Graphene oxide mediated dispersive micro solid phase extraction (Dμ-SPE) and quantification of rare earth elements (REEs) from seawater and coal fly-ash by ICP-OES

Abstract

A novel graphene oxide (GO) mediated dispersive micro solid phase extraction method (Dμ-SPE) was developed for the extraction of rare earth elements (REEs) from seawater and digests of coal fly-ash, and the REE concentrations were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES). This method involves the quantitative sorption of REE³⁺ ions from the samples onto the negatively charged surface of GO through electrostatic interactions. The extraction was carried out in the pH range of 7–9, where GO acquires a negative surface charge due to de-protonation of surface functional groups such as –COOH. The increased number of reactive sites at higher pH for metal sorption improved its efficiency. The challenges posed in the separation of REE sorbed GO (REE-GO) were addressed by charge neutralization using an electrolyte, NaCl. The REE-GO was centrifuged and REE was ultrasonically back extracted into dilute nitric acid for their determination using ICP-OES. Under optimized conditions, the limits of detection for REEs were in the range of 10–50 ppb with a relative standard deviation of 5–8%. The method was successfully applied to the extraction of trace REEs in seawater matrices and leachates of different coal fly-ash samples. The sample preparation procedure with the GO nanoparticles was found to be simple and fast with good extraction recoveries.