Removal of aflatoxin B1 from contaminated peanut oils using magnetic attapulgite.

The efficient magnetic adsorbent (Fe3O4@ATP) was prepared by precipitation through the dispersion of Fe3O4 nanoparticles on the natural attapulgite (ATP) and then tested as an adsorbent for aflatoxin B1 (AFB1) removal from contaminated oils. The adsorbent characterization results revealed that the Fe3O4 were incorporated into the ATP, affording the Fe3O4@ATP composite. This magnetic composite displayed a good ability to eliminate AFB1 from contaminated oils with a removal efficiency of 86.82% using a 0.3% dosage. The Fe3O4@ATP possessed paramagnetic character with a saturation magnetization of 50.86 emu/g, enabling its easy separation from the medium using an external magnet. The adsorption process followed the pseudo-second-order model and fitted the Freundlich isotherm well. Moreover, the thermodynamic studies showed that AFB1 adsorption onto Fe3O4@ATP was exothermic and spontaneous. The novelty of this study lies in the fabrication of magnetic composite adsorbents for AFB1 elimination from oils.

Detoxification of Aflatoxin B1 by magnetic graphene composite adsorbents from contaminated oils.

Safety concerns pertaining towards fungal occurrence in oil commodities have been a significant threat to human health. In this research, magnetic composite adsorbents were fabricated for the removal of aflatoxin B1 (AFB1) from contaminated oils. To this goal, graphene oxides (GO) were synthesized using Hummer's method, and graphenes (rGO) were obtained by the reduction of GO by sodium borohydride. Thereafter, magnetic graphene oxides (MGO) and magnetic graphenes (MrGO) were prepared by coprecipitation of iron oxides on GO and rGO nanosheets, respectively. The as-prepared MGO and MrGO were characterized by SEM, TEM, FT-IR, XRD, VSM, and nitrogen adsorption-desorption techniques. Results showed that MGO had two-dimensional layered nanostructure with many wrinkles on its surface, and the Fe3O4 nanoparticles were essentially encapsulated onto the composite. The adsorption behaviors for the composite adsorbents especially for the removal of AFB1 from contaminated oils were systematically explored by varying adsorbent dosage, contact time, adsorption temperature and initial AFB1 concentration. The MGO adsorbent could have great potential in the application of AFB1 removal from contaminated oils, with the merits of facile magnetic separation and high removal efficiency. However, the removal process also causes a loss of the triglyceride, pigment, and beneficial micronutrients in the oil feedstocks.

Lipase immobilized on ionic liquid-functionalized magnetic silica composites as a magnetic biocatalyst for production of trans-free plastic fats.

The main objective of this study is to develop an efficient and environmentally gentle process for production of trans-free plastic fats. To acheive this, the core-shell structured magnetic composites were prepared, and then imidazole-based ionic liquids (ILs) were covalently grafted on the magnetic composites. Thereafter, Candida rugosa lipase was immobilized on the magnetic IL-functionalized composites. The immobilized lipase could be facilely separated using an external magnetic filed. With the magnetic biocatalyst, enzymatic interesterifications of solid palm stearin and liquid rice bran oil blends were performed at 45 °C. It was shown that the total fatty acid (FA) compositions of the binary blends were almost unchanged after the interesterifications, whereas the FA positional distribution and triacylglycerol species were significantly varied. As compared with the physical blends, the interesterified products had a lower slip melting point, and the interesterification could result in an obvious change in the microstructure of the final products.

Covalent immobilization of lipase onto aminopropyl-functionalized hydroxyapatite-encapsulated-γ-Fe2O3 nanoparticles: A magnetic biocatalyst for interesterification of soybean oil.

Hydroxyapatite-encapsulated γ-Fe2O3 nanoparticles were prepared, and lipase from Candida rugosa was then covalently bound onto the magnetic materials via covalent linkages. The magnetic carrier and immobilized lipase were characterized by enzyme activity assays, XRD, FT-IR, TEM, VSM and N2 adsorption-desorption techniques. Results demonstrated that γ-Fe2O3 nanoparticles were coated with the hydroxyapatite, and the lipase was indeed tethered to the magnetic carriers without damage to their structure. The immobilized lipase showed a strong magnetic responsiveness and displayed high catalytic activities towards the interesterification of soybean oil. The interesterified products were evaluated for their total fatty acid (FA) composition, slip melting point (SMP), iodine value, triacylglycerols (TAGs) profile and FA composition at sn-2 position in TAGs. The FA positional distributions and TAG species significantly changed after the enzymatic interesterification. Besides this, the interesterified products showed an obvious reduction in their SMP in comparison with the physical blends.

