Design and Construction of a Novel Green Optode for Hafnium Determination in Real Environmental Samples

A highly selective and sensitive Hf optode was developed, which uses a triacetylcellulose membrane to immobilize 4-(2-benzothiazolylazo)2,3-biphenyldiol (BTABPD). The membrane optode responds to hafnium ions by color changing reversibly from yellow-orange to pink in thiel buffer at pH 5.0. The proposed membrane under optimum experimental conditions exhibits a linear dynamic range of 5.0–185 ng cm−3 of the Hf(IV) with detection and quantification limits of 1.58 and 4.95 ng cm−3, respectively. The newly developed optode has a response time of 15–30 s based on the Hf4+ ion level. The optode’s response is determined by the pH range of 4.5–5.5. The complex’s quantification and detection limits, Sandell sensitivity, molar absorptivity, Ringbom, calibration ranges, and relative standard deviation (RSD) have all been accurately calculated. The presented optode records fast response time, low detection limit, and, most significantly, excellent selectivity towards a number of lanthanide and transition ions (Sc3+, Y3+, La3+, Ce3+, Gd3+, Sm3+, Lu3+, Tm3+, Ho3+, Dy3+, Eu3+, Cd2+, Cu2+, Ni2+, Co2+, Pb2+, Bi3+, Al3+, Sn2+, Mn2+, Tl+, Ag+, Zn2+, Fe2+, Cr3+, and Zr4+ ions). The optode was regenerated successfully with thiourea and its response was reproducible (RSD ≤ 1.9%) and reversible. The proposed optode was successfully applied to detect Hf(IV) ions in real samples.