Soursop Biomass-Based Activated Carbon as a Textile Dye Adsorbent

Abstract

Textile industries discharge vast amounts of polluted wastewater, with dyes being major contributors to severe environmental issues. Activated carbon (SBAC) was synthesized from residual soursop biomass via ZnCl2 chemical activation at 450 °C for 1 h to remove Remazol Black B dye from aqueous media. Activation increased the fixed carbon content from 14.80 to 84.62%. SBAC exhibited an amorphous carbon framework, a Brunauer-Emmett-Teller (BET) surface area of 431.3 m2 g-1 with micro-mesoporosity, and a point of zero charge of 5.04. Adsorption assays revealed optimal performance in acidic conditions, achieving ca. 95% dye removal at pH 2 using 20 mg of SBAC (50 mg L-1 dye concentration) at room temperature. An increase in temperature to 80 °C reduced the efficiency to 47%, indicating an exothermic process (ΔH° = –49.32 kJ mol-1). Thermodynamic parameters revealed that adsorption is spontaneous and favorable between 25 and 60 °C (ΔG° < 0), driven by strong electrostatic physisorption with reduced interfacial randomness (ΔS° = –141.65 J mol-1 K-1). Kinetic profiles were best fitted by the Elovich (coefficient of determination (R2) > 0.994) and pseudo-second-order models, confirming uptake onto energetically heterogeneous surface sites controlled by electrostatic interactions. These results highlight SBAC as a promising, low-cost, and high-performance adsorbent aligned with circular economy principles.