Fe₂O₃/Mn₂O₃ nanocomposites and impregnated porous silicates (Fe₂O₃/Mn₂O₃@SiO₂ [FMS]) were prepared and investigated as catalytic adsorbents. The catalysts were applied for cationic and anionic dye pollutants in the adsorption, Fenton reaction, and photocatalysis processes at a pH of 7. Fe₂O₃/Mn₂O₃ nanoparticles (FM-NPs) were prepared using the co-precipitation method and were impregnated in SiO₂ by the sol–gel process. The synthesized materials were characterized using various sophisticated techniques. Results indicated that the impregnation of bi-metallic NPs in SiO₂ increased the surface area, and the function of the adsorbent also improved. FMS showed a significant adsorption effect, with 79.2% rhodamine B removal within 15 min. Fenton and photocatalyst reaction showed removal rates of 85.3% and 97.9%, respectively, indicating that negatively charged porous silicate attracts cationic pollutants. In the case of the anionic pollutant, Congo red, the adsorption reaction of FMS did not occur, and the removal rate of the photocatalyst reaction was 79%, indicating the repulsive force between the negatively charged silica and the anionic dye. Simultaneously, bi-metal-bonded FM-NPs facilitated the photocatalytic reaction, reducing the recombination of electron-hole pairs. This study provides new insights into the synthesis of FM-NPs and FMS as photocatalytic adsorbents and their photocatalytic mechanisms based on reaction conditions and contaminant characteristics. The developed materials have potential applications for environmental mitigation.

Perfluoroalkyl substances (PFAS) are emerging contaminants present in various water sources. Their bioaccumulation and potential toxicity necessitate proper treatment to ensure safe water quality. Although iron-based monometallic photocatalysts have been reported to exhibit rapid and efficient PFAS degradation, the impact of bimetallic photocatalysts is unknown. In addition, the mechanistic effects of utilizing a support are poorly understood and solely based on physicochemical properties. This study investigates the efficacy of bimetallic photocatalysts (Fe₂O₃/Mn₂O₃) in inducing the photo-Fenton reaction for the degradation of perfluorooctane sulfonate (PFOS) and perfluorononanoic acid (PFNA) under various conditions. The rapid removal of both PFAS was observed within 10 min, with a maximum efficiency exceeding 97 % for PFOS under UV exposure, aided by the photocatalytic activation (photo-Fenton) of the oxidant (H₂O₂). Contrary to expectations, the use of the SiO₂ support material did not significantly improve the removal efficiency. The efficacy of PFNA decreased despite SiO₂ providing larger surface areas for Fe₂O₃/Mn₂O₃ loading. Further analysis revealed that the adsorption of PFAS onto the catalyst surfaces owing to electrostatic interactions contributed to the removal efficiency, where the degradation efficacy was worse than that of the catalyst with SiO₂. This is because adsorption hindered the effective contact of H₂O₂ with catalytic reaction sites, thereby impeding the generation of hydroxyl (·OH) radicals. This study indicates the importance of considering chemical properties, including surface charge, in catalyst design to ensure effective degradation, focusing on physicochemical properties, such as surface area might overlook crucial factors.

In this study, the effect of UV treatment on the physicochemical properties and structural variation of metal oxide-silica nanocomposites (Mn₂O₃-Fe₂O₃@SiO₂) has been investigated. Based on the results, UV irradiation significantly affects the nanocomposite structure, where SiO₂ network reconfiguration, change in surface OH group density, and surface area were observed. Erythromycin (ERY) has been chosen as a module pollutant to compare the performance of the pristine and UV-treated nanocomposites. The pristine nanocomposite had a high adsorption efficiency (99.47%) and photocatalytic activity (99.57%) at neutral pH for ERY in the first cycle, and this efficiency decreased significantly for the multiple cycles. However, different results have been observed for the UV-treated nanocomposite, where it retained its performance for ten consecutive cycles. This enhanced performance is attributed to the structural modifications after UV exposure, where increased surface area, pore volume, and OH group density resulted in an increased number of the possible mechanisms responsible for the adsorption/oxidation of ERY. Moreover, oxidation of adsorbed molecules by UV light after each cycle can also be another reason for enhanced removal. For the first time, the fate of ERY is studied using regenerated nanocomposites after the last cycle. LC/MS/MS results showed that ERY degraded in 20 min, and the produced reaction by-products were adsorbed by nanocomposites. This study could be a foundation research for the practical approaches for the regeneration of nanomaterials and the successful removal of organic pollutants from aquatic environments.

In this study, we developed a thermal storage medium comprising porous activated carbon filled with organic phase-change materials (PCMs) that utilizes the latent heat of phase-change to absorb heat during heating and release heat during cooling. For the activated carbon, we used both charcoal-based powdered activated carbon (250–350 mesh) and granular activated carbon. The organic phase-change materials used in the experiments were dodecane, tridecane, tetradecane, and pentadecane. Material properties such as thermal conductivity, latent heat, and melting temperature range were evaluated experimentally and theoretically, with the results observed to be consistent. The cyclic thermal performance of the proposed medium was also evaluated. Notably, filling the activated carbon with a mixture of organic PCMs resulted in the highest temperature-moderating effect. The procedure and results presented in this study are expected to aid in further improvement in the performance of thermal storage media containing PCM where stable temperatures are required, including building heating and cooling.