Surfactant-loaded graphene oxide sponge for the simultaneous removal of Cu²⁺ and bisphenol A from water

The objective of this study was to develop a novel graphene oxide (GO)-based adsorbent by loading the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) to simultaneously scavenge copper ion, a charged species, and bisphenol A, an uncharged organic compound, from water. The HDTMA modification process was studied and the GO/HDTMA composites characterized using SEM (scanning electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier Transform Infrared) spectroscopy. Within the concentration range of 6.4-11.5%, HDTMA caused the 2D GO sheets to form into solid 3D networks by reducing the repulsive forces and increasing the hydrophobic interactions between the adjacent GO sheets. The unique feature of this material is the simultaneous uptake of charged heavy metal ions and uncharged organic contaminants. The negative charges on GO results in the retention of heavy metal ions, while the hydrophobic phase created by the alkyl chain in HDTMA enables the adsorption of organic contaminants. The adsorption capacity of Cu²⁺ and bisphenol A reached 59.7 mg/g and 141.0 mg/g, respectively. The adsorption processes for both Cu²⁺ and bisphenol A were rapid, attaining ∼100% removal in 1 h and 2 h, respectively. Increasing the pH favored the adsorption of the two solutes. The presence of NaCl reduced the retention of Cu²⁺, but was beneficial for the adsorption of bisphenol A. The results demonstrate that the 3D structure and the adsorption of the target species can be achieved by tailoring the surface coverage of HDTMA on GO.