Pb (II) adsorption by nanogoethite loaded with chestnut shell pigment

Nanogoethite (nano-α-FeOOH) was modified with chestnut shell pigment (CSP), the melanin from a food-processing waste, for the first time. The prepared nanocomposite was used for lead (II) (Pb²⁺) adsorption from aqueous solution by a batch method. The effects of pH, adsorbent dosage, contact time and lead (II) concentration on the adsorption performance were studied. The adsorption mechanisms were investigated by kinetics, isothermal equilibrium and thermodynamics. The CSP modification enhanced the adsorption capacity of nanogoethite although it drastically reduced the specific surface area. The optimized pH for the adsorption is 5.0–5.8. The pseudo-second-order kinetic model can fit the adsorption dynamic data well, and the process is controlled by chemical adsorption. The equilibrium data can be described well with the Langmuir isotherm, indicating the presence of monolayer adsorption. The maximum saturated adsorption capacity was 199.4 mg/g. The adsorption is a spontaneous endothermic reaction driven by entropy. CSP/nanogoethite has a fair prospect of application for heavy-metal wastewater treatment.