Milena Pijović Radovanović

In this study, a novel activated carbon (AC) (AC-Ba(OH)₂) was synthesized through a three-step process (including hydrothermal carbonization (at 250 °C), alkali activation by Ba(OH)₂, and pyrolysis (at 850 °C)), from Plane tree fruits (PTFs). By using various experimental methods for material characterization, it was established that the resulting material possesses a variety of oxygen functional groups, rich in alkaline earth oxides (BaO/CaO), SiO₂, consisting of graphitized carbon with graphene structures. A detailed kinetic and thermodynamic analysis of AC-Ba(OH)₂ thermal restoring was also carried out. Thermodynamic analysis revealed the existence of a true thermodynamic compensation effect (TCE) during restoration. Restoration was controlled by entropy, where experimental temperatures are above the iso-entropic temperature, i.e., the temperature where contributions of enthalpy and entropy to activation free energy are balanced. Kinetic modeling has shown that restoration allows carbon material to be significantly modified by removing oxygen-containing groups via diffusion, changing active sites on the surface, and preparing material for catalyst support. CaO and SiO₂ act as catalysts, while BaO alters graphene surface properties. Isothermal prediction tests have shown an extremely high long-term stability of modified AC-Ba(OH)₂, supporting an elevated activity, selectivity, and lifetime, as well. The restoring process resulted in an energy consumption of 0.762 kWh, which is equivalent to the reactivation of AC with a lower specific surface area. Manufactured AC and its thermally modified counterpart can be used as both a catalyst support and catalyst for reforming processes, such as methanol synthesis, biogas purification, and dry reforming of methane.

Apricot kernel shells were evaluated as a sustainable activated carbon precursor for wastewater treatment using experimental and theoretical methods. Two adsorbents were synthesized: physically activated with CO₂ (AKS-CO₂) and chemically activated with H₃PO₄ (AKS-H₃PO₄). Comprehensive materials characterization and adsorption tests using Pb²⁺ ions and Rhodamine B dye (RhB) as model pollutants revealed that AKS-H₃PO₄ significantly outperformed its physically activated counterpart. With an exceptionally high specific surface area (1159.4 m²/g) enriched with phosphorus-containing functional groups, the chemically activated carbon demonstrated outstanding removal efficiencies of 85.1% for Pb²⁺ and 80.3% for RhB. Kinetic studies showed Pb²⁺ adsorption followed pseudo-second-order kinetics, indicating chemisorption, while RhB adsorption fitted pseudo-first-order kinetics, suggesting intra-particle diffusion control. The thermodynamic analysis confirmed the spontaneity of both processes: Pb²⁺ adsorption was exothermic under standard conditions with positive isosteric heat at higher concentrations, reinforcing its chemisorption nature, whereas RhB adsorption was endothermic, consistent with physisorption. Density Functional Theory (DFT) calculations further elucidated the mechanisms, revealing that Pb²⁺ preferentially binds to oxygen-containing functional groups, while RhB interacts through hydrogen bonding and π–π stacking. These findings establish chemically activated apricot kernel shell carbon as a high-performance adsorbent, exhibiting exceptional removal capacity for both ionic and molecular contaminants through distinct adsorption mechanisms.

This study addresses the crucial role of oxygen reduction reaction (ORR) in enhancing the performance of fuel cells and metal-air batteries, vital to the advancement of green energy technologies. The primary challenge with ORR lies in its inherently slow kinetics, which necessitates the development of efficient and stable electrocatalysts. Our research introduces a novel, low-cost bifunctional carbon-based electrocatalyst, dual-doped with selenium (Se) and vanadium (V), synthesized through a straightforward direct carbonization mixtures of 1-butyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide with Se and V. This method proves effective in reducing overpotential and enhancing ORR kinetics, demonstrating significant promise for improving the efficacy of renewable energy technologies.

This paper explores the feasibility and efficacy of employing whole CPU (Central Processing Unit) recycling as a sustainable source of metals for catalyst coatings in the Hydrogen Evolution Reaction (HER). With the escalating global issue of electronic waste (e-waste), repurposing discarded CPUs offers a promising avenue for metal recovery and utilization. Through systematic experimentation, CPU preparation technique was evaluated for formation of electrode catalytic layer and the kinetics of HER in alkaline media. The resulting electrodeposited cathode was assessed for electrocatalytic efficiency. Our findings highlight the potential of utilizing e-waste-derived metals, particularly gold and copper, as effective catalyst coatings for HER, thus contributing to sustainable metal recovery and utilization strategies.

Thermo-chemical conversion of cigarette butt filters (CBFs) waste was investigated using various thermal analysis techniques (simultaneous TG-DTG-DTA and DSC methods) at different heating rates in an inert atmosphere. Thermo- and thermophysical properties of waste material were discussed, from the point of view of chemical structure and the influence of experimental parameters on the conversion process. It was established that acetyl groups of plasticizer (triacetin, TAC) interact with cellulose acetate (CAc) through dipolar interactions and hydrogen bonding’s. Influence of these polar interactions can affect the position of glass transition temperature (Tg) of CBF. Based on estimated value of Tg from DSC analysis, it was found that CAc present in CBF has degree of substitution (DS) equals to 2.8 (DS = 2.8), where the presence of cellulose triacetate (CTA) was confirmed. It was assumed that an increase of DS leads to decline in the crystallinity. A decline of crystallinity causes the reduction of hydroxyl groups, leading to less organized chains, and whereby decreasing of inter-molecular interactions through hydrogen bonding. Based on the examination of thermophysical characteristics of the tested material, it was found that both, the heat capacity and the thermal inertia (TI) of material linearly increase with temperature, during pyrolysis progression. It was concluded that the type of bio-char produced in this process would have a large capacity to store the heat, which may depend on the formed particles size diameter and porosity. Furthermore, it was inferred that magnitude drops of thermal conductivity (κ) after Tg depends on the material fibrillation.