Metal oxide and carbide nanomaterials : catalysis, photocatalysis, and oxygen adsorption applications

Abstract

Nanomaterials are anticipated to play a crucial role in the advancement of future technologies, exhibiting great potential for various applications. The field of study concerning nanomaterials is extensive, thus necessitating a focused approach on specific classes of materials and applications. In this study, we specifically investigated nanomaterials for the following applications: 1) Food packaging, as it contributes to enhanced food security; 2) Catalysis, which contributes to fuel generation through water-gas-shift reactions or catalytic hydrocracking of plastics, thereby promoting clean energy and a circular economy; 3) Photocatalysis for environmental remediation, addressing water pollution and ensuring a clean water supply. This thesis focuses on the investigation of metal oxide and metal carbide nanomaterials, specifically mesoporous silica, photocatalytically active metal oxide semiconductors (ZnO, TiO2), and catalytically active metal carbides (MoxC, TiCx). Mesoporous silica nanomaterials possess a large surface area, adjustable porosity and pore sizes, and can be easily modified. In this study, we synthesized mesoporous silica nanoparticles (MSNs) using the Stöber method, resulting in a specific surface area exceeding 800 m2/g. Subsequently, we deposited FeOx and TiOx coatings on the surfaces of MSNs using atomic layer deposition (ALD). Additionally, we applied a layer of carbonized glucose to the MSNs using the hydrothermal method, varying the amount of glucose. Notably, the MSNs with 60 mg of glucose exhibited exceptional performance in dry air with the oxygen absorption capacity of 164.8 mL/g, which was approximately five times higher than that of the commercially iron-based oxygen scavenger. Moreover, metal oxides such as TiO2 and ZnO have been extensively utilized for the degradation of organic pollutants, including dye and plastics. In this study, we aimed to investigate the degradation of organic dye by depositing a layer of self-doped black TiO2 onto the surfaces of P25, ZnO, and SnO2 particles, respectively. Through the adjustment of various parameters, we discovered that amorphous black titanium dioxide on P25 exhibited the highest photocatalytic performance. The photocatalytic mechanism was examined by ESR and the results indicated that the presence of oxygen vacancies and Ti3+ defects significantly contributed to the exceptional catalytic performance of black TiO2. In the degradation of microplastics, TiO2/ZnO core-shell tetrapods were employed as photocatalysts for the degradation of PE, PES, and PP plastics collected from the environment. These microplastics share common characteristics of having a highly stable structure, making them resistant to biodegradation. However, with the addition of an electron scavenger, complete degradation of these three plastics was achieved within a timeframe ranging from 400 to 816 h. Additionally, apart from photocatalytic degradation, microplastics can also be degraded through thermochemical methods, which offer the advantage of generating value-added products (such as fuels) as byproducts of the degradation process. Notably, MoCx and TiCx exhibit exceptional thermal stability, and excellent corrosion resistance, making them highly suitable for catalytic applications. In our study, we investigated the catalytic hydrocracking of plastics using metal clusters supported on different metal carbide catalysts (TiCx, MoxC). Remarkably, we observed that the Ru clusters/MoC catalyst resulted in excellent plastic degradation performance.