Janis Kleperis

In this work, three samples of primary aluminium dross were investigated and compared to construction aluminium waste. The composition was determined, and an evaluation of hydrogen generation via hydrolysis in a low-concentration alkali solution was performed. The composition revealed low to moderate aluminium content and the presence of various crystalline phases; hydrolysis reactions showed hydrogen generation’s direct dependence on the amount of aluminium present, which translated into variation in the volume per sample mass. It was found that the composition played a substantial role in the evolution of hydrogen and its purity, simultaneously indicating a possible opportunity for dross use in hydrogen generation and power production. It was revealed that, in addition to the expected hydrogen, methane was released from some dross samples during the hydrolysis reaction. To compare the reaction kinetics, the reaction rate was obtained using the spherical solid particle shrinking core model and compared with that of construction aluminium waste. Hydrogen generation was compared to that in the known literature, and the dependence on the sample composition was determined.

Photocatalytic degradation of pollutants have a high potential for sustainable and renewable uses. TiO₂ is a widely studied photocatalyst due to its high chemical and photochemical stability and wide range of applications. However, the wide band gap and low capacity of photo-induced charge separation provide lower catalytic activity; thus, improvement of these properties must be found. The doping of TiO₂ with other elements, such as carbon nanoparticles (CNP) in a quantum dot form, offers a promising pathway to improve the aforementioned properties. In addition, in situ doping methods should be investigated for practical scalability, as they offer the advantage of integrating dopants directly during material synthesis, ensuring a more uniform distribution and better interaction between the dopant and the host material, in turn leading to more consistent photocatalytic properties. Current technologies primarily involve nanoparticle combinations. This work focuses on the development of a novel in situ synthesis methodology by the introduction of three different graphene-based quantum nanodots into anodic TiO₂ and the following investigation of structural, morphological, and photocatalytic properties. Results indicate that the introduction of CNP allows for the shift of a set of parameters, such as the optical band gap, increased photo-induced charge carrier density of TiO₂/CNP composite, and, most importantly, the change of crystalline phase composition depending on added CNP material. Research indicates that not only a higher concentration of added CNP enhances higher photocatalytic activity as tested by the degradation of methylene blue dye, but also the type of CNP determines final crystalline phase. For the first time brookite and rutile phases were obtained in anodic titania synthesized in inorganic electrolyte by introducing hydrothermally treated exfoliated graphene.

This study investigates nitrogen-doped carbon synthesis and electrochemical properties as electrode material for energy storage devices, an additional focus of the work is on the electrochemical exfoliation synthesis of nitrogen-doped carbon using various precursors and doping methods. The physical properties of the synthesized sample are characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, and Raman spectroscopy. The electrochemical properties of the N-doped carbons are studied using cyclic voltammetry and galvanostatic charge-discharge cycling. Finally, the work explores the potential application of the N-doped carbons as electrode material for energy storage devices, such as supercapacitors. The results show that N-doped carbons exhibit electrochemical performance superior to that of graphene oxide, with higher electrical capacitance. The results demonstrate the potential of N-doped carbons as high-performance electrode materials for electrochemical energy storage applications. This paper aims to explain the advantages of N-doping in carbon materials more precisely in graphene and the use of these materials in creating electrodes for application in supercapacitors and batteries.

This study investigates the low-temperature hydrogen plasma treatment approach for the improvement of hydrogen generation through waste aluminum (Al) reactions with water and electricity generation via proton-exchange membrane fuel cell (PEM FC). Waste Al scraps were subjected to ball milling and treated using two different low-temperature plasma regimes: Diode and magnetron-initiated plasma treatment. Hydrolysis experiments were conducted using powders with different treatments, varying molarities, and reaction temperatures to assess hydrogen generation, reaction kinetics, and activation energy. The results indicate that magnetron-initiated plasma treatment significantly enhances the hydrolysis reaction kinetics compared to untreated powders or those treated with diode-generated plasma. Analysis of chemical bonds revealed that magnetron-initiated hydrogen plasma treatment takes advantage by promoting a dual procedure: Surface cleaning and Al nanocluster deposition on top of Al powders. Moreover, it was modeled that such H₂ plasma could penetrate up to 150 Å depth. Meanwhile, electricity generation tests demonstrate that only 0.2 g of treated Al powder can generate approximately 1 V for over 300 s under a constant 2.5 Ω load and 1.5 V for 2700 s with a spinning fan.

