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The arsenic removal efficiency of iron-modified activated carbons depends greatly on the number of available iron oxide surface sites,which are given by the surface area of the anchored particles.In this sense,aiming the generation of an adsorbent with superior arsenic adsorption capacity,we developed a protocol to anchor interconnected fibrils of iron oxyhydroxides,using Mn2+ as a morphology regulator.The protocol was based on a microwave-assisted hydrothermal method,using bituminous based activated carbon and both Fe2+ and Mn2+ ions in the hydrolysis solution.The elemental analysis of modified carbons revealed that Mn does not anchor to the carbon.However,when Mn is included in the hydrolysis solution,the iron content in the activated carbon increased up to 3.5 wt％,without considerable decreasing the adsorbent surface area.Under specific hydrothermal conditions,the Mn2+ promoted the formation of iron oxide nanoparticles shaped as interconnected fibrils.This material showed a superior arsenic adsorption capacity in comparison to similar iron modified activated carbons (5 mg As/g carbon,at 2 mg As/L),attributed to the increase in quantity and availability of active sites located on the novel interconnected fibrils of iron oxyhydroxides nanostructures.