Theano Petsi

Towards the local structure of the Co(II), Ni(II), Cr(VI) and W(VI) ionic species formed upon impregnation on titania

The mode of interfacial deposition and the local structure of the Co(II), Ni(II), Cr(VI) and W(VI) ionic species formed upon impregnation on titania surface has been studied using various techniques provided by the interface science.

Interfacial Impregnation Chemistry in the Synthesis of Chromium Catalysts Supported on Titania

The interfacial impregnation chemistry involved in the synthesis of CrVI catalysts supported on titania is presented. The mode of interfacial deposition of the CrVI oxo‐species at the titania/electrolyte solution interface, the interfacial species, and the local structure of the deposited species were investigated. Several methodologies based on potentiometric titrations, microelectrophoresis, and adsorption experiments were used. Modeling of the interfacial deposition based on experimental results provided an integrated picture concerning the deposition features. The interfacial species were confirmed by using laser Raman spectroscopy. The deposited CrO42−, HCrO4−, and Cr2O72− ions are retained above the positively charged bridging hydroxyl groups (Ti2OH) of the titania surface as electrostatic forces cause the formation of ion‐pairs. Each CrO42− or HCrO4− ion is located above a bridging hydroxyl, and each Cr2O72− ion above two bridging hydroxyl groups. Only the CrO42− and HCrO4− ions are deposited, with a preference for the CrO42− ions, at low CrVI surface concentrations (up to 0.3 μmol CrVI m−2). Cr2O72− ions were deposited in addition to CrO42− and HCrO4− ions at higher CrVI concentrations. The direct probing of the interfacial species by using laser Raman spectroscopy confirmed the interfacial species determined by modeling the deposition data. The deposition model developed describes all of the experimental data (from adsorption, titration, and microelectrophoresis experiments) very well. Moreover, it accurately predicts the displacements of pzc and iep caused by the presence of these species in the solution.

Tubular cellulose/starch gel composite as food enzyme storehouse

The objective of this study was to produce a composite biocatalyst, based on porous cellulosic material, produced after wood sawdust delignification (tubular cellulose; TC) and starch gel (SG), for the development of bioprocesses related to enzyme applications. The composite biocatalyst was studied by Scanning Electron Microscopy to observe the SG deposition in the TC pores, and porosimetry analysis to determine the average pore diameter and surface area. The deposition of SG into the TC tubes provided a TC/SG composite with reduced pore sizes. X-ray powder diffractometry showed a decrease of crystallinity with increased SG ratio in the composite. The composite was used as an insoluble carrier for entrapment of the dairy enzyme rennin, leading to the production of an active biocatalyst for milk coagulation (initiation of milk clotting at about 20 min and full coagulation at about 200 min), creating perspectives for several applications in food enzyme research and technology.

Immobilized rennin in TC/SG composite in cheese production.

The object of the current study was to develop a new process for continuous Feta-type cheese production using a biocatalyst consisting of immobilized rennin on a tubular cellulose/starch gel (TC/SG) composite, which has been proven to be an appropriate carrier for enzyme immobilization. Different methodologies were used in order to prepare four biocatalysts. The most effective was selected for cheese production in a 1L continuous system, providing two economically useful results for the dairy industries: (i) increase of productivity by the continuous coagulation of milk, and (ii) saving of the rennin enzyme expenses of the batch coagulation of milk. The criteria used to choose the appropriate biocatalyst was based on the time of coagulation in successive batches, the concentration of immobilized rennin combined with the filter efficiency and its application in the continuous system. Physicochemical analyses of the cheeses at various stages of the ripening were performed. No significant differences compared to cheeses prepared with the traditional method were found. Aroma compounds were determined by SPME GC-MS.

Production of nanotubes in delignified porous cellulosic materials after hydrolysis with cellulase.

In this study, tubular cellulose (TC), a porous cellulosic material produced by delignification of sawdust, was treated with a Trichoderma reesei cellulase in order to increase the proportion of nano-tubes. The effect of enzyme concentration and treatment duration on surface characteristics was studied and the samples were analyzed with BET, SEM and XRD. Also, a composite material of gelatinized starch and TC underwent enzymatic treatment in combination with amylase (320U) and cellulase (320U) enzymes. For TC, the optimum enzyme concentration (640U) led to significant increase of TC specific surface area and pore volume along with the reduction of pore diameter. It was also shown that the enzymatic treatment did not result to a significant change of cellulose crystallinity index. The produced nano-tubular cellulose shows potential for application to drug and chemical preservative delivery systems.

Elucidation of the surface configuration of the Co(II) and Ni(II) aqua complexes and of the Cr(VI), Mo(VI) and W(VI) monomer and polymer oxo–species deposited on the titania surface during impregnation

Abstract The structure of the precursor Co(II) and N(II) aqua complexes and the Cr(VI), Mo(VI) and W(VI) monomer and polymer oxo–species formed upon impregnation at the interface developed between the surface of the titania grains and the impregnating solution was thoroughly elucidated. Moreover, the interfacial speciation was determined for various surface concentrations of the precursor species regulated by adjusting the corresponding solution concentrations and the pH of the impregnating solution.