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The formation of giant hailstones is a rare weather event that has devastating consequences in inhabited areas. This hazard has been occurring more frequently and with greater size of hailstones in recent years, and thus needs to be better understood. While the generally accepted mechanism is thought to be a process similar to the formation of smaller hailstones but with exceptional duration and stronger updrafts, recent evidence suggests that biotic and abiotic factors also influence the growth of these unusually large ice chunks. In this study, we improved these findings by determining the distribution of a wide variety of these factors throughout the hail volume and expanding the search to include new particles that are common in the environment and are of anthropogenic origin. We melted the concentric layers of several giant hailstones that fell to the ground over a small region in Slovenia in 2019. The samples, up to 13 cm in diameter, were analyzed for biotic and abiotic constituents that could have influenced their formation. Using 16S rRNA-based metagenomics approaches, we identified a highly diverse bacterial community, and by using scanning electron microscopy and Raman spectroscopy, we found natural and synthetic fibers concentrated in the cores of the giant hailstones. For the first time, we were able to detect the existence of microplastic fibers in giant hailstones and determine the changes in the distribution of sand within the volume of the samples. Our results suggest that changes in the composition of hail layers and their great diversity are important factors that should be considered in research. It also appears that anthropogenic microfiber pollutants were a significant factor in the formation of the giant hailstones analyzed in this study.

The presence of an increasing number of organic pollutants in the water poses serious issues to human health and the environment. Many of these organic pollutants are persistent and non- biodegradable. The pollutants of fresh water by harmful pollutants require researchers to develop innovative, efficient, sustainable, and cost- effective materials for water treatment. Advanced oxidation processes have the potential to efficiently degrade organic pollutants from water. The photocatalytic process uses catalyst and light to produce radicals. Radicals possess a high redox potential, e.g., hydroxyl radicals E° = 2.72 V that react with the molecular structure of various pollutants and degrade pollutants into harmless products. Thus, photocatalysis is recognized as a favorable approach to tackling pollutant removal and saving energy. However, semiconductor photocatalysts have limitations such as photo- generated charge carrier recombination, wide band gap energy, and slow surface reaction kinetics. Disadvantages can be remedied by appropriate modifications of physico-chemical, and optical properties of TiO2. Overcoming the limitations present in TiO2-based photocatalysis, as well as the search for potentially efficient materials, is extremely important, and the modification of TiO2 with carbon-based materials like graphene is promising due to its unique properties. Therefore, graphene and its derivatives have widely used as supports for semiconductor materials and photocatalysts due to their distinctive physio- chemical, optical, and electrical features. In this research, an attempt has been made to utilize the excellent properties of graphene by coupling it with TiO2 nanoparticles. Synthesis of nanocomposites of TiO2 with reduced graphene oxide has been done by hydrothermal/solvothermal synthesis followed by calcination at 300 ºC. Prepared nanomaterials were characterised using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. Photocatalytic degradation was performed using methylene blue as a model pollutant under simulated solar light (300W Osram Ultra Vitalux bulb) as a source of irradiation. The obtained results of performed photocatalytic tests show the improved removal rate of methylene blue dye from an aqueous solution using prepared TiO2@rGO nanocomposite in comparison with bare TiO2 nanoparticles.

The accelerated development of the dye industry in recent years contributes to an overload of wastewater, which has a negative influence on human health and aquatic ecosystems [1]. Methylene blue (MB) is a commonly used cationic dye and is very harmful to human health above a certain concentration due to its toxicity. In addition, MB is difficult to biodegrade because of its chemical persistence. Nowadays, treatment methods such as biological, physical, and chemical have been used to remove dye wastewater. However, those methods have some drawbacks like high cost as well as toxic by-products. Therefore, advanced oxidation processes, like heterogeneous photocatalytic degradation can be used as a more appropriate method for MB removal from wastewater [2], [3]. In this research, the binary TiO2-rGO nanocomposite catalyst was successfully synthesized as a mixture of pure TiO2 particles and reduced graphene oxide (rGO). The graphene oxide (GO) was synthesized by Hummer's method using natural graphite flakes (particle size ≤ 50 µm) as a precursor. The binary TiO2-rGO nanocomposite has been self-assembled through one- pot hydrothermal synthesis followed by a calcination treatment. The structural and morphological analysis of the synthesized nanocomposites have been performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transforms infrared spectroscopy (FTIR). Photocatalytic experiments under ultraviolet (UV) and solar-like irradiation were performed in order to evaluate the efficiency of the synthesized catalysts. Further, the influence of rGO concentration on TiO2 performance for photodegradation of the MB dye was determined. It was found that the photodegradation of MB was increased as irradiation time for both sources of irradiation increased. The obtained results showed that the photocatalytic activity was increased as rGO concentration increased in the prepared nanocomposite, which can be attributed to the synergistic effect of the incorporation of rGO with TiO2.

