Graphene oxide nanosheets in basic medium: a new potential adsorbent for microwave assisted cloud point extraction of beryllium from industrial effluents prior to ICP-OES determination

Abstract

A novel and rapid graphene oxide mediated microwave assisted cloud point extraction (GO-MW-CPE) procedure is developed, in basic solution, for the separation and pre-concentration of ultra trace levels of beryllium from natural water and plant waste water. This method is based on the quantitative adsorption of beryllium species formed at pH 10 onto the hydrophobic reactive sites of a graphene oxide nanosheet (GO) suspension followed by their pre-concentration from a bulk aqueous phase into a small volume of a surfactant rich phase, using a hydrophilic non-ionic Triton X-114 surfactant (hydrophilic–lipophilic balance, HLB = 12.3). In basic solution, GO forms a well dispersed hydrophilic suspension and quantitatively adsorbs neutral Be(OH)₂ species through van der Waals interactions. Its phase separation is induced by efficient intermolecular hydrogen bonding and van der Waals interaction with Triton X-114 micelles followed by fast dehydration using microwave irradiation. This process enhances the hydrophobicity of the formed mixed GO–Triton X-114 aggregates and enhances the phase separation of GO, without which gravitational/centrifugal separation of GO in basic media is very difficult. Ultrasonic-assisted extraction is used to back extract the beryllium from the surfactant rich phase into a dilute nitric acid phase. Inductively couple plasma optical emission spectrometry (ICP-OES) is used for its determination. The main parameters affecting the extraction process are evaluated and optimised. Under the optimized conditions, the pre-concentration factor and limit of detection are 50 and 0.005 ng mL⁻¹, respectively for a 50 mL sample volume. The recoveries are 95 to 110%, when beryllium is in the range 10–1000 ng mL⁻¹ with 2–6% relative standard deviation. The accuracy of the procedure is verified by analyzing certified reference materials such as NIST 1640, 1640a and 1643e trace elements in natural water. The developed method is applied to influents, effluents, and natural water like seawater, tap water and ground water samples.