Metallic nanoparticles embedded in the polymer matrix are considered a significant category of heterogeneous catalysts with strong catalytic performance. Functionalized polymers are inexpensive building blocks that make good catalytic platforms for stabilizing metallic nanoparticles. In this study, Fe3O4@CMC-Cu magnetic nanocomposites were successfully synthesized and characterized by XRD, FTIR, BET, XPS, VSM, HR-TEM, and EDX mapping. Morphology observation shows that spherical Fe3O4 magnetic nanoparticles and Cu NPs are distributed uniformly and encapsulated inside the polymer structure with an average diameter of ~ 11 nm without substantial agglomeration. Additionally, the inclusion of CMC polymer and Cu NPs gradually reduces the magnetic saturation of Fe3O4. The reduction of 4-nitrophenol (4-NP) and the organic dyes Congo red (CR) and acriflavine (ACF) in aqueous medium at room temperature was used to test the nanocomposites’ catalytic activity. The effects of reaction parameters, catalyst amount and Cu NPs percentages on the catalytic effectiveness were determined. The induction time of the reaction decreases with increasing the nanocomposite amount and the Cu NPs loading percentages. Excellent catalytic activity was demonstrated by the Fe3O4@CMC-Cu (10 %) nanocomposite for the elimination of all three intended organic contaminants (4-NP, CR and ACF). For the reduction of 4-NP, CR, and ACF, the calculated Kapp values were 1.55 min− 1 , 0.3 min− 1 , and 2.3 min− 1 , respectively. The magnetic nanocomposite was easily separated from the reaction solution and recycled for up to five successive cycles without suffering a substantial decrease in the catalytic activity. Such magnetic nanocomposites provide light on highly effective catalysts for applications in environmental protection