Triple activation (thermal-chemical-physical) in the development of an activated carbon from tobacco: characterizations and optimal conditions for Cd2+ and Pb2+ removal from waters

Abstract

Abstract This research aimed to transform tobacco that originated from smuggled cigarettes into activated carbons, and to study its application in the remediation of water contaminated by cadmium and lead. For this, a triple activation was performed (thermal – chemical H3PO4 – physical CO2), resulting in the studied activated carbon (CT H3PO4 + CO2). The carbon was characterized by its chemical composition, pHPZC, Scanning Electron Microscopy (SEM), FT-IR, Brunauer-Emmett-Teller (BET), and BJH. The influence of the pH of Cd2+ and Pb2+ solutions, and the influence of the adsorbent dose, were studied. Isotherms were constructed by linear and nonlinear models of Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin. CT H3PO4 + CO2 has carbonates, hydroxyls, carboxylic, and carbonic acids as surface functional groups. The triple activation caused changes in pHPZC (from 5.40 to 9.59). The SEM revealed a carbon surface full of irregular and heterogeneous structures, spongy aspect, with an estimated Specific Surface Area (SSA) increase of 395x and pore volume of 37x. The produced activated carbon has applicability over a wide pH range (3.00–7.00), with an ideal dose estimated at 4 g L−1 for greater efficiency in removing Cd2+ and Pb2. The linear and nonlinear models reveal that metal adsorption is predominantly physical and multi-layered, with a possible reuse in new sorption cycles.