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Item Thermal Properties and Microstructure Evolution of the as‑cast and Annealed Al–Cu–Si Eutectic Alloy(Springer Nature, 2025) Manasijević, Dragan; Marković, Ivana; Cimpoesu, Nicanor; Chelariu, Romeu; Stamenković, Uroš; Balanović, Ljubiša; Gorgievski, MilanThe Al–28%Cu–6%Si (mass%) eutectic alloy represents a possible high-temperature phase change material (PCM) for latent heat thermal energy storage (LHTES). In this paper, its microstructural characteristics and thermal properties were examined in the as-cast and annealed conditions using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), and light flash method. The microstructure of the studied alloy consists of (Al) solid solution phase, θ-Al2Cu intermetallic phase, and (Si) phase. The annealing at 450°C for 50 h led to significant changes in the morphology of the θ-Al2Cu and (Si) eutectic phases. The temperature dependences of thermal diffusivity and thermal conductivity were investigated within the temperature range from 25 to 400 °C. It was found that the thermal diffusivity and thermal conductivity of the annealed alloy are considerably higher than that of the as-cast alloy at temperatures lower than 300 °C. With increasing temperature, due to changes in the microstructure of the as-cast alloy, these differences decrease and finally diminish at 400 °C. The measured eutectic temperature is 522.3 °C and latent heat of melting is 358.3 Jg-1. The findings suggest that the Al–Cu–Si eutectic alloy shows good potential for use in phase change energy storage technologies.Item Enhancing Wastewater Treatment Through Python ANN-Guided Optimization of Photocatalysis with Boron-Doped ZnO Synthesized via Mechanochemical Route(MDPI, 2025) Nedelkovski, Vladan; Radovanović, Milan B.; Medić, Dragana; Stanković, Sonja; Hulka, Iosif; Tanikić, Dejan; Antonijević, MilanThis study explores the enhanced photocatalytic performance of boron-doped zinc oxide (ZnO) nanoparticles synthesized via a scalable mechanochemical route. Utilizing X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), the structural and morphological properties of these nanoparticles were assessed. Specifically, nanoparticles with 1 wt%, 2.5 wt%, and 5 wt% boron doping were analyzed after calcination at temperatures of 500 °C, 600 °C, and 700 °C. The obtained results indicate that 1 wt% B-ZnO nanoparticles calcined at 700 °C show superior photocatalytic efficiency of 99.94% methyl orange degradation under UVA light—a significant improvement over undoped ZnO. Furthermore, the study introduces a predictive model using the artificial neural network (ANN) technique, developed in Python, which effectively forecasts photocatalytic performance based on experimental conditions with R2 = 0.9810. This could further enhance wastewater treatment processes, such as heterogeneous photocatalysis, through ANN-guided optimization.Item Application of Graphite Electrodes Prepared from Waste Zinc−Carbon Batteries for Electrochemical Detection of Xanthine(MDPI, 2025) Radovanović, Milan B.; Simonović, Ana T.; Petrović Mihajlović, Marija B.; Tasić, Žaklina Z.; Antonijević, Milan M.Waste from zinc−carbon batteries poses a serious environmental protection problem. One of the main problems is also the reliable and rapid determination of some compounds that may be present in food and beverages consumed worldwide. This study addresses these problems and presents a possible solution for the electrochemical detection of xanthine using carbon from spent batteries. Cyclic voltammetry and differential pulse voltammetry are electrochemical methods used for the detection of xanthine. The techniques used demonstrate the mechanism of xanthine oxidation in the tested environment. A linear correlation was found between the oxidation current peaks and the xanthine concentration in the range of 5·10−7 to 1·10−4 M, as well as the values for the limit of detection and the limit of quantification, 7.86·10−8 M and 2.62·10−7 M, respectively. The interference test shows that the electrode obtained from waste Zn-C batteries has good selectivity, which means that the electrode can be used for xanthine determination in the presence of various ions. The data obtained show that carbon sensors from used zinc−carbon batteries can be used to detect xanthine in real samples.Item Electrochemical Detection of Cadmium Using a Bismuth Film Deposited on a Brass