Surface Modification of Graphene Oxide With HDTMA: Advancing Energy-Efficient Technologies for Sustainable Nitrate Removal in Water Treatment

The adsorption of hexadecyltrimethylammonium (HDTMA) on graphene oxide (GO) was investigated to probe the molecular interaction of HDTMA adsorbed GO (GO-HDTMA) with nitrates. Physicochemical techniques including scanning electron microscope (SEM), transmission electron microscope (TEM), fourier transform infrared spectrometer (FTIR), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and Raman spectroscopy were used to characterize GO-HDTMA, and the effect of GO functionalization on nitrates adsorption was examined. Unmodified physical GO exhibited the weakest adsorption capability (~1.0 mmol g⁻¹). However, nitrate adsorption was markedly enhanced by chemical GO modified with 10 mmol HDTMA (GO-HDTMA-10 mM). Which can be attributed to the various functional groups on GO and increased active sites inducing HDTMA longer chain and higher carbon content. The nitrates adsorption process attain equilibrium in 3 h with maximum adsorption density of 16 mM g⁻¹. HDTMA adsorption was enhanced by pH changes, with pH 6 exhibiting the highest adsorption. It was found that the negative charges on GO results in the retention of HDTMA, while the hydrophobic phase created by the alkyl chain in HDTMA enables the adsorption of nitrates. The X-ray photoelectron spectrometer (XPS) analysis revealed a chemical shift caused by the adsorption of HDTMA and nitrates on the surface of GO. The reusability of the adsorbent was evaluated over four consecutive cycles. GO-HDTMA showed good removal efficiency for up to third regeneration cycles. Results reveal that the nitrates can be adsorbed more efficiently by modifying the HDTMA’s surface coverage on GO.