Flexible film-type catalysts encapsulating urease within κ-carrageenan hydrogel network

• We successfully immobilized urease in a thin film of a κ-carrageenan gel.
• The film-type catalyst is flexible enough to be molded into various shapes suitable for a specific reactor configuration.
• Urease is retained within the film during the hydrolysis reaction of urea.
• The immobilized urease exhibited catalytic activity comparable to that of free urease.
• The film-type catalysts can be used multiple times with minimal activity loss.

Flexible film-type catalysts were synthesized by encapsulating urease within a κ-carrageenan gel network supported on a cellulose-acetate membrane filter. Synthesized film-type catalysts are flexible and can be easily formed into a shape that is suitable for a specific process configuration. The filter membrane has macropores about 200 nm, which are formed by interconnected bead-shaped membrane material. Scanning electron microscopy shows that the surface of the membrane material is coated homogeneously with the κ-carrageenan hydrogel. Urease entrapped within the gel network hardly leaches out during urea hydrolysis catalysis conducted at 310 K in a batch reactor and exhibits high catalytic performance. Analysis of the reaction data by the Michaelis–Menten equation shows that the film-type catalyst shows kinetic parameters (KM and Vmax) and apparent activation energy (24 kJ mol−1), which are all similar to those found for free urease. Estimation of the mass transfer rate of urea within the κ-carrageenan network and the urea hydrolysis rate show that the diffusion rate of urea within the thin film is five orders of magnitude higher than the reaction rate. The film catalyst can be recycled at least 7 times with <20% decrease in activity. High flexibility as well as high catalytic performance of the film catalyst shows prospective features of this catalyst for future applications.