Synthesis of a novel succinic acid-functionalized cellulose and its speciation model in the presence of Cd(II) ions.

Recently, the demand for new renewable materials to be employed in remediation has grown exponentially. Furthermore, despite the availability of many chelating agents able to efficiently bind metal cations in solution, only few of them are actually suitable to be used to treat metal-polluted wastes. The non-biodegradable EDTA, for instance, ended up being overused, thus becoming a polluting agent itself. In this context, this research is focused on the development of a novel ecofriendly material with potential application in all fields in which metal ion sequestration is desirable. The core idea of biocompatibility lead to the design and synthesis of a novel cellulose derivative (CS) functionalized with succinic acid (SA). Results from NMR, qNMR and FT-IR ATR experiments evidenced the successful substitution of the succinic acid on the microcrystalline cellulose backbone, with an estimated substitution rate of one SA for every six glucose units. The resulting material was investigated in aqueous solution to determine its acidic constants, sorption capability and establish a reliable speciation model in the presence of Cd2+. The acid-base properties and the CS binding constants towards Cd2+ were checked by potentiometry in NaCl(aq) (0.1 ≤ I / mol dm-3 ≤ 1.0) at T = 298.15 K in a pH range between 3 and 11. Two species (CS)Cd(OH) (logβ = -5.8) and (CS)Cd(OH)2 (log β = -13.41) are formed. Sorption tests were performed by means of kinetic and batch experiments and the residual Cd2+ concentration in solution was measured by differential pulse anodic stripping voltammetry. In conclusion, CS appears to be promising as a tool for heavy metals removal.