The molybdenum oxide (MoO₃) and MoO₃@SiO₂ nanoparticles were successfully prepared using the chemical bath deposition (CBD) method. The photocatalytic activities of molybdenum oxide (MoO₃), SiO₂, and MoO₃@SiO₂ nanoparticles composite have shown a synergistic photocatalytic effect of SiO₂ combined with MoO₃. The first-order degradation rate constants for MoO₃, SiO₂, and MoO₃@SiO₂ nanocomposite were 10.3 × 10⁻³ min⁻¹, 15.1 × 10⁻³ min⁻¹, and 16.3 × 10⁻³ min⁻¹, respectively. The MoO₃@SiO₂ composite showed degradation efficiencies in the methylene blue solution close to 100% after 60 min of UV irradiation. The X-ray diffraction (XRD) showed that the MoO₃ powder has a hexagonal crystal structure and the silica is the tridymite type of SiO₂. The crystallite size was about 94 nm, 32 nm, and 125 nm for MoO₃, silica, and MoO₃@SiO₂, respectively, as calculated by the Scherrer equation. The scanning electron microscopy (SEM) images revealed that the MoO₃ powder consisted of a uniform hexagonal structure; the silica showed a rod-like micro-flake morphology and the MoO₃@SiO₂ composite had the appearance of coral-like structures.

Undoped and Mg-doped (y = [Mg²⁺]/[Fe³⁺] = 1, 2, 3, and 4 at.%) Fe₂O₃ thin films were synthesized by a simple spray pyrolysis technique. The thin films were extensively characterized. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) analysis confirmed the successful insertion of Mg in the rhombohedral structure of Fe₂O₃. In addition, scanning electronic microscope (SEM) and confocal microscope (CM) images showed a homogenous texture of the film, which was free of defects. The rough surface of the film obtained by spray pyrolysis is an important feature for photocatalysis and gas sensor applications. The direct band gap of the doped Fe₂O₃ films obtained for [Mg²⁺]/[Fe³⁺] = 3 at.% was E_dir = 2.20 eV, which recommends the Mg-doped iron oxide as an optical window or buffer layer in solar cell devices. The photodegradation performance of Mg-doped Fe₂O₃ was assessed by studying the removal of methylene blue (MB) under sunlight irradiation, with an effective removal efficiency of 90% within 180 min. The excellent photodegradation activity was attributed to the strong absorption of Mg-doped Fe₂O₃ in the UV and most of the visible light, and to the effective separation of photogenerated charge carriers.

CuO nanosheets have been synthesized via the hydrothermal method at 120°C for 3 h, without using any surfactant or structure directing agent. The structural and morphological characteristics of the copper oxide have been examined with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), scanning electron microscopy (SEM), UV-visible spectroscopy, and BET surface area analyses. The as-prepared materials have been used for the catalytic degradation of methylene blue dye (MB) in the presence of hydrogen peroxide (H₂O₂). The results have demonstrated that the CuO nanosheets showed an enhanced catalytic performance with good reusability up to the fourth cycle. In addition, the effect of several parameters, including the catalyst and hydrogen peroxide quantities, the reaction temperature and the dye concentration have been also investigated for the degradation reactions of the MB. The kinetic data have revealed that the dye degradation process follows a pseudo-first order model. It should be noted that the activation energy (E_a), enthalpy (ΔH^#), entropy (ΔS^#) and activation free energy (ΔG^#) have been calculated for the oxidation reaction. The CuO nanosheets exhibite an excellent catalytic performance for the degradation of MB. This also provides a newer route for promising dye degradation in wastewater treatment.

The effects of various additives (Y₂O₃, Ga₂O₃, and WO₃) on photocatalytic degradation efficiency under UV light-emitting diodes (LEDs) and the optical properties of TiO₂ Degussa P25 were investigated using ketoprofen and diclofenac, two non-steroidal anti-inflammatory drugs commonly detected in German rivers. Experimental results demonstrated that thin films containing these additives exhibited similar photocatalytic degradation efficiencies as pure TiO₂, achieving a 30% degradation of ketoprofen over 150 min. In contrast, the Y₂O₃/TiO₂ thin film showed significantly improved performance, achieving a 46% degradation of ketoprofen in 180 min. Notably, the Y₂O₃/TiO₂ system was three times more effective in degrading diclofenac compared to pure TiO₂. Additionally, the Y₂O₃/TiO₂ photocatalyst retained its activity over three successive cycles with only a slight decrease in efficiency. The photocatalytic degradation of both organic pollutants followed first-order kinetics with all photocatalysts. The investigation included SEM imaging to assess the surface homogeneity of the thin films and UV-vis solid-state spectroscopy to evaluate the impact of the additives on the energy band gap of TiO₂.