This work aimed to valorise cork powder waste by converting it into activated carbons (ACCKs) for use as adsorbents and catalysts in the removal of oxalic acid, a refractory by-product formed during ozonation-based water treatment. The ACCKs were prepared via direct physical activation with CO2, and their characteristics were tailored by changing pyrolysis temperature (500–800 °C), CO₂ percentage in the activation stream (30–70%, v/v), and activation time (1–3 h) according to a Box–Behnken design. The materials obtained were characterised by nitrogen adsorption–desorption, thermogravimetric analysis, point of zero charge, Fourier-transform infrared spectroscopy, Boehm titration and Raman spectroscopy. The ACCK produced at 800 °C for 3 h with 50% CO₂ showed the highest adsorption capacity, following pseudo-second-order kinetics and a Langmuir isotherm, with a predicted maximum capacity of 89 mg g⁻1. The predictive model for adsorption identified temperature, activation time, the quadratic effect of temperature, and the temperature–time interaction as the most influential parameters. The ACCK prepared at 500 °C for 2 h with 30% CO₂ showed the best catalytic performance, achieving 61.5 ± 1.5% oxalic acid removal within 60 min. This material exhibited lower surface area, fewer acidic surface groups and a lower degree of graphitization than the others ACCK produced, features that favoured catalytic ozone decomposition. Quenching tests identified superoxide radicals and singlet oxygen as the main reactive species. Reusability tests showed only a slight performance loss (~ 19%) after three cycles, demonstrating the potential of ACCKs as cost-effective materials for advanced water treatment processes.
Graça et al. (Mon,) studied this question.