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High-performance reverse osmosis membranes are expected to simultaneously exhibit high solute rejection, elevated water permeability, excellent chemical stability, and strong resistance to compaction, particularly in aqueous separation applications.1 For several decades, aryl diazonium salts have been employed as reagents to modify a wide range of substrates, including carbons, metals, metal oxides (e.g., ZnO, Al₂O₃), nanomaterials, semiconductors, and polymer surfaces, with aryl moieties.2 The resulting grafted layers have diverse applications, including surface modification of membranes.3 The methods used for the modification of material surfaces involve both physical and chemical processes. Membrane surface properties - including charge density, hydrophobicity/hydrophilicity, and fouling resistance - can be tuned by grafting organic molecules. Such modifications enhance separation performance while maintaining mechanical and chemical robustness.
This paper examines the role of aryldiazonium salt concentration in an aqueous acid medium in the chemical grafting of aryl moieties onto the coal surface, which is subsequently used for reverse osmosis (RO) membrane preparation. Coal particles' surfaces were modified by chemical reduction of 4-nitrobenzene diazonium salt of different concentrations at aqueous acid solution (hypophosphoric and sulfuric). The ATR-FTIR spectra show that the nitrophenyl groups were strongly bonded on the surface of coal particles. The introduction of aryl groups onto the coal surface and thus in RO membranes alters their characteristics, as shown by reverse osmosis parameters as well as SEM images. The resulting membranes showed the best results with coal particles modified with a middle concentration of aryldiazonium salt in aqueous medium with hypophosphoric acid. At an acceptable reverse osmosis salt rejection level (94.55 %) of NaCl-H2O of concentration of 0.4 g/dm3 as a referent system at 1.76 MPa, the flux was 42.6 L/hm2.