Optimization and characterization of a castor oil (Ricinus communis L.)- and 1,10-phenanthroline-based polyurethane...

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 C[double bond, length as m-dash]C 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 (R ² = 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.