Mesoporous SBA-15 Silica-supported Diisopropylguanidine: an Efficient Solid Catalyst for Interesterification of Soybean Oil with Methyl Octanoate or Methyl Decanoate.

The organosilane agent, namely 3-(N,N'-diisopropylguanidine)-propyltriethoxysilane, was firstly prepared by the reaction of diisopropylcarbodimide with (3-aminopropyl)triethoxysilane, and then employed for grafting guanidine base onto the surface of the mesoporous SBA-15 silica to afford an organic-inorganic hybrid catalyst. The prepared solid catalyst was fully characterized by various techniques such as small-angle X-ray power diffraction, Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption and elemental analysis techniques. The obtained results showed that the guanidine base was successfully tethered onto the SBA-15 silica and the ordered mesoporous structure of the SBA-15 material remained almost unchangeable after the orgnofunctionalization. The solid catalyst was found to have appreciable catalytic activities to the interesterification of soybean oil with methyl octanoate or methyl decanoate under solvent-free conditions. Influence of various reaction parameters, such as the substrate molar ratio, reaction temperature, catalyst loading and reaction time, on the catalytic interesterification was investigated to optimize the interesterification condition for the production of structured lipids containing medium-chain fatty acids. The hybrid solid catalyst was easily separated and reused for four runs without significant loss of catalytic activity.

Propylsulfonic and arenesulfonic functionalized SBA-15 silica as an efficient and reusable catalyst for the acidolysis of soybean oil with medium-chain fatty acids.

The objective of this work was to develop a feasible ecofriendly process to produce medium-chain fatty acid (MCFA)-enriched structured lipids (SLs) in heterogeneous manners. For this purpose, the propyl-SO3H or arene-SO3H-modified SBA-15 materials were prepared through a surface functionalization of SBA-15 silica with propyl-SO3H and arene-SO3H groups. The organosulfonic acid-functionalized SBA-15 materials were characterized by Brönsted acidity determination, elemental analysis, XRD, C(13) MAS NMR, FT-IR, SEM, TG, TEM, and N2 adsorption-desorption techniques. Results showed that the propyl-SO3H and arene-SO3H groups were successfully tethered on the SBA-15 support, and the ordered mesoporous structure of SBA-15 silica was well retained after the organofunctionalization. This organic-inorganic hybrid material displayed high surface acidities and high activities in the acidolysis of soybean oil with caprylic or capric acid to produce SLs containing MCFAs. The influences of processing parameters on the reaction were investigated. The two studied catalysts showed an excellent recyclability for the reaction.

Immobilized lipase on core-shell structured Fe3O4-MCM-41 nanocomposites as a magnetically recyclable biocatalyst for interesterification of soybean oil and lard.

A core-shell structured Fe3O4-MCM-41 nanocomposite was prepared by means of a surfactant-directed sol-gel process. Candida rugosa lipase was then bound to the magnetic core-shell material by using glutaraldehyde as a cross-linking reagent. The as-prepared Fe3O4-MCM-41 support and the immobilized lipase were characterized in detail using enzyme activity assays, TEM, XRD, FTIR, VSM and nitrogen adsorption-desorption techniques. Results showed that the magnetite nanoparticles were coated with the MCM-41 silica with the formation of core-shell structured materials, and the lipase was successfully immobilized on the core-shell structured support. The catalytic performance of the bound lipase was tested in the interesterification of lard and soybean oil. It was shown that the immobilized lipase had a better catalytic activity towards the interesterification reaction. The slip melting point of the final product was lower than that of the original blend, and the interesterification led to an obvious variation in the microstructure of the product.

Biguanide-functionalized mesoporous SBA-15 silica as an efficient solid catalyst for interesterification of vegetable oils.

