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 nan otubes (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 syn thesis of carbon nanofibers (CNFs) in SiO 2 xerogel in the course of the pyrolysis of C 3 -C 4 alkanes on Ni cat alysts; 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 syn thesized 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 m 2 /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.

Synthesis of nanostructured carbon on Ni catalysts supported on mesoporous silica, preparation of carbon-containing adsorbents, and preparation and study of lipase-active biocatalysts

“…The lowest specific activity of lipase was observed with the crust type adsorbent. The adverse effect of the carbon surface on the activity of adsorbed lipase was also reported in our previous works [17,29]. It was hypothesized in those works that, in lipase adsorption on hydrophobic carbon, there can be a "wrong" orientation of lipase on the surface.…”

“…The catalytic pyrolysis of the С 3 -С 4 alkanes + hydrogen (8 : 1 v/v) gas mixture was performed in a fixed bed reactor at 500°C for 1 h, as was described in earlier works [17,23]. The amount of synthesized car bon was determined by thermal analysis (TA) using an STA 449 C Jupiter system (Netzsch, Germany) and was also calculated from the change in the catalyst weight measured after the pyrolysis run (500°C, 1 h) or after annealing (800°C, 4 h).…”

“…The reactor was placed in a KT 104 temperature con trolled shaker reciprocating at a rate of 90 min -1 . The duration of one reaction cycle was 5 min to 24 h. The following reactions were investigated: hydrolysis of tributyrin (I) under the conditions described in our earlier study [17], esterification of capric acid with isoamyl alcohol (II), and transesterification of sun flower oil triglycerides involving an acyl group donor (methyl acetate) or acceptor (dimethyl carbonate), and transesterification of linseed oil triglycerides involving ethyl acetate (III). The hydrolysis of emulsi fied tributyrin (reaction (I)) was carried out in a buffer solution at pH 7.0, and reactions (II) and (III) were performed in organic nonaqueous solvents (hexane or a hexane-diethyl ether mixture).…”

“…Nanostructured carbon is synthesized by hydrocar bon pyrolysis on metallic catalysts (Ni, Cu, Fe, and their alloys) supported on an inorganic material [8,9]. In particular, Ni catalysts are commonly supported on SiO 2 [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The following methods are used to pre pare silica supported Ni catalysts: (1) impregnation of a support with a nickel salt solution (Impr) [12,14,15], (2) intercalation of nickel compounds into a sili cate matrix using sol-gel processing [12,16,17], and (3) homogeneous precipitation (HP) [18][19][20][21][22][23].…”

“…The hydroxide ion reacts with Ni 2+ to yield colloidal α Ni(OH) 2 particles (since the solubility product of nickel hydroxide is SP < 10 -15 ), and these particles precipitate on the surface of an inorganic support [20,21,23]. The pyrolysis of alkanes (С 1 , С 3 -С 4 ) or ethyl [17,26]. This work continues a series of our studies on the synthesis of catalytic filamentous carbon by the pyrol ysis of С 3 -С 4 alkanes on supported Ni and Co cata lysts.…”