Iron-modified activated carbon derived from agro-waste for enhanced dye removal from aqueous solutions

Finding a cost-effective adsorbent can be an obstacle to large-scale applications of adsorption. This study used an efficient activated carbon adsorbent based on agro-waste for dye removal.

Pistachio shells as abundant local agro-wastes were used to prepare activated carbon. Then, it was modified with iron to improve its characteristics. Acid red 14 was used as a model dye in various conditions of adsorption (AR14 concentration 20-150 mg L^-1, pH 3-10, adsorbent dosage 0.1-0.3 g L^-1, and contact time 5-60 min).

A mesoporous adsorbent was prepared from pistachio shells with 811.57 m² g^-1 surface area and 0.654 cm³ g^-1 pore volume. Iron modification enhanced the characteristics of activated carbon (surface area by 33.3% and pore volume by 64.1%). Adsorption experiments showed the high effectiveness of iron-modified activated carbon for AR14 removal (>99%, >516 mg g^-1). The adsorption followed the pseudo-second kinetic model (k = 0.0005 g mg^-1 min^-1) and the Freundlich isotherm model (K_f = 152.87, n = 4.61). Besides, the reaction occurred spontaneously (ΔG⁰ = -36.65 to -41.12 kJ mol^-1) and was exothermic (ΔH⁰ = -41.86 kJ mol^-1 and ΔS⁰ = -3.34 J mol^-1 K^-1).

Iron-modified activated carbon derived from pistachio shells could be cost-effective for the treatment of industrial wastewater containing dyes.