The biguanide-functionalized SBA-15 materials were fabricated by grafting of organic biguanide onto the SBA-15 silica through covalent attachments, and then this organic-inorganic hybrid material was employed as solid catalysts for the interesterification of triacylglycerols for the modification of vegetable oils. The prepared catalyst was characterized by FTIR, XRD, SEM, TEM, nitrogen adsorption-desorption and elemental analysis. The biguanide base was successfully tethered onto the SBA-15 silica with no damage to the ordered mesoporous structure of the silica after the organo-functionalization. The solid catalyst had stronger base strength and could catalyze the interesterification of triacylglycerols. The fatty acid compositions and triacylglycerol profiles of the interesterified products were noticeably varied following the interesterification. The reaction parameters, namely substrate ratio, reaction temperature, catalyst loading and reaction time, were investigated for the interesterification of soybean oil with methyl decanoate. The catalyst could be reused for at least four cycles without significant loss of activity.

Heterogeneous interesterification of triacylglycerols catalyzed by using potassium-doped alumina as a solid catalyst.

Heterogeneous interesterification of vegetable oils offers an environmentally more attractive option for the modification of edible oils to meet the specifications for certain food applications. In this work, potassium-doped alumina (KNO3/Al2O3) was prepared using an impregnation method, followed by calcinations at a temperature of 700 °C, and was then employed as heterogeneous catalysts for the interesterification of triacylglycerols. The solid catalyst was characterized by means of Hammett titration method, power X-ray diffraction, scanning electron microscopy, and nitrogen adsorption-desorption techniques. It was determined that the catalyst with KNO3 loading of 35% on alumina support and calcined at 700 °C exhibited the best catalytic activities toward the interesterification between soybean oil and methyl stearate under solvent-free conditions. Also, the solid base catalyst was successfully applied to the interesterification of soybean oil and lard blends in a heterogeneous manner. The physicochemical properties of the interesterified products were investigated using gas chromatography, high-performance liquid chromatography, and confocal laser scanning microscopy. It was found that the slip melting point and crystal morphology had a significant variation after the interesterification reaction as a result of the modification in the TAG profile. With the solid base catalyst, an environmentally friendly approach for the interesterification of triacylglycerols in a heterogeneous manner was developed.

Enzymatic interesterification of soybean oil and methyl stearate blends using lipase immobilized on magnetic Fe3O4/SBA-15 composites as a biocatalyst.

The magnetic Fe3O4/SBA-15 composites were prepared, and treated with 3-aminopropyltriethoxysilane as a carrier material for enzyme immobilization. The immobilization of Candida rugosa lipase onto the amino-functionalized Fe3O4/SBA-15 composite was investigated by using glutaraldehyde as a coupling reagent. The immobilized lipase was then employed as a biocatalyst for the interesterification of soybean oil and methyl stearate in a laboratory-scale operation at 45°C. Various techniques, such as Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), and vibrating sample magnetometry (VSM), were used for the characterization of the immobilized lipase composite. The immobilized lipase behaved superparamagnetic and showed excellent response at applied magnetic field. The obtained results showed that the immobilized lipase could efficiently catalyze the interesterification reaction. Moreover, the interesterification reaction parameters, such as reaction temperature, substrate ratio and reaction time were investigated regarding the stearoyl incorporation into the triacylglycerols. Further, the immobilized lipase proved to be easily separated from the reaction mixture by applying an external magnetic field and to be stable in the repeated use for four cycles.

Preparation of low calorie structured lipids catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene(TBD)-functionalized mesoporous SBA-15 silica in a heterogeneous manner.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD, a strong bicyclic guanidine base) functionalized SBA-15 material has been found to be an efficient solid catalyst for the interesterification between tributyrin and methyl stearate in a solvent-free system for the production of low-calorie structured lipid (LCSL). The solid base catalyst was characterized by using small-angle X-ray scattering, Fourier transform infrared spectra, thermo gravimetric analysis, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption, and elemental analysis techniques. The obtained LCSL was analyzed by reverse-phase high-performance liquid chromatography for triacylglycerol composition. The influence of various reaction parameters, such as the substrate ratio, reaction temperature, and reaction time, on the interesterification reaction was investigated systematically. More than 90% LCSL was obtained at 80 °C within 1 h when the methyl stearate/tributyrin molar ratio of 2:1 was employed. The obtained solid catalyst could be recovered easily and reused for several recycles with a negligible loss of activity. By using the solid base catalyst, an eco-friendly more benign process for the interesterification reaction in a heterogeneous manner was developed.

