This study aimed at preparing three types of biochar derived from rice husk via pyrolysis, including unactivated biochar, biochar chemically activated after with H₃PO₄, and biochar impregnated with γ-Fe₂O₃ nanoparticles. These materials were subsequently characterized using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analysis, which revealed favorable textural properties, such as an increased surface area and porosity, as well as the presence of functional groups that facilitate the adsorption of methylene blue and malachite green in aqueous solutions. Several factors that affect the adsorption capacity, including the type of material, pH effect, and adsorbent dosage, were evaluated and optimized. The adsorption behavior was analyzed using isotherm and kinetic models to better understand the mechanisms involved. Under optimal conditions, biochar@γ-Fe₂O₃ NPs emerged as the most effective material due to its high surface area, functionalized surface, and magnetic properties, allowing easy water recovery without the need for complex instrumentation. Among the kinetic models evaluated, the pseudo-second-order model exhibited the highest linear regression coefficient (R² = 0.99), supporting a chemisorption process driven by strong interactions and stable chemical bond formation between the adsorbate and the adsorbent, while equilibrium data fit well with the Sips isotherm model, indicating a combination of monolayer and multilayer adsorption mechanisms. This magnetic biochar achieved removal efficiencies of 97% for methylene blue and 95% for malachite green, demonstrating a high performance and reusability over four cycles. Moreover, a possible adsorption mechanism of MB on the magnetic biochar was proposed to explain the interaction between the dye and the adsorbent surface. Thus, this work demonstrates that magnetic biochar is a sustainable and cost-effective adsorbent for wastewater treatment, integrating circular economy principles by transforming rice husk into a high-value material. The incorporation of γ-Fe₂O₃ nanoparticles enhances adsorption while enabling magnetic recovery, providing an eco-friendly and scalable solution for dye removal.

The present study describes the tribological properties of thermal sprayed WC–14Co–3Cr (wt-%) coatings produced by using the high velocity oxyfuel (HVOF) deposition process. The coatings have been characterised with respect to their chemical composition and microstructural features (SEM-EDX) and roughness (profilometry). Experiments using a tribometer (pin on disk configuration) under non-lubricating conditions have been performed with the aim of determining the wear resistance of these coatings. To ensure reproducibility of the wear tests, the coated samples have been ground to an average superficial roughness R_a of 0·230 μm. Steel balls of AISI 1086, 6 mm in diameter, were tested against coated and uncoated samples. The morphology of the wear tracks on both pins and discs was characterised using SEM and three-dimensional profilometry. An average friction coefficient of 0·596 and average wear rate of 1·21 × 10^-4 mm³ Nm^-1 werefound for the tribological pair AISI 1086 pin/ WC–14Co–3Cr coated disc. For this pair a mixed wear mechanism of both abrasive and adhesive wear was observed for the pin with unidirectional material transfer from the pin toward the coating.