Selective lead (II) sorption using aminophosphonate-based sorbents: Effect of amine linker, characterization and sorption performance

A one-pot synthesis procedure is designed for preparing two alpha-aminophosphonate-based-sorbents (DA and TA sorbents). The reaction takes place between amine precursors (two different aliphatic amines with different chain lengths and amino group content; i.e., ethylenediamine (DA) or diethylenetriamine (TA), respectively) and both salicylaldehyde and diphenyl phosphite. Ionic liquid may be used under controlled conditions as an alternative to TiCl4 catalyst. These materials are first characterized by SEM-EDX, AFM, BET, XRD, FTIR, H-1-, C-13-, and P-31 NMR, XPS, TGA, elemental analysis (CHNP), and titration (PZC). Combined with the study of pH effect on Pb(II) sorption, FTIR and XPS analyses are used for exploring the mechanisms involved in metal binding. In a second step, the sorption properties are compared for Pb(II) recovery at pH approximate to 5. Maximum sorption is influenced by the length of the chain: DA (0.694 mmol Pb g(-1)) > TA (0.494 mmol Pb g(-1)). The sorption isotherms are modelled by the Sips equation for DA (and the Langmuir Dual Site equation) and by the Langmuir equation for TA. Thermodynamic parameters (Delta G degrees, Delta H degrees and Delta S degrees) indicate the spontaneous, endothermic nature and randomness increases during the sorption process. The uptake kinetics (equilibrium reached approximate to 120 min) is almost equally fitted by the pseudo-first-order rate equation and the pseudo-second-order rate equation. The sorbents show selective Pb(II) sorption against heavy base metals in multi-component solutions. QSAR tools (quantitative activity structure-activity relationships) are used for evaluating the correlation between their intrinsic metal characteristics and their affinities for sorbents. The sorbents are efficiently recycled for at least 5 cycles using 0.2 M HCl as the eluent (loss in sorption and desorption performances approximate to 10-14% at the fifth cycle, compared with the first cycle).