A chemically-carbonized sorbent was prepared from date palm leaflets by sulphuric acid treatment at 170°C. Carbonization took place via the dehydration effect of the hot sulphuric acid producing a carbon with reduction property. Sorption of Cu²⁺ and Ag⁺ from aqueous solution was investigated in terms of pH, contact time, metal concentration and temperature. A peculiar behaviour was found for the sorption of the two metals on the produced carbon. Sorption of Cu²⁺ was fast, reaching equilibrium within ∼2 h, whilst Ag⁺ sorption was slow and required ∼60 h to reach equilibrium. Activation energy (E _a ) for Cu²⁺ sorption was ∼16.1 kJ/mol indicating a diffusion-controlled ion exchange process; however, E _a for Ag⁺ sorption was ∼44.3 kJ/mol indicating a chemically controlled process. Equilibrium sorption data were tested for the Langmuir and Freundlich equations. Sorption capacity appears to be much higher for Ag⁺ than for Cu²⁺ with increased uptake, for both metals, when increasing the temperature (25–45°C). Ag⁺ was reduced to elemental silver on the sorbent surface and this was confirmed using scanning electron microscopy and x-ray powder diffraction; however, no reduction processes were involved in Cu²⁺ sorption. This paper discusses the sorption mechanism.

Due to the shortage of freshwater resources, and the limitations of commonly used ion exchangers, this study aims to prepare, characterize, and test new graphene-based ion exchangers for salt removal. Graphene oxide (GO) was prepared using an oxidative exfoliation method. Using amide coupling, the GO surface was functionalized with taurine to produce a cation exchanger (GOT), and pentaethylenehexamine (PEHA) to produce a chelating ion exchanger (GOP) which was converted to a quaternary ammonium salt (GOQ) which acts as an anion exchanger. The surface area of GO was 220 m²/g, however, decreased tremendously on surface functionalization. X-ray diffraction (XRD) showed that the produced ion exchangers possess amorphous nature. Energy dispersive spectroscopy (EDS) showed the presence of nitrogen in GOP, GOQ, and GOT; and sulfur on GOT. X-ray photon spectroscopy (XPS) showed the presence of -SO₃ and S-O on GOT, amine on GOP, and quaternary ammonium group (-NHR₂ ⁺) on GOQ. TGA shows that GO functionalization is covalent. The produced ion exchangers show an efficient removal of both the cations and anions from the individual salt solution of Ca(NO₃)₂, MgSO₄, and NaCl. GOP sorbs both Ca²⁺ and Mg²⁺ via chelation while their anions are sorbed via ion pairing. GOT sorbs the cations via ion exchange while anions are sorbed via ion pairing. GOQ sorbs the anions via electrostatic interaction while the cations are sorbed via ion pairing. Under the experimental conditions in this study, GOP shows the best removal of Ca²⁺ (80.2 %) and Mg²⁺ (64 %) while GOT shows the best removal of Na⁺ (30 %). For anions, GOQ shows the best removal of NO₃ ^- (53.5 %), SO₄ ^2- (84 %), and Cl^- (81.8 %). The GO-based ion exchangers seem promising for salt removal from water in addition to being robust at high temperatures and pH.