Research over the last few decades has shown that the pollutant contamination of the aquatic environment become a serious global problem. Due to the continuous and commonly ignorant release of pollutants without their prior treatment, we persistently influence the ecosystem and impact the living organisms. With this study, we present an attempt to degrade one of the pollutants, namely caffeine, with the non-toxic photocatalytic approach. Caffeine (CAF) was dispersed in a suspension of graphitic carbon nitride (CN) nanopowder, which was prepared by a simple thermal method at several treatment temperatures (at 500, 550, and 600 °C) using urea as a precursor. Synthesized CN catalysts were characterized using X-ray diffraction analysis (XRD) and photoluminescence (PL). Photocatalytic experiments were performed in an incubator under an ultraviolet A (UV-A) lamp (Supratec 18W/73, Osram) with a specified wavelength between 300 and 400 nm and a simulated solar lamp (Osram Ultra Vitalux 300W). We show that after the photo-degradation process, the concentration of CAF as a model pollutant was lower compared to the initial concentration (10 mgL-1 ). Furthermore, we also show how the thermal treatment of the CN influences the photocatalytic degradation of CAF. We also noticed that the degradation is faster under simulated solar irradiation compared to UV-A irradiation. For future work, we expect that the studied photocatalyst will be reusable through immobilization, which is also of utmost significance for their implementation under real conditions

Nano zinc oxide (ZnO) gained a lot of attention for photocatalytic applications and is frequently used to degrade many organic pollutants in water, from dyes to microplastics. Photocatalysis, is a chemical oxidation processes, where commonly nanostructured semiconductor (photocatalyst) is irradiated with an appropriate light energy to create electron-hole pairs, that react with the surrounding water and produce superoxide and hydroxyl radical that can oxidize given chemical species/pollutant. As photocatalysis is an exclusively surface driven process, its activity depends on the particle size, specific surface area and morphology of the used photocatalyst. Nanostructured materials with high surface to volume ratio have high photocatalytic degradation efficiency. Nano ZnO can be prepared with many different techniques. In our study, first nanodots of ZnO was prepared. After the distillation of Zn‐acetate ethanol solution, ZnO nanoparticles were precipitated by the addition of LiOH. Further solvothermal treatment, in autoclave at 150 and 200°C for 24 or 120 hours, transformed nanodots to nanorods. Synthesized nanopowders were characterized using X-ray diffraction analysis (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activity of prepared ZnO nanostructures was investigated by caffeine and molybdenum blue degradation. These common pollutants were dissolved in miliQ water with concentration of 10 mg/L. The photocatalytic degradation was carried out in cylindrical reactor with quartz cover, where 5 mg of photocatalyst was added to 5 mL of solution. Before irradiation, samples were kept in the dark for 60 min to reach the adsorption desorption equilibrium. Suspensions of ZnO in pollutant solution were irradiated under stirring using a UV-vis simulated sun spectrum (Ultra Vitalux, 300 W, Osram). At pre- defined time intervals, the caffeine/MB concentration was analyzed by spectrophotometer (Lambda 950 UV/Vis/NIR, PerkinElmer). We correlate the obtained degradation rate with the crystallinity, crystal size, aspect ratio, specific surface area and structural and surface defects. Nanorods solvothermally synthesized at 200 °C for 24 h showed the highest photocatalytic activity, and consequently we tested them also for photocatalytic degradation of synthetic microfibers (PET, PA). SEM and Raman analysis, after the exposure by simulated sun light irradiation, showed changes on surface of plastic fibers

