Arsenic removal from contaminated water by ultrafine δ-FeOOH adsorbents

• Efficient δ-FeOOH adsorbents were prepared by a simple and cheap method.
• δ-FeOOH nanoparticles exhibited high adsorption capacity for arsenic.
• Arsenic was better adsorbed by δ-FeOOH nanoparticles at acidic pH.
• δ-FeOOH is a promising adsorbent for heavy metal in contaminated water.

δ-FeOOH nanoparticles were prepared by a fast, simple and cheap synthesis method for use as an adsorbent for As(V) in water. Rietveld refinement on XRD pattern confirmed that δ-FeOOH was successful synthesized. TEM images evidenced that the average particle sizes for δ-FeOOH is 20 nm, which provided a high surface area of 135 m2 g−1 and average pore sizes of 18 nm, as verified with BET measurements. Zeta potential revealed that the point of zero charge of δ-FeOOH is 8.4, which favored the As(V) adsorption on the δ-FeOOH surface even at neutral pH. The As(V) adsorption capacity of δ-FeOOH was estimated to be 37.3 mg g−1 at pH 7. The kinetics data were best fitted with a pseudo-second order, thus suggesting chemical adsorption on the surface and pores of δ-FeOOH nanoparticles. The interaction between As(V) and δ-FeOOH nanoparticles was suggested to be mainly inner sphere complexes. The adsorption isotherm obtained at pH 7 was best fitted to the Langmuir and Redlich–Peterson models and, therefore, a non-ideal monolayer adsorption model for As(V) on δ-FeOOH nanoparticles was proposed. The small particle size, high surface area and adsorption capacity make δ-FeOOH a promising adsorbent for toxic metals in contaminated water.