Electrode(MDPI, 2025) Radovanović, Milan B.; Petrović Mihajlović, Marija B.; Simonović, Ana T.; Tasić, Žaklina; Antonijević, Milan M.Cadmium is one of the most dangerous pollutants found in the environment, where it exists mainly due to human activities. High cadmium concentrations can cause serious problems, which is why the detection and determination of Cd is one of the most important tasks. Electroanalytical methods provide rapid and accurate results in the detection of cadmium in various solutions. In this study, the possibility of using a bismuth film electrode deposited on a brass surface and electroanalytical techniques for the detection of cadmium is investigated. The bismuth film was deposited on the surface of the brass electrode using a chronoamperometric technique. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the synthesized bismuth film electrode. The current peaks obtained by anodic square-wave stripping voltammetry under optimized conditions showed a linear relationship in the investigated concentration range of cadmium. The study of the interference of different cations (Cr3+, Mn2+, Zn2+, Ca2+, K+, Mg2+ and Na+) showed that the tested cations have no influence on the determination of Cd2+ ions in the investigated solution. This finding provides a good opportunity for the use of the synthesized electrode in real samples.Item Simultaneous determination of serotonin, dopamine, and ascorbic acid at a glassy carbon electrode modified with chitosan-alginate hydrogel and reduced graphene oxide(Elsevier, 2025) Postolović, Katarina S.; Radovanović, Milan B.; Stanić, Zorka D.Detection of biologically active components, such as ascorbic acid, dopamine, and serotonin, is significant from the perspective of biomedicine, particularly in the process of disease diagnosis and in the quality control of commercial pharmaceutical products. In this work, a novel electrochemical sensor was developed by modifying a glassy carbon electrode with a hydrogel composed of a polyelectrolyte complex of alginate and chitosan, along with the addition of electrochemically reduced graphene oxide. This biocompatible sensor was applied for the simultaneous determination of ascorbic acid, dopamine, and serotonin using adsorptive square wave voltammetry. The modified GCE demonstrated an excellent electrochemical response towards the target analytes, thanks to the enhanced adsorption of the analytes on the surface of the electrode, facilitated by favorable interactions between analytes and the modifiers. This approach increased the electrode’s active surface area and ensured excellent electrode response. The sensor exhibited a broad linear range of the anodic current relative to analyte concentration, achieving low detection limits of 0.094 μM, 4.18 nM and 3.23 nM for ascorbic acid, dopamine and serotonin, respectively. Additionally, the proposed sensor exhibited good stability, reproducibility of results, selectivity, as well as effectiveness, in the determination of target biological compounds in real sample matrices.Item Wetting behavior of Sn-Bi solder alloy and composites obtained by powder metallurgy(Fakultet Tehničkih nauka, Kosovska Mitrovica, 2025) Stamenković, Uroš; Marković, Ivana; Nedeljković, Milan; Božinović, KristinaThis study examined the wetting behavior of solders composed of tin-bismuth (SnBi) alloys and their composites. To produce the SnBi12 (wt. %) alloy, pure powders of tin (Sn) and bismuth (Bi) were used. After that, the composites were produced by adding 0.2 wt.% of graphite (C) and boron carbide (B4C) to the SnBi12 alloy. The alloys and composites were fabricated using a powder metallurgy technique. Initially, the powders were weighed in specific ratios to create the SnBi12 matrix powder. After this, 0.2 wt.