Magnetite graphene oxide encapsulated in alginate beads for enhanced adsorption of Cr(VI) and As(V) from aqueous solutions: Role of crosslinking metal cations in pH control

Abstract

Graphene oxide has been utilized effectively for the adsorption of heavy metals. Incorporation of graphene oxide with magnetite nanoparticles through co-precipitation enhances separation of a newly designed magnetite graphene oxide by a magnetic field. Considering the instability of magnetite graphene oxide under different water chemistry conditions, we designed encapsulated magnetite graphene oxide inside a non-toxic alginate bead as a high-performance green chemical for the uptake of Cr(VI) and As(V) in water treatment applications (mGO/bead). The alginate, itself revealed low contribution for metal ions uptake, however this could potentially inhibit the aggregation of magnetite graphene oxide powder showing enhanced performance to extract metals from water. Material capacity minimally altered over a range of pH values for As(V), while Cr(VI) uptake varied with pH changes, which were explained by a local pH-controlled mechanism. Induced hydrolysis was facilitated by the release of Fe3+ from Fe3+-crosslinked mGO/beads, thus enhancing the removal of Cr(VI). For a complex mixture of heavy metals, influence of the presence of co-occurring ions in a mixed contaminant system (Cr(VI), As(V), Cu(II), Cd(II)) revealed an excellent performance (∼80–100% removal) by the composite material. The mGO/bead maintained its activity in wastewater and exhibited greater adsorption efficiency for both Cr(VI) and As(V) compared with activated carbon and carbon nanotube. The mGO/beads could be collected and reused for at least 5 cycles without the leaching of core mineral contents. The results indicate the advantages of mGO/beads over the popular adsorbents that can be developed as a versatile material for water treatment.