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• Superparamagnetic iron oxide nanoparticles loaded on commercial cube-shaped open-celled cellulose sponge adsorbent was synthesized for the first time. • Adsorption capacity of sponge increased ∼63% at 800 mg• L −1 initial concentration when loading ∼2.6 wt.% mass fraction of nanoparticles due to the good affinity of dispersed SPION to arsenic. • Arsenic K-edge X-ray absorption spectroscopy results indicated that no redox mechanism is involved in the adsorption process. • Sponge-loaded superparamagnetic iron oxide nanoparticles retain high adsorption capacity after five adsorption/desorption cycles. In this study, a commercial cube-shaped open-celled cellulose sponge adsorbent was modified by in-situ co-precipitation of superparamagnetic iron oxide nanoparticles (SPION) and used to remove As(V) from aqueous solutions. Fe K-edge X-ray absorption spectroscopy (XAS) and TEM identified maghemite as the main iron phase of the SPION nanoparticles with an average size 13 nm. Batch adsorption experiments at 800 mg/L showed a 63% increase of adsorption capacity when loading 2.6 wt.% mass fraction of SPION in the cube-sponge. Experimental determination of the adsorption thermodynamic parameters indicated that the As(V) adsorption on the composite material is a spontaneous and exothermic process. As K-edge XAS results confirmed that the adsorption enhancement on the composite can be attributed to the nanoparticles loaded. In addition, adsorbed As(V) did not get reduced to more toxic As(III) and formed a binuclear corner-sharing complex with SPION. The advantageous cube-shape of the sponge-loaded SPION composite together with its high affinity and good adsorption capacity for As(V), good regeneration capability and the enhanced-diffusion attributed to its open-celled structure make this adsorbent a good candidate for industrial applications. [Display omitted] [ABSTRACT FROM AUTHOR]