Arsenic (III,V) removal from aqueous solution by ultrafine α-Fe₂O₃ nanoparticles synthesized from solvent thermal method

Ultrafine iron oxide (α-Fe₂O₃) nanoparticles were synthesized by a solvent thermal process and used to remove arsenic ions from both lab-prepared and natural water samples. The α-Fe₂O₃ nanoparticles assumed a near-sphere shape with an average size of about 5nm. They aggregated into a highly porous structure with a high specific surface area of ∼162m²/g, while their surface was covered by high-affinity hydroxyl groups. The arsenic adsorption experiment results demonstrated that they were effective, especially at low equilibrium arsenic concentrations, in removing both As(III) and As(V) from lab-prepared and natural water samples. Near the neutral pH, the adsorption capacities of the α-Fe₂O₃ nanoparticles on As(III) and As(V) from lab-prepared samples were found to be no less than 95mg/g and 47mg/g, respectively. In the presence of most competing ions, these α-Fe₂O₃ nanoparticles maintained their arsenic adsorption capacity even at very high competing anion concentrations. Without the pre-oxidation and/or the pH adjustment, these α-Fe₂O₃ nanoparticles effectively removed both As(III) and As(V) from a contaminated natural lake water sample to meet the USEPA drinking water standard for arsenic.