Optimization and characterization of a castor oil (Ricinus communis L.)- and 1,10-phenanthroline-based polyurethane membrane for Al3+ ion-selective applications

Abstract

Ion-selective membrane technology is a key for accurately measuring specific ions in different solutions. A study on Al³⁺ ion selective electrodes (ISEs) based on polyurethane (PU) membranes using an active substance, i.e., 1,10-phenanthroline, was successfully conducted. The results showed the highest sensitivity and linear range with a PU membrane composition of castor oil, toluene diisocyanate, 1,10-phenanthroline, and acetone in the ratio of 37.80 : 18.90 : 43.20 : 0.10 (%w/w) and internal solution composition 0.1 : 0.1 (M) of KCl and Al(NO₃)₃ Fourier transform infrared (FTIR) analysis indicated the presence of urethane bonds at a wavenumber of 3390 cm⁻¹. 1,10-Phenanthroline aromatic CC and C–N functional group peaks appeared at wavenumbers of 1600 cm⁻¹ and 1325 cm⁻¹, respectively. X-ray diffraction (XRD) characterization suggested a decrease in the degree of crystallinity of PU, PU/Phen membranes, and PU/Phen/Al. Scanning electron microscopy (SEM) analysis showed that the PU/Phen/Al membrane had a homogeneous dense outer layer and tended to be porous in the inner layer, and the Al³⁺ ISE system showed an average sensitivity, linear range, and detection limit of 19.94 ± 0.26 mV/decade, 10⁻¹⁰–10⁻⁴ M (R² = 0.998), and 5.17 × 10⁻¹² M, respectively. Furthermore, the ISE had a response time of 180 s, was stable in the pH range of 6–8 and allowed 33 days of use without any interference from foreign ions. The recovery was in the range of 99.21–101.57%. Therefore, the prepared PU/Phen/Al membrane is promising for ISE sensors, especially for the detection of Al³⁺ ions.