Nano zinc oxide (ZnO) gained a lot of attention for photocatalytic applications and is frequently used to degrade many organic pollutants in water, from dyes to microplastics. Photocatalysis, is a chemical oxidation processes, where commonly nanostructured semiconductor (photocatalyst) is irradiated with an appropriate light energy to create electronhole pairs, that react with the surrounding water and produce superoxide and hydroxyl radical that can oxidize given chemical species/pollutant. As photocatalysis is an exclusively surface driven process, its activity depends on the particle size, specific surface area and morphology of the used photocatalyst. Nanostructured materials with high surface to volume ratio have high photocatalytic degradation efficiency. In our study, ZnO nanodots was prepared by sol-gel technique, and additional solvothermal treatment, in autoclave at 150 or 200°C for 24 or 120 hours, transformed nanodots to nanorods. Synthesized nanopowders were characterized using X-ray diffraction analysis (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activity of prepared ZnO nanostructures was investigated by caffeine and molybdenum blue degradation. The photocatalytic degradation was carried out in cylindrical reactor with quartz cover, where 5 mg of photocatalyst was added to 5 mL of pollutant solution. Before irradiation, samples were kept in the dark for 60 min to reach the adsorption desorption equilibrium. Suspensions of ZnO in pollutant solution were irradiated under stirring using a UV-vis simulated sun spectrum (Ultra Vitalux, 300 W, Osram). At pre-defined time intervals, the caffeine/MB concentration was analyzed by spectrophotometer (Lambda 950 UV/Vis/NIR, PerkinElmer). We correlate the obtained degradation rate with the crystallinity, crystal size, aspect ratio, specific surface area and structural and surface defects. Nanorods solvothermally synthesized at 200 °C for 24 h showed the highest photocatalytic activity, and consequently we tested them also for photocatalytic degradation of synthetic microfibers (PET, PA). SEM and Raman analysis, after the exposure by simulated sun light irradiation, showed changes on surface of plastic fibers.

Plastic pollution has been identified as a global problem that endangers the entire ecosystem. Numerous studies have shown that water systems are full of plastic particles degraded into microplastics (MP) and nanoplastics (NP). This has prompted investigations to assess the impact of MPs on global ecologies and human health. We aim to find synergies between two naturally occurring processes with the potential to break down toxic microplastics after they have been released into the environment ; namely, photodegradation and biodegradation. While biodegradation slowly converts plastic into harmless residues through biological processes, photodegradation breaks down plastics bonds whit the assistance of photocatalysis. Photocatalytic and microbial degradation was performed on commercial polyethylene terephthalate (PET) fibers. Fibers were dispersed in suspension of TiO2 photocatalysts while photocatalytic experiments were carried out in an incubator with UV/Vis illumination source for 48 hours. Microbial degradation of PET plastics was performed by selected species of fungi. Fibers were sterilized and transferred to a tube with sterile M9 liquid medium. Cell suspension of each selected strain was added to the tube and incubated at 24°C. We sampled after 14 days, 2 and 6 moths. Scanning electron microscope (SEM) and Raman spectroscopy (in Raman shift range from 400-3300 cm-1) were used to characterize fibers surface before and after degradation experiments. SEM analysis showed that the surface of individual PET fiber become rough after photodegradation, the deformations are numerous and very obvious. Raman spectroscopy showed change in the intensity of particular peaks, as a consequence of bond cleavage on the surface of the fibers during photocatalytic treatment. In addition, we compered the growth kinetics of selected fungal species when intact or partially degraded fibers were the only source of carbon in our growth medium. SEM analysis also showed successful growth of fungi and that the presence of a photocatalyst did not inhibit fungal growth. In future, our work will be focused on the development of a hybrid geometry which simultaneously harnesses biological and photocatalytic degradation processes.

Textile industries significantly contribute to the generation of wastewater containing various raw materials such as cotton, synthetic fibres, and dyes. Textile dyes are harmful to the environment and human health. Therefore, dye-containing wastewater should be treated to preserve the environment, human health, and natural water resources. Nowadays, conventional wastewater treatment methods can be used in the textile industry. However, those methods have some drawbacks like high cost as well as toxic by- products. Therefore, advanced oxidation processes, like heterogeneous photocatalytic degradation can be used as a more appropriate method for dye removal from wastewater. The present research is focused on the graphitic carbon nitride as a photocatalyst immobilised on the surface of the alumina ceramic ring for photocatalytic degradation of methylene blue (MB) from an aqueous medium under different radiation sources. A metal- free graphitic carbon nitride was prepared through a simple thermal method using urea as a precursor. Deposition of prepared photocatalysts was performed by dip-coating method. The photocatalyst was characterized by XRD, FTIR, and SEM. The photocatalytic activity under ultraviolet (UV-A), visible (warm light), and simulated solar irradiation was examined. The photocatalytic degradation of MB from an aqueous medium was found to increase with increasing irradiation time for all irradiation sources. Furthermore, the radiation source wavelength spectrum plays a significant role in the photocatalytic degradation rate of MB. The immobilised graphitic carbon nitride on alumina ceramic can be convenient for environmental applications, due to easy separation and reusability with high- efficiency removal of MB dye from an aqueous medium.

Nowadays, investigations based on nanotechnology undertake breakthroughs in many application areas such as manufacturing, materials, nanoelectronics, energy, biotechnology, medicine, information technology, and others. The excellent properties of graphene-based materials, which are crucial in a wide range of applications, continuously highlight this promising new compound. Among them is for example graphene oxide (GO). It is an oxidized form of graphene with oxygen functional groups (carboxyl, hydroxyl, carbonyl, and epoxy) in the carbon lattice. However, the oxidation of graphite to GO introduces defects into the carbon structure that result in significantly altered physio-chemical properties, which are in some applications undesirable. One way to overcome the difficulties is to consider reduced graphene oxide (rGO) with decreased oxygen content. Material has altered physicochemical properties such as optical and surface functionalities, originating predominantly from higher electron mobility. The present work addresses the synthesis of GO, and rGO by introducing a simple approach and provides structural, morphological, chemical, and physical analysis of the synthesized material. GO was prepared by chemical oxidation and exfoliation of graphite flakes (particle size ≤ 50 μm) using Hummer’s method. rGO was, on the other hand, prepared by the hydrothermal method. Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Raman spectroscopy were used to evaluate the characteristics of this already known material. Results show that GO and rGO synthesized by the presented method, exhibit properties suitable for a wide range of applications such as in supercapacitors, water purification, and also as composite materials in coatings and even solar cells.

In this research, the hydrothermal synthesis was used to prepare nanocomposites titanium dioxide/reduced graphene oxide (TiO2/rGO) with additional annealing at different temperatures (300 °C, 400 °C, and 500 °C). The TiO2 colloidal sol was prepared using titanium (IV) isopropoxide (Ti(C3H5O12)4, TTIP) as a precursor. Graphene oxide (GO) was synthesized using graphite flakes (≤50 µm) by a Hummer’s method. The prepared photocatalysts were characterized by means of Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Raman spectroscopy. The photoactivity of nanocomposites was evaluated by the degradation of Rhodamine B (RhB) dye as a model of an organic pollutant. Tests were performed under sun-like irradiation. It was found that the annealing temperatures have an influence on the investigated properties of as- prepared nanocomposites.

Accelerated industrial development in recent years has a negative influence on the aquatic ecosystem. Pollutants such as pesticides, microplastics, persistent organic pollutants, and dyes are present. In several industries, including cosmetics, plastic, paper, textiles, and rubber, synthetic dyes are used to give color to the products. The massive scale of used synthetic dyes, which are chemically and thermally stable in water, represents a potential hazard to the environment. The photocatalytic removal/degradation and wastewater treatment under solar-like irradiation have their own limitations. It is necessary to solve major challenges to overcome the drawbacks of the conventional water treatment processes. In this research, the hybridized photocatalyst was successfully synthesized as a mixture of pure TiO2 particles, reduced graphene oxide (rGO), and graphitic carbon nitride (g-C3N4). The graphene oxide (GO) material was synthesized by Hummer's method using natural graphite flakes (particle size ≤ 50 µm). The bulk g-C3N4 was prepared by a simple pyrolysis procedure using urea as a precursor. The hybridised rGO/TiO2/g-C3N4 photocatalyst has been self-assembled through one-pot hydrothermally synthesis followed by an annealing treatment. The morphological and structural analysis of the fabricated photocatalysts have been analyzed by X- ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Photocatalytic experiments with solar-like irradiation were performed to evaluate the efficiency of the synthesized materials. Composites were used as photocatalysts in the degradation of dye Methylene blue (MB) dye in an aqueous medium at a pH of 5.9. In addition to the natural pH of the solution (5.9), four other pH values (3.3, 7.3, 10.5, and 12.5) were adjusted and the efficiency of MB degradation was studied. The synthesized rGO/TiO2/g-C3N4 hybrid shows higher photocatalytic activity than pure TiO2 particles, TiO2/rGO, and TiO2/g-C3N4 composites in the degradation of MB dye in an aqueous medium (10 mg/L) under solar-like irradiation. The obtained results show that the photocatalytic activity of TiO2 increases with a higher amount of added rGO and g-C3N4. The pH of the solution also affects the MB degradation rate. Therefore, the highefficient hybridised rGO/TiO2/g-C3N4 photocatalyst could have the potential for environmental remediation.

A widespread use of plastic represents a serious environmental issue, mostly because debris, such as microplastic and nanoplastics, are found everywhere. Especially in water ecosystem. A huge amount of microplastics, if not the largest, enters the water system through washing synthetic textile. ZnO is commonly used to degrade many chemical pollutants and for the purpose of this study we showed how it can be synthesized with different morphologies, namely dots, rods and hexagons, by similar solution-based methods. For the characterization, we employed standard technique such as XRD, SEM, TEM and Raman. For photocatalytic degradation of plastic pollutant, we utilized ZnO nanorods. Along we also performed experiments, for degradation of caffeine, to better explain which characteristics of nanomaterial influence the degradation. The rate of degradation for different particles on caffeine was evaluated by standardized UV/Vis spectroscopy, while SEM and Raman analysis had to be employed to notice the decomposition of plastic material.

At the beginning of the 21st century, mankind has to face the problem of availability of water as an important threat, due to the loss of the balance between the quantity and quality of available water [1]. The ubiquitous organic pollutants (drugs, pesticides, and organic dyes) have become a matter of increasing concern. They have raised considerable concerns due to their frequent detection in drinking water, groundwater, and surface water, usually in the very low concentration [2]. Organic pollutants and also their metabolites can be toxic and some of them even carcinogenic for humans. Therefore, pollutants should be removed by an appropriate purification method. It was shown how various organic pollutants can be efficiently removed by photocatalytic processes in the presence of different catalysts. Heterogeneous photocatalysis with appropriate photocatalysts is among the most promising methods for the efficient removal of pollutants. It is a clean, green, sustainable and cheap method [1, 2]. The nanocomposite photocatalyst based on titanium dioxide (TiO2) and reduced graphene oxide (rGO) was produced. The material was prepared using a direct sol- gel method followed by hydrothermal treatment at different experimental conditions (e.g., pH, time, temperature) with the aim to optimize photocatalytic degradation. Graphene oxide (GO) was produced from graphite flakes following a Hummer’s method [3]. TiO2 sol was prepared from titanium tetraisopropoxide as a precursor, i- propanol as a solvent, acetylacetone as a chelating agent and nitric acid as a catalyst [4]. TiO2 nanoparticles and TiO2/rGO nanocomposites, with different amounts of GO, were obtained by a hydrothermal method, where also time, temperature and pH of the treated suspensions were adjusted. The influence of the preparation conditions on the physico-chemical properties of synthesized powders was established by different characterization methods such as (powder X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and Raman spectroscopy). Photocatalytic degradation of organic pollutants (caffeine, methylene blue) under visible light irradiation was used as a test reaction. The efficiency of the photocatalytic degradation was monitored by UV- Vis spectrophotometry. Obtained results show how photocatalytic properties of prepared TiO2 nanoparticles and TiO2/rGO nanocomposites depend on different experimental parameters of their synthesis.