% of C and B4C were added to the matrix powder. The mixing was done using a three-axis mixer at a speed of 50 rpm for 4 hours. The mixed powders were then mechanically stirred in a ball mill at a speed of 150 rpm for 2 hours. Following this, the powders were compacted with a hydraulic press, and the samples were sintered in an inert argon atmosphere at a temperature of 185 °C for 3 hours. For the wetting behavior investigation, the copper plates were polished and cleaned in acetone. Small samples weighing 0.1 grams were taken from the sintered samples and placed on copper plates along with 0.02 grams of flux RMA218. These copper plates were then heated to 250 °C for 20 seconds to initiate the soldering. After cooling, the solders were cleaned with acetone, photographed, and cut to examine their cross-sections under an optical microscope. The contact angle and spreading area were measured using ImageJ software. The results indicate that the pure tin sample exhibited the highest wetting angle. The addition of bismuth to form the tin-bismuth alloy reduced the wetting angle by approximately 20%. Furthermore, when reinforcements of carbon (C) and boron carbide (B4C) were added, the wetting angles increased slightly but remained lower than that of the pure tin sample. The surface area values mirrored the trends observed in the wetting angles: as the wetting angles decreased, the surface areas increased, and vice versa.Item Melting temperatures and thermal properties of Sn-Bi alloys and composites(Fakultet Tehničkih nauka, Kosovska Mitrovica, 2025) Stamenković, Uroš; Marković, Ivana; Manasijević, Dragan; Ćosović, Vladan; Gorgievski, Milan; Kovačević, Avram; Nedeljković, Milan; Minić, DuškoThis study investigates the melting temperatures and thermal properties of tin-bismuth (Sn-Bi) alloys and their composites. The investigation involved the preparation of pure tin, two alloys (SnBi12 and SnBi21, by weight percentage), and two composites (SnBi12 + 0.2 wt.% Cu and SnBi12 + 0.2 wt.% C) through casting. The pure metals were melted in a graphite crucible at 400 °C for 20 minutes, followed by mechanical stirring. During stirring, 0.2 wt.% of pure carbon powder (with a particle size of less than 45 µm) and pure copper powder (also with a particle size of less than 45 µm) were added separately to the SnBi12 melt to create the two different composites. After melting and stirring, the mixture was cast in a steel mold. Samples were extracted from the cast ingots for differential thermal analysis (DTA) to determine the melting temperatures of the investigated samples. Additionally, samples were prepared to assess thermal diffusivity, thermal conductivity, and specific heat using the Xenon flash method at room temperature. The DTA analysis revealed that the melting temperature was the highest for the pure tin sample. The addition of bismuth reduced the melting temperature from 237.43 °C for pure tin to 222.59 °C for SnBi12 and 211.35 °C for SnBi21. The melting temperatures of the SnBi12 + Cu and SnBi12 + C composites were nearly identical to that of the SnBi12 alloy, indicating that the dispersed particles did not influence the melting temperature. Furthermore, thermal diffusivity, thermal conductivity, and specific heat values were lower for the alloys compared to those of the pure tin sample. The composites also exhibited lower thermal diffusivity and thermal conductivity values compared to the SnBi12 alloy. In conclusion, bismuth affects both the melting temperature and the thermal properties of Sn-Bi alloys, while Sn-Bi composites influence thermal properties without affecting the melting temperature of Sn-Bi alloys.Item Chemometric Evaluation of 16 Priority PAHs in Soil and Roots of Syringa vulgaris and Ficus carica from the Bor Region (Serbia): An Insight into the Natural Plant Potential for Soil Phytomonitoring and Phytoremediation(MDPI, 2025) Papludis, Aleksandra D.; Alagić, Slađana Č.; Milić, Snežana M.; Nikolić, Jelena S.; Jevtović, Snežana Č.; Stankov Jovanović, Vesna P.; Stojanović, Gordana S.; Gianniantonio PetruzzelliThe soil phytomonitoring and phytostabilization potential of Syringa vulgaris and Ficus carica was evaluated regarding 16 priority polycyclic aromatic hydrocarbons (PAHs) using a chemometric approach and the calculation of bioconcentration factors (BCFs) for each individual PAH in plants’ roots from each selected location in the Bor region. PAHs in roots and the corresponding soils were analyzed using the QuEChERS (Quick, Effective, Cheap, Easy, Rugged, Safe) method with some new modifications, gas chromatography/mass spectrometry, Pearson’s correlation study, hierarchical cluster analysis, and BCFs. Several central conclusions are as follows: Each plant species developed its own specific capability for PAH management, and root concentrations ranged from not detected (for several compounds) to 5592 μg/kg (for fluorene in S. vulgaris). In some cases, especially regarding benzo(a)pyrene and chrysene, both plants had a similar tactic—the total avoidance of assimilation (probably due to their high toxicity). Both plants