Дисертації (ФХ)

Постійне посилання зібрання

https://ela.kpi.ua/handle/123456789/14895
У зібранні розміщено дисертації, які захищені працівниками кафедри.

Переглянути

Перегляд Дисертації (ФХ) за Автор "Lazzara Giuseppe"

Зараз показуємо 1 - 1 з 1
  • Ескіз
    ДокументВідкритий доступ
    Composites of manganese oxides and oxidehydroxides with halloysite as degradation photocatalysts
    (Igor Sikorsky Kyiv Polytechnic Institute, 2025) Kovinchuk, Iryna Vasylivna; Sokolskyi, Heorhii Volodymyrovych; Lazzara Giuseppe
    Kovinchuk I.V. Composites of manganese oxides and oxidehydroxides with halloysite as degradation photocatalysts. – Qualification scientific work in the form of a manuscript. Joint doctoral thesis for the degree of Doctor of Philosophy in specialty 161 “Chemical Technologies and Engineering”. – National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Ministry of Education and Science of Ukraine and Doctor of Philosophy in “Physical and Chemical Sciences”. – University of Palermo (Italy), Kyiv, 2025. The dissertation is devoted to the study of the influence of synthesis conditions, phase composition, and structure on the functionality of composites based on manganese oxides and oxidehydroxides for the photocatalytic degradation of model organic compounds: aqueous solutions of dyes and polyethene films under UV- and Vis. light irradiation. The work considers the relationship between synthesis conditions and phase composition, morphology, band gap width, and specific surface area of the products with their efficiency as photocatalysts. In addition, the influence of halloysite aluminosilicate nanotubes on the physicochemical properties and photocatalytic activity of composite materials, as well as the behavior of manganese oxides and oxyhydroxides relative towards their surface, was investigated. The photocatalytic activity of standard materials MnO2, TiO2 and their mechanical mixture was studied at the photocatalytic degradation of polyethylene films under the influence of UV- and visible light irradiation. This study included a comparison of the mass loss of containing photocatalyst PE films with the pure film. The MnO2/TiO2 mixture demonstrated the highest efficiency with a film mass loss of 21.3% after 90 hours of irradiation. The degradation mechanism was evaluated by the relative intensity of the peaks of the FTIR spectra corresponding to the carbonyl, hydroxyl and ether indices. It was established that the mechanical mixture of y-MnO2 with TiO2 causes synergy action with a greater degree of degradation at all intermediate stages of PE oxidation since the vibrations of functional groups of the intermediates are more intense compared with the PE/TiO2 film. In addition, the carbonyl index shows a relatively more significant accumulation of the corresponding groups. Therefore, the conversion occurs much faster than in other samples at all stages, which indicates the nonspecificity of the catalytic action of the formed radicals towards PE oxidation intermediates on the y-MnO2 photocatalyst with TiO2. It was found that during chemical precipitation from MnSO4 solution using hydrogen peroxide as an oxidant composite material with different ratios of manganese oxides and oxidehydroxides with valences from +2 to +4 are formed. The medium's acidity and the presence of NH4 + dopants in the reaction medium play a decisive role. It was shown that at pH = 10 the main phase formed are the low-valent manganese oxides hausmannite Mn3O4 in the presence of excess ammonium ions, and bixbyite Mn2O3 in its absence. While at lower pH values = 5-7 the main product is manganite y-MnOOH and groutite a-MnOOH with traces of manganese oxide 4+ in excess NH4 + . The nature of the interaction of manganese oxides with the surface of halloysite nanotubes was studied by the transmission electron microscopy. It was found that in TEM images of samples synthesized in the presence of an excess of ammonium ions in the reaction mixture (CS2 and CS-6), a darkening of the lumen area of the nanotubes is observed, which may indicate its filling, while in the absence of an excess of ammonium (CS-1 and CS-7), particles of manganese oxides and oxidehydroxides decorate the outer surface of halloysite. The measured specific surface area of the synthesized samples is by 3-3.5 times higher (55-66 m2 /g) compared to the standard MnO2 PCP sample. At the same time, the presence of halloysite nanotubes did not significantly affect this parameter. The diffuse reflection spectra were recorded and the band gap width using the Tauk plot was calculated. The band gap values of Eg = 2.28-2.38 eV were established for samples CS5-CS-9. In turn, the values of 2.52 and 2.7 eV were measured for the lower-valence samples CS-1 and CS-2, respectively. Thus, in accordance with semiconductor properties of these composites, their potential photocatalytic activity belongs to the visible light range. The dynamic light scattering method data on the average size of composite material aggregates and the TEM image analysis data of sizes of individual nanoparticles were evaluated. In both cases, the synthesized samples exhibit smaller sizes compared to the standard MnO2 PCP sample, ranging between 117–175 nm for aggregates and 7–12 nm for nanoparticles. A series of electrochemically deposited samples was synthesised to expand the range of phase states of the materials studied. The influence of acidity and the presence of dopant ions of NH4 + and Cr3+on the synthesised samples’ morphology, phase composition, and physicochemical properties was investigated. X-ray diffraction analysis confirmed the formation of composite oxide materials consisting of a-, y-, e- and b-phases of MnO2 in various proportions. It was established that NH4 + ions in excess stabilise the electrodeposition of hollandite, a-, and birnessite, b-, phases of MnO2, while their absence favours the formation of the ramsdellite y- and e-MnO2 phases. The samples with a predominant hollandite phase of MnO2 demonstrated the highest specific surface area, reaching a maximum of 215 m²/g for sample ED-12, indicating the achievement of a diffusion-controlled deposition regime. In comparison, samples with a predominant e- MnO2 phase exhibited smaller surface areas, specifically 65.65 m²/g for ED-13 and 82.88 m²/g for ED-2. The particle size distribution and morphology of MnO2 were evaluated using scanning electron microscopy images. For samples ED-2 and ED-6, which are composites of y- and e-MnO2, plate-like formations with an average nanoparticle size of 70 ± 15 nm were observed. Samples with a predominant alpha-phase exhibited a needlelike morphology. The synthesized manganese dioxide electrodeposited (ED) samples are semiconductors with a band gap width ranging from 2.16 to 2.36 eV. Doping with Cr3+ ions reduced the band gap by approximately 0.3–0.5 eV due to introducing new electron donor levels. The Mulliken electronegativity and the positions of the valence and conduction bands were calculated for the electro-synthesized samples. Sample ED-6 demonstrated a conduction band position at 0.12 eV (vs the standard hydrogen electrode, SHE) and a valence band at 2.49 eV (SHE), with the broadest band gap of 3.36 eV, indicating the potential of this sample for photocatalytic water splitting to produce hydrogen. Differential scanning calorimetry combined with mass spectrometry was performed on selected electro-synthesized samples. This analysis enabled the identification of the thermal decomposition products and temperature intervals of their release. These findings provide insight into defect levels based on the Ruetschi cation vacancy model. According to this model, the content of cation vacancies () in manganese dioxide samples, predominantly of the ramsdellite modification, can be estimated. As energetically non-equivalent positions, these crystal lattice defects being in the material’s surface layers can significantly enhance its catalytic activity. The calculated formulas for the electrodeposited samples are presented below. Mn0.81 4+ Mn0.15 3+ 0.04 O1.69 2− OHO.3 ED-6 MN0.68 4+ Mn0.28 3+ 0.04 O1.55 2− OHO.45 ED-8 Both y-MnO2 (ED-6) and a-MnO2 (ED-8) Samples (see the names of Samples in the text below) exhibit the same content of cation vacancies; however, ED-8 is distinguished by two times higher Mn3+ content. It was established that the composite samples of low-valent manganese oxides, CS2 and CS-1, exhibit the highest photocatalytic activity toward the cationic dye Methylene Blue. This is likely due to the presence of halloysite nanotubes in the composites, which feature is a negatively charged outer surface. This