Development of copper(II) and ammonia sensors based on poly (NBA)/bis-thiourea and poly aniline/carbon black sensing materials

Abstract

This work was aimed to develop chemical sensors for detection of copper(II) and ammonia in water. The copper(II) sensor was developed based on bis-thiourea derivative as ionophore. In this study, a total of 18 new compounds of bis-thiourea derivatives (2a-2c, 3a-3c, 4a-4b and 5a-5j) were successfully synthesised using a facile synthetic pathway between benzoyl chloride, ammonium thiocyanate and diamine, and were characterised using fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). Six bis-thiourea (3b, 4a, 5a, 5b, 5c, and 5e) with different substituents were selected in binding study to evaluate the binding affinity of the bis-thiourea towards Cu2+ ion using colorimetric detection and UV-Vis titration. Analysis of colorimetric detection revealed that most of the analysed bis-thiourea showed promising interaction towards Cu2+ ion. The UV-Vis titration suggested a 1:2 stoichiometric ratio of bis-thiourea and Cu2+ ion for all compounds tested. Optical Cu2+ ion sensor was developed based on immobilisation of the bis-thiourea 3b onto acrylic poly(n-butyl acrylate) [poly(nBA)] microspheres. The sensor exhibited a dynamic linear range from 7.80 × 10-7 - 1.60 × 10-4 M Cu2+ ion with a limit of detection (LOD) of 6.12 × 10-7 M and a fast response time (<1 min). The Cu2+ ion sensor also demonstrated a good reproducibility and reversibility with relative standard deviation (RSD) of 2.6% and 2.3%, respectively. The sensor showed good selectivity with respects to several metal ions, except only Fe3+ and Hg2+ ions displayed significant positive interference towards the sensor at molar concentration ratio of 1.0:1.0 and 1.0:100.0, respectively. On the other hand, an electrochemical sensor for the detection of Cu2+ ion using poly(n-butyl acrylate)-graphene-(bis)thiourea [poly(nBA)-rGO-5b] was developed. The response of the electrochemical Cu2+ ion sensor was measured by differential pulse anodic stripping voltammetry (DPASV) and showed an electrocatalytic ability for the oxidation of Cu2+ ion at −0.18 V. The electrochemical sensor exhibited a dynamic linear range from 1-500 µg L-1 Cu2+ ion with a good LOD of 0.7 µg L-1 Cu2+ ion. The sensor displayed a good reproducibility with RSD value of 1.7% and selectivity towards several metal ions, which only Ag+ , Hg2+ and Ni2+ ions interfered the sensor on detection of 300 µg L-1 Cu2+ ion. Both of the optical and electrochemical copper sensors were successfully applied for the determination of Cu2+ ion in river water and tap water samples respectively, and the results were in good agreement with ICP-OES method. A chemiresistive ammonia gas sensor was successfully developed based on deposition of polyaniline/carbon black composites onto interdigitated electrode. The results revealed that the gas sensor displayed a good sensitivity towards ammonia with the linear response in the range of 27 to 545 ppb with a LOD of 18 ppb. The sensor exhibited rapid response and recovery rates of 15 s and 45 s respectively. The sensor also demonstrated a good repeatability, reproducibility, selectivity and stability towards exposure of ammonia at room temperature.