retained significant quantities of different PAHs in their roots (many calculated BCFs were higher than 1 or were even extremely high), which recommends them for PAH phytostabilization (especially fluorene, benzo(b)fluoranthene, and benzo(k)fluoranthene). In soil monitoring, neither of the plants are helpful because their roots do not reflect the actual situation found in soil. Finally, the analysis of the corresponding soils provided useful monitoring information.Item Change in pH and conductivity during the rinsing and the biosorption of copper ions onto pumpkin peel(University of Zenica, Faculty of Metallurgy and Technology, 2025) Marković, Marina; Gorgievski, Milan; Marković, Miljan; Grekulović, Vesna; Štrbac, Nada; Zdravković, Milica; Božinović, KristinaThe changes in pH and conductivity during the rinsing of the pumpkin peel, and the biosorption of Cu2+ ions, were the subject of this work. The obtained data showed that the pH value of the solutions increased during the rinsing of the biosorbent, as a result of the transfer of H+ ions from the aqueous phase into the structure of the pumpkin peel. An increase in the conductivity value was observed in the initial period of rinsing the pumpkin peel, followed by a decrease. The increase in conductivity in the initial phase contributed to the self-leaching of the alkali and alkaline earth metal ions from the structure of the pumpkin peel, which were transferred into the aqueous phase. The further decrease in conductivity is a result of the dilution of the aqueous phase. The pH value decreased during the biosorption of Cu2+ ions, as hydrogen ions were transferred from the pumpkin peel structure into the solution, and then exchanged with Cu2+ ions. The conductivity value increased during the biosorption process, with a rapid increase in the initial period of 5 minutes, due to the transfer of alkali and alkaline earth metal ions into the solution.Item Characterization of electrode materials from spent batteries in the process of recovering valuable metals(University of Belgrade, Technical Faculty in Bor, 2025) Medić, Dragana; Nujkić, Maja; Tasić, Žaklina; Nedelkovski, Vladan; Đorđievski, Stefan; Alagić, Slađana; Milić, SnežanaThe chemical and phase analysis of electrode materials from spent batteries is essential for identifying recyclable components and optimizing metal recovery processes. In this study, the electrode material from a spent cell of an unknown manufacturer was analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and powder X-ray diffraction (XRD). XRD results revealed that the anode material consists of three crystalline phases: NiO, LaCoO3, and CeO₂, while the cathode material contains Ni(OH)₂ and Ni. ICP-MS analysis confirmed the presence of lanthanides in the anode material. Given that lanthanide deposits are concentrated in only a few countries, their recovery from spent batteries presents an opportunity for nations without natural reserves to secure their supply through recycling. This study highlights the potential for sustainable resource management by recovering metals from electronic waste.Item Raspberry and blackberry grown in Serbia from the aspect of the green agenda(Naučno-stručno Društvo za zaštitu životne sredine Srbije ECOLOGICA, 2024) Zdravković, Milica; Grekulović, Vesna; Štrbac, Nada; Zdravković, Bojan; Gorgievski, Milan; Marković, Miljan; Marković, MarinaSerbia is one of the leading countries in the world in terms of raspberry and blackberry production. Production is focused on the cultivation of raspberries and blackberries for the purpose of the fruit selling, so large amounts of leaves of these two plants remain unused on plantations or are burned. In tradicional medicine, the healing effects of raspberry leaves and blackberry leaves are known, but due to the large production, it is impossible to use all the leaves for these purposes. Newer research indicates numerous possibilities of application of raspberry leaves and blackberry leaves. An important aspect is the use of raspberries and blackberries that grow near the mine. In addition to being used in medicine and pharmacy, extracts can be used as metal corrosion inhibitors. Depleted plant mass that can be used for biosorption, as a binding agent and starting component of cellulose production. Obtaining the extract instead of burning the leaves fulfills the first condition of the Green Agenda, which is decarbonization and