and Temkin suggest the occurrence of Cd²⁺ chemisorption and physisorption in mono and multilayers. The values of ∆G° < 0 kJ mol^-1 indicate that the observed phenomena are energetically favorable and spontaneous; the values of ∆H° < 0 and the effective desorption rates (58.52% and 44.64%) suggest that the adsorption of Cd²⁺ is ruled mainly (but not only) by physical interactions.

Our excellent results on Cd²⁺ removal allow us to state that tobacco use as a raw material for adsorbent development is a renewable and eco-friendly technique, allowing the production of highly effective activated carbons and providing an adequate destination for this waste.

The online version contains supplementary material available at 10.1007/s40201-021-00740-8.