Carbon-in-silica matrices for the preparation of heterogeneous biocatalysts: The synthesis of carbon nanofibers on a Ni/SiO₂ catalyst and the characterization of the resulting adsorbents for the immobilization of thermostable lipase

Abstract

Comparative studies of nanocarbons and nanocarbon-in-silica adsorbents for the immobilization of enzymes, for example, thermostable lipase from Thermomyces lanuginosus, were performed. Carbon nanotubes (CNTs) with different diameters, specific surface areas, and concentrations of surface carboxy groups were studied as the nanocarbon adsorbents. The nanocarbon-in-silica adsorbents were prepared by the synthesis of carbon nanofibers (CNFs) in SiO₂ xerogel in the course of the pyrolysis of C₃-C₄ alkanes on Ni catalysts; their physicochemical and textural characteristics were studied by thermal analysis, scanning electron microscopy, and nitrogen porosimetry. It was found that carbon nanofibers of different diameters were synthesized in the bulk of a silica matrix only at Ni contents higher than 1–1.5%. The CNFs-in-silica supports were nanoporous: the mean pore diameter and the specific surface area were ∼10 nm and 250–300 m²/g, respectively. The heterogeneous biocatalysts prepared by the adsorption of thermostable lipase on the CNTs and CNFs-in-silica supports were investigated in the reaction of triglyceride (tributyrine) hydrolysis; the physicochemical properties of biocatalysts and their enzymatic activity and stability were studied depending on the hydrophobicity-hydrophilicity of the support/matrix.