The present study demonstrates the synthesis and application of Ag/ZnO powder films (thickness of 4 μm) as photocatalysts for natural sunlight and ultraviolet (UV, 315–400 nm) irradiation. The synthesis procedure is simple and eco-friendly, based on the photo-fixation of silver ions onto commercial ZnO powder via UV illumination for the first time. The photocatalytic efficiency of the newly developed films is evaluated through degradation of paracetamol in distilled and drinking water. Our experimental evidences show that the Ag/ZnO nanostructure films are more active than pristine ZnO films in the photodegradation process. Namely, the photocatalytic efficiency of the films modified with 10⁻² M concentration of silver ions achieve the highest degradation (D) percentages for paracetamol in both types of water (D_distilled = 80.97%, D_drinking = 82.5%) under natural sunlight. Under UV exposure, the degradation percentages are slightly lower but still higher than those achieved by pure ZnO films (D_distilled = 53.13%, D_drinking = 61.87%). It is found that the photocatalytic activity grows in direct proportion to the concentration of Ag⁺ ions: ZnO < Ag 10⁻⁴/ZnO < Ag 10⁻³/ZnO < Ag 10⁻²/ZnO. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance and photoluminescence spectroscopy are used to characterize the as-prepared ZnO and Ag/ZnO nanostructures. The improved photocatalytic performance of the Ag/ZnO films is mostly attributed to the combination of excited electron transfer from ZnO to Ag and the inhibition of photogenerated electron–hole pair recombination. Furthermore, Ag/ZnO nanostructure films can retain their photocatalytic activity after three cycles of use, highlighting their potential practical application for the treatment of pharmaceutical wastewater in real-world scenarios where natural sunlight is often more readily available than artificial UV light.

Tribocatalysis is a promising environmental remediation technique that utilizes the triboelectric effect, produced when dissimilar materials interact through friction, to generate charges promoting catalytic reactions. In this work, the tribocatalytic degradation of an organic dye—Rhodamine B (RhB)—has been experimentally realized using pure and 2 mol.% La-modified/ZnO powders, synthesized via a simple hydrothermal method. The effects of annealing on the tribocatalytic activity of the La/ZnO catalysts are also studied at 100 and 500 °C. The La/ZnO-modified catalysts showed an enhanced RhB degradation efficiency with 92% removal within 24 h, compared to only 58% for the pure ZnO. The effects of annealing were found to be detrimental, with RhB removal efficiencies dropping from 92 to 69% in the 100–500 °C range. The catalysts’ cycling stability was found to be excellent within three cycles. Ultimately, it is demonstrated that by utilizing La/ZnO powders, contaminated wastewater can be efficiently treated through employing tribocatalysis.

Tribocatalysis is an emerging advanced oxidation process that utilizes the triboelectric effect, based on friction between dissimilar materials to produce charges that can initiate various catalytic reactions. In this study, pure and rare-earth-modified ZnO powders (La₂O₃, Eu₂O₃, 2 mol %) were demonstrated as efficient tribocatalysts for the removal of the tetracycline antibiotic doxycycline (DC). While the pure ZnO samples achieved 49% DC removal within 24 h at a stirring rate of 100 rpm, the addition of Eu₂O₃ increased the removal efficiency to 67%, and La₂O₃-modified ZnO powder exhibited the highest removal efficiency, reaching 80% at the same stirring rate. Additionally, increasing the stirring rate to 300 and 500 rpm led to 100% DC removal in the ZnO/La case within 18 h, with the pronounced effect of the stirring rate confirming the tribocatalytic effect. All tribocatalysts exhibited excellent recycling properties, with less than a 3% loss of activity over three cycles. Furthermore, a scavenger assay confirmed the importance of superoxide radical generation for the overall reaction rate. The results of this investigation indicate that the rare-earth-modified ZnO tribocatalysts can effectively utilize mechanical energy to decompose pollutants in contaminated water.

Mechanical energy is a plentiful, environmentally friendly, and sustainable energy source in the natural world. In this work, we successfully use friction to transform mechanical energy into ZnO and ZnO/Nd₂O₃ (1, 2, 3, 4 and 5 mol%) tribocatalysts. Under magnetic stirring, the catalyst particles and the polytetrafluoroethylene (PTFE)-sealed magnetic bar rubbed against one another, transferring electrons across the contact interface. While the PTFE absorbed the electrons, holes were simultaneously left on the catalyst. Because of their potent oxidative power, the holes in the valence band of sol–gel catalysts can efficiently oxidize organic pollutants, much like photocatalysis. In the absence of light, the tribocatalytic tests showed that ZnO and ZnO/Nd₂O₃ flowers could remove antibiotics (Doxycycline) when magnetized. We could further improve the tribocatalytic performance by adjusting the quantity of rare earth elements (1, 2, 3, 4 and 5 mol%), stirring speed, and magnetic rod type. Besides creating a green tribocatalysis method for organic pollutants’ oxidative purification, this work provides a possible pathway for transforming environmental mechanical energy into chemical energy, which may be applied to environmental remediation and sustainable energy.

This study focuses on the fabrication and characterization of nanostructured zinc oxide films deposited on glass substrates using sol–gel dip-coating methods. The thin films are functionalized with silver ions at various Ag⁺ concentrations (10⁻², 10⁻³, 10⁻⁴ M) through room temperature ion fixation process with and without ultraviolet (UV) illumination. Physicochemical characterization techniques, such as employing Scanning Electron Microscopy with Energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Ultraviolet–Visible Spectroscopy and Electron Paramagnetic Resonance (EPR) techniques. The SEM-EDX and XRD confirmed a characteristic ganglia-like structure with a hexagonal crystalline structure. The photocatalytic performance and available surface area of the pure and Ag films are investigated in the removal of methylene blue dye under UV and visible light illumination and in darkness. It is observed that the photocatalytic activity increases proportionally to the Ag⁺ ion concentration: ZnO < Ag(10⁻⁴ M)/ZnO, < Ag(10⁻³ M)/ZnO < Ag(10⁻² M)/ZnO. Moreover, the catalysts modified under UV illumination during the fixation treatment (Ag-UV/ZnO) exhibited a higher photocatalytic efficiency and degraded the dye in comparison with those without a light source (Ag/ZnO). The experimental results are confirmed using total organic carbon (TOC) analysis. The optimal silver concentration (10⁻² M) is established, which shows the highest photocatalytic efficiency (in both cases of ion fixation treatment). The results can be used as a guideline for the development of co-catalyst-functionalized semiconductor photocatalysts.

In the natural environment, mechanical energy is widely available as a sustainable and green energy source. In this paper, we successfully convert mechanical energy on ZnO and ZnO/Eu₂O₃ tribocatalysts via a friction route. Electrons were transferred across the contact interface when the catalyst particles and the polytetrafluoroethylene (PTFE)-sealed magnetic bar rubbed against each other under magnetic stirring. At the same time, holes were left on the catalyst while the PTFE absorbed the electrons. Similar to photocatalysis, organic pollutants can be effectively oxidized by the holes in the valence band of sol-gel catalysts due to their strong oxidative ability. The tribocatalytic tests demonstrated that ZnO and ZnO/Eu₂O₃ could eliminate organic analgesics (paracetamol) under magnetic stirring in the dark. By controlling the quantity of rare earth elements (1, 2, and 3 mol%), stirring speed, and the number of magnetic rods, we could further enhance the tribocatalytic performance. In addition to developing a green tribocatalysis approach for the oxidative purification of organic pollutants, this work offers a potential route for converting environmental mechanical energy into chemical energy, which could be used in sustainable energy and environmental remediation.