Soft synthesis and characterization of goethite-based nanocomposites as promising cyclooctene oxidation catalysts

Towards optimization of mechanical and microstructural performances of Fe-rich laterite geopolymer binders cured at room temperature by varying the activating solution

In the present study, the performances of the end products prepared using calcined iron-rich laterite at 600 °C (LAT600) with different alkaline solution (AS) to calcined laterite (AS/LAT600) mass ratio (0.45-0.65) were investigated. The effect of AS/LAT600 mass ratio on microstructural and mechanical properties of consolidated geopolymer samples, such as compressive strength, porosity, bulk density, water absorption, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) analysis were determined. Geopolymer made with AS/LAT600 ratio of 0.55 yields the highest compressive strength (54 ± 0.38 MPa) and compact structure. Increasing the AS/LAT600 mass ratio (0.45-0.65) increased the setting time, flowability and decreased the SiO₂/Fe₂O₃ and Al₂O₃/Fe₂O₃ molar ratios and compressive strength leading to a weak structure. Both cumulative volume intrusion and cumulative pore area increased from 0.11 to 0.20 mL g^-1 and 65.20 to 90.93 m² g^-1, respectively. Such enhancement is linked to changes that occur into the geopolymer network when high alkaline activator/laterite is used. Therefore, further increase of AS/LAT600 mass ratio improved the workability, delaying the polycondensation rate of dissolved calcined laterite and not positively affecting the mechanical strength development. Nevertheless, the performance of the end products could be found application in building engineering.

Progress toward Room-Temperature Synthesis and Functionalization of Iron-Oxide Nanoparticles

Novel magnetic nanohybrids composed of nanomaghemite covered by organic molecules were successfully synthesized at room temperature with different functionalization agents (sodium polystyrene sulfonate, oxalic acid, and cetyltrimethylammonium bromide) in low and high concentrations. Structural, vibrational, morphological, electron energy-loss spectroscopy, magnetic, and Mössbauer characterizations unraveled the presence of mainly cubic inverse spinel maghemite (γ-Fe₂O₃), whilst X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy showed that most samples contain a minor amount of goethite phase (α-FeOOH). Raman analysis at different laser power revealed a threshold value of 0.83 mW for all samples, for which the γ-Fe₂O₃ to α-Fe₂O₃ phase transition was observed. Imaging microscopy revealed controlled-size morphologies of nanoparticles, with sizes in the range from 8 to 12 nm. Organic functionalization of the magnetic nanoparticles was demonstrated by vibrational and thermogravimetric measurements. For some samples, Raman, magnetic, and Mössbauer measurements suggested an even more complex core-shell-like configuration, with a thin shell containing magnetite (Fe₃O₄) covering the γ-Fe₂O₃ surface, thus causing an increase in the saturation magnetization of approximately 11% against nanomaghemite. Field cooling hysteresis curves at 5 K did not evidence an exchange bias effect, confirming that the goethite phase is not directly interacting magnetically with the functionalized maghemite nanoparticles. These magnetic nanohybrids may be suitable for applications in effluent remediation and biomedicine.

Synthesis and Characterization of Hematite-Based Nanocomposites as Promising Catalysts for Indigo Carmine Oxidation

The hematite-based nanomaterials are involved in several catalytic organic and inorganic processes, including water decontamination from organic pollutants. In order to develop such species, a series of bimetallic hematite-based nanocomposites were obtained by some goethite composites-controlled calcination. Their composition consists of various phases such as α-FeOOH, α-Fe₂O₃ or γ-Fe₂O₃ combined with amorphous (Mn₂O₃, Co₃O₄, NiO, ZnO) or crystalline (CuO) oxides of the second transition ion from the structure. The component dimensions, either in the 10–30 or in the 100–200 nm range, together with the quasi-spherical or nanorod-like shapes, were provided by Mössbauer spectroscopy and powder X-ray diffraction as well as transmission electron microscopy data. The textural characterization showed a decrease in the specific area of the hematite-based nanocomposites compared with corresponding goethites, with the pore volume ranging between 0.219 and 0.278 cm³g⁻¹. The best catalytic activity concerning indigo carmine removal from water in hydrogen peroxide presence was exhibited by a copper-containing hematite-based nanocomposite sample that reached a dye removal extent of over 99%, which correlates with both the base/acid site ratio and pore size. Moreover, Cu-hbnc preserves its catalytic activity even after four recyclings, when it still reached a dye removal extent higher than 90%.