Charikleia Prochaska

The structural and surface characteristics of supported heterogeneous catalysts were investigated using a combination of nitrogen adsorption-desorption porosimetry and Atomic Force Microscopy (AFM). A Au/γ-Al₂O₃ catalyst was characterized in terms of specific surface area, pore size distribution, surface morphology and roughness. Nitrogen adsorption measurements revealed type IV isotherms, confirming their mesoporous nature. The Au/γ-Al₂O₃ catalyst exhibited a BET surface area of 266 m² g⁻¹ and a dominant mesopore size distribution centred approximately within the 9–13 nm range. AFM imaging was employed to investigate the nanoscale surface topography and revealed a heterogeneous surface. Quantitative image analysis was further performed using threshold segmentation and grain analysis to identify nanoscale topographical depressions and surface features. A total of 2539 surface features were detected, corresponding to a planar surface fraction of 6.71%. Characteristic lateral dimensions of surface features derived from the image analysis were found to be in the range of approximately 9–12 nm, indicating that these can be correlated with pores since they bear similar dimensions to the latter (as estimated by porosimetry). Statistical validation using Student’s t-test demonstrated good agreement between local measurements obtained from representative scan lines and the overall image-based analysis. Surface roughness measurements yielded average roughness (Ra) and root mean square roughness (Rq) values of 2.06 ± 1.90 nm and 3.42 ± 1.91 nm, respectively, indicating a moderately rough nanostructured surface. The characteristic dimensions of the AFM-derived surface features were found to be consistent with the mesopore size range determined independently by nitrogen adsorption but they do not directly represent internal pores. AFM probes only the external surface morphology and does not directly characterise the internal pore network. The combined approach demonstrates that AFM image analysis can provide valuable complementary information on catalyst surface morphology, roughness and nanoscale textural features alongside conventional gas adsorption techniques.

Antimony (Sb) contamination in groundwater, drinking water, and industrial wastewater is of growing concern because its mobility, toxicity, and treatability depend strongly on oxidation state and water chemistry. This review examines Sb occurrence and aqueous speciation, the effects of water-matrix constituents, and the main technologies investigated for its removal. Particular attention is given to the contrasting behavior of Sb(III) and Sb(V) and to the influence of pH, competing ions, natural organic matter (NOM), and redox conditions on treatment performance. Biological processes, oxidation, adsorption, coagulation–precipitation, electrochemical methods, membrane separation, and hybrid systems are assessed in terms of effectiveness, practical limitations, and residual generation. By considering Sb speciation, matrix effects, and residual fate together, this review shows that treatment suitability cannot be judged from removal efficiency alone. Oxidation is best regarded mainly as a speciation-control step rather than a stand-alone removal process, whereas adsorption and coagulation remain important for dissolved Sb capture and bulk removal. Membrane and electrochemical processes offer options for high-quality separation and recovery, while hybrid systems can combine transformation and capture. Future studies should emphasize realistic matrices, environmentally relevant conditions, continuous operation, regeneration, and long-term residual stability.

This mini-review presents the major research trends in the synthesis, performance, and mechanisms of clay-supported magnetic iron oxide nanocomposites for the adsorption of heavy metals in water and wastewater treatment applications. The immobilization of iron oxide nanoparticles onto the hydrophilic natural or synthetic nanoclay matrices not only minimized the magnetic nanoparticles’ tendency to aggregate in aquatic solutions but also facilitated their recovery from the solutions via magnetic separation after adsorption. For these reasons, research on such materials emerged in the early 2010s, leading to the development of highly efficient nanocomposite adsorbents. At optimum conditions, including solution pH values between 5 and 7, rapid equilibrium times ranging from 30 to 180 min, and ambient or moderately elevated temperatures (up to 60 °C), maximum adsorption values of up to 225 mg/g were reported for certain heavy metals. Moreover, the nanocomposites demonstrated reusability, maintaining adsorption performance towards heavy metals for up to five adsorption–desorption cycles when common acids (such as HNO₃ and HCl) were used as regenerating agents. However, the current findings are all based on batch-scale laboratory experiments. To move toward industrial-scale applications, further research is necessary to address scale-up challenges and evaluate the performance of the clay-supported magnetic iron oxide nanocomposites under real-world conditions. All the critical limitations are highlighted in the context of this mini review to support future efforts toward achieving their economic and environmentally sustainable application for the adsorption of heavy metals from water/wastewater streams.

