Immobilized ZnO-based Photocatalysts for Solar Light-Driven Photodegradation of Organic Contaminants in Water
Creators: Li, Yanan
Publisher: name: University of Alberta Library
Year: 2024

<p>Solar light driven-photocatalytic degradation has attracted increasing attention for the oxidation of organic contaminants in aquatic ecosystems by photogenerated highly reactive species. However, the complexity of separating and recycling them from the treated matrix are the main challenges for large-scale application in the water treatment. One promising solution is the immobilization of the photocatalyst onto supporting substrates.<br>
This Ph.D. thesis focuses on immobilizing ZnO-based photocatalysts on the planar, curved and floatable substrates, aiming to maximize their photocatalytic performance for the degradation of organic contaminants. Additionally, the photocatalytic degradation of several typical organic pollutants in pure water and oil sands process water (OSPW) was monitored using immobilized photocatalysts under the irradiation of solar light.<br>
This thesis will start with an Introduction, then a Literature review. The main findings are covered in Chapter 3 to 6. <br>
In Chapter 3, Catalytic ZnO nanocaps (NCs) were immobilized on both planar and curved substrates via in-situ fabrication from surface nanodroplets, using the solvent exchange process (SEP) to achieve controllable size distribution, surface coverage, and porosity of the NCs. The photocatalytic performance of ZnO NCs under solar light was evaluated by comparing the degradation of three model compounds. Immobilized non-porous ZnO NCs exhibited good photodegradation performance, achieving over 90% removal of micropollutants (MPs) in 20 h SSL irradiation, compared to the negligible degradation percentages (except for norfloxacin (NOR)) without NCs. Our results suggest that non-porous ZnO NCs immobilized on the inner surface of a transparent container is promising and sustainable approach for solar-driven water treatment. <br>
In Chapter 4, we propose a novel approach to fabricate floatable ZnO-coated micro glass bubbles (MGBs) using cold plasma as a surface modification method. Pre-treating MGBs with cold plasma improves surface wettability and roughness, which enhances the adhesion of ZnO nanoparticles to their surface. Based on the results, the photodegradation performance of ZnO-coated MGBs under simulated solar light (SSL) is directly affected by the cold plasma pre-treatment time, coating concentration of zinc acetate, solution depth, and amount of the floatable material on the contaminated solution surface. Remarkably, ZnO-coated MGBs under 10 h of simulated solar radiation achieved almost 100% removal of a mixture containing seven different MPs commonly detected in aquatic environments. Finally, ZnO-coated MGBs exhibit excellent reusability and stability, suggesting their viability as a sustainable option for efficiently degrading organic pollutants in water.<br>
In Chapter 5, we developed highly stable, porous ZnO NRs immobilized on the inner surface of glass vials using the SEP followed by hydrothermal calcination. It was observed that the oleic acid concentration in the SEP and hydrothermal growth time are the most important parameters for maximizing the active surface area of the ZnO NRs. With the optimal fabrication conditions, the ZnO NRs-coated vial showed a good performance in degrading SMX, achieving almost 100% photodegradation in 10 hours of SSL irradiation. The photocatalytic properties were further enhanced by doping with silver nanoparticles (Ag/ZnO NRs), reaching SMX elimination in only 4 hours and enhancing the stability of the photocatalyst. The Ag/ZnO NRs-coated vial was also applied for the degradation of eight organic MPs, resulting in high degradation rates (&gt;99.0%) for four cycles of reuse. This study introduces an innovative and tunable approach for immobilizing photocatalysts on glass substrates, obtaining high active surface area and excellent photocatalytic and mechanical properties, making it highly suitable for water treatment applications.<br>
In Chapter 6, effective photocatalyst ZnO-NRs was fabricated in-situ over a lager area of glass surface for the solar-driven photodegradation of NAs. Six different model NAs in water were degraded with the efficiency of 95% by using the ZnO NRs-coated glass container with 10 hours SSL irradiation. Furthermore, over 93.3% of O2-NAs in the real OSPW was degraded using the same system in 16 hours of treatment using SSL. Notably, similar results were achieved using nature solar light (NSL). Moreover, the ZnO NRs-coated vials demonstrated excellent reusability and stability, achieving 88.3% degradation of O2-NAs in real OSPW after four consecutive cycles of reuse. Finally, the seeds germination experiments suggest a reduction in the pre-existing toxic effect of OSPW. These results suggest that immobilized ZnO NRs is a promising environmentally friendly, and sustainable approach for the effective photodegradation of NAs in OSPW.</p>