The development of a single-phase Fe/Mn oxy-hydroxide (δ-Fe0.76Mn0.24OOH), highly efficient at adsorbing both As(III) and As(V), is reported. Its synthesis involves the coprecipitation of FeSO4 and KMnO4 in a kilogram-scale continuous process, in acidic and strongly oxidizing environments. The produced material was identified as a manganese feroxyhyte in which tetravalent manganese is homogeneously distributed into the crystal unit, whereas a second-order hollow spherical morphology is favored. According to this structuration, the oxy-hydroxide maintains the high adsorption capacity for As(V) of a single Fe oxy-hydroxide combined with enhanced As(III) removal based on the oxidizing mediation of Mn(IV). Ion-exchange between arsenic species and sulfates as well as the strongly positive surface charge further facilitate arsenic adsorption. Batch adsorption tests performed in natural-like water indicate that Mn(IV)-feroxyhyte can remove 11.7 μg As(V)/mg and 6.7 μg As(III)/mg at equilibrium pH 7, before residual concentration overcomes the regulation limit of 10 μg As/L for drinking water. The improved efficiency of this material, its low cost, and the possibility for scaling-up its production to industry indicate the high practical impact and environmental importance of this novel adsorbent.

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We apply near-edge x-ray absorption fine structure spectroscopy, at the N K edge, in order to identify the signature of implantation-induced defects in the partial density of empty states in GaN implanted with O, Mg, and Si ions. The dose range was 1014–1018 cm−2. It is found that two of the implantation-induced defects introduce characteristic resonances (hereafter called RL1 and RL2) in the near-edge x-ray absorption fine structure spectra. RL1 appears 1.7 eV below the absorption edge, its formation is independent of the projectile and the implantation dose, and is attributed to nitrogen interstitials. RL2, which appears at about 1.0 eV above the absorption edge, is generated when the dose exceeds 1016 cm−2 and is attributed to nitrogen dangling bonds.

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