Ioannis Anastopoulos

Alizarin Red S (ARS) is a persistent anthraquinone dye whose discharge into aquatic environments represents an important concern due to its chemical stability, intense coloration, and potential ecological impact. Adsorption has emerged as one of the most practical approaches for its removal from aqueous media because of its operational simplicity, adaptability, and compatibility with low-cost and regenerable materials. This review critically examines recent progress in the adsorption of Alizarin Red S using a broad spectrum of adsorbents, including biomass-derived materials, activated carbons, carbon nanotubes, graphene-based systems, polymeric sorbents, metal oxides, metal–organic frameworks, hydrogels, magnetic composites, and hybrid nanostructures. Particular attention is given to the relationship between adsorbent composition, surface chemistry, porosity, functional groups, and adsorption performance. The effects of pH, adsorbent dosage, initial dye concentration, contact time, temperature, and coexisting ions are discussed as key factors controlling dye uptake, equilibrium behavior, and removal efficiency. The reviewed studies indicate that ARS adsorption is commonly governed by electrostatic attraction; hydrogen bonding; π–π interactions; surface complexation; pore diffusion; and, in some systems, dye–metal complex formation. Langmuir and Freundlich isotherms, together with pseudo-second-order kinetics, are the most frequently reported models. Despite significant laboratory-scale advances, challenges remain regarding adsorbent regeneration, selectivity in complex matrices, long-term stability, cost-effective synthesis, and scale-up. Future research should prioritize real wastewater validation, multicomponent systems, circular adsorbent design, computational modeling, machine learning-assisted optimization, and life cycle assessment to support the transition of ARS adsorption technologies toward practical wastewater treatment applications.

Despite a growing interest in biochar for olive orchard fertility management, little is known about its effects on nitrogen (N) dynamics and greenhouse gas (GHG) emissions in Mediterranean soils, particularly when comparing neutral (pH 6.7) and alkaline (pH 8.2) soils using farmer-accessible flame-curtain pyrolysis biochar. In this 60-day soil mesocosm study, we hypothesized that biochar amendments in fertilized soils would enhance soil N availability and potentially reduce N₂O emissions, with effects modulated by soil pH. Treatments included: control, urea fertilizer, and urea plus biochar (5% w/w). Urea fertilization significantly increased soil ammonium (NH₄⁺) and total oxidized nitrogen (NO₃⁻ + NO₂⁻) in both soils, and co-application of biochar further increased these pools, particularly in the neutral soil (NH₄⁺: + 91% and + 62% in neutral and alkaline soil, respectively). Biochar addition consistently reduced cumulative carbon dioxide (CO₂) emissions in both soils, supporting its role in stabilizing soil organic carbon. However, impacts on nitrous oxide (N₂O) emissions were soil-pH-dependent: biochar slightly reduced N₂O emissions in neutral soil, though nearly doubled N₂O emissions in alkaline soil, highlighting that biochar’s efficacy for GHG mitigation is context-specific. These findings underscore biochar’s potential to improve soil N availability and reduce carbon losses but reveal clear limitations for N₂O mitigation in alkaline soils, necessitating site-specific application strategies that explicitly consider soil pH when targeting climate benefits in Mediterranean olive production.

This study investigates the interaction of humic acid (HA) with magnetite nanoparticles and its impact on the adsorption behavior of the HA-coated magnetite (Fe₃O₄) nanoparticles towards uranium (U-232) in aqueous solutions. The particle surface modification was performed using HA solutions of varying concentrations (0.01, 0.1, and 1.0 g/L). Zeta potential measurements revealed a significant shift in surface charge—from positive values (+13 mV) for unmodified particles to negative values (down to −30 mV) due to the presence of carboxylic moieties on the particle surface. Batch adsorption experiments at pH 5.6 demonstrated that increasing HA coating markedly improves the U-232 adsorption, with K_d values rising by up to an order of magnitude compared to unmodified Fe₃O₄ nanoparticles. The enhanced performance is linked to both the greater number of surface-active sites and the increased negative surface charge introduced by the HA layer. Despite the HA coating, the hydrodynamic diameter of the particles remains largely unaffected, preserving colloidal stability. The latter is also corroborated by SEM-EDX analysis. Overall, this work highlights the role of HA in the adsorption behavior of magnetite particles towards (radio)toxic metal ions, which is of particular interest regarding their mobility in the geosphere and their removal from contaminated waters.

It is generally accepted that the nanoscale realm frontiers are situated below 100 nm at least in one dimension

The main goal of the work was to study the Moringa oleifera leaves and seeds as sorbents against Pb(II), Cd(II), Co(II), and Ni(II) from aqueous solutions, to explore the effect of various parameters (such as contact time, biosorbent dosage, and initial concentration of metals) and to determine the adsorption mechanisms

Biochar is the solid carbonaceous product of biomass pyrolysis. The properties of biochar depend on the biomass feedstock as well as the pyrolysis temperature and time. Therefore, biochars with different properties and functionalities can be produced. Biochar research has been intensive in the past 15 years, focusing mainly on soil applications, wastewater treatment, and contaminant remediation. However, a formal definition of biochar and related terms is missing, which hinders the standardization of scientific results worldwide and the scaling-up of research at the industrial level. Furthermore, an official terminology may promote the development of a harmonized legal framework for biochar production and applications, both at regional and national levels. This glossary of terms consists of 178 scientifically sound definitions of the most commonly used terms in biochar research. The definitions of this glossary are interconnected, allowing the reader to further explore the synergies between terms. The distribution of terms reflects the multidisciplinarity of biochar research: chemistry, material science and engineering, and soil science are the main disciplines represented here. The list of terms is by no means exhaustive and the strategic objective of this effort is to develop a dynamic document in which more terms will be added in the future, and the existing ones will be refined, as biochar research evolves.