•Simple approach to fabricate OANI superstructures with controllable morphology.•Stable pH value to form the uniform morphologies.•Investigate the forming mechanism for the complex morphologies of OANI.Oligoanilines (OANI) with hierarchical structures were synthesized via chemical oxidative polymerization within a stable weak-acid system. Acetic acid was used as the buffer and dopant, and low concentration of ammonium peroxydisulfate (APS) and aniline were added to tune the pH value and to obtain different morphologies. With the pH value varied from 4.26 to 4.11 to 3.26, flake-like structure, flower-like morphology consisted of dozens of nanoflakes and lath-like structure composed of parallel alignment of nanorods are produced, respectively. Under different reaction conditions, OANI with different chemical structures are formed and simultaneously assemble into hierarchical structures. The formation mechanism of these hierarchical structures is proposed. These hierarchical OANI were used as support to load Mo catalyst and flower-like OANI/Mo catalyst shows a good property in epoxidation of cyclooctene.

•A simple approach for assembly structures of polyaniline nanofibers.•Simultaneously form and array of PANI nanofibers on PS microspheres.•Special morphology with large BET surface area.Polystyrene/polyaniline (PS/PANI) composite microspheres with sea urchin-like morphology, radial array of PANI nanofibers on the surface, are synthesized by seeded swelling polymerization with polystyrene (PS) microspheres as seed. The redox potential of the oxidants and the concentrations of reactants have important influences on the morphology of the obtained composite microspheres. The formation mechanism of the sea urchin-like microspheres has been clearly revealed. When removing the PS template with tetrahydrofuran, the sea urchin-like hollow PANI microspheres are obtained. This approach is simple and can produce these microspheres in bulk. The sea urchin-like PS/PANI composite microspheres display high BET surface areas and can be further used as catalyst supports.Radial array of PANI nanofibers on PS microspheres.