Modified barley straw as a potential biosorbent for removal of copper ions from aqueous solution

Barley straw (BS), a very low-cost material, has been utilized as a biosorbent material for the removal of copper (Cu 2+ ) ions from aqueous solutions after treatment with citric acid. Barley straw was thermochemically modified with citric acid (CA–BS) for the purpose of improving the Cu 2+ ion sorption capacity of the straw. Biosorption studies have been carried out to determine the effect of pH, adsorbent concentration, contact time, extent of modification, and adsorbate concentration on the biosorption capacity of Cu 2+ ions by the esterified straw. The equilibrium sorption capacities of Cu 2+ were 4.64 mg/g and 31.71 mg/g for BS and CA–BS, respectively. The optimum pH for the removal of Cu 2+ ions by CA–BS was around pH 7.0 and the removal of Cu 2+ ions was 88.1%. Langmuir, Freundlich, Scatchard and D–R (Dubinin–Radushkevich) isotherms have been used to characterize the observed biosorption phenomena of Cu 2+ ions on CA–BS. The carboxyl groups on the surface of the modified barley straw were primarily responsible for the sorption of Cu 2+ ions.