Diethylene triamine penta (methylene phosphonic acid) functionalized magnetic nanosilica for adsorptive removal of heavy metals (Pb2+ and Ni2+) from aqueous solution

• Magnetic Fe 3 O 4 @SiO 2 -DTPMP can be used for the selective removal of toxic Pb 2+ and Ni 2+ ions from aqueous solution. • Fe 3 O 4 @SiO 2 -DTPMP nanocomposites have an equilibrium time within 60 min and 30 min for Pb 2+ and Ni 2+ ions, respectively. • The Fe 3 O 4 @SiO 2 -DTPMP can be easily regenerated and reused for at least five adsorption cycles. • The thermodynamic analysis of this study revealed that sorption is endothermic and spontaneous in nature. Magnetic nanosilica nanoparticles are used for the remediation of wastewater. In this study, a robust nano-adsorbent material was fabricated by functionalising magnetic nanosilica with diethylene triamine penta methylene phosphonic acid (DTPMP) using a reflux method. The synthesised Fe 3 O 4 @SiO 2 -DTPMP nano-adsorbent was applied in the removal of lead (Pb 2+ ) and nickel (Ni 2+ ) ions from aqueous solution. The synthesised magnetic nano-adsorbent material was characterised by various techniques such as FT-IR, XRD, SAXS, FESEM coupled with Thermo Scientific Ultra dry EDS detector, TEM, VSM, BET and Zeta potential measurements. VSM analysis showed enhanced magnetic separation ability for Fe 3 O 4 @SiO 2 -DTPMP as was shown by a saturation magnetisation of 24 emug −1 , while EDS analysis gave spectra showing high purity of the synthesised nanocomposite. Batch adsorption experiments on the effects of pH, initial metal ion concentration, adsorbent dose, temperature, and contact time were conducted on the removal of metal ions from aqueous solution. The as-prepared Fe 3 O 4 @SiO 2 -DTPMP nano-adsorbent was easily separated from aqueous solution using an external permanent magnet. The adsorption isotherm models follow the Langmuir model and pseudo-second-order kinetics. From the results of this study, Fe 3 O 4 @SiO 2 -DTPMP showed enhanced adsorption performance for the Pb 2+ and Ni 2+ after 60 min and 30 min, respectively. Metal ions removal reached 92 % for Pb 2+ at pH 6 and 54 % for Ni 2+ at pH 5, with Q e max of 13.28 and 8.56 mg g −1 , respectively. The Fe 3 O 4 @SiO 2 -DTPMP nano-adsorbents were regenerated and reused without the leaching of core mineral contents for at least 5 cycles. Therefore, the results of the study showed the Fe 3 O 4 @SiO 2 -DTPMP nano-adsorbent as a promising adsorbent material for water/wastewater treatment.