Developing an efficient recycling route for spent single-use medical devices is essential for recovering precious metals. The proposed complete hydrometallurgical route goes through the initial pyrolysis and acid digestion steps, expanding upon our previous relevant work in the field, followed by solvent extraction, stripping, and precipitation procedures. In this study, a complete hydrometallurgical process was developed for the recovery of gold, platinum, iridium, and tantalum, separating them from other metals, i.e., from iron, chromium, and nickel, also present in the examined medical devices, i.e., (i) diagnostic electrophysiology catheters, containing gold, (ii) diagnostic guide wires, containing platinum and iridium alloys, and (iii) self-expanding stents, containing tantalum. This study reports the experimental results of selecting an efficient extractant, stripping, and precipitation agent, along with the effects of key factors that influence each consecutive step of the process, i.e., agent concentration, aqueous to organic phase ratio, contact time, and pH, using simulated metal solutions and also applying the obtained optimal conditions to the treatment of real sample solutions. For the selective separation of gold, Aliquat 336 was used to extract it in the organic phase; it was then stripped using a thiourea solution and precipitated by utilizing an iron sulfate (II) solution and proper pH adjustment. The selective separation of platinum was achieved by using Aliquat 336 for the organic phase extraction and a perchlorate acid solution for stripping it back into the aqueous solution and adding a sodium bromate solution to precipitate it. Due to the similar chemical behavior, the selective recovery of iridium followed the same processes as that of platinum, and the separation between them was achieved through selective precipitation, as heating the solution and adjusting the pH value resulted in the selective precipitation of iridium. Lastly, the selective recovery of tantalum consists of extraction by using Alamine 336, then stripping it back to the aqueous phase by using sodium chloride, and precipitation by using potassium salt solution and proper pH adjustment. A total recovery of 88% for Au, 86% for Pt, 84% for Ir, and 80% for Ta was obtained, thus achieving a high uptake of precious metals from the examined real spent/waste samples.

Due to their unique properties, i.e., fluoroscopy response and inertness, noble metals and alloys are present in several widespread medical–technological products, such as catheters, guide-wires, and stents. Despite their value, these products serve as single-use consumables, following a fate of solid waste disposal and loss of their valuable metals. This work studies the development of a treatment methodology to recover noble metals such as Pt, Ir, Au, and Ta from certain commercial products commonly used for medical practices. In particular, a sequence of preliminary pyrolysis, aiming at polymer elimination, as well as an acid digestion step for selective metals dissolution, is suggested. Pyrolysis was capable of enriching samples with the targeted metals, though a small change in their oxidation states was observed. Still, acid digestion was fully able to successfully separate Au using a 50% v/v aqua regia solution for 30 min at room temperature and the Pt/Ir using concentrated aqua regia for 72 h under heating. Dissolution of Ta required a different leaching solution, i.e., a 50% v/v HF/H₂SO₄ mixture for 10 h under heating. According to the developed method, selective extraction of such noble metals in a concentrated slurry provides a high potential for the complete recovery and valorization of otherwise disposed medical wastes.

Noble metals (Pt, Ir, Au, Ta, etc.) have found several applications in specific medical technology products since they present inertness and visibility when examined via fluoroscopy by an external observer/operator. These products are usually applied as single-use materials and, as a result, the corresponding waste streams may be quite rich in valuable metals. In this work, it was proven that noble metals can be recovered from such waste streams. Initially, pyrolysis may completely remove the plastic covering of medical products. In addition, selective dissolution of noble metals can be achieved by applying different inorganic acids or their mixtures.

Transparent supercapacitors find a large number of applications as components of many electronic devices and circuits. Mixed Ni–Co oxides (NCOs) are among the most promising supercapacitor electrode materials exhibiting high pseudo-capacitance and good electronic conductivity, while inkjet printing is a low cost and versatile technique for electrode printing. Surprisingly, although there have been many studies of NCO supercapacitor films on ITO glass substrates, these have not been prepared by the inkjet technique, and their optical properties were not fully characterized. Hereby, we report the fabrication and characterization of thin (295 and 477 nm thick; 0.017 and 0.035 mg cm⁻² NCO loading) semi-transparent NiCo₂O₄/ITO supercapacitor electrodes, showing transparency to visible light (60–30%, from the thinner to the thicker electrode layers tested), typical mass specific capacitance for NCO-based supercapacitor electrodes (1294–829 Fg⁻¹ at 1 mA cm⁻² discharge current density) and high volumetric capacitance (746–608 F cm⁻³ at 1 mA cm⁻²). The NCO nanoparticles were prepared by hydrothermal synthesis followed by thermal treatment and ball milling (ZrO₂ balls, 0.5 mm diameter), resulting in a cubic nickel–cobalt oxide structure and particle size in the 30–150 nm range, whereas the electrode layers were printed from water-propylene glycol solutions using a Dimatix DMP-2850 drop-on-demand (DoD) inkjet printer. Constant current charge–discharge experiments of the supercapacitor electrode (at ca 0.5 mA cm⁻²) for 1000 cycles confirmed stability of performance.

Municipal wastewater management is a well-established field in most parts of the world nowadays