Depozice fotokatalytických nanomateriálů na tkaniny a jejich využití při degradaci polutantů

Abstract

This thesis deals with the problem of repeated filter usage when viruses, bacteria, and pollutants accumulate on their surfaces over time. Such accumulation poses the risk of the filter becoming a potential source of infection or toxic substances after such contamination. Using photocatalytic particles adhered to filter fibers is an effective tool to mitigate and eliminate such contamination through physicochemical actions of charges. The first part of this thesis focuses on the preparation and characterization of photocatalytic graphitic carbon nitride (g-C3N4), synthesized from urea and melamine in their bulk forms and followed by exfoliation methods: thermal, ultrasound cavitation, and mill exfoliation. The University of Porto, Portugal, collaborated to assess the photocatalytic efficacy through phenol degradation under visible light. Results indicated that the urea-derived bulk form displayed superior photocatalytic activity over its melamine-derived opposite, although with a notable mass loss. Milling was found to be ineffective from urea precursor; in contrast, for melamine, this exfoliation technique was efficient. Thermal exfoliations resulted in the highest photocatalytic activity and induced the highest increases in specific surface areas and the highest fluorescence values. The thesis then focused on preparing and characterizing polymeric fiber membranes using polyvinylidene fluoride (PVDF) and polyvinyl butyral (PVB), onto which photocatalytic g-C3N4 were deposited. These particles have demonstrated virucidal and bactericidal properties upon exposure to visible light, with no observed toxicity in tests. Membranes were synthesized in their pure form and assessed alongside membranes featuring g-C3N4 particles deposited through blend, thermal, and chemical methods. Among these, the blend method exhibited the highest areal density of deposited particles, nevertheless, it resulted in particle encapsulation within the polymer fiber, decreasing photocatalytic effectiveness. The thermal method is unsuitable for PVDF polymer due to its high thermal stability. PVDF's structural and chemical properties were modified with potassium hydroxide allowing g-C3N4 particles deposition to the fibers surface. This method achieved a higher areal density of particles, and the surface particles binding to the fibers resulted in the highest photocatalytic activity. Moreover, the reproducibility of the preparation methods was successfully confirmed for a series of three PVB membranes prepared using the same techniques. The study revealed that membranes exhibit photocatalytic activity and are reusable. However, morphology before and after reactions (12 hours) highlighted degradation of the polymeric PVB fibers, whereas no changes were observed in the PVDF membranes. Another aspect of the research was assessing filtration efficiency according to European standard EN 14683:2019+AC. A semi-empirical mathematical model describes the dependency between particle filtration efficiency and cross-sectional airflow velocity through the membrane. This mathematical formulation was effectively validated through regression analysis on experimental data obtained from four commercial filters. The measurement indicated consistent limiting efficiencies at high velocities and affirmed the model's assumption that filters cannot attain 100% filtration efficiency due to the Brownian motion of particles, even at zero flow velocities.