Synthesis, characterisation and application of thiol-based spectroscopic and electrochemical sensors for detection of iron(III) in environmental samples – A DFT supported comparative study

In the present work, a thiol, 4-((4-hydroxybenzylidene)amino)-N-(4-mercaptophenyl)benzamide (HBMB) was synthesised and subjected to UV-visible measurements for assessing its sensing potential towards diverse metal ions. HBMB was found to exhibit sensitivity towards Fe³⁺ over a wide linear concentration range from 0.66 µM to 38.46 µM (r² = 0.986 ± 0.005) with a detection limit of 3.60 × 10⁻⁷ M. Electrochemical behaviour of HBMB was investigated using CV and DPV which displayed oxidation peaks at 1.01 V and 0.949 V, respectively. In DPV titration, HBMB exhibited sensitivity towards Fe³⁺ in a linear concentration range from 0.2 µM to 5.56 µM with a detection limit of 5.17 × 10⁻⁶ M. HBMB incorporating Fe³⁺-CPE was found to exhibit Nernstian slope of 18.3 mVdec⁻¹ in the concentration range of 1.00 × 10⁻⁵ <i>M</i> - 1.00 × 10⁻¹ M and detection limit of 3.98 × 10⁻⁶ M with a short response time of 10 s. DFT studies also confirmed HBMB-Fe³⁺ complexation with increase in HOMO-LUMO gap from 0.05 hartree to 0.14 hartree and negative binding energy of −0.013 hartree. Moreover, HBMB-based sensors was successfully applied for estimating Fe³⁺ content in different real samples of water, soil and food grains which could be extended to other samples of biological and environmental importance.