A molecular approach to remove lead from drinking water

Corrosion of lead-containing plumbings is responsible for significant contamination of tap water, which can reach several hundreds of micrograms per liter. According to a decision of the European Council applicable in 2013, the maximal lead level in tap water should not exceed 10 μg l−1. A new concept has been explored that relies on solid-phase extraction by covalent attachment of a lead-selective macrocyclic sequestering agent onto the surface of silica gel. An N-carbamoylmethyl substituted 1,4,8,11-tetraazacyclotetradecane (cyclam) derivative was shown to exhibit favorable protonation properties together with an almost 106-fold selectivity for lead over calcium. Structural studies evidenced the formation of an octadentate molecular cage around the encapsulated Pb2+ cation. Extensive simulations of lead speciation diagrams further indicated that the selected tetraacetamide cyclam ligand was able to successfully compete in a large pH and alkalinity range with complexing anions usually present in tap water to uptake the target metal. Materials were prepared by grafting closely related derivatives onto silica gel and their lead fixation efficiency was investigated in various flow tests using a packed column. Breakthrough and regeneration experiments at low flow rate confirmed the predicted efficiency. In order to validate the concept of a domestic cartridge-based purification system that could be mounted directly on a kitchen faucet, the performance of the extracting material was finally evaluated on a pilot system that incorporates a lead-pipe loop. Effective decontamination could be achieved for conditions simulating real applications.