Semiconductor-based photocatalysis is a probable approach to overcoming many pollution problems and eradicating toxic organic materials from wastewater. This research endeavor aimed to explore the synergistic potential of different semiconductor nanocomposites for photocatalytic degradation of organic pollutants in contaminated water. A facile hydrothermal approach was employed to synthesize bismuth oxide and cobalt ferrite nanoparticles from their precursors—bismuth nitrate pentahydrate, ferric chloride hexahydrate and cobalt chloride hexahydrate—with various concentrations and conditions to optimize the product. Subsequently, nanocomposites of bismuth oxide and cobalt ferrite were prepared by solid-state mixing in varying concentrations followed by calcination. UV/visible diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and elemental dispersive X-ray spectroscopic techniques have corroborated the successful synthesis of nanocomposites. The energy gaps of bismuth oxide and cobalt ferrite nanocomposites were computed in the range of 1.58–1.62 eV by Tauc plots. These nanocomposite materials were ascertained for photocatalytic potential to degrade methyl orange organic dye in water. A nanocomposite with equiquantic proportions has shown the best photocatalytic degradation activity, which may be attributed to the type-II band configuration and a synergistic effect, because Bi₂O₃ acts as an electron sink. This synergism has reduced the cogent band gap, hindered electron hole recombination and increased electron hole availabilities for photodegradation reactions, thus ensuing an efficient photodegradation co-work of Bi₂O₃/CoFe₂O₄ nanocomposites.

In the present paper, simple hydrothermal and solid-state methods are reported for the synthesis of metal chalcogenide (ZnSe), metal oxide (Co₃O₄) and their nano-heterostructure (ZnSe/Co₃O₄ 3:1, 1:1 and 1:3 ratios by weight), while their photocatalytic efficiencies are also investigated. The X-ray diffraction results corroborate the good crystallinity and purity of all synthesized products, i.e., ZnSe, Co₃O₄ and their nanocomposites. The scanning electron micro-images of ZnSe show a mixed morphology of nanoparticles (≈16 nm), including spherical and distorted cubes, while Co₃O₄ has a worm-like morphology (≈20 × 50 nm). The EDX results show that all the elements are present in accordance with their anticipated amounts in the products. The UV/visible absorption spectrum of ZnSe depicts a sharp absorption at around 480 nm, while Co₃O₄ demonstrates two prominent peaks, 510 nm and 684 nm. The prepared samples were employed for the photocatalytic degradation of Congo red dye and the nano-heterostructure (ZnSe/Co₃O₄ 3:1) shows an exceptional photocatalytic degradation efficiency of 96%. This enhanced photocatalytic activity was due to the synergic effect of ZnSe and Co₃O₄ that reduced the electron/hole recombination and caused suitable bandgap alignment.