This paper describes the preparation of lepidocrocites (gamma-FeOOH) via the air oxidation of Fe(OH)(2) under visible light irradiation in the presence of oxalic acid. Experimental results show that lepidocrocites with different degrees of crystallization can be obtained by controlling the concentration of oxalic acid under visible light irradiation. The crystallization of gamma-FeOOH is found to gradually decrease with the increase of oxalic acid concentration. This provides an alternative approach for the synthesis of low-crystalline gamma-FeOOH. Based on the results, a possible oxidation mechanism of Fe(II) has been proposed, which involves the formation of an Fe(II)-oxalate complex under light irradiation to produce oxidizing species, leading to an increase of the oxidation rate. The higher oxidation rate favors the formation of low-crystalline gamma-FeOOH. In contrast to the high-crystalline gamma-FeOOH, the low-crystalline gamma-FeOOH with high specific surface shows higher adsorption and photocatalytic activity toward the photodegradation of orange II.
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