reduction of industrial emissions. Environmental pollution is reduced with a focus on air quality. Better energy efficiency is achieved by an adequate selection of extragens. The circular economy is achieved by a system in which production resources (fruit and leaves) are encouraged, and waste, waste emission and energy outflow are significantly reduced. In addition to encouraging the economy and sustainable plant food systems that are characteristic of the Western Balkans, protection and investment in ecosystems is achieved.Item Malina i kupina gajene u Srbiji sa aspekta Zelene agende(Naučno-stručno Društvo za zaštitu životne sredine Srbije ECOLOGICA, 2024) Zdravković, Milica; Grekulović, Vesna; Štrbac, Nada; Zdravković, Bojan; Gorgievski, Milan; Marković, Miljan; Marković, MarinaSrbija je jedna od vodećih zemalja u svetu po proizvodnji maline i kupine. Proizvodnja je usmerena na gajenje maline i kupine radi prodaje ploda, pa velike količine lista ove dve biljke ostaju neiskorišćene na plantažama ili bivaju spaljene. U narodnoj medicini je poznato lekovito dejstvo lista maline i lista kupine, ali je zbog velike proizvodnje nemoguće iskorititi svu količinu listova u ove svrhe. Novija istraživanja ukazuju na brojne mogućnosti primene lista maline i lista kupine. Važan aspekt predstavlja upotreba maline i kupine koja raste u blizini rudnika. Pored upotrebe u medicini i farmaciji ekstrakti se mogu koristiti kao inhibitori korozije metala. Osiromašena biljna masa se može primeniti za biosorpciju, kao vezivno sredstvo i polazna komponenta proizvodnje celuloze. Dobijanjem ekstrakta umesto spaljivanja listova ispunjava se prvi uslov Zelene agende, a to je dekarbonizacija i smanjenje industrijskih emisija. Smanjuje se zagađenje životne sredine sa fokusom na kvalitet vazduha. Adekvatnim izborom ekstragensa postiže se bolja energetska efikasnost. Cirkularna ekonomija se postiže sistemom u okviru kojeg se podstiču proizvodni resursi (plod i list), a otpad, emisija otpada i energetski odliv bitno umanjuju. Pored podsticanja privrede i održivih prehrambenih sistema biljaka koje su karakteristične za Zapadni Balkan, postiže se zaštita i investiranje u ekosisteme.Item Application of AI in environmental protection: corrosion and biosorption(Naučno-stručno Društvo za zaštitu životne sredine Srbije ECOLOGICA, 2025) Zdravković, Milica; Marković, Miljan; Marković, Marina; Grekulović, Vesna; Gorgievski, Milan; Štrbac, Nada; Božinović, KristinaArtificial intelligence (AI) plays an important role in the field of scientific research. This paper aims to review the application of AI in corrosion and biosorption. The use of AI can advance the research process in terms of prediction, environmental and cost management, optimization and determination of the influence of parameters. Corrosion is a highly complex process that depends on many factors. Studying the interaction of these factors using AI enables better corrosion control. By applying AI, it is possible to determine the diverse influence of factors under real conditions using the database of numerous researches. In addition to the prevention and monitoring of corrosion and biosorption processes, it is important to focus the application of AI on environmentally friendly methods and chemicals. In this way, it is possible to identify compounds and materials of natural origin that can serve as substitutes for toxic compounds for corrosion protection or heavy metal removal. The importance of using non-destructive methods and monitoring data in real time is particularly emphasized, in order to avoid statistical errors. Optimization with the RSM method for corrosion and biosorption processes is widely used, determining process parameters where the best effect of corrosion protection and biosorption is achieved.Item White willow bark extract as a copper corrosion inhibitor in 0.5 M NaCl solution(University of Split, Faculty of Chemistry and Technology, 2025) Zdravković, Milica; Grekulović, Vesna; Štrbac, Nada; Huseinović, Edina; Gorgievski, Milan; Marković, Miljan; Božinović, KristinaCorrosion can generally be defined as the degradation of materials in a reaction between the material and its environment.1 Due to its corrosive effects, the corrosion of copper and its alloys in chloride-containing media has been widely studied.2 Copper Cu-DHP is phosphorus-oxygen-free copper that does not contain arsenic and is mainly used for the manufacture of