Doping starch-gelatin mixed hydrogels with magnetic spinel ferrite@biochar@molybdenum oxide as a highly efficient nanocomposite for removal of lead (II) ions

Abstract Hydrogels and mixed hydrogels are 3D-hydrophilic polymeric structures with high porosity, soft consistency and excellent absorbing capability of large amounts of water and organic/inorganic pollutants. Therefore, the present work is aimed to graft starch-gelatin mixed hydrogels with magnetic spinel ferrite@biochar@molybdenum oxide to produce a novel nanocomposite (MoO3/MSB@CoFe2O4@Gel/Starch) with high Pb(II)uptake efficiency. The nanocomposite was assembled from MoO3, super magnetic CoFe2O4, waste mallow stems biochar (MSB) and gelatin-esterified starch mixed hydrogels (Gel/Starch) and characterized by FT-IR, EDX, XRD, SEM and XPS techniques. The EDX analysis of nanocomposite referred to existence of C, O, Na, N, Mo, Fe and Co with 26.68%, 29.44%, 4.55%, 3.48%, 19.72%, 10.39% and 5.74%, respectively. The swelling properties of MoO3/MSB@CoFe2O4@Gel/Starch produced 438% maximum swelling. The average size (27.66 nm) of nanocomposite was estimated from the XRD analysis. The maximum adsorption capacities of Pb(II) onto hydrogels were 2075, 4375 and 5000 μmol g−1 as optimized and established using 20 mg and 40 min reaction time by 0.05, 0.1 and 0.15 mol L−1 Pb(II) ions, respectively. The XPS analysis referred to a peak at BE 138.42 eV corresponding to Pb 4 f as the main product for adsorption of Pb(II). The kinetics and adsorption isotherm models referred to a combination of chemi-physi-sorption processes. The kinetic analysis and the mechanisms for removal of Pb(II) and conversion into Pb(0) were explored and characterized in this study based on the XPS analysis. The reusability test of MoO3/MSB@CoFe2O4@Gel/Starch mixed hydrogels-loaded-Pb(II)/Pb(0) was investigated and referred to a slight loss (~ 2%) after five continuous recycles.