A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Facile sonochemical synthesis of Cu doped CeO2 nanostructures as a novel dual-functional photocatalytic adsorbent

In this paper, doped CeO₂ nanostructures with various percentages of copper were synthesized via a simple sonochemical method. Sonication was conducted using a high-intensity ultrasonic probe operating at 20 kHz with a maximum power output of 80 Wcm^-3. The effects of different parameters such as ultrasonic time and power, solvent, and OH^- source on the morphology of final products were well investigated. XRD, EDS, XPS, SEM, TEM, and DRS analyzes were utilized for precise identification of as-synthesized samples. Then, the adsorption capability in the dark and photocatalytic activity of nanostructures under visible light were evaluated for methyl orange degradation. The results showed that doped samples have a very favorable adsorption in the dark and 5 wt% Cu/CeO₂ with flower-like morphology can adsorb more than 99% of the color at 45 min. Also, photocatalytic activity under visible light showed a degradation of more than 81% and 99% for samples 2 wt% Cu/CeO₂ and 5 wt% Cu/CeO₂, respectively, after 45 min.

Biomimetic synthesis of urchin-like CuO/ZnO nanocomposites with excellent photocatalytic activity

Highly photocatalytic urchin-like CuO/ZnO nanocomposites were synthesized using glutamine as a growth regulator by a hydrothermal process with subsequent calcination.

Fe-doped CeO2 nanorods for enhanced peroxidase-like activity and their application towards glucose detection

Surface defects of Fe-doped CeO₂ nanorods were found to be active sites for increasing peroxidase mimetic activity.

Synthesis of Ordered Mesoporous CuO/CeO₂ Composite Frameworks as Anode Catalysts for Water Oxidation

Cerium-rich metal oxide materials have recently emerged as promising candidates for the photocatalytic oxygen evolution reaction (OER). In this article, we report the synthesis of ordered mesoporous CuO/CeO₂ composite frameworks with different contents of copper(II) oxide and demonstrate their activity for photocatalytic O₂ production via UV-Vis light-driven oxidation of water. Mesoporous CuO/CeO₂ materials have been successfully prepared by a nanocasting route, using mesoporous silica as a rigid template. X-ray diffraction, electron transmission microscopy and N₂ porosimetry characterization of the as-prepared products reveal a mesoporous structure composed of parallel arranged nanorods, with a large surface area and a narrow pore size distribution. The molecular structure and optical properties of the composite materials were investigated with Raman and UV-Vis/NIR diffuse reflectance spectroscopy. Catalytic results indicated that incorporation of CuO clusters in the CeO₂ lattice improved the photochemical properties. As a result, the CuO/CeO₂ composite catalyst containing ~38 wt % CuO reaches a high O₂ evolution rate of ~19.6 µmol·h-1 (or 392 µmol·h-1·g-1) with an apparent quantum efficiency of 17.6% at λ = 365 ± 10 nm. This OER activity compares favorably with that obtained from the non-porous CuO/CeO₂ counterpart (~1.3 µmol·h-1) and pure mesoporous CeO₂ (~1 µmol·h-1).