piping, construction, and appliances.3 The study of white willow bark extract (WWBE) on the corrosion process of Cu-DHP in a 0.5 M NaCl solution was carried out using a non-destructive electrochemical method of electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS). The 0.5 M NaCl solutions without and with the addition of WWBE (0.1-0.5 g/L) were used as electrolytes. The 0.5 M NaCl solution with the addition of 0.5 g/L WWBE, without and with a copper plate was analyzed by ultraviolet-visible spectroscopy (UV-VIS). The white willow bark extract was prepared by evaporating the aqueous extract obtained by extracting dry white willow bark, with distilled water. The experiments were carried out at room temperature. The EFM results show that WWBE acts as a cathodic copper corrosion inhibitor.4 The highest value for the inhibition efficiency was obtained in the 0.5 M NaCl solution with 0.5 g/L WWBE. The Bode and Nyquist diagrams were created based on the EIS results. The results were fitted using an electrochemical equivalent circuit. The Nyquist diagram shows imperfect semicircles due to frequency dispersion.5 A linear line corresponding to the Warburg coefficient was found.4 An increase in the phase angle in the Bode plot in the presence of WWBE indicates the formation of a protective inhibitor film. The calculated values show that the corrosion process is diffusion-controlled without and with the addition of WWBE. Both electrochemical methods show that WWBE is adsorbed on the copper surface in 0.5 M NaCl solution by physisorption according to the Langmuir adsorption isotherm4. The Gibbs free energy values of adsorption are similar for EFM and EIS. The UV-VIS results show that immersion of copper in an electrolyte containing 0.5 g/L WWBE for 24 hours leads to a change in the absorbance maximum, indicating the presence of a copper-WWBE complex.6Item UV-VIS identification of copper complexes with inhibitor organic components in the electrolyte(University of Belgrade, Technical Faculty in Bor, 2025) Zdravković, Milica; Grekulović, Vesna; Huseinović, Edina; Vianello, Robert; Štrbac, Nada; Huremovic, Melita; Gorgievski, MilanThe UV-VIS method is an effective, non-destructive method that enables a better understanding of the electrolyte during corrosion. The aim of the study presented in this paper is to determine the existence of an organometallic complex in a 0.5 M NaCl solution with the addition of Rubus fruticosus L. leaf extract (RFLE). The experiments were conducted in a 0.5 M NaCl solution with the addition of RFLE (5 g/L and 10 g/L) with and without the immersion of a copper coupon. The results show that after the copper coupon standing in the electrolyte, there is a change in the absorbance maximum in the solution with 5 g/L RFLE, while no change is observed in the solution with 10 g/L RFLE. Such a change indicates the existence of a copper-RFLE complex in the solution with lower inhibitor concentration. In the case of RFLE, forming a copper complex with caffeic acid, isoquercetin and astragalin is possible. The absence of the complex at a concentration of 10 g/L RFLE can be attributed to a change in the mechanism and the lack of copper ions in the solution due to adequate corrosion protection.Item Application of AI in Environmental Protection: Corrosion and Biosorption(Naučno-stručno Društvo za zaštitu životne sredine Srbije ECOLOGICA, 2025) Zdravković, Milica; Marković, Miljan; Marković, Marina; Grekulović, Vesna; Gorgievski, Milan; Štrbac, Nada; Božinović, KristinaArtificial intelligence (AI) plays an important role in the field of scientific research. This paper aims to review theapplication of AI in corrosion and biosorption. The use of AI can advance the research process in terms of prediction,environmental and cost management, optimization and determination of the influence of parameters. Corrosion is a highlycomplex process that depends on many factors. Studying the interaction of these factors using AI enables better corrosioncontrol. By applying AI, it is possible to determine the diverse influence of factors under real conditions using the databaseof numerous researches. In addition to the prevention and monitoring of corrosion and biosorption processes, it is importantto focus the application of AI on environmentally friendly methods and chemicals. In this way, it is possible to identifycompounds and materials of natural origin that can serve as substitutes