ABSTRACT In this study, a facile thermal condensation method was employed to prepare graphitic carbon nitride (g-C3N4) nanoparticles, and characterised by different advanced techniques. The TEM results proved that g-C3N4 had an average size of 49.7–89.3 nm. The EDX analysis of g-C3N4 confirms the existence of only C and N elements. Polyethylene oxide/polyacrylamide (PEO/PAAm) hydrogel and PEO/PAAm/g-C3N4 nanocomposite of different ratios of g-C3N4 (5, 10, and 15%) were synthesised by gamma irradiation-induced crosslinking reaction. In addition, novel magnetic (PEO/PAAm/g-C3N4/Fe3O4) nanocomposite was successfully fabricated by alkaline co-precipitation of swollen PEO/PAAm/g-C3N4 in Fe3+/Fe2+ solutions for use in the removal of Sr2+, Zn2+, and Cd2+ ions from wastewater. The PEO/PAAm/g-C3N4/Fe3O4 nanocomposite was characterised by FTIR, XRD, SEM, EDX, and VSM techniques. The XRD of PEO/PAAm/g-C3N4/Fe3O4 nanocomposite showed the presence of the typical peaks of both g-C3N4 and Fe3O4 nanoparticles. The VSM analysis indicated that the saturation magnetisation value of the nanocomposite was 18.96 emu/g, which is suitable for magnetic separation and adsorption processing. The uptake ability of PEO/PAAm/g-C3N4/Fe3O4 nanocomposite towards the Sr2+, Zn2+, and Cd2+ was examined under the effect of pH, reaction time, pH, and adsorbent dosage as well as different adsorption kinetics and isotherms models were applied. The maximum removal percentage of Cd2+, Zn2+, and Sr2+ ions was 89.8%, 97.3%, and 91.5% and achieved after 25 min at the optimum pH of 6 for Cd2+ and Zn2+, and pH 4.0 for Sr2+ ions. The fast and easy uptake of PEO/PAAm/g-C3N4/Fe3O4 nanocomposite adsorbent for the pollutants owing to the synergistic effect of existing functional groups of PEO/PAAm as well as g-C3N4 and Fe3O4 improved the removal performance of metal ions for great application in environmental remediation of wastewater treatments.