Cell-shape assemblage and nanostructure of akaganéite bioformed in FeCl2 solutions

Synthesis of β-FeOOH/polyaniline heterogeneous catalyst for efficient photo-Fenton degradation of AOII dye

Discharge of the untreated dye-containing wastewaters will induce water source pollution and further harm aquatic organisms. In this study, the akaganéite/polyaniline catalyst (β-FeOOH/PANI, about 1.0 μm) could be successfully composed by polyaniline (PANI, (C₆H₇N)_n, 200-300 nm) and akaganéite (β-FeOOH, FeO(OH)_1-xCl_x, less than 200 nm), according to the identification and characterization results of XRD, Ramon, FTIR, XPS, SEAD, EDS, and FESEM (or HRTEM). Due to PANI providing more photogenerated electrons, the β-FeOOH/PANI composite (compared with β-FeOOH) in photo-Fenton system had the more highly catalytic degradation capacity to Acid Orange II (AOII) under an optimal condition (7.5 mmol/L of H₂O₂ oxidant, 40 mg/L of AOII, 0.2 g/L of catalyst dosage, and pH 4.0). The AOII degradation kinetics could be well fitted by pseudo-first-order model. In photo-Fenton catalytic process of AOII dye, the ∙OH and h⁺ were the main reaction substances. The AOII in solutions could be gradually mineralized into non-toxic inorganic H₂O molecule and CO₂. The β-FeOOH/PANI catalyst also had a good reusable ability of about 91.4% AOII degradation after 4 runs. These results can provide a reference for synthesis of catalyst used in photo-Fenton system and the applications in degradation removal of organic dye from wastewaters.

Schwertmannite and akaganéite for adsorption removals of Cr(VI) from aqueous solutions

Iron hydroxides have received high attention in the treatment of chromium (Cr) polluted wastewater. In this study, the obtained chemical (or biological) pincushion-schwertmannite spheres had a diameter of 2 - 5 μm (0.5-1 μm), and akaganéite rods had a length of 300-500 nm (100-150 nm) at an axial ratio of about 3. The average diameters (μm) of their agglomerated particles in solutions were 20.6-32.5 (only 0.480 for Aka-Chem). Schwertmannites and akaganéites were used to investigate Cr(VI) adsorption behaviors in aqueous solutions by batch experiments, under various reaction times, initial Cr(VI) and adsorbent levels, pH values, temperature and anions of NO₃^-, Cl^-, CO₃^2-, SO₄^2-, and H₂PO₄^-. Adsorption data well fitted to pseudo-second-order rate model (R² = 0.999), and Langmuir (R² = 0.954-0.988) and Freundlich (R² = 0.984-0.996) isothermal models at pH 7.0. Maximum Cr(VI) adsorption capacities were 119/133 for Sch-Chem/Sch-Bio, and 14.6/83.6 for Aka-Chem/Aka-Bio. The H₂PO₄^- than SO₄^2-/CO₃^2- had a stronger effect on Cr(VI) adsorption. Adsorbents with pH_ZPC of near to 4.0 still had a good Cr(VI) removal ability at pH 3.0-8.0. The possible Cr(VI) adsorption mechanisms by FTIR and XPS results for schwertmannite and akaganéite were electrostatic attractions and ion exchanges between hydroxyl (or sulfate) and chromate ions. The Cr(VI) adsorption of optimal schwertmannite and bioakaganéite was a spontaneous, endothermic and random process at the temperatures of 288-318 K. They had a good regeneration ability for Cr(VI) adsorption, and removal ratios could reach to about 80% of original values (60-70% in aqueous solution with 60 mg/L Cr(VI) and pH7.0, and 35-50% in wastewater with 120 mg/L Cr(VI) and about pH4.0), after three cycles. Herein, schwertmannite/bioakaganéite have a promising application in treatment of acidic/neutral wastewater with chromate.