Publicação
Biocatalytic fibers for bioremediation
| Resumo: | Enzymes can exhibit excellent catalytic properties, namely high activity at different environmental conditions, high specificity and selectivity. Despite these advantages, they exhibit some limitations that can hinder their application in industry. The immobilization of enzymes on fibers can lend good mechanical properties, high surface area, and resistance against high temperature, alkaloids and humidity to the resulting catalytic materials. This work consists in the production, using electrospinning, of biocatalytic membranes containing laccase with a view to enzymatic bioremediation. The initial work plan consisted in the production of coaxial fibers with an outer layer of silica, lending strength and protection, and a core containing an ionic gelatin resulting from the cross-linking of gelatin and an ionic liquid, containing the laccase. For the preparation of silica layers, it was selected the sol-gel process using as precursors tetrametoxysilane (TMOS) or tetraethoxysilane (TEOS) through acid catalysis with HCl, using methanol as co-solvent. To confer flexibility and porosity to the silica structure, a polyvinyl alcohol (PVA) solution was added to the electrospinning solution. Among the various formulations tested, the composition (in molar ratios) 1:1,8:1.1:7,9E-03 TMOS:H2O:methanol:HCl led to regular fibers with low size dispersion, as revealed by scanning electron microscopy. Also for the preparation of co-axial fibers it was tested formulations for the core of the fibers. The temperature control available did not prevent the solidification of the solution of porcine gelatin and ionic liquid choline dihydrogenphosphate in the needle, making it impossible to carry out the electrospinning process. To overcome this difficulty, the concentration of gelatin was decreased, which resulted in the production of electrospray instead of fibers. Then a change was made in the nature of gelatin, which was replaced by fish gelatin, whose dissolution occurs at room temperature. However, the cross-linking of this type of gelatin with the ionic liquid was not efficient and the membrane obtained dissolved immediately in water. It was then decided to produce a multi-layered membrane, consisting of a layer of silica-based fibers on each side, and an inner section comprising reactive fibers based on a different polymer than gelatin. Given that the production of silica fibers via the sol-gel process had already been optimized, the focus was on the production of the inner layer of bioreactive fibers. Two polymers were tested, namely polycaprolactone (PCL) and PVA. In order to preserve enzyme activity, different solvents were used to dissolve PCL, but in no case was there evidence of activity of the laccase immobilized within the fibers. On the other hand, the enzyme remained active in PVA-based fibers. Thus membranes were produced with silica surface layers and a core of PVA with enzyme. These membranes exhibited catalytic activity, allowing the main goal of the work plan to be fulfilled. |
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| Autores principais: | Khalili, Shayan |
| Assunto: | Electrospinning Silica Biocatalytic fibers PVA Laccase Bioremediation |
| Ano: | 2016 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade Nova de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório Institucional da UNL |
| Resumo: | Enzymes can exhibit excellent catalytic properties, namely high activity at different environmental conditions, high specificity and selectivity. Despite these advantages, they exhibit some limitations that can hinder their application in industry. The immobilization of enzymes on fibers can lend good mechanical properties, high surface area, and resistance against high temperature, alkaloids and humidity to the resulting catalytic materials. This work consists in the production, using electrospinning, of biocatalytic membranes containing laccase with a view to enzymatic bioremediation. The initial work plan consisted in the production of coaxial fibers with an outer layer of silica, lending strength and protection, and a core containing an ionic gelatin resulting from the cross-linking of gelatin and an ionic liquid, containing the laccase. For the preparation of silica layers, it was selected the sol-gel process using as precursors tetrametoxysilane (TMOS) or tetraethoxysilane (TEOS) through acid catalysis with HCl, using methanol as co-solvent. To confer flexibility and porosity to the silica structure, a polyvinyl alcohol (PVA) solution was added to the electrospinning solution. Among the various formulations tested, the composition (in molar ratios) 1:1,8:1.1:7,9E-03 TMOS:H2O:methanol:HCl led to regular fibers with low size dispersion, as revealed by scanning electron microscopy. Also for the preparation of co-axial fibers it was tested formulations for the core of the fibers. The temperature control available did not prevent the solidification of the solution of porcine gelatin and ionic liquid choline dihydrogenphosphate in the needle, making it impossible to carry out the electrospinning process. To overcome this difficulty, the concentration of gelatin was decreased, which resulted in the production of electrospray instead of fibers. Then a change was made in the nature of gelatin, which was replaced by fish gelatin, whose dissolution occurs at room temperature. However, the cross-linking of this type of gelatin with the ionic liquid was not efficient and the membrane obtained dissolved immediately in water. It was then decided to produce a multi-layered membrane, consisting of a layer of silica-based fibers on each side, and an inner section comprising reactive fibers based on a different polymer than gelatin. Given that the production of silica fibers via the sol-gel process had already been optimized, the focus was on the production of the inner layer of bioreactive fibers. Two polymers were tested, namely polycaprolactone (PCL) and PVA. In order to preserve enzyme activity, different solvents were used to dissolve PCL, but in no case was there evidence of activity of the laccase immobilized within the fibers. On the other hand, the enzyme remained active in PVA-based fibers. Thus membranes were produced with silica surface layers and a core of PVA with enzyme. These membranes exhibited catalytic activity, allowing the main goal of the work plan to be fulfilled. |
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