Immobilizing catalysts on textiles : case of zerovalent iron and glucose oxidase enzyme
Abstract: Catalytic systems are one of the most effective technologies of modern chemical processes. The system uses a molecule called ‘catalyst’ that is capable of catalyzing a reaction without being produced or consumed during the process. A catalytic system requires the separation of catalysts from products after each cycle, which is an expensive and resource-intensive process. This brought to the relevance of immobilization of catalyst, where catalysts are bind to a solid support material that will ensure the easy separation of catalyst. Immobilized catalysts are reusable and usually show better stability than the free catalyst. However, immobilization of catalyst is challenging, as it requires exclusive support material involving a complex preparation process. In many instances, the preparation of support material is more resource-intensive and expensive than the catalyst themselves. Therefore, this doctoral thesis focused on the innovative concept of using textile as reliable, widely accessible, and versatile support material for catalyst immobilization. Evidence from systematic experiments was gathered for the case of immobilization of an inorganic catalyst (zerovalent iron-Fe0) and a biocatalyst (glucose oxidase -GOx) on textile support. The goal of this thesis is to establish the feasibility of textile as support material for immobilization of catalyst in the pursuit of fabrication of heterogeneous catalytic system (oxidative and reductive) for wastewater treatment. Polyester nonwoven fabric (PF) was chosen as textile support material for catalyst immobilization due to both qualitative (high strength, porosity, biocompatibility and resistance to most acids, oxidizing agents, and microorganisms) and commercial (availability, cheap and easily customizable) advantages. A combination of eco-friendly and resource-efficient processes (such as plasma treatment, hyperbranched dendrimer, bio-based polymers) has been used for tailoring the PF surface with favorable surface chemical properties in the view of high and stable immobilization yield of the catalyst.The thesis has three distinct parts related to immobilizing catalyst on textiles- (a) immobilization of Fe0 on PF and optimizing their feasibility in both oxidative and reductive catalytic system; (b) immobilization of GOx on PF and optimizing their use in a bio-catalytic system; (c) design of the complete heterogeneous bio-Fenton system using immobilized catalysts (Fe0 and GOx). In all parts, the hydrophobic surface of PF was activated by plasma ecotechnology (either air atmospheric -AP or cold removal plasma-CRP) followed by chemical grafting of hyperbranched dendrimers (polyethylene glycol-OH or polyamidoamine ethylene-diamine core) or functional polymers (3-aminopropyl-triethoxysilane, polyethylenimine, chitosan, or 1-thioglycerol) before immobilizing either of two catalysts. The immobilization of Fe0 was carried out through either the in-situ or ex-situ reduction-immobilization method, whereas GOx was immobilized through the physical adsorption method. Several approaches were explored in search of optimum conditions for catalyst immobilization as well as to improve the catalytic performance of immobilized catalysts.Diverse analytical and instrumental techniques were used to monitor the surface modification of textiles, efficiency of immobilization of catalysts, Physico-chemical properties of immobilized catalysts, and their catalytic activities in the removal of dyes, phenols, or pathogenic pollutants from water. Results from plasma treatment showed that both AP and CRP successfully activated the PF surface through integrating polar functional groups (–COOH and –OH) by AP and carboxyl/hydroxyl (–COOH/–OH), amino (–NH2) functional groups by CRP. Along with that, grafted hyperbranched dendrimers and functional polymers on plasma-activated PF provided a tailor-made surface with specific end functional groups. Regarding the immobilization of Fe0 on PF, the results revealed that the reduction method (in-situ or ex-situ) of producing Fe0 have synergistic effects on the morphology, stability, particle size, and distribution of the immobilized Fe0. The surface chemical properties of PF also influenced the stability of immobilized Fe0 and related properties as observed throughout various studies. Detailed results revealed that a PF surface rich in –COOH, –OH, and –SH functional groups favors the loading and stabilization of Fe0 over surface rich in – NH2 functional groups. To end with, all Fe0-immobilized PF showed high catalytic activates in the removal of pollutants from water in both oxidative and reductive systems. In the case of GOx-immobilized PF, the success of immobilization of enzyme on textile was found to be related to the type and extent of surface functional groups present on the PF surface. The results demonstrated that PF surface rich in –COOH, – NH2 functional groups guaranteed higher loading and stability of GOx compared to –COOH, –OH functional groups-rich surface. These results carry great importance as they provide evidence of textile:enzyme interactions and grounds for further robust immobilization of GOx on textile support through surface engineering. As a proof of concept, this thesis also reveals the first successful design of a complete heterogeneous bio-Fenton system for wastewater treatment using immobilized catalysts (Fe0 and GOx). The novelty of the research presented in this doctoral thesis is primarily attributed to the novelty of immobilizing two different types of catalysts (inorganic catalyst and biocatalysts) on synthetic textile support for wastewater treatment application. In general, this thesis contributes to general knowledge of the heterogeneous catalytic system, Fenton/Fenton-like system, and the bio-Fenton system as well as it opens promising prospects of the use of textile as support material for immobilizing different catalysts for a wide range of applications.
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