Upcycling Used Tyre Rubber into Carbon Adsorbents: Effect of Physical Activation on Porous Structure and Comparative Evaluation for p-Chlorophenol Removal

The porous architecture of carbons derived from polymeric waste is largely governed by the physical activation atmosphere. In this work, used tyre rubber (UTR) was converted into carbonaceous adsorbents by pyrolysis followed by physical activation in air, CO2 or steam. The influence of the activation route on porous structure, surface chemistry and adsorption performance was systematically investigated. The materials were characterised by N2 adsorption at −196 °C, mercury intrusion porosimetry, scanning electron microscopy (SEM), FT-IR spectroscopy and point-of-zero-charge (pHpzc) measurements. The resulting materials were evaluated for the removal of p-chlorophenol from aqueous solution and comparatively assessed against three commercial carbon materials. Steam activation proved to be the most effective treatment, increasing the BET surface area from 64 to 344 m2 g−1 and the micropore volume from 0.05 to 0.23 cm3 g−1 while generating a hierarchical micro-/mesoporous structure that significantly enhanced pore accessibility and mass transport. Among the UTR-derived carbons, the steam-activated sample exhibited the highest equilibrium p-Cp uptake and adsorption kinetics approaching those of a commercial activated carbon despite its lower specific surface area. Kinetic and equilibrium analyses demonstrated that adsorption performance depends not only on the extent of microporosity but also on pore accessibility and network connectivity, highlighting the critical role of transport mesoporosity in facilitating molecular diffusion towards adsorption sites. The adsorption results are consistent with an important contribution from accessible microporosity, while π–π interactions between p-chlorophenol and aromatic carbon domains may also contribute. These findings demonstrate that tailoring porous structure through physical activation provides an effective strategy for transforming UTR into high-performance carbon adsorbents and establishes robust processing–structure–property relationships that can guide the rational design of waste-derived carbon adsorbents.