Activated Carbon Synthesis and Sulfur Composite Preparation

Activated carbon (ASC) was synthesized from almond shells that had previously been milled using a ball mill (Restch PM100, Retsch GmbH, Haan, Germany) and sieved after grinding to obtain a fine powder. Phosphoric acid (85%, Sigma-Aldrich, San Luis, CA, USA) was used as the activating agent in an H₃PO₄/ASC mass ratio of 1:1; this agent was contacted with the ASC for 3 h at 85 °C. After this process, the obtained product was dried for 24 h at 120 °C and then ground in a mortar. The conditions of the carbonization process were analysed in this study by varying the heating ramp, the target temperature, and the maintenance time at temperature. The calcination process was carried out under a nitrogen atmosphere (flow: 50 mL min⁻¹). Afterwards, carbonized ASC was washed with distilled water until the reaction had been neutralized. ASC was finally obtained by drying at 120 °C in an oven (Buchi, Flawil, Switzerland) for 12 h, and it was ground in an agate mortar.
The activated carbon/sulfur composite (ASC/S) was obtained by a process known as the “disulphide method”, based on the dissolution of elemental sulfur in an organic solvent, carbon disulphide and its subsequent mixing with activated carbon. The conditions were as follows: Elemental sulfur (700 mg) was dissolved in carbon disulphide (5 mL) under magnetic stirring for one hour. Then, the ASC (300 mg) was added, and the stirring was maintained for a further 15 min. The resulting suspension was subjected to ultrasound to promote homogeneity until the solvent evaporated. Finally, the obtained ASC/S composite was dried overnight at 80 °C (Scheme 1).