Magnetically separable mesoporous alginate polymer beads assist adequate removal of aqueous methylene blue over broad solution pH

Abstract Adsorption is a promising technology for removal of organic and inorganic contaminants from soil and water system. In this study, magnetically separable mesoporous polymeric beads (NiZnFe4O4-HNT@alg) were synthesised for efficient removal of methylene blue (MB, cationic dye) under broad solution pH (from pH 3.41 to pH 8.43). Alginate biopolymer were used to stabilize halloysite nanotubes (HNTs) and nickel zinc iron oxide nanoparticles (NiZnFe4O4   intraparticle diffusion (R2 = 0.93) > pseudo-first-order (R2 = 0.87). Energy-dispersive X-ray spectroscopy (EDS) elemental mapping demonstrated that MB has a co-distribution with silicon, aluminium, and alginate carbon phase but is limited with iron and nickel, indicating HNTs and alginate polymer performed as sorption sites, whereas NiZnFe4O4 performed as a catalyst. The presence (post-sorption) and absence (pre-sorption) of inorganic, total carbon or total organic carbon content at different solution pH, contact time, and initial concentration of MB demonstrated that the adsorbent act as a catalyst as well for degradation of MB. NiZnFe4O4-HNT@alg triggers efficient removal of MB with the assist of adsorption and catalytic degradation at broad solution pH. A comparison in removal of MB by various adsorbents including, biochars, clays, activated carbon, nanoparticles, polymers, nano composites, graphene oxides, carbon nanotubes, and polymer beads with the result of this study were performed, illustrating competitive sorption capacity of NiZnFe4O4-HNT@alg.