for toxic compounds for corrosion protection orheavy metal removal. The importance of using non-destructive methods and monitoring data in real time is particularlyemphasized, in order to avoid statistical errors. Optimization with the RSM method for corrosion and biosorption processesis widely used, determining process parameters where the best effect of corrosion protection and biosorption is achieve.Item Change in pH and conductivity during the rinsing and the biosorption of copper ions onto pumpkin peel(Univerzitet u Zenici, Fakultet inženjerstva i prirodnih nauka, 2025) Marković, Marina; Gorgievski, Milan; Marković, Miljan; Grekulović, Vesna; Štrbac, Nada; Zdravković, Milica; Božinović, KristinaThe changes in pH and conductivity during the rinsing of the pumpkin peel, and the biosorption of Cu2+ ions, were the subject of this work. The obtained data showed that the pH value of the solutions increased during the rinsing of the biosorbent, as a result of the transfer of H+ ions from the aqueous phase into the structure of the pumpkin peel. An increase in the conductivity value was observed in the initial period of rinsing the pumpkin peel, followed by a decrease. The increase in conductivity in the initial phase is contributed to the self-leaching of the alkali and alkaline earth metal ions from the structure of the pumpkin peel, which were transferred into the aqueous phase. The further decrease in conductivity is a result of the dilution of the aqueous phase. The pH value decreased during the biosorption of Cu2+ ions, as hydrogen ions were transferred from the pumpkin peel structure into the solution, and then exchanged with Cu2+ ions. The conductivity value increased during the biosorption process, with a rapid increase in the initial period of 5 minutes, due to the transfer of alkali and alkaline earth metal ions into the solution.Item DTA-TGA and thermodynamic studies of walnut shells used for the biosorption of Cu2+ ions from synthetic solutions(Fakultet Tehničkih nauka, Kosovska Mitrovica, 2025) Marković, Marina; Gorgievski, Milan; Marković, Miljan; Štrbac, Nada; Grekulović, Vesna; Zdravković, Milica; Milošević, NemanjaBiosorption is a simple, economical and environmentally friendly process of removing pollutants by binding them to biological material [1]. Biological materials that can be used to remove or recover organic and inorganic substances from aqueous solutions include living or dead microorganisms and their components, seaweed, plant material, industrial and agricultural waste and natural residues [2]. In this paper, the thermodynamic analysis of the biosorption of copper ions on walnut shells, as well as the DTA-TGA analysis of walnut shells, are presented. Thermogravimetry was used to study the thermal degradation characteristics of walnut shells. The sample was heated in an inert atmosphere from 20 to 900 oC, using a simultaneous DSC-TGA device SDT Q600 (TA Instruments). The TGA curve showed two stages of weight loss during heating. In the interval from 20 to 150 oC, a weight loss of 6.64% was recorded, which was due to the evaporation of moisture from the sample. Further weight loss of 69.05% was observed in the temperature range from 150 to 900 oC, which was due to the decomposition of hemicellulose, cellulose and lignin present in the biosorbent structure [3]. The DTA curve showed that the process was accompanied by an endothermic peak at a temperature of 279.81 oC. The total weight loss was 75.69%. Thermodynamic studies are conducted to investigate the influence of temperature on the biosorption process and to obtain information about the feasibility, spontaneity and nature of the process [4]. Therefore, thermodynamic parameters such as the change in Gibbs free energy (ΔG0), the change in enthalpy (ΔH0) and the change in entropy (ΔS0) were determined. In order to determine the thermodynamic parameters, 0.5 g of walnut shells were brought into contact with 50 mL of a synthetic solution of copper ions with a concentration of 0.2 g L-1, at different temperatures (25 oC, 35 oC and 40 oC). The obtained results for the change in Gibbs free energy (ΔG0 ) were negative at all three temperatures, indicating the feasibility of the process and spontaneous nature of the biosorption. The obtained positive value of enthalpy (ΔH0 = 1.12 kJ mol-1) indicates that the biosorption reaction is endothermic and consequently consumes energy. The negative value of