Novel TiO2 nanoparticle-based sensor for xanthate quantification in mineral flotation samples

Abstract

A voltammetric method for xanthate quantification was developed by fabricating a new electrode based on TiO2 nanoparticles (TiO2 NPs). The nanomaterial in the anatase phase was synthesized by a simple sol-gel method followed by a thermal treatment (9 h at 500 °C). The nanoparticles have a spheroidal morphology with an average size of 20.61 ± 6.01 nm. The band gap energy (3.7 eV) was determined by means of UV–visible spectroscopy from the absorption band at 335 nm. The TiO2 based sensor was employed as working electrode (electroactive area: 0.02248 cm2) in a cyclic voltammetry study, and a greater peak current was observed for the electrooxidation of isopropyl xanthate at pH 10 as compared to the unmodified electrode. The electrode optimization showed that the percentage of TiO2 and the amount of mineral oil in the electrode have a significant influence on the electrochemical response, with 18.4 % of TiO2 NPs, 0.74 mL of mineral oil, and 18 h of electrode rest before the first use as optimal conditions. In the polarization studies, the charge transfer reaction occurred through a lower overpotential with respect to the open circuit potential. The exchange current density was three times higher for the modified electrode. Electrochemical impedance spectroscopy indicated the detection of xanthate with lower charge transfer resistance than when the unmodified electrode was used. The electrochemical sensor allows the quantification of xanthate from 5 μmol/L to 10 mmol/L by cyclic voltammetry and the square wave technique. For the cyclic voltammetry calibration, the limits of detection and quantification were 40.6 μmol/L and 135 μmol/L, respectively. The limit of detection by square wave voltammetry was 2.4 μmol/L, and the limit of quantification was 7.9 μmol/L. The repeatability of the method showed a relative dispersion of 3.1 % at 0.51 mmol/L. The electroanalytical response of the sensor was reproducible up to 30 days. The recoveries of xanthate in real flotation samples were 91.9 % and 94.6 % for concentrations of 0.55 and 1.1 mmol/L, respectively. No statistically significant differences were found between the quantification using the sensor and the UV spectrophotometric method. Dicresyl dithiophosphate showed statistically significant interference with the xanthate oxidation signal.