Immobilization of tetramethylguanidine on mesoporous SBA-15 silica: a heterogeneous basic catalyst for transesterification of soybean oil.

An active heterogeneous catalyst, namely 1,1,3,3-tetramethylguanidine (TMG) immobilized on mesoporous SBA-15 silica (SBA-15-pr-TMG), was prepared and the catalytic activity was investigated for transesterification of soybean oil with methanol. The heterogeneous catalysts were characterized using Hammett titration method, Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, and X-ray photoelectron spectroscopy techniques. It is shown that the activity of the catalysts for the transesterification reaction is closely related to their basic properties. By using this catalyst, an environmentally benign process for biodiesel production in a heterogeneous manner was developed. When the reaction was carried out at reflux of methanol, with a molar ratio of methanol to soybean oil of 15:1, a reaction time 12h and a catalyst amount 5 wt%, the oil conversion of 91.7% was achieved. The catalyst could be recovered easily and reused without significant degradation in activity.

Interesterification of soybean oil and lard blends catalyzed by SBA-15-pr-NR3OH as a heterogeneous base catalyst.

A novel heterogeneous SBA-15-pr-NR3OH catalyst has been prepared by reactions of dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride with mesoporous SBA-15 materials. The solid base catalysts were characterized by using Fourier transform infrared spectra, thermogravimetric analysis, nitrogen adsorption-desorption, and elemental analysis techniques. By using the solid catalyst, an environmentally benign process for the interesterification of soybean oil and lard blends in a heterogeneous manner was developed. The interesterification was investigated regarding the slip melting point (SMP), iodine value (IV), triacylglycerols (TAGs) profile, fatty acid composition at the sn-2 position in TAGs, and differential scanning calorimetry (DSC). The obtained results revealed that the solid base catalyst was capable of catalyzing TAG interesterification. It was shown that interesterification significantly modified the physicochemical properties of the oil and fat blends. The interesterified products had lower SMPs than their corresponding physical blends. These changes in melting behaviors were mostly due to the alterations in TAG compositions. The DSC cooling and melting thermograms showed an obvious change in thermal properties after the interesterification reaction.

Transesterification of soybean oil over WO3 supported on AlPO4 as a solid acid catalyst.

WO(3)/AlPO(4) catalysts were prepared by impregnation of AlPO(4) with ammonium metatungstate. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermo gravimetric and differential thermal analysis (TG-DTA) demonstrated that the tungsten compound was incorporated into AlPO(4) forming the catalyst with an enhanced acidity. When transesterification of soybean oil over the catalysts was performed, the catalyst with 30 wt.% WO(3) loading and calcined at 1073 K, exhibited the best catalytic activity with a conversion of 72.5%. The transesterification was optimal at 453 K for 5h with a methanol/oil ratio of 30:1 and catalyst dosage of 5 wt.%. Free fatty acid (FFA) and water did not affect the catalytic activity. The catalyst proved to be stable over four transesterification cycles as it lost only 4% of its activity after being reused four times. The catalyst could be used for the transesterification of low-cost oils for biodiesel production.

Silica-bonded N-propyl sulfamic acid used as a heterogeneous catalyst for transesterification of soybean oil with methanol.

The transesterification of soybean oil with methanol was carried out, to produce biodiesel, over silica-bonded N-propyl sulfamic acid in a heterogeneous manner. Results showed that a maximum conversion of 90.5% was achieved using a 1:20 M ratio of soybean oil to methanol and a catalyst amount of 7.5 wt.% at 423 K for 60 h. It was found that the free fatty acid (FFA) and water present in the feedstock had no significant influence on the catalytic activity to the transesterification reaction. Besides, the catalyst also showed activities towards the esterification reaction of FFAs, in terms of the FFA conversion of 95.6% at 423 K for 30 h. Furthermore, the catalyst could be recovered with a better reusability.

Impact of degree heterogeneity on the behavior of trapping in Koch networks.

