Synthesis and Characterization of Poly(pyrrole-1-carboxylic acid) for Preconcentration and Determination of Rare Earth Elements and Heavy Metals in Water Matrices

Abstract

Pyrrole was N-functionalized with solid carbon dioxide followed by chemical polymerization to create a new air-stable, granular, and water-insoluble sorbent, poly(pyrrole-1-carboxylic acid) (PPy-CO₂). PPy-CO₂ exhibited enhanced affinity for the sorption of metal ions compared to unfunctionalized PPy due to the incorporation of carboxylate functional groups directly onto the polymer backbone. As a freestanding sorbent material, immobilization to an additional solid support is not needed. Sorption, and therefore preconcentration, occurs simultaneously to achieve efficient removal and recovery of metal ions by a pH-dependent sorption–desorption mechanism. PPy-CO₂ was evaluated on the analytical scale for the solid-phase extraction of a range of metal ions and found to efficiently preconcentrate rare earth elements (REEs), Th, and heavy metals (Cr, Fe, Cd, and Pb), which allowed quantitation by inductively coupled plasma mass spectrometry (ICP-MS). The impact of sorption parameters, such as solution pH, amount of sorbent, and sorption time, and the effect of desorption flow rate for recovery were investigated and optimized using ultrasound-assisted dispersive solid-phase extraction (UAD-SPE) with ICP-MS analysis. Maximum efficiency for sorption and recovery of most metal ions was achieved at a solution pH of 6.0, 10 mg of sorbent, a sorption time of 5 min, and desorption conditions of 1 mL of 2 M nitric acid applied at a flow rate of 0.25 mL min^–1. Detection limits for REEs and Th ranged from 0.2–3.4 ng L^–1 for REEs and Th and 0.9–5.7 ng L^–1 for heavy metals. Linear ranges from 0.1–1000 μg L^–1 for REEs and 0.1–500 μg L^–1 for heavy metals and Th were also observed. PPy-CO₂ successfully preconcentrated and facilitated the determination of the targeted metal ions in water matrices of varying complexity, including tap water, well water, river water, and produced water samples. These results indicate the potential application of PPy-CO₂ for larger-scale recovery and removal of valuable or hazardous metal ions.