INTRODUCTION Polyamidoamines (PAA)-based resins have recently emerged as an advantageous tool for metal ion pollutant sorption in water treatments, complying with nearly all desirable requirements for this application, such as bio-and eco-compatibility, effectiveness in aqueous systems, low cost and easy scaling up of preparation, biodegradability, fast and quantitative sorption even at low pollutant concentration, reversibility, and chemical versatility allowing a virtually unlimited range of target-oriented architectures. 1,2 Recently, two novel PAA resins carrying amine and carboxyl groups, LYMA (Scheme 1) and LMT85 (Scheme 2) were prepared and tested for their sorption ability 3 adopting a standard set of six heavy metal ions (Cu 2þ , Pb 2þ , Ni 2þ , Co 2þ , Cd 2þ , and Zn 2þ ) corresponding to the DIN 38406-16 protocol for trace determination in water. 4 LYMA, whose repeating unit contained one carboxyl and two amine groups and was a mimic of L-lysine, proved selective for Cu 2þ and Ni 2þ , the other ions tested being negligibly sorbed. LMT85, whose repeating unit contained two amine and five carboxyl groups and was a mimic of EDTA, proved capable of rapidly and quantitatively sorbing all the ions tested either singly or in mixed solution. The sorption process was reversible and both resins were easily regenerated by acidification.Mn 2þ was not included in the set of ions so far considered. The problem of its removal from waters, typically concerning local environmental contexts and often concurrent with a high iron amount, arises from esthetic (dark brown/blackish layers on pipings that can collapse resulting in dark stains in laundry clothes and/or dark particles suspension in water), organoleptic (unpleasant taste of beverages such as tea or coffee), and health issues (particularly regarding neurological pathologies). 5,6 For instance, a Greek study testing the effects of Mn 2þ in drinking waters on aged people found a progressively higher prevalence of neurological signs of chronic poisoning with increasing metal concentration (from 0.04 to 2.3 ppm). 7 The maximum Mn 2þ concentration in drinking water in the US is presently 0.05 ppm. 8,9 Only very few studies of Mn-sorbing resins are presently available in the literature, 10-13 and the proposed materials do not fulfill all the aforementioned requirements. Among these, it is worth mentioning that an Mn 2þ chelating resin containing iminodiacetate groups recently proposed to obtain high-purity Mn for advanced electronics devices. 14 Lysine is reported to give complexes with many ions including Co 2þ , 15 in this respect behaving differently from LYMA that does not sorb this ion, and Mn 2þ . Further investigation has proved that Mn 2þ is well sorbed by LYMA, which toward this ion behaves as lysine mimic. The aim of this communication is to report on the performance of both LYMA and LMT85 as Mn 2þ sorbing resins by in situ monitoring the sorption kinetics with voltammetric techniques and using ad hoc-developed protocols.
EXPERIMENTAL
SynthesisLYMA and LMT85...
