Al-doped magnetite encapsulated in mesoporous carbon: A long-lasting Fenton catalyst for CWPO of phenol in a Fixed-bed reactor at mild conditions

Al-doped magnetite spinel nanoparticles encapsulated in mesoporous carbon (MC) were identified as promising heterogeneous Fenton catalyst towards phenol degradation in continuous system for practical applications. At the working conditions inside the fixed-bed reactor hercynite in the fabricated 21%γ-Fe 2 O 3 /28%FeAl 2 O 4 @MC material reacts with H 2 O 2. In this reaction Al ions occupied the vacant octahedral cationic sites in the framework of γ-Fe2O3 component converting it to Al substituted magnetite spinel. The Al in the obtained Fe 3+ 0.66Fe 2+ 0.33(Fe 2+ 0.33Fe 3+ 0.33Al 3+ 0.33)2O4@MC polarizes electrons of iron ions through its Lewis acid property imparting more positive charge on iron ions (Fe n+(δ+)). This expedites the rate of the challenging reduction reaction Fe 3+ → Fe 2+ with H2O2 to produce HOO˙ and reinforce the bonding of iron ions in the spinel improving their activity and stability. Hence, at the mild operating conditions (pH5, 40°C, 8.6 mlwater/mlcat*h, 0.036mol H2O2, 200ppm phenol) the in situ produced catalyst Fe(Fe0.66Al0.33)2O4@MC of 35 nm containing 19.9%Fe and 2.4%Al with surface area of 335 m 2 /g exhibited long-lasting high catalytic activity and stability in 500h run. 80% TOC conversion and ~1ppm of leached Fe in treated water were obtained without visible changing of catalytic performance.