Crystal violet removal from aqueous solution: adsorption studies, Box-Behnken optimization, safety, and reuse in...

The discharge of toxic crystal violet (CV) dye poses significant environmental and health risks, necessitating sustainable treatment solutions. This study presents sulfuric acid-functionalized activated carbon derived from frankincense (SAC) as a high-performance adsorbent for CV removal. Characterization revealed a mesoporous structure with a high surface area of 842.97 m² g^-1, adorned with functional groups that facilitate CV binding. Process optimization via Box-Behnken design achieved an exceptional adsorption capacity of 638.51 mg g^-1 at pH 8, with a 0.075 g dose and 60 min contact time, following the Langmuir-Freundlich isotherm model. A pivotal finding from in vitro cytotoxicity assessment (HepG2 cells) was the effective detoxification of CV, where the half-maximal cytotoxic concentration (CC₅₀) increased dramatically from 84.7 µg mL^-1 (untreated CV) to >1000 µg mL^-1 (SAC-treated solution). Embodying circular economy principles, the spent adsorbent was successfully repurposed as an electrocatalyst for methanol oxidation, yielding a current density of 22.40 mA cm^-2. The process demonstrated economic viability at a low manufacturing cost of $0.06438 g^-1 SAC and excelled in green chemistry metrics (Eco-Scale: 90/100). This work underscores the dual utility of SAC as a sustainable, safe, and reusable material for advanced wastewater treatment and energy conversion applications.