provides a synergistic effect, facilitating pollutant degradation by more efficient transport of the dye from the solution bulk to the photocatalyst surface. For the anionic dye Congo Red, the highest efficiency was demonstrated by sample CS-8, which consists of higher valent a-MnOOH and y-/BMnO2. This sample has the narrowest band gap (1.99 eV) among all chemically synthesized samples. The further insight was made by analysis of the band gap potential diagrams of CS-series of samples and MO-diagram with HOMO and LUMO of a dye. It was revealed that CS-1,CS-2 samples have well aligned EC edges of HNTs, MnxOy and LUMO MB levels. It can be suggested that this feature is responsible for the positive influence of HNT’s surface decoration by MnxOy on photocatalytic activity of MB degradation due to new option of direct electron transfer of photoelectron from EC of both HNTs & MnxOy and following MB dye reduction. It is also evident from this diagram for CR dye that only CS-8 Sample has favorably aligned EV to HOMO level of CR dye and, probably, this feature can be responsible for the faster direct oxidation of CR by holes from the valence band of CS-8 as a photocatalyst. Thus, distinctly active behavioir of CS- 1&CS-2 photocatalysts toward MB degradation as well as CS-8 Sample high activity toward CR destruction can be explained by the semiconducting properties of these photocatalysts. According to the results obtained, it was proposed to apply the materials synthesized in this work for photodegradable coatings on PE surface, compared to their incorporation into the bulk of a film. A method of attaching nanomaterials onto polyethylene films through the partial dissolution of their surface has been developed. The introduction of 2.59% by mass of halloysite nanotubes was achieved when immersing the PE film in a suspension of HNTs in cyclohexane at 50°C for 120 s, and 2.51% at a suspension temperature of 60°C for 60 s. The decrease in the contact angle in the first case is more pronounced than in the second one. Considering the hydrophilic properties of halloysite, it can be assumed that treatment at 50°C leaves a greater amount of HNTs onto the surface, while at 60°C, the nanomaterial penetrates in-depth of the film. In addition, an adhesive composition was developed for applying nanomaterials to PE films without the need to dissolve polyethylene and heat. Polyvinylpyrrolidone was chosen as the base, polyethylene glycol was added as a plasticizer in a ratio of 7:1 by weight. The optimal ratios of solvent and polymer base for applying the composition to PE films using a spray and a sponge were determined. For the spray, they were 1 to 18, for the sponge - 1 to 15. Studies of decorated films using an optical microscope confirmed the uniform distribution of nanomaterial over the entire surface of the film using the developed compositions. A block diagram for the chemical synthesis of a composite material for further use as a photocatalyst for the degradation of aqueous solutions of organic pollutants (dyes) has been developed. The material balance for the synthesis of 1 kg of the sample was calculated and the heat of its formation was estimated. The practical significance is confirmed by the following. The developed methods for introducing photocatalysts into and onto polyethylene films are intended for practical use for the photodegradation of polymers. To achieve effective degradation, it is possible to coat an already manufactured film with composite materials with halloysite nanotubes and manganese oxides/oxydehydroxides. A promising candidate for such a coating, which is considered in this study, is a mechanical mixture of TiO2 and MnO2. Electrostatic interactions between metal ions and the HNT surface allow for controlled decoration of HNTs with deposited particles of Mn oxides and oxydehydroxides. This effect is especially relevant for the development of new functional materials in photocatalysis and catalysis. The study showed that composites CS-2 and CS-1 exhibit high activity in the photodegradation of methylene blue dye, while CS-8 and CS-9 effectively photodegrade Congo red. This opens up promising opportunities for practical application. A technology for the synthesis of manganese oxides and oxide-hydroxide photocatalytic material with halloysite CS-2 is proposed.