Forced hydrolysis of FeCl3 solutions in the presence of Cr3+ ions

• Published in: The Journal of physics and chemistry of solids 2021-09, Vol.156, p.110166, Article 110166
• Main Authors: Robić, Marko, Ristić, Mira, Kuzmann, Erno, Homonnay, Zoltan, Krehula, Stjepko, Musić, Svetozar
• Format: Article
• Language: English
• Subjects: Kinetics; Mössbauer spectroscopy; Oxide materials; Scanning electron microscopy; X-ray diffraction
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2021.110166

Forced hydrolyses of FeCl3 solutions in the presence of Cr3+ ions without alkali addition were investigated at 160 and 200 °C. These precipitation systems were compared to corresponding reference systems. The isolated precipitates were characterized with XRD, 57Fe Mössbauer, FT-IR, FE SEM and photocatalytic measurements. Although chromium was not detected by EDS (Energy Dispersive X-ray Spectroscopy), the analysis of samples precipitated in the presence of Cr3+ ions showed several effects which can be attributed to the presence of these ions in the starting solutions. These effects are specifically well pronounced for samples obtained at 200 °C. For the highest concentration of Cr3+ ions and upon heating at 200 °C the transformation kinetics β-FeOOH to α-Fe2O3 was impeded. Relative intensities of prominent diffraction lines 104 and 110 of α-Fe2O3 changed as a result of the presence of Cr3+ ions. Changes in the size and formation of lemon-like particles instead of cube-like α-Fe2O3 particles were also noticed. The presence of Cr3+ ions in hydrolysing FeCl3 solution influenced the photocatalytic degradation of rhodamine B. Since no specific adsorption of Cr3+ ions occurred in the acidic pH medium, it was inferred that traces of Cr3+ ions enter into the structural tunnels of β-FeOOH crystals. The associates Cl−-Cr3+ are formed, which in the next step destabilize the crystal structure of β-FeOOH particles. Cr3+ ions leave the crystal structure upon dissolution of β-FeOOH. It can be assumed that α-Fe2O3 crystals start to grow on very fine and thin β-FeOOH crystallites which were not completely dissolved, but were previously affected by Cr3+ ions. •Cr3+ ions influenced forced hydrolysis of FeCl3 solutions at pH