Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Charpentier, Paul

Abstract

Designing new antimicrobial surfaces which are effective under visible light irradiation without leaching toxic ions is a current challenge for effective disinfection. A new polymeric system poly[2,11’-thiophene-ethylene-thiophene-alt-2,5-(3-carboxyl) -thiophene] (PTET-T- COOH) with broad light absorption was synthesized. Its photocatalytic disinfection performance against staphylococcus aureus (S. aureus) and streptococcus suis (S. suis) was evaluated, showing over 99.999% inactivation (higher than 5-log inactivation) in 2 h for both bacteria, under visible light irradiation at a low concentration of PTET-T-COOH (0.1 mg/mL). In addition, a PTET-T-COOH/polyurethane (PU) polymeric coating was designed and fabricated. Chemical attachment was confirmed between PTET-T-COOH and PU using various thermophysical techniques (FTIR, XPS and UV-Vis absorption spectra). The coating was found to possess excellent photocatalytic disinfection effect on S. aureus (7-log inactivation) in 4 h under visible-light exposure. PTET-T-COOH and PTET-T-COOH/PU coating demonstrated good stability, showing excellent antibacterial activity after five runs. The chemical interaction was generated and confirmed between PTET-T-COOH and PU. The active species generated and responsible for the photocatalytic disinfection were confirmed to be singlet oxygen and free electrons by using scavengers and electron spin resonance spectroscopy (ESR) in PTET-T-COOH based systems. In addition, ultrathin graphitic carbon nitride (g-C3N4) nanosheets with rich amino groups (g-C3N4-NH2) were also fabricated to inactivate more than 80 % of S. aureus in 2 h upon visible light exposure. The photocatalytic activities of g-C3N4-NH2 and g-C3N4 were compared and the reasons for improved performance of g-C3N4-NH2 were also analyzed. The results from this thesis will open a new strategy for exploring novel high-efficiency and durable disinfection coatings for living environmental and industrial applications.

Summary for Lay Audience

Bacteria, viruses and fungi in our surroundings can lead to a variety of diseases. As the current COVID-19 pandemic is illustrating, it is of paramount importance to develop efficient antimicrobial materials which are both active and processable into various products. With the emergence of antibiotic-resistance, a range of conventional bactericides such as metal-based compounds, 2D antimicrobials, antibacterial polymers and chemical oxidizing agents have been extensively reported. However, some disadvantages of these materials are evident, including harmful heavy metals, hazardous by-products and side effects are always involved in the above materials. In addition, although ultraviolet irradiation as a disinfection technique was widely used in wastewater treatment, the cost is high, and the efficiency is limited when it was applied alone.

Photocatalytic technology has attracted tremendous attention and achieved a variety of successful applications in water splitting to produce H2, CO2 reduction and pollutants removal. Photocatalytic disinfection has also demonstrated effective inactivation of microbials. Compared with conventional antimicrobials and techniques, photocatalytic disinfection is more simple, environmental-friendly and sustainable. Under ambient condition with UV or visible light irradiation, electrons and holes can be generated in the photocatalysts and then react with water and oxygen to form a series of reactive oxygen species which can kill microbials efficiently.

A wide range of photocatalysts including inorganic and organic photoactive agents have been explored for disinfection applications. Compared to inorganic photocatalysts, organic photocatalytic antimicrobials such as polymers possess more potential for practical applications, needing the processability of the polymeric system. The objectives of this work are to explore efficient antibacterial polymers, including the following: (1) design and synthesis of polythiophene derivative (PTET-T-COOH) for efficient inactivation of bacteria upon visible light exposure, (2) fabrication of bilayer coating where polyurethane (PU) acts as protective layer and PTET-T-COOH/PU functions as a photoactive layer for efficient killing of bacteria. A robust chemical bonding was generated between PTET-T-COOH and PU which offered the excellent recycling stability of coating, (3) exploration of rich amino modified carbon nitride (g-C3N4) polymer with thin layers for efficient inactivation of bacteria.

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