Removal of Noble Metal Ions (Ag+) by Mercapto Group-Containing Polypyrrole Matrix and Reusability of Its Waste Material in Environmental Applications

A novel approach was introduced to remove metal (Ag+) ions from aqueous solution and subsequently restate the metal-loaded materials for a number of environmentally friendly applications. A versatile adsorbent, polypyrrole with mercapto-functionalized chelating groups (PPy/MAA), successfully adsorbed Ag+ ions through subsequent reduction to silver nanoparticles (Ag-0 NPs) into the composite matrix. The as-prepared composite (PPy/MAA) and Agadsorbed PPy/MAA (PPy/MAA/Ag-0) were fully characterized by FE-SEM, EDS, HR-(S)TEM, XRD, FTIR, BET, XPS, and zeta potential measurements. Batch adsorption results showed that the adsorption process can be explained well by a pseudo second -order model. The maximum adsorption capacity calculated using a Langmuir isotherm model was 714.28 mg/g at 25 degrees C. XRD, XPS, and HR-TEM analyses confirmed the presence of metallic silver nanoparticles on the surface of the composite matrix after the in situ reduction of Ag+ to Ag-0. Among the applications tested, the metal-loaded waste (PPy/MAA/Ag-0) was found to have antimicrobial activity, as it inhibited the growth of Escherichia coli, while pure adsorbent without silver showed no killing effect toward E. coli. PPy/MAA/Ag-0 also played an important role in the catalytic reduction of 4-nitrophenol and also exhibited good sensitivity to NO2 in gas-sensing applications. Therefore, the developed PPy/MAA composite achieved 2-fold environmental benefits, not only remediating Ag+ from polluted waterways but also opening a new window for subsequently acting as an agent for antibacterial ability, catalytic activity, and gas-sensing efficiencies.