Infrared spectroscopy and Raman spectroscopy were used to characterize mullite ceramics prepared from fly ash and kaolin by annealing at 1000 °C, 1100 °C, 1200 °C, and 1300 °C. IR spectroscopy confirmed the presence of SiO₄ tetrahedra and AlO₆ octahedra in samples. The presence of mullite has been confirmed at all temperatures. The presence of quartz has been confirmed up to a temperature of 1100 °C, and the presence of an amorphous form of SiO₂ has been confirmed at temperatures of 1200 °C and 1300 °C. The transformation of quartz into the amorphous form of SiO₂ at temperatures above 1100 °C is assumed. Transformation was performed on the percentage intensity decrease of the bending vibration of Si-O-Si (at about 450 cm⁻¹) and Al-O-Si (at about 550 cm⁻¹). Raman spectroscopy confirmed the presence of mullite at different stages of structural ordering (a well-ordered structure at a temperature of 1100 °C and a disordered structure at a temperature of 1300 °C).

Here, the comparison of two different semiconductor materials is demonstrated, TiO₂ and melem/g-C₃N₄ composites—modified with balls of approximately 5 nm Ag nanoparticles (NPs) as photocatalysts for the degradation of the model dye acid orange 7 (AO7). The melem molecule synthesized here is one of a series of organic compounds consisting of triazine ring compounds with a structure similar to that of melam and melamine. The photodegradation process of AO7 was carried out to examine all powder materials as a potential photocatalyst. Additionally, two different lamps of wavelengths 368 nm (UV light) and 420 nm (VIS light) were applied to compare the photodegradation tests. A new synthesis route for the acquisition of Ag NPs (Ag content 0.5, 1.0 and 2.5 wt%), based on a wet and low temperature method without the use of reducing reagents was proposed. The best photocatalytic performances under UV and VIS light were obtained for both, TiO₂ and melem/g-C₃N₄ materials (new synthesis route) modified with a very low Ag content—0.5 wt%. The photodegradation activities using UV lamp (3 h, 368 nm irradiation) for samples with 0.5 wt% of Ag: TiO₂ and melem/g-C₃N₄, in excess of 95 and 94%, respectively, were achieved. The highest photoactive materials melem/g-C₃N₄ with 0.5 and 1 wt% Ag revealed 98% of activity under the VIS lamp after 3 h long irradiation. Our work demonstrates a novel, environmentally acceptable, and cost-effective chemical strategy for preparation of photocatalysts suitable for degradation of organic contaminants in wastewater treatment.

Identification of clay minerals based on chemometric analysis of measured infrared (IR) spectra was suggested. IR spectra were collected using the diffuse reflection technique. Discriminant analysis and principal component analysis were used as chemometric methods. Four statistical models were created for separation and identification of clay minerals. More than 50 samples of various clay mineral standards from different localities were used for the creation of statistical models. The results of this study confirm that the discriminant analysis of IR spectra of clay minerals could provide a powerful tool for identification of clay minerals. Differentiation of muscovite from illite and identification of mixed structures of illite–smectite were achieved.

The aim of this work was to deposit cost-effective g-C₃N₄/ZnO nanocomposite photocatalysts (weight ratios of g-C₃N₄:ZnO from 0.05:1 to 3:1) as well as pure ZnO and g-C₃N₄ on Al₂O₃ foam and to study their photocatalytic efficiency for the photocatalytic decomposition of N₂O, which was studied in a home-made batch photoreactor under ultraviolet A irradiation (λ = 365 nm). Based on the photocatalysis measurements, it was found that photocatalytic decomposition of N₂O in the presence of all the prepared samples was significantly higher in comparison with photolysis. The photoactivity of the investigated nanocomposite photocatalysts increased in the following order: g-C₃N₄/ZnO (3:1) ≈ g-C₃N₄/ZnO (0.45:1) ≤ g-C₃N₄/ZnO (2:1) ZnO < g-C₃N₄ < g-C₃N₄/ZnO (0.05:1). The g-C₃N₄/ZnO (0.05:1) nanocomposite showed the best photocatalytic behavior and the most effective separation of photoinduced electron–hole pairs from all nanocomposites. The key roles played in photocatalytic activity were the electron–hole separation and the position and potential of the valence and conduction band. On the other hand, the specific surface area and band gap energy were not the significant factors in N₂O photocatalytic decomposition. Immobilization of the photocatalyst on the foam permits facile manipulation after photocatalytic reaction and their repeated application.