Fe3O4 nanospheres (Nsps) and chitosan (Cts)/Fe3O4 Nsps were prepared using a one-pot hydrothermal method and subsequently used as photocatalysts against the degradation of Congo red (CR) dye molecules. The sphere-shaped Fe3O4 nanoparticles were heterogeneously decorated by the Cts matrix, which was confirmed by powder X-ray diffraction, scanning and transmission electron microscopies. The Cts/Fe3O4 Nsps demonstrated 98% efficient photocatalytic activity against CR dye molecules upon 60 min exposure to visible light compared to Fe3O4 Nsps (77% for 60 min). When compared to Fe3O4 Nsps, the visible light photocatalytic efficiency of Cts/Fe3O4 Nsps against CR dye molecules was significantly improved. (C) 2021 Elsevier B.V. All rights reserved.