Copper oxide (CuO) nanoparticles have received considerable interest as active and inexpensive catalysts for various gas–solid reactions. The CuO reducibility and surface reactivity are of crucial importance for the high catalytic activity. Herein, we demonstrate that the reducibility and stability of CuO nanoparticles can be controlled and tailored for the high catalytic activity of CO oxidation. The synthesized CuO nanoparticles possessed enhanced reducibility in CO atmosphere at lower reduction temperature of 126 °C compared to 284 °C for that of reference CuO particles. Moreover, the CuO catalysts with tailored reducibility demonstrated a reaction rate of 35 μmol s⁻¹ g⁻¹ and an apparent activation energy of 75 kJ mol⁻¹. Furthermore, the tailored catalysts exhibited excellent long-term stability for CO oxidation for up to 48 h on stream. These readily-reducible CuO nanoparticles could serve as efficient, inexpensive and durable catalysts for CO oxidation at low temperatures.

We demonstrate, for the first time, the synthesis of highly ordered titanium oxynitride nanotube arrays sensitized with Ag nanoparticles (Ag/TiON) as an attractive class of materials for visible-light-driven water splitting. The nanostructure topology of TiO₂, TiON and Ag/TiON was investigated using FESEM and TEM. The X-ray photoelectron spectroscopy (XPS) and the energy dispersive X-ray spectroscopy (EDS) analyses confirm the formation of the oxynitride structure. Upon their use to split water photoelectrochemically under AM 1.5 G illumination (100 mW/cm², 0.1 M KOH), the titanium oxynitride nanotube array films showed significant increase in the photocurrent (6 mA/cm²) compared to the TiO₂ nanotubes counterpart (0.15 mA/cm²). Moreover, decorating the TiON nanotubes with Ag nanoparticles (13 ± 2 nm in size) resulted in exceptionally high photocurrent reaching 14 mA/cm² at 1.0 V_SCE. This enhancement in the photocurrent is related to the synergistic effects of Ag decoration, nitrogen doping, and the unique structural properties of the fabricated nanotube arrays.

Supported copper oxide nanoparticles have attracted considerable attention as active and non-precious catalysts for many catalytic oxidation reactions. Herein, mesoporous xCuO-TiO₂ nanotube catalysts were fabricated, and their activity and kinetics toward CO oxidation were studied. The morphology and structure of the prepared catalysts were systematically studied using SEM, TEM, EDS, EDX, XRD, TGA, BET, XPS, H₂-TPR, and Raman techniques. The BET surface area study revealed the effect of the large surface area of the mesoporous TiO₂ nanotubes on promoting the catalytic activity of prepared catalysts. The results also revealed the existence of strong metal-support interactions in the CuO-TiO₂ nanotube catalyst, as indicated by the up-shift of the E_2g vibrational mode of TiO₂ from 144 cm⁻¹ to 145 cm⁻¹ and the down-shift of the binding energy (BE) of Ti 2p_3/2 from 458.3 eV to 458.1 eV. The active phase of the catalyst consists of fine CuO nanoparticles dispersed on a mesoporous anatase TiO₂ nanotube support. The 50-CuO-TiO₂ nanotube catalyst demonstrated the highest catalytic activity with 100% CO conversion at T₁₀₀ = 155 °C and a reaction rate of 36 µmole s⁻¹ g⁻¹. Furthermore, the catalyst demonstrated excellent long-term stability with complete CO conversion that was stable for 60 h under a continuous stream. The enhanced catalytic activity is attributed to the interplay at the interface between the active CuO phase and the TiO₂ nanotubes support.