High-performance microporous carbon for efficient tartrazine dye adsorption: experimental investigation coupled with...

This study reports the preparation of potassium hydroxide-impregnated corn-cob-derived activated carbon (AC₅₀₀-K_1.1) as an efficient adsorbent for the rapid removal of the azo dye tartrazine (TZ) from aqueous solutions. The raw corn-cob (CC) powder was chemically activated at various KOH-to-biomass ratios and activation temperatures to optimise surface chemistry and porosity. Under optimal conditions (1.1 ratio at 500 °C), the prepared activated carbon exhibited an amorphous structure, a BET surface area of 276.34 m² g⁻¹, and a well-developed porous morphology. FTIR, XRD, FESEM-EDX, TEM, TGA, and BET characterisation confirmed the formation of abundant oxygen-containing acidic functional groups (which can also significantly enhance dye adsorption through electrostatic attraction and hydrogen-bond interactions). The batch adsorption studies revealed that the optimum adsorbent dosage was 0.04 g, with a contact time of 60 min, an initial dye concentration of 100 mg L^-1, a pH of 7, and a temperature range of 15-40 °C. The adsorption of TZ onto AC₅₀₀-K_1.1 was best represented by the Freundlich isotherm model (R² ≈ 0.9986), suggesting heterogeneous and multilayer adsorption, whereas the kinetic behavior was adequately described by the pseudo-first-order model. Thermodynamic parameters demonstrated that the adsorption process was spontaneous and exothermic (ΔH° =  - 8.157 kJ mol⁻¹). Moreover, the prepared adsorbent exhibited excellent performance, achieving a maximum experimental adsorption capacity of 675.88 mg g⁻¹ and a removal efficiency of 95.07% under the optimized conditions. All of them were shown to exhibit much higher stability in regeneration experiments with up to 10 adsorption-desorption cycles and in recycling experiments. For the TZ-spiked real water samples (distilled water, tap water, and river water), significant dye uptake (> 73%) was observed with AC₅₀₀-K_1.1 and was marginally affected by ionic strength. This process establishes its practical applicability for actual real effluent decontamination. Molecular dynamics simulations performed using BIOVIA Materials Studio indicated that van der Waals interactions play a major role in the adsorption of TZ on activated carbon, with additional contributions from electrostatic interactions, hydrogen bonding, and π-π stacking. RDF and adsorption energy analyses further supported the spontaneous and stable adsorption configuration of TZ molecules on the carbon surface. These results provide molecular-level evidence supporting the experimentally observed adsorption behavior.