A hierarchical Co-Fe LDH rope-like nanostructure: facile preparation from hexagonal lyotropic liquid crystals and intrinsic oxidase-like catalytic activity

Hierarchical rope-like structures based on Co-Fe layered double hydroxide (LDH) nanosheets were synthesized by the coprecipitation method from a hexagonal lyotropic liquid crystal (LLC) nanoreactor, and were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TG) and inductively coupled plasma (ICP) analyses. It was found that the rope-like LDH structures were composed of LDH nanosheets with a lateral size of about 200-400 nm and an average thickness of 4.47 nm in the form of face-to-edge interactions. The length and the diameter of the rope-like assemblies were about 3-6 μm and 150-300 nm, respectively, and their aspect ratio was as high as 20. Interestingly, the LDH rope-like assemblies were ordered to form an array with the oriented directions parallel to each other. A formation mechanism for the hierarchical LDH structures in the LLC media was proposed. In addition, the catalytic activity of the hierarchical rope-like LDH assemblies for the oxidation reaction of the typical horseradish peroxidase (HRP) substrate, 3,3',5,5'-tetramethylbenzidine (TMB), was examined, and results revealed that they had a higher oxidase-like catalytic activity towards the oxidization of TMB by dissolved oxygen. We expect that the hierarchical rope-like LDHs can offer the potential applications in aqueous redox catalysts, biosensors, medical diagnostics and so on.