We report in this paper antibacterial activity of Ag-doped TiO₂ and Ag-doped ZnO nanoparticles (NPs) under visible light irradiation synthesized by using a sol-gel method. Structural, morphological, and basic optical properties of these samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectrum, and UV-Vis reflectance. Room temperature X-ray diffraction analysis revealed that Ag-doped TiO₂ has both rutile and anatase phases, but TiO₂ NPs only have the anatase phase. In both ZnO and Ag-doped ZnO NPs, the hexagonal wurtzite structure was observed. The morphologies of TiO₂ and ZnO were influenced by doping with Ag, as shown from the SEM images. EDX confirms that the samples are composed of Zn, Ti, Ag, and O elements. UV-Vis reflectance results show decreased band gap energy of Ag-doped TiO₂ and Ag-doped ZnO NPs in comparison to that of TiO₂ and ZnO. Pathogenic bacteria, such as Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, were used to assess the antibacterial activity of the synthesized materials. The reduction in the viability of all the three bacteria to zero using Ag-doped ZnO occurred at 60 μg/mL of culture, while Ag-doped TiO₂ showed zero viability at 80 μg/mL. Doping of Ag on ZnO and TiO₂ plays a vital role in the increased antibacterial activity performance.

We report the photocatalytic activities of ZnO, Ag-doped ZnO, and Mn-doped ZnO nanoparticles (NPs). Ag-doped and Mn-doped ZnO samples were synthesized using a coprecipitation method and calcined at 600°C. XRD, SEM, EDX, and UV-vis spectroscopy techniques were employed for characterization of the synthesized samples. The photocatalytic activities of the samples were evaluated by measuring the photocatalytic decolorization of methyl violet with sunlight being the source of energy. XRD patterns of the samples confirmed the wurtzite structure without change which was indicative of the absence of Mn- and Ag-related secondary phases for the doped ZnO. The UV-vis spectra indicated the band gap energy of ZnO, Ag-doped ZnO, and Mn-doped ZnO to be 2.98, 2.80, and 2.64 eV, respectively. Photocatalytic decolorization of methyl violet for the synthesized samples was found to be favorable at a pH of 9.0, catalyst dose of 1 g/L, and initial dye concentration of 4.5 × 10⁻⁴ g/L. Mn-doped ZnO and Ag-doped ZnO photocatalytic decolorization efficiency was significantly higher than undoped ZnO. Incorporation of Mn and Ag enhanced the visible-light photocatalytic activity of ZnO; this could be due to the ability of these metals to increase the surface defects of ZnO which in turn shift their optical absorption towards the visible region.

In this study, a N-doped Cu₂O/ZnO nanocomposite was prepared by a co-precipitation and thermal decomposition technique from CuCl₂, 2H₂O, ZnSO₄, 7H₂O and CO(NH₂)₂ as precursors. The as-synthesized nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared analysis (FT–IR) and an ultraviolet–visible (UV–Vis) reflectance spectrometer. From the XRD diffractogram of N-doped Cu₂O/ZnO nanocomposite, cubic and hexagonal wurtzite crystal structures of Cu₂O, and ZnO, respectively were identified. The UV-vis reflectance spectra illustrated that the absorption edge of N-doped Cu₂O/ZnO nanocomposite is more extended to the longer wavelength than ZnO, Cu₂O and Cu₂O/ZnO nanomaterials. FT–IR bands confirmed the presence of ZnO, Cu₂O, and nitrogen in the N-doped Cu₂O/ZnO nanocomposite. Photocatalytic activity of the as-synthesized nanocomposite was tested for methyl red degradation using sunlight as an energy source by optimizing the concentration of the dye and amount of the catalyst loaded. The degradation efficiency was greater in N-doped Cu₂O/ZnO nanocomposite as compared to ZnO, Cu₂O and Cu₂O/ZnO nanomaterials. This is due to the coupling of the semiconductors which increases the absorption and exploitation capability of solar light and increases the charge separation as well. Besides that, nitrogen doping can extend absorption of light to the visible region by decreasing the energy gap. Therefore, N-doped Cu₂O/ZnO nanocomposite is a solar light-active photocatalyst which can be used in the degradation of organic pollutants.

Magnetically recyclable C-doped TiO₂/Fe₃O₄ (C-TiO₂/Fe₃O₄) nanocomposite was successfully synthesized via a sol–gel method. The synthesized samples were characterized using SEM, energy-dispersive X-ray spectroscopy (EDS), FTIR, and UV-VIS diffuse reflectance spectroscopy (DRS) techniques. The results clearly showed that a C-TiO₂/Fe₃O₄ nanocomposite was produced. The photocatalytic activities of the prepared pristine (TiO₂), C-doped TiO₂ (C-TiO₂) and C-TiO₂/Fe₃O₄ were evaluated by the photodegradation of methyl orange (MO) under natural sunlight. The effect of catalyst loading and MO concentration were studied and optimized. The C-TiO₂/Fe₃O₄ nanocomposite exhibited an excellent photocatalytic activity (99.68%) that was higher than the TiO₂ (55.41%) and C-TiO₂ (70%) photocatalysts within 150 min. The magnetic nanocomposite could be easily recovered from the treated solution by applying external magnetic field. The C-TiO₂/Fe₃O₄ composite showed excellent photocatalytic performance for four consecutive photocatalytic reactions. Thus, this work could provide a simple method for the mass production of highly photoactive and stable C-TiO₂/Fe₃O₄ photocatalyst for environmental remediation.

Propylene oxide (PO) is an essential feedstock in the plastic industry. Herein, unprecedented, inexpensive, and robust zinc oxide (ZnO)-based materials were prepared. A ZnO nanorod (ZnO-NR) catalyst was synthesized using a solvothermal method. Another type of ZnO materials supported and immobilized on mesoporous MCM-41 material (ZnO/MCM-41(x)) was also prepared with varied proportions (x = 0.82−9.41 wt %) of Zn content. The catalytic reactions of propylene epoxidation over ZnO-NR and ZnO/MCM-41(x) with H₂O₂ as an oxidant and acetonitrile as a solvent were studied at 30−70 ºC and 5−20 bar. The ZnO catalysts were found capable of catalyzing the reaction with high H₂O₂ utilization and PO selectivity. Among them, the ZnO/MCM-41 (7.99) achieved nearly 100% PO selectivity and the highest turnover number of 124.4 (moles of PO per moles of Zn). The fresh catalysts of ZnO-NR, ZnO/MCM-41(7.99), the spent materials, and the ZnO₂ nanoparticles were characterized by synchrotron powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectroscopy. The fractions of ZnO₂ in the spent materials were quantified to be higher than 50%. Electron paramagnetic resonance and X-ray photoelectron spectroscopies revealed that the ZnO₂ phase formed by reacting ZnO with H₂O₂ in acetonitrile, stored as green redox oxide materials, contained species of hydroperoxide, peroxide and superoxide, which can be essential for catalytic production of PO. The fact of ¹⁸O enrichment to PO using H₂ ¹⁸O₂ suggested that the reactive oxygenated species are generated from H₂O₂ and anchored on/in ZnO₂ for the electrophilic epoxidation, with the assistance of acetonitrile.