This work reports the synthesis of nanosilica-coated magnetic carbonaceous adsorbents ([email protected]₂) using low-temperature hydrothermal carbonization technique (HCT) and the feasibility to utilize it for methylene blue (MB) adsorption. Initially, a carbon precursor (CP) was synthesized from corn starch under saline conditions at 453 K via HCT followed by the magnetization of CP again via HCT at 453 K. Subsequently, MCA was coated with silica nanoparticles. MCA and [email protected]₂ were characterized using X-ray diffraction, Fourier transform infrared, scanning electron microscopy/energy-dispersive spectroscopy, transmission electron microscopy, and Brunauer–Emmett–Teller (BET) N₂ adsorption–desorption isotherms. The BET surface area of MCA and [email protected]₂ were found to be 118 and 276 m² g^–1, respectively. Adsorption of MB onto [email protected]₂ was performed using batch adsorption studies and in the optimum condition, [email protected]₂ showed 99% adsorption efficiency with 0.5 g L^–1 of [email protected]₂ at pH 7. Adsorption isotherm studies predicted that MB adsorption onto [email protected]₂ was homogeneous monolayer adsorption, which was best described using a Langmuir model with the maximum adsorption capacity of 516.9 mg g^–1 at 25 °C. During adsorption kinetics, a rapid dye removal was observed which followed pseudo-first- as well as pseudo-second-order models, which suggested that MB dye molecules were adsorbed onto [email protected]₂ via both ion exchange as well as the chemisorption process. The endothermic and spontaneous nature of the adsorption of MB onto [email protected]₂ was established by thermodynamics studies. Mechanism of dye diffusion was collectively governed by intraparticle diffusion and film diffusion processes. Furthermore, MB was also selectively adsorbed from its mixture with an anionic dye, that is, methyl orange. Column adsorption studies showed that approximately 500 mL of MB having 50 mg L^–1 concentration can be treated with 0.5 g L^–1 of [email protected]₂. Furthermore, [email protected]₂ was repeatedly used for 20 cycles of adsorption–desorption of MB. Therefore, [email protected]₂ can be effectively utilized in cationic dye-contaminated wastewater remediation applications.

CO₂ adsorbents comprising various alkaline sorption active phases supported on mesoporous Al₂O₃ were prepared. The materials were tested regarding their CO₂ adsorption behavior in the mid-temperature range, i.e., around 300 °C, as well as characterized via XRD, N₂ physisorption, CO₂-TPD and TEM. It was found that the Na₂O sorption active phase supported on Al₂O₃ (originated following NaNO₃ impregnation) led to the highest CO₂ adsorption capacity due to the presence of CO₂-philic interfacial Al–O^––Na⁺ sites, and the optimum active phase load was shown to be 12 wt % (0.22 Na/Al molar ratio). Additional adsorbents were prepared by dispersing Na₂O over different metal oxide supports (ZrO₂, TiO₂, CeO₂ and SiO₂), showing an inferior performance than that of Na₂O/Al₂O₃. The kinetics and thermodynamics of CO₂ adsorption were also investigated at various temperatures, showing that CO₂ adsorption over the best-performing Na₂O/Al₂O₃ material is exothermic and follows the Avrami model, while tests under varying CO₂ partial pressures revealed that the Langmuir isotherm best fits the adsorption data. Lastly, Na₂O/Al₂O₃ was tested under multiple CO₂ adsorption–desorption cycles at 300 and 500 °C, respectively. The material was found to maintain its CO₂ adsorption capacity with no detrimental effects on its nanostructure, porosity and surface basic sites, thereby rendering it suitable as a reversible CO₂ chemisorbent or as a support for the preparation of dual-function materials.