Water contamination by synthetic dyes such as malachite green (MG) remains a significant environmental and public health challenge due to their high toxicity, chemical stability, and resistance to biodegradation. In this study, a CaO-CuFe₂O₄ composite was synthesized through a sustainable route using eggshells and orange peel as agro-industrial waste precursors. Comprehensive structural, spectroscopic and microscopic analyses confirmed the coexistence of a predominant CaO-based phase with spinel CuFe₂O₄, together with nanometric features, satisfactory elemental dispersion and practical magnetic recoverability. Under the experimental conditions employed, the composite exhibited high adsorption performance towards MG, reaching an equilibrium capacity of 2288.4 mg g⁻¹ and 99.98% decolorization within 60 min. The kinetics were better described by the pseudo-second-order model, while the equilibrium behavior was more satisfactorily fitted by the Langmuir isotherm than by the Freundlich model. Thermodynamic analysis indicated that the adsorption process was favorable over the temperature range studied and became more pronounced at higher temperature. The results suggest that the adsorption behavior arises from the combined influence of surface chemistry, calcium-derived basic sites, ferrite-associated metal centers and interfacial accessibility, rather than from surface area alone. In addition, the material could be readily separated from aqueous solution using an external magnetic field, highlighting its practical post-treatment recoverability. Overall, this work demonstrates a viable waste valorization strategy for the development of a magnetically recoverable CaO-CuFe₂O₄ adsorbent for cationic dye removal. Beyond the specific case of MG, the study underscores the potential of agro-waste-derived hybrid oxides as application-relevant materials for water remediation.

Rapid removal of chemically diverse organic pollutants remains a major challenge in aqueous decontamination. In this study, atmosphere-controlled defect engineering was used to activate anatase TiO₂ as a rapid adsorbent operating on the minute scale, exhibiting low charge selectivity under the investigated conditions. A reduced black TiO₂ (B–TiO₂), produced by inert annealing, achieved ≈100% removal of cationic methylene blue within ~6 min and ≈91% uptake of anionic methyl orange within ~3 min, whereas pristine and air-annealed TiO₂ showed only marginal adsorption under identical conditions. Correlative structural and surface-sensitive analyses indicated that this behaviour was associated with a chemically activated near-surface region enriched in reduced titanium contributions, defect-associated or non-lattice oxygen environments and a locally perturbed anatase framework, together with finely dispersed carbon-related motifs integrated within the oxide matrix. Adsorption kinetics were described, within experimental resolution, by pseudo-second-order fitting, while intraparticle diffusion analysis supported sequential regimes initiated by rapid interfacial attachment. Equilibrium analysis yielded apparent maximum capacities of 6.116 mg g⁻¹ for methylene blue and 2.950 mg g⁻¹ for methyl orange, reflecting adsorption governed by surface heterogeneity for cationic species and an apparent saturation-type response for anionic uptake. Overall, controlled surface non-stoichiometry emerges as a viable strategy to enhance adsorption kinetics in TiO₂, providing a transferable design framework for developing oxide-based adsorbents for sustainable water-treatment applications.

In this study, V₂O₅ nanoparticles were prepared using agate containers and balls in the ball milling technique. The structural, morphological, compositional, optical, and CO gas sensing properties of nanostructured V₂O₅ samples were thoroughly investigated. The primary objective of this research was to explore the correlation between the synthesis conditions and the properties of V₂O₅ materials prepared in an agate environment. The morphological study revealed that the ball milling technique altered the geometrical shapes and irregular grain sizes (ranging from 500 to 2000 nm) into nanograins (with sizes reduced to approximately 200 nm). Energy dispersive x-ray spectroscopy (EDS) spectra confirmed the presence of vanadium and oxygen elements in the samples, and the EDS mapping demonstrated their homogeneous distribution. The formation of the orthorhombic crystal structure of V₂O₅ was observed through structural analysis. It was found that the intensity of the peaks and the crystallinity of the V₂O₅ samples decreased with increasing milling time. Optical properties showed an improvement in the bandgap of the V₂O₅ semiconductors at higher milling times, which can be attributed to lattice deformation effects. BET analysis indicated an increase in surface area and a reduction in pore size after the milling process. The CO gas sensing properties were associated with changes in the surface electrical resistance upon exposure to CO gas at various concentrations, with the milled samples showing a relatively high response. Therefore, nanostructured V₂O₅ has the potential for use in gas sensing applications. However, further investigations are required to optimize the CO gas sensing properties.