Waste valorization towards hierarchical porous carbon with ultra-high surface area and dye adsorption efficiency

Waste valorization is an important ally in the effort to reduce waste volumes since not only restricts their accumulation but may also provide useful second-life products as hierarchical porous carbon. The latter usually combines microporosity with mesoporosity exhibiting satisfactory specific surface areas and broad applicability and efficiency due to its hierarchy. Nevertheless, producing such materials with ultra-high surface areas is not trivial. The present work reports a comprehensive study for determining parameters to produce ultra-high surface area hierarchical porous carbons in a reproducible manner. Materials are waste-derived and particularly by cigarette butts which in addition are one of the most common forms of litter. Four main parameters, i.e., KOH/char mass ratio, activation temperature, heating rate, and activation time, were explored to provide a roadmap for producing materials with surface areas of up to 4300 m²/g according to the Brunauer-Emmett-Teller method which is one of the highest ever reported specific surface area values for porous carbon materials. The final materials have been proven to be superadsorbents with high efficiency towards the adsorption of a common cationic dye, methylene blue, reaching record uptake values of over 2.5 g/g, following fast kinetics, exhibiting a pseudo-second order kinetic model response, with more than 85% of the dye adsorption taking place in just 15 min.