Visible light induced photocatalytic reduction of Cr(VI) by self-assembled and amorphous Fe-2MI
Visible-light-active Fe-2MI assemblies were prepared at room temperature using 2-Methylimidazole (2MI) as organic ligand to form complex with Fe(II) or Fe(III). TGA and XRD characterizations indicated that Fe(II) can form more stable complex and higher coordinating percentage with 2MI relative to Fe(III). Besides, Fe(II)-2MI displayed amorphous state with larger BET surface area and higher photocurrent response. At very low catalyst dosage (0.1 g/L), highest activity for Cr(VI) reduction can be achieved using Fe(II)-2MI as photocatalyst. The estimated pseudo-first-order rate constant (0.021 min −1 ) was 1.4 and 2.1 times that on Fe(III)-2MI and Fe(II)-NaOH, respectively. The well-known ZIF-67 (Co-2MI), ZIF-7 (Zn-2MI) and Fe-MOFs with other organic ligands (H 2 BDC, NH 2 -H 2 BDC or FA) were also used as control samples. Optimal activity for photocatalytic reduction of Cr(VI) was achieved by Fe(II)-2MI. The operating factors was optimized at acidic pH (2.0), higher catalyst dosage (0.3 g/L) and appropriate concentration of coexisting organics (2.0 mM) within the tested range. The stability of Fe(II)-2MI was investigated at different pH values (2, 3 and 4.64), which all displayed good stability. Mechanism study indicated that Fe(II)-2MI has adequate conduction and valence band positions for Cr(VI) reduction and organics oxidation, respectively. Therefore, the as-prepared amorphous Fe(II)-2MI assemblies may be cheap, stable and easy available candidate for the photocatalytic disposal of Cr(VI)-containing wastewaters.
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