Facile preparation of aminosilane-alginate hybrid beads for enzyme immobilization: Kinetics and equilibrium studies.

A simple, facile and potential platform for enzyme immobilization using alginate-based beads has been demonstrated by simultaneous gelation and modification of alginate using calcium chloride (CaCl2) and 3-aminopropyltriethoxysilane (APTES). In this method, sodium alginate solution containing enzyme was simply dripped into a crosslinker solution containing CaCl2 and APTES, leading to the formation of APTES-alginate hybrid beads (AP-beads). The optical observation, FT-IR analysis and amino group measurements provided evidence that APTES was successfully adsorbed to the alginate chain via electrostatic interaction. On the assumption that the binding of Ca2+ ion to polymannuronate residues of alginate via bidentate bridging coordination is competitive with APTES, the equilibrium isotherm and kinetics for the adsorption of APTES to AP-beads was found to follow extended Langmuir isotherm in binary system. Formate dehydrogenase (FDH) as a model enzyme was successfully immobilized in AP-beads and the immobilization yield of ca. 100% could be achieved under optimal conditions of CaCl2 and APTES concentrations in crosslinker solution. Furthermore, the AP-beads were reused efficiently for 9 cycles without loss of FDH activity. The above results demonstrated that AP-beads were effective support for enzyme immobilization.

Microcapsule with a heterogeneous catalyst for the methanolysis of rapeseed oil.

This study has demonstrated that microcapsules can be used as a microreactor for the transesterification of rapeseed oil with calcium oxide (CaO) base catalyst. CaO-loaded microcapsules were prepared by coextrusion technique, and the transesterification reaction was carried out by adding methanol into the prepared microcapsules and oil in a batch-type reactor. Results showed that the microcapsules system could promote the transesterification and hinder the dissolution of the catalyst, in contrast to a biodiesel production with CaO particles. The optimal conditions for methanol to oil molar ratio, catalyst content in the microcapsules and reaction temperature were found to be 8:1, 20 wt.%, and 65 °C, respectively. The results of reusability tests showed that CaO-loaded microcapsules could be successfully reused for three times without loss of the catalytic activity. It was concluded from these results that microcapsules have the potential to improve the performance of solid base catalyst for biodiesel production.

Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation.

A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO(2)) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO(2) nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2 min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80 nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV-visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO(2) nanoparticles, respectively. The prepared Ag@SiO(2) nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on Stöber method, which need 4-24 h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO(2) nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO(2) nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).

Facile method for preparing organic/inorganic hybrid capsules using amino-functional silane coupling agent in aqueous media.

A new and facile method for preparing microcapsules with 3-aminopropyltriethoxysilane (APTES)/alginate hybrid shell (AP-capsule) is proposed based on gelling and sol-gel processes. In this method, conventional capsules with alginate shells (Alg-capsule) are produced by dripping carboxymethyl cellulose solution containing calcium chloride into a sodium alginate solution. Subsequently, addition of the Alg-capsules to an aqueous APTES solution induces the formation of APTES/alginate hybrid shells. The optical observation shows that the texture of AP-capsules is more glossy and transparent than that of Alg-capsules. The surface morphology and elemental composition of microcapsules were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The results suggest that APTES molecules are incorporated to the framework of the alginate shells via electrostatic interaction between amino groups of APTES and carboxyl groups of alginate and the hybrid shells have a dense and homogeneous structure. In the formation reaction, the shrinking of the capsule shells occurs and the accumulation of APTES in the capsule shells proceeds with pseudo first-order kinetics. Moreover, these behaviors are greatly influenced by pH of the reaction solution, especially promoted under acidic and alkaline conditions.