Photocatalytic oxidation activity enhanced by iron-oxalate chelates for Fenton-like oxidation of As(III) in oxalate systems

This study investigated the Fenton-like oxidation of As(III) by three types of iron oxides in oxalate systems. The effects of pH, oxalate concentration and atmosphere on the oxidation of As(III) by iron oxide photocatalyst were studied. Firstly, hydrothermal carbon (HTC) was used as the carrier to load three kinds of iron oxides to prepare new composite materials, including α–FeOOH, α Fe 2 O 3 and Fe 3 O 4 , which can solve the dispersion problem of iron oxide by using a large number of rich functional groups on the HTC surface. The experiment results showed that under the conditions of O 2 , pH = 5.0 and oxalate concentration of 0.5 mmol·L 1 , As(III) was completely oxidized by α–FeOOH and α–Fe 2 O 3 at 15 min and 20 min, respectively. Density functional theory (DFT) was used to study the surface adsorption energy of iron oxide and oxalate. The calculated results showed that the order of adsorption energy of three iron oxides for the oxalate is α FeOOH > α Fe 2 O 3 > Fe 3 O 4 . Fe III (C 2 O 4 ) + , a mononuclear bidentate iron oxalate chelate with the strongest photosensitivity, was constructed in the Fe-Oxalate system containing only Fe(III), resulting in the photocatalytic efficiency of α–FeOOH and α Fe 2 O 3 was superior to that of Fe 3 O 4 . These findings contribute to arsenic remediation of water bodies by using iron materials and oxalate in the natural environment. • α-FeOOH, α-Fe 2 O 3 and Fe 3 O 4 supported on HTC are used for Fenton-like oxidation of As(III). • The metal-ligand structure of Fe(III) oxalate accelerates photogenic electron conduction. • α–FeOOH has the greatest binding capacity and better photocatalytic activity with oxalate. • A photosensitive mononuclear bidentate chelate was constructed in α-FeOOH/oxalate system. • Oxygen activates iron oxalate complex to produce active oxygen free radicals.