Adsorption studies of methyl orange on an immobilized Mn-nanoparticle: kinetic and thermodynamic

In this paper, a novel nano-adsorbent containing Mn-nanoparticle decorated organo-functionalized SiO2-Al2O3 mixed-oxide was introduced as a new scavenger of dyes such as methyl orange. The SiO2-Al2O3 mixed-oxide was functionalized with a Schiff base ligand and thereafter, in the next step, Mn-nanoparticles were prepared over the organo-functionalized SiO2-Al2O3 mixed-oxide. The synthesized materials were characterized by several methods, such as FT-IR spectroscopy, UV-vis, CHN elemental analysis, SEM, TEM, ICP-OES, EPR and XPS. The contact time to obtain equilibrium for maximum adsorption was 15 min. EPR and XPS of the Mn ions evidenced that most of the covalently bonded active sites of the nano-adsorbent are in the form of Mn(III) ions. The heterogeneous Mn(III) ions were found to be an effective adsorbent for the removal of methyl orange ions from solution. The adsorption process was spontaneous and endothermic in nature and followed a pseudo-second-order kinetic model.