This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch precursors treated with H2SO4 and HNO3 and finally annealed at 1000°C and 2000°C. Our experimental investigations combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and micro-spot near-edge X-ray absorption fine structure (μ-NEXAFS) spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of the carbon foams. The high-resolution microscopy data indicate the formation of carbonaceous amorphous microspheres (average diameters of 0.28±0.01μm) embedded in the partially graphitized carbon foam matrix at 1000°C. The microspheres are enriched with sp-bonded species and their microstructural characteristics depend on the reagent (nitric vs. sulfuric acid) used for pitch treatment. A complete chemical transformation of the microspheres at temperatures >1000°C occurs and at 2000°C they are spectroscopically identical with the bulk material (sp(2)- and sp(3)-hybridised forms of carbon). The microstructure-property relationship is exemplified by the compressive strength measurements. These results allow a better description of coal-tar pitch-derived carbon foams at the atomic level, and may account for a better understanding of the processes during graphitization step.

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.

Zinc oxide arouses considerable interest since it has many applications—in microelectronics, environmental decontaminations, biomedicine, photocatalysis, corrosion, etc. The present investigation describes the green synthesis of nanosized ZnO particles using a low-cost, ecologically friendly approach compared to the classical methods, which are aimed at limiting their harmful effects on the environment. In this study, ZnO nanoparticles were prepared using an extract of Mentha arvensis (MA) leaves as a stabilizing/reducing agent, followed by hydrothermal treatment at 180 °C. The resulting powder samples were characterized by X-ray diffraction (XRD) phase analysis, infrared spectroscopy (IRS), scanning electron microscopy (SEM), and electron paramagnetic resonance (EPR). The specific surface area and pore size distribution were measured by the Brunauer–Emmett–Taylor (BET) method. Electronic paramagnetic resonance spectra were recorded at room temperature and at 123 K by a JEOL JES-FA 100 EPR spectrometer. The intensity of the bands within the range of 400–1700 cm⁻¹ for biosynthesized ZnO (BS-Zn) powders decreased with the increase in the Mentha arvensis extract concentration. Upon increasing the plant extract concentration, the relative proportion of mesopores in the BS-Zn samples also increased. It was established that the photocatalytic performance of the biosynthesized powders was dependent on the MA concentration in the precursor solution. According to EPR and PL analyses, it was proved that there was a presence of singly ionized oxygen vacancies (V₀⁺) and zinc interstitials (Zn_i). The use of the plant extract led to changes in the morphology, phase composition, and structure of the ZnO particles, which were responsible for the increased photocatalytic rate of discoloration of Malachite Green dye.