Interactions between reactive oxygen groups on nanoporous carbons and iron oxyhydroxide nanoparticles: effect on arsenic(V) removal

In the present work, composites of oxidized-nanoporous activated carbon (AC) and iron oxyhydroxide nanoparticles were prepared by the iron-phosphate thermal hydrolysis method. The interactions between the oxygen groups on the nanoporous AC and the iron hexaaquo-complexes during the materials’ synthesis were studied. The role of the nanopores dimensions and the surface charge features of the functionalized AC during the As(V) adsorption in aqueous solution were also studied. Reactive oxygen groups incorporated into the AC matrix served as nucleation centers for the iron hexaaquo-complexes’ condensation. However, due to the nanoporous structure of the matrix, the condensation of bulk particles onto the pores seems to be the major parameter controlling the anchorage of iron onto the materials. The low concentration of surface oxygen groups on the pristine AC promoted the agglomeration of particles in and around the pores. In contrast, a severe oxidation of the AC induced the formation of well-dispersed small nanoparticles (about 2–10 nm) on the surface of the modified materials. As a result, a minimal blockage of the AC pores was achieved. The surface charge was affected during the oxidation and functionalization of the AC. Repulsive forces played a significant role during the uptake of As(V) from aqueous solution. Therefore, even when well dispersed reactive nanoparticles are anchored on the surface of the materials, the negatively charged surface acts like a barrier for the ligand-interchange of the arsenate anions. The un-oxidized material was efficient for the adsorption of As(V) at low concentrations.