In this work various sample of primary aluminum dross were investigated for composition and evaluation of hydrogen generation via hydrolysis in low concentration alkali solution. Composi-tion revealed low to moderate aluminium content and hydrolysis reactions showed low hydrogen generation volumes per sample mass as well as purity, where composition plays substantial role in the hydrogen evolution, yet showing that there is possible place for dross use in hydrogen generation. It was revealed that some dross samples in addition to hydrogen also release methane via hydrolysis. Rection rate was obtained by the shrinking core model, written for spherical solid particles. Sample composition on hydrogen generation volume is compared to known literature.

It is shown that increase in the hydrogen production process efficiency can be ensured by integrating radiochemical and electrochemical processes. In this case, the obtained effect depends not only on the direct radiolysis of water, but also on the involvement of the ionizing radiation energy in the electrolysis process for the excitation of water molecules that undergo electrolysis, which leads to a decrease in the consumption of electricity for the decomposition of its gaseous components. An analysis of the main factors influencing the reduction of electricity consumption during electrolysis is presented, and the affinity of the spectra of radical ions involved in the radiation and electrochemical processes of water decomposition is shown. As a result of radiation exposure, the most energy-intensive stage of water decomposition, associated with the breaking of intermolecular bonds and the formation of active particles involved in the electrochemical process, begins. It was established that the formation of hydrogen increases due to the addition of its direct output during radiolysis and indirect production during electrolysis, initiated by the activation effects caused by ionizing radiation. It is shown that in order to increase the direct radiolytic yield of hydrogen, elements containing nanosized zirconium dioxide powder should be placed in the interelectrode space of the electrolyzer. It has also been proven that the irradiation of zirconium dioxide placed in water leads to a 4-fold increase in the yield of hydrogen compared to the option of irradiating pure water. To increase the energy potential utilization coefficient of nuclear fuel at NPPs, it is expedient to use the energy of fuel elements located in spent nuclear fuel storage pools for the application of the proposed technology. This will ensure the utilization of the ionizing radiation energy, which in existing technologies is irretrievably lost, because it is discharged in the form of low-temperature thermal emissions into the environment, which leads to thermal pollution of the atmosphere.

This work aims to explain aluminum hydrolysis reaction kinetics based on a properly chosen theoretical model with machined aluminum waste chips as well as alkali solutions up to 1M as a promoter and to estimate the overall reaction profit. The purpose of this work is to assess the optimal alkali concentration in the production of small- and medium-scale green hydrogen. To obtain results with better accuracy, we worked with flat Al waste chips, because a flat surface is preferable to maximally increase the time for the created hydrogen bubbles to reach the critical gas pressure. Describing the reaction kinetics, a flat shape allows for the use of a planar one-dimensional shrinking core model instead of a much more complicated polydisperse spheric shrinking core model. We analyzed the surface chemical reaction and mass transfer rate steps to obtain the first-order rate constant for the surface reaction and the diffusion coefficient of the aqueous reactant in the byproduct layer, respectively. We noted that measurements of the diffusion coefficient in the byproduct layer performed and discussed in this paper are rare to find in publications at alkali concentrations below 1M. With our reactor, we achieved a H₂ yield of 1145 mL per 1 g of Al with 1M NaOH, which is 92% of the theoretical maximum. In the estimation of profit, the authors’ novelty is in paying great attention to the loss in alkali and finding a crucial dependence on its price. Nevertheless, in terms of consumed and originated materials for sale, the conversion of aluminum waste material into green hydrogen with properly chosen reaction parameters has positive profit even when consuming an alkali of a chemical grade.

The present work aims to explain the aluminum hydrolysis reaction kinetics based on properly chosen theoretical model with machined aluminum waste chips and alkali solutions up to 1M as a promoter, and to estimate overall reaction profit. In order to obtain results of better accuracy, we work with flat Al waste chips because a flat surface is preferable to maximally increase the time for created hydrogen bubbles to reach the critical gas pressure. At describing the reaction kinetics, flat shape allows using a planar one-dimensional shrinking core model instead of much complicated polydisperse spheric shrinking core model. We analyze the surface chemical reaction and mass transfer rate steps to obtain the first order rate constant for surface reaction and the diffusion coefficient of aqueous reactant in the byproduct layer, respectively. With our reactor we achieved H2 yield of 1145 mL per 1 g Al with 1M NaOH, which is 92% of the theoretical maximum. At estimation of the profit, we pay much attention to the loss of alkaline and find a crucial dependence on its price. Nevertheless, in terms of consumed and originated materials for sale, conversion of the aluminum waste material into green hydrogen by properly chosen reaction parameters has a positive profit even by consuming alkali of chemical grade.