Previous work shows that the mean first-passage time (MFPT) for random walks to a given hub node (node with maximum degree) in uncorrelated random scale-free networks is closely related to the exponent γ of power-law degree distribution P(k) ∼ k(-γ), which describes the extent of heterogeneity of scale-free network structure. However, extensive empirical research indicates that real networked systems also display ubiquitous degree correlations. In this paper, we address the trapping issue on the Koch networks, which is a special random walk with one trap fixed at a hub node. The Koch networks are power-law with the characteristic exponent γ in the range between 2 and 3, they are either assortative or disassortative. We calculate exactly the MFPT that is the average of first-passage time from all other nodes to the trap. The obtained explicit solution shows that in large networks the MFPT varies lineally with node number N, which is obviously independent of γ and is sharp contrast to the scaling behavior of MFPT observed for uncorrelated random scale-free networks, where γ influences qualitatively the MFPT of trapping problem.

Standard random walks and trapping on the Koch network with scale-free behavior and small-world effect.

A vast variety of real-life networks display the ubiquitous presence of scale-free phenomenon and small-world effect, both of which play a significant role in the dynamical processes running on networks. Although various dynamical processes have been investigated in scale-free small-world networks, analytical research about random walks on such networks is much less. In this paper, we will study analytically the scaling of the mean first-passage time (MFPT) for random walks on scale-free small-world networks. To this end, we first map the classical Koch fractal to a network, called Koch network. According to this proposed mapping, we present an iterative algorithm for generating the Koch network; based on which we derive closed-form expressions for the relevant topological features, such as degree distribution, clustering coefficient, average path length, and degree correlations. The obtained solutions show that the Koch network exhibits scale-free behavior and small-world effect. Then, we investigate the standard random walks and trapping issue on the Koch network. Through the recurrence relations derived from the structure of the Koch network, we obtain the exact scaling for the MFPT. We show that in the infinite network order limit, the MFPT grows linearly with the number of all nodes in the network. The obtained analytical results are corroborated by direct extensive numerical calculations. In addition, we also determine the scaling efficiency exponents characterizing random walks on the Koch network.

Exact solution for mean first-passage time on a pseudofractal scale-free web.

The explicit determinations of the mean first-passage time (MFPT) for trapping problem are limited to some simple structure, e.g., regular lattices and regular geometrical fractals, and determining MFPT for random walks on other media, especially complex real networks, is a theoretical challenge. In this paper, we investigate a simple random walk on the the pseudofractal scale-free web (PSFW) with a perfect trap located at a node with the highest degree, which simultaneously exhibits the remarkable scale-free and small-world properties observed in real networks. We obtain the exact solution for the MFPT that is calculated through the recurrence relations derived from the structure of PSFW. The rigorous solution exhibits that the MFPT approximately increases as a power-law function of the number of nodes, with the exponent less than 1. We confirm the closed-form solution by direct numerical calculations. We show that the structure of PSFW can improve the efficiency of transport by diffusion, compared with some other structure, such as regular lattices, Sierpinski fractals, and T-graph. The analytical method can be applied to other deterministic networks, making the accurate computation of MFPT possible.

Distinct scalings for mean first-passage time of random walks on scale-free networks with the same degree sequence.

In general, the power-law degree distribution has profound influence on various dynamical processes defined on scale-free networks. In this paper, we will show that power-law degree distribution alone does not suffice to characterize the behavior of trapping problems on scale-free networks, which is an integral major theme of interest for random walks in the presence of an immobile perfect absorber. In order to achieve this goal, we study random walks on a family of one-parameter (denoted by q) scale-free networks with identical degree sequence for the full range of parameter q, in which a trap is located at a fixed site. We obtain analytically or numerically the mean first-passage time (MFPT) for the trapping issue. In the limit of large network order (number of nodes), for the whole class of networks, the MFPT increases asymptotically as a power-law function of network order with the exponent obviously different for different parameter q, which suggests that power-law degree distribution itself is not sufficient to characterize the scaling behavior of MFPT for random walks at least trapping problem, performed on scale-free networks.

Soybean oil methyl esters preparation using NaX zeolites loaded with KOH as a heterogeneous catalyst.

The transesterification of soybean oil with methanol to methyl esters was carried out using NaX zeolites loaded with KOH as a solid base catalyst. Best result was obtained with NaX zeolite loaded with 10% KOH, followed by heating at 393 K for 3 h. When the transesterification reaction was carried out at reflux of methanol (338 K), with a 10:1 molar ratio of methanol to soybean oil, a reaction time of 8 h and a catalyst amount of 3 wt.%, the conversion of soybean oil was 85.6%.