Mechanochemical synthesis of Zn-bionanohybrids: size effect at the nanoscale to improve their enzyme-like activity†

The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field owing to its simplicity, scalability, and eco-friendliness. In this work, we synthesised new zinc bionanohybrids via a mechanochemical method involving a size effect at the nanoscale and microscale levels of the final nanostructure. This effect translates into an improvement in the catalytic properties of this nanomaterial, such as enzyme-like activities, compared to that synthesized in an aqueous media. One-pot synthesis was performed by combining Candida antarctica lipase B (CALB) solution, solid zinc salts and phosphate or bicarbonate salts using the ball-milling approach, where overall reaction times were drastically reduced in comparison with the traditional aqueous method. The reaction was carried out at r.t. and the synthesis process was evaluated by considering the use of steel balls with different sizes, completely dry conditions or in the presence of a very small amount of water as an additive (2 mL), and incubation methods (planetary or horizontal ball milling). The final nanostructure of the Zn biohybrids was determined using XRD, FT-IR, TEM and SEM analysis, demonstrating changes in metal species and drastic changes in the nanostructure conformation of the biohybrids obtained through the mechanical approach compared to those obtained through the aqueous method. The size effect at the nanoscale was also demonstrated in the final species, showing a reduced size. This nanoscale effect of the material had a positive impact on the catalytic properties of the materials, in some cases showing up to 2000 times greater activity compared to the counterpart synthesised under aqueous conditions.