entropy (ΔS0 = -6.26 J mol-1 K-1) indicates that there is less randomness at the interface between solid and solution.Item Al-Sn alloys as composite phase change materials for thermal energy storage: microstructural and thermal characterization(Fakultet Tehničkih nauka, Kosovska Mitrovica, 2025) Manasijević, Dragan; Balanović, Ljubiša; Marković, Ivana; Gorgievski, Milan; Stamenković, Uroš; Kovacević, AvramAl–Sn alloys are well known for their excellent resistance to wear and corrosion, as well as their solid mechanical performance, making them popular choices for bearing applications [1,2]. More recently, however, they have attracted attention as potential composite phase change materials (C-PCMs) for thermal energy storage (TES) systems. To determine their suitability for such applications, a thorough investigation of their thermal characteristics is essential. In this study, Al–Sn alloys containing 11.7, 22.4, 32.8, 41.1, and 53.4 atomic percent Sn were prepared by melting high-purity metals. Continuous stirring of the melt was employed to prevent segregation, followed by casting into stainless steel molds. The resulting ingots displayed uniform microstructures, free of cracks and pores. Thermal diffusivity of the solid Al–Sn samples was measured between 25°C and 150°C using the light flash method. Density at room temperature was determined via the Archimedes principle, while specific heat capacities across different temperatures were calculated using the CALPHAD (Calculation of Phase Diagrams) approach. Thermal conductivity values were then derived using an appropriate conversion relationship. Additionally, phase transition temperatures and the associated thermal effects were analyzed by differential scanning calorimetry (DSC). The study mapped how thermal conductivity changes with both alloy composition and temperature, and also assessed how latent heat of fusion varies across the compositions. Microstructural and phase composition analyses were performed using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS). The findings offer valuable insights into the thermal behavior and microstructural characteristics of Al–Sn alloys, contributing to the development of advanced PCMs for thermal energy storage applications.Item Kinetic and DTA-TGA analysis of Cu2+ biosorption on hazelnut shells(Fakultet Tehničkih nauka, Kosovska Mitrovica, 2025) Gorgievski, Milan; Marković, Miljan; Štrbać, Nada; Manasijević, Dragan; Grekulović, Vesna; Jovanović, Dalibor; Marković, MarinaBiosorption can be defined as the ability of biomaterials to accumulate and concentrate heavy metals from even the most dilute aqueous solutions. The biosorption process involves a solid phase (biological material) and a liquid phase (solvent, usually water) containing the dissolved metal. [1]. In this work, hazelnut shells were used as biosorbents for the biosorption of Cu2+ ions from synthetic solutions. This paper presents the results of kinetic and DTA-TGA analysis of the biosorption of Cu2+ ions on hazelnut shells. A pseudo-first order kinetic model, a pseudo-second order kinetic model, an intraparticle diffusion kinetic model and an Elovich kinetic model were used to describe the kinetics of biosorption of Cu2+ ions with hazelnut shells. The change in the adsorption capacity of copper ions with time was determined by contacting a series of solutions of copper ions with an initial concentration of 0.2 g dm-3 with 0.5 g of the sample for different contact times. Biosorption was terminated after 90 minutes, assuming that this time was long enough to establish equilibrium in the system [2]. It can be seen from Fig. 1a that at the beginning of the process (in the first 10 minutes) the adsorption capacity increases sharply with the contact time. The sudden increase in capacity in the first 10 minutes of the process is due to the large number of active sites available on the surface of the adsorbent. Thereafter, until the end of the experiment, a slight increase in adsorption capacity can be observed, which is due to the decrease in available active sites and the decrease in the concentration of copper ions in the solution [3]. The pseudo-second order kinetic model, with the correlation coefficient R2 = 0.961, showed the best agreement with the experimental data. Based on this model it can be concluded that chemisorption is a possible binding mechanism of copper ions on the surface of hazelnut shells [4].