abstract

Water with high levels of heavy metals needs sensing materials which are sensitive, selective, low cost and environmentally friendly. The conventional instrumental methods, like atomic absorption spectroscopy and inductively coupled plasma mass spectrometry are reliable but are expensive, centralised and cannot be used for rapid field screening. Here presented to readers, is a paper study, which is related to the engineering science of noble metal nanoparticle – hydrogel nanocomposites for detection of heavy metal ions in water. The process of synthesis of silver and gold nanoparticles was done with the use of polyphenol-rich extract from the discards of a plant as a reducing and stabilizing system and in situ immobilization within a chitosan-polyacrylamide hydrogel matrix was used to obtain a porous Ag-Au/hydrogel nanocomposite. The material design is based on the two complementary properties of noble metal nanoparticles: the localized surface plasmon resonance, and the swelling, preconcentration and binding to ions of hydrogels. The synthesised nanocomposite was tested using the following techniques; UV-visible spectroscopy, visual colour response, swelling behaviour, selectivity analysis, calibration response, limit of detection estimation and real water recovery tests. The plasmonic peaks characteristic of the model experimental results were found to be near 425 nm and 535 nm; the hydrogel swelling ratio was 23.4 g/g at neutral pH; The linear range for detecting Hg(II) was found to be 5-100 µM (R² = 0.996); The limit of detection was estimated at 1.14 µM and the recovery values were found to be 94.6%-103.8% for tap, river and industrial effluent water samples. The best results were found for Hg(II) followed by Pb(II) and Cu(II) where the aggregation caused by the metals, the coordination with hydroxyl, amine and carbonyl groups and the change of the refractive index near the plasmonic particles were responsible. The study suggests that the green synthesized noble metal nanoparticle – hydrogel nanocomposites are potential to utilize as optical sensing platform for preliminary screening of toxic metal ions in water.