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this study, tchemical stability of Y-TZP dental ceramic was determined by the modified standard method ISO 6872. The phase composition of Y-TZP dental ceramic was determined by X-ray diffraction (XRD) analysis, the microstructure was analyzed by Scanning Electron Microscopy (SEM). Chemical stability of investigated Y-TZP dental ceramic was determined by measuring eluted Al3+, Na+, Ca2+, K+, Si4+, Fe3+, Zn2+, Mg2+, Sr2+, Ba2+, Y3+ and Zr4+ions by High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS). According to the standard ISO 6872 chemical stability of dental ceramic is carried out in 4 wt. % CH3COOH aqueous solution at 80 °C during16 h. In this work, exposure time was extended up to 768 hours (32 days) in order to determine the corrosion rate constant. The parabolic reaction rate constant was 5.3 × 10-5 g2 cm-4 h-1. XRD analysis showed that the corrosion process course of partial tetragonal to monoclinic phase transformation of ZrO2.

In this study, the corrosion behaviour of alumina ceramics was observed under different conditions: 0.5, 1.25 and 2 mol dm–3 of nitric acid at 25, 40 and 55 °C through 10 days. The results show that Al2O3 ceramics exhibit good corrosion resistance at higher HNO3 concentration. Al2O3 corrosion behaviour varies depending on the temperature, time and HNO3 concentration. In view of the reaction kinetics, it proceeds in the parabolic law in HNO3 aqueous solution and decreases with increase of the HNO3 concentration. The corrosion rate and activation energy were calculated and compared for all experimental conditions. It was found that the corrosion rate of Al2O3 was found to be in the range 0.08 - 0.34 µg2 cm–4 h–1 where the highest rate was achieved at lower HNO3 concentration and highest temperature. Finally, the highest activation energy was determined for the 0.50 mol dm–3HNO3 concentration, which was more than twice as high as the activation energy observed at the 2.00 mol dm–3 HNO3 concentration.

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.

Here we study the photocatalytic degradation of the antibiotic ciprofloxacin (CIP) supported by sol-gel Ce-doped TiO2 photocatalyst nanoparticles. The photocatalyst samples consist of Ce in 0.08, 0.40, 0.80, 2.40 and 4.10 wt.%. For the preparing of the sols we used titanium isopropoxide and cerium (III) nitrate hexahydrate as precursors, 2-propanol as a solvent, acetylacetone as a complexation agent, distilled water as a hydrolysis agent, and nitric acid as a hydrolysis/polycondensation catalyst. The Ce-TiO2 sol was deposited on borosilicate glass samples using a flow coating method. After deposition, films were dried at 100 °C for 1 hour and heat-treated at 450 °C for 2 hours at a heating rate of 3 °C/min. The activity and efficiency of Ce- TiO2 films for photocatalytic degradation of the CIP under simulated solar radiation was investigated, especially the influence of the changing irradiation intensity. The weight loss as well as exothermic and endothermic reactions during the thermal treatment, were obtained by simultaneous differential thermal and thermogravimetric analysis (DSC/TGA). The phase composition and parameters and volumes of the unit cells were determined by X-ray diffraction (XRD). Atomic force microscopy (AFM) was used to describe surface morphology and roughness parameters of the films. Photocatalytic studies indicate that TiO2 photocatalyst with 0.80 wt. % Ce showed the highest rate of degradation of ciprofloxacin using simulated solar radiation.

Sintering process has one of the key roles in achieving the density close to the theoretical density. Sintering may be conducted by conventional and non conventional sintering method. Density level obtained by certain sintering method and regime might be changed by the exposure of material to highly corrosive media. Furthermore, final product’s performance and lifespan might be determined by the corrosive media-ceramic interaction. Impact of acidic media on density of highly pure aluminium oxide (Al2O3) sintered by conventional (electric kiln) and non-conventional (hybrid microwave kiln) sintering method was explored. Effects of nitric acid (HNO3) concentration (0.5, 1.25 and 2 mol dm-3), temperature (25, 40 and 55 °C) and exposure time (24, 132 and 240 h) on bulk density of alumina were statistically investigated by using Box-Behnken design. Bulk density was determined before and after the corrosion in aqueous solution of HNO3 by the Archimedes' method. Bulk density results underwent statistical analysis (ANOVA). Equations for bulk density of corroded conventionally and non-conventionally sintered ceramics were generated which enabled estimation of the theoretical values for applied conditions. The statistical analysis showed also the most significant factors that have an impact on the ceramic’s corrosion, which occurred to be temperature and concentration, no matter on sintering method applied.

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

Trimethoprim (2, 4-diamino-5(3’, 4’, 5’-trimetoxybenzylpyrimidine) (TMP) is an antifolate antibacterial agent used worldwide in veterinary and human medicines for the treatment of bladder infections. It is often prescribed in combination with sulfamethoxazole due to their complementary and synergistic mechanisms but may be used as a monotherapy [1]. Due to its frequent use and very low elimination rate in WWTPs, TMP has been often detected in wastewater effluents and surface waters. Previous study has shown that TMP is resistant to biodegradation and hydrolysis, while solar radiation can cause slow degradation of TMP in favourable environmental conditions and lead to a decrease in its environmental concentration [1]. In this work, the mechanism of TiO2 photocatalytic and photolytic (without photocatalyst) degradation of TMP was investigated. TiO2 photocatalyst was used in a form of nanostructured film on glass ring placed on the bottom of the reactor [2]. As a source of radiation a simulated solar radiation lamp was used both for photolytic and photocatalytic experiments. The photocatalytic mechanism has been elucidated by scavenger studies using isopropanol, ammonium oxalate and triethanolamine as hydroxyl radicals, positive holes and superoxide radicals scavengers, respectively [3]. The results showed strong inhibition of photocatalytic degradation of TMP in presence of isopropanol and triethanolamine, which means that •OH and superoxide radicals were the primary reactive radicals responsible for the degradation process. No inhibition of the photocatalytic degradation of TMP in presence of ammonium oxalate was observed.

Photocatalytic oxidation process, with heterogeneous photocatalysts, as one of the Advanced Oxidation Processes (AOPs), can be effective technology in the oxidation/degradation of different water pollutants. The main problem with manipulation with photocatalyst (usually TiO2 particles in the size range 20-30 nm) is the need to separate them after the photocatalytical oxidation process and reuse them for further process of degradation of pollutants. In this study two different methods (growth of magnetite crystals on the photocatalyst surface and formation of photocatalytic nano-film on the magnetite core) for preparation of magnetic photocatalysts was applied and magnetic technology was used for separation of particles from water. Photocatalysts were successfully prepared and reused with the efficiency of more than 90% and also successfully used for different water pollutants –pharmaceutics and natural organic matter.

Alumina powder is categorized as inert and non- toxic, which means that it can be safely reused after machining a green body. The green body is usually obtained in advanced ceramic manufacturing by compacting raw alumina powder into a rigid shape using applied pressure. The possibility of reusing generated alumina solid waste as secondary raw material has been investigated. The alumina samples were formed by slip casting, which utilizes an aqueous slip of commercial alumina powder mixed with 20 dwb. % of alumina waste powder (expressed on a dry weight basis) and porous mould. The prepared alumina samples were characterized and successfully sintered. The applied sintering methods were one-step and hybrid microwave sintering methods. Finally, alumina samples without the addition of waste alumina powder were also sintered to compare two sets of samples. The sintered samples with the addition of alumina waste powder showed higher theoretical density, which reflected onto slightly better mechanical properties such as indentation fracture toughness and Vickers hardness. The better mechanical properties of ceramic samples containing waste alumina are a consequence of lower porosity due to a higher amount of magnesium oxide present in alumina waste powder. The conducted research strongly suggests the possibility of reusing waste alumina